# Forest fire

Forest fire
You are encouraged to solve this task according to the task description, using any language you may know.
 This page uses content from Wikipedia. The original article was at Forest-fire model. The list of authors can be seen in the page history. As with Rosetta Code, the text of Wikipedia is available under the GNU FDL. (See links for details on variance)

Implement the Drossel and Schwabl definition of the forest-fire model.

It is basically a 2D   cellular automaton   where each cell can be in three distinct states (empty, tree and burning) and evolves according to the following rules (as given by Wikipedia)

1. A burning cell turns into an empty cell
2. A tree will burn if at least one neighbor is burning
3. A tree ignites with probability   f   even if no neighbor is burning
4. An empty space fills with a tree with probability   p

Neighborhood is the   Moore neighborhood;   boundary conditions are so that on the boundary the cells are always empty ("fixed" boundary condition).

At the beginning, populate the lattice with empty and tree cells according to a specific probability (e.g. a cell has the probability 0.5 to be a tree). Then, let the system evolve.

Task's requirements do not include graphical display or the ability to change parameters (probabilities   p   and   f )   through a graphical or command line interface.

## 6502 Assembly

<lang asm> ORG \$4357

SYS 17239 or CALL 17239

EMPTY2 = \$00 TREE2 = \$44 FIRE2 = \$99

common available zero page

GBASL = \$26 GBASH = \$27

SEED2 = \$28 SEED0 = \$29 SEED1 = \$2A

H2 = \$2B V2 = \$2C PLOTC = \$2D COLOR = \$2E PAGE = \$2F TOPL = \$30 TOPH = \$31 MIDL = \$32 MIDH = \$33 BTML = \$34 BTMH = \$35 PLOTL = \$36 PLOTH = \$37 lastzp = \$38

tablelo = \$5000 tablehi = tablelo+25

JSR START STA V2 LDA #\$4C ; JMP instruction STA SEED2 ; temporary JMP LDX #\$00 ; y coord table: TXA JSR SEED2 ; temporary JMP GBASCALC LDA GBASL STA tablelo,X LDA GBASH STA tablehi,X LDY #\$00 TYA clrline: STA (GBASL),Y INY CPY #40 BNE clrline

INX CPX V2 BNE table

JSR sseed0 JSR sseed2

LDX #\$60 STX PAGE STX TOPH LDY #\$00 STY TOPL TYA zero: STA (TOPL),Y INY BNE zero INX STX TOPH CPX #\$80 BNE zero

loop3: LDX #0 STX TOPL LDA #41 STA MIDL STA PLOTL LDA #83 STA BTML LDA PAGE STA TOPH STA MIDH STA BTMH EOR #\$10 STA PLOTH STA PAGE loop2: TXA STX V2 LSR  ; F800 PLOT-like... ; PHP  ; F801 TAY  ; save A in Y without touching C LDA #\$0F BCC over2 ADC #\$E0 over2: STA PLOTC  ; PLOT... LDA tablelo,Y ; lookup instead of GBASCALC STA GBASL LDA tablehi,Y STA GBASH ; PLP  ; continue PLOT LDY #\$01 ; x coord loop1: STY H2 LDA (MIDL),Y STA (PLOTL),Y BEQ empty BPL tree LDA #EMPTY2 doplot: LDY H2 STA (PLOTL),Y DEY EOR (GBASL),Y AND PLOTC EOR (GBASL),Y STA (GBASL),Y noplot: LDY H2 INY CPY #41 BNE loop1 LDA MIDL STA TOPL LDA MIDH STA TOPH LDA BTML STA MIDL STA PLOTL CLC ADC #42 STA BTML LDA BTMH EOR #\$10 STA PLOTH EOR #\$10 STA MIDH ADC #\$00 STA BTMH LDX V2 INX CPX #48 BNE loop2 JSR QUIT JMP loop3 empty: DEC SEED2 BNE noplot JSR sseed2 ; probability f LDA #TREE2 BNE doplot ignite: LDA #FIRE2 BNE doplot tree: DEC SEED0 BNE check DEC SEED1 BNE check JSR sseed0 ; probability p BNE ignite check: LDA (TOPL),Y ; n ORA (BTML),Y ; s DEY ORA (TOPL),Y ; nw ORA (MIDL),Y ; w ORA (BTML),Y ; sw INY INY ORA (TOPL),Y ; ne ORA (MIDL),Y ; e ORA (BTML),Y ; se BMI ignite BPL noplot

sseed0: LDA #\$17 ; 1 in 10007 (prime) STA SEED0 LDA #\$27 STA SEED1 RTS sseed2: LDA #\$65  ; 1 in 101 (prime) STA SEED2 RTS

default: LDA #<GBASCALC ; setup GBASCALC STA SEED0 LDA #>GBASCALC STA SEED1 LDA #25 ; screen rows RTS GBASCALC: LDY #\$00 STY GBASH ASL ASL ASL STA GBASL ASL ROL GBASH ASL ROL GBASH ADC GBASL STA GBASL LDA GBASH ADC #\$04 STA GBASH RTS

QUIT: LDA \$E000

APPLE II

CMP #\$4C BNE c64quit

BIT \$C000 ; apple ii keypress? BPL CONTINUE ; no keypressed then continue BIT \$C010 ; clear keyboard strobe BIT \$C051 ; text mode

end APPLE II specific

ABORT: PLA PLA

LDX #GBASL restorzp: LDA \$5100,X STA \$00,X INX CPX #lastzp BNE restorzp

CONTINUE: RTS

START: LDX #GBASL savezp: LDA \$00,X STA \$5100,X INX CPX #lastzp BNE savezp

machine ???

LDA \$E000 ; terribly unreliable, oh well

APPLE II

CMP #\$4C ; apple ii? BNE c64start ; nope, try another

BIT \$C056 ; low resolution BIT \$C052 ; full screen BIT \$C054 ; page one BIT \$C050 ; graphics

GBASCALC = \$F847

LDA #\$47 STA SEED0 LDA #\$F8 STA SEED1 LDA #24 ; screen rows RTS

end APPLE II specific
COMMODORE 64 specific

c64quit:

COMMODORE 64

CMP #\$85 ; commodore 64? BNE CONTINUE ; nope, default to no keypress

LDA \$C6 ; commodore keyboard buffer length BEQ CONTINUE ; no keypressed then continue

LDA #\$00 STA \$C6 LDA \$D016 ; Screen control register #2 AND #\$EF  ; Bit #4: 0 = Multicolor mode off. STA \$D016 LDA #21 ; default character set STA \$D018 BNE ABORT

c64start:

CMP #\$85 ; commodore 64? BEQ c64yes ; yes JMP default ; no, default to boringness c64yes: LDA #\$00  ; black STA \$D020 ; border LDA #\$00  ; black STA \$D021 ; background LDA #\$05  ; dark green STA \$D022 ; Extra background color #1 LDA #\$08  ; orange STA \$D023 ; Extra background color #2 LDA \$D016 ; Screen control register #2 ORA #\$10  ; Bit #4: 1 = Multicolor mode on. STA \$D016

LDA #\$30  ; 0011 0000 \$3000 charset page STA PLOTH LSR LSR STA PLOTC ; 0000 1100 #\$0C

53272 \$D018
POKE 53272,(PEEK(53272)AND240)+12
REM SET CHAR POINTER TO MEM. 12288
Bits #1-#3
In text mode, pointer to character memory
(bits #11-#13), relative to VIC bank, memory address \$DD00
%110, 6
\$3000-\$37FF, 12288-14335.

LDA \$D018 AND #\$F0 ORA PLOTC STA \$D018

setup nine characters
00- 00 00

LDA #\$00 ; chr(0) * 8 STA PLOTL ; --- LDA #\$00 ; already zero TAX ; LDX #\$00 JSR charset

04- 00 55

LDA #32 ; chr(4) * 8 STA PLOTL LDA #\$55 ; LDX #\$00 ; already zero JSR charset

09- 00 AA

LDA #72 ; chr(9) * 8 STA PLOTL LDA #\$AA ; LDX #\$00 ; already zero JSR charset

40- 55 00

LDA PLOTH ; 512 = chr(64) * 8 CLC ADC #\$02 STA PLOTH LDX #\$00 STX PLOTL LDA #\$00 LDX #\$55 JSR charset

44- 55 55

LDA #32 ; chr(68) * 8 STA PLOTL TXA ; LDA #\$55 ; LDX #\$55 ; already 55 JSR charset

49- 55 AA

LDA #72 ; chr(73) * 8 STA PLOTL LDA #\$AA ; LDX #\$55 ; already 55 JSR charset

90- AA 00

LDA PLOTH ; chr(144) * 8 CLC ADC #\$02 STA PLOTH LDA #128 STA PLOTL LDA #\$00 LDX #\$AA JSR charset

94- AA 55

LDA #160 ; chr(148) * 8 STA PLOTL LDA #\$55 ; LDX #\$AA ; already AA JSR charset

99- AA AA

LDA #200 ; chr(153) * 8 STA PLOTL TXA ; LDA #\$AA ; LDX #\$AA ; already AA JSR charset JMP default charset: LDY #\$00 chartop: STA (PLOTL),Y INY CPY #\$04 BNE chartop TXA charbtm: STA (PLOTL),Y INY CPY #\$08 BNE charbtm RTS

end COMMODORE 64 specific

</lang>

## 8086 Assembly

This program expects to run on an IBM PC with a CGA-compatible video card. It uses a field size of 320x200 (the CGA screen) and runs at about one frame per second on a 20mhz 286.

<lang asm> ;;; Simulation settings (probabilities are P/65536) probF: equ 7 ; P(spontaneous combustion) ~= 0.0001 probP: equ 655 ; P(spontaneous growth) ~= 0.01 HSIZE: equ 320 ; Field width (320x200 fills CGA screen) VSIZE: equ 200 ; Field height FSIZE: equ HSIZE*VSIZE ; Field size FPARA: equ FSIZE/16+1 ; Field size in paragraphs ;;; Field values EMPTY: equ 0 ; Empty cell (also CGA black) TREE: equ 1 ; Tree cell (also CGA green) FIRE: equ 2 ; Burning cell (also CGA red) ;;; MS-DOS system calls and values TOPSEG: equ 2 ; First unavailable segment puts: equ 9 ; Print a string time: equ 2Ch ; Get system time exit: equ 4Ch ; Exit to DOS ;;; BIOS calls and values palet: equ 0Bh ; Set CGA color pallette vmode: equ 0Fh ; Get current video mode keyb: equ 1 ; Get keyboard status CGALO: equ 4 ; Low-res (4-color) CGA graphics mode MDA: equ 7 ; MDA monochrome text mode CGASEG: equ 0B800h ; CGA memory segment cpu 8086 org 100h section .text ;;; Program set-up (check memory size and set video mode) mov sp,stack.top ; Move stack inwards mov bp,sp ; Set BP to first available paragraph mov cl,4 shr bp,cl inc bp mov dx,cs add bp,dx mov bx,[TOPSEG] ; Get first unavailable segment sub bx,bp ; Get amount of available memory cmp bx,FPARA*2 ; Enough to fit two fields? ja mem_ok mov dx,errmem ; If not, print error message err: mov ah,puts int 21h mov ah,exit ; And stop int 21h mem_ok: mov ah,vmode ; Get current video mode int 10h push ax ; Keep on stack for later retrieval cmp al,MDA ; MDA card does not support CGA graphics, mov dx,errcga ; so print an error and quit. je err mov ax,CGALO ; Otherwise, switch to 320x200 CGA mode int 10h mov ah,palet ; And set the black/green/red/brown palette mov bx,0100h int 10h mov ah,time ; Get the system time int 21h mov [rnddat],cx ; Use it as the RNG seed mov [rnddat+2],dx ;;; Initialize the field (place trees randomly) mov es,bp ; ES = field segment xor di,di ; Start at first field mov cx,FSIZE ; CX = how many cells to initialize mov ah,TREE ptrees: call random ; Get random byte and al,ah ; Place a tree 50% of the time stosb loop ptrees mov ds,bp ; DS = field segment ;;; Write field to CGA display disp: xor si,si ; Start at beginning mov dx,CGASEG ; ES = CGA memory segment .scrn: mov es,dx xor di,di ; Start of segment .line: mov cx,HSIZE/8 ; 8 pixels per word .word: xor bx,bx ; BX will hold CGA word xor ah,ah ; Set high byte to zero %rep 7 ; Unroll this loop for speed lodsb ; Get cell or bx,ax ; Put it in low 2 bits of BX shl bx,1 ; Shift BX to make room for next field shl bx,1 %endrep lodsb ; No shift needed for final cell or ax,bx stosw ; Store word in CGA memory loop .word ; Do next byte of line add si,HSIZE ; Even and odd lines stored separately cmp si,FSIZE ; Done yet? jb .line ; If not, do next line add dx,200h ; Move to next segment cmp dx,CGASEG+200h ; If we still need to do the odd lines, mov si,HSIZE ; then do them jbe .scrn ;;; Stop the program if a key is pressed mov ah,1 ; Check if a key is pressed int 16h jz calc ; If not, calculate next field state pop ax ; Otherwise, restore the old video mode, cbw int 10h mov ah,exit ; and exit to DOS. int 21h ;;; Calculate next field state calc: mov ax,ds ; Set ES = new field segment add ax,FPARA mov es,ax xor di,di ; Start at beginning xor si,si .cell: lodsb ; Get cell dec al ; A=1 = tree jz .tree dec al ; A=2 = fire jz .fire call rand16 ; An empty space fills with a tree cmp ax,probP ; with probability P. jc .mtree ; Otherwise it stays empty .fire: xor al,al ; A burning tree turns into an empty cell stosb jmp .cnext .mtree: mov al,TREE stosb .cnext: cmp si,FSIZE ; Are we there yet? jne .cell ; If not, do next cell push es ; Done - set ES=old field, DS=new field, push ds pop es pop ds mov cx,FSIZE/2 xor si,si xor di,di rep movsw ; copy the new field to the old field, push es ; set DS to be the field to draw, pop ds xor di,di ; Instead of doing edge case handling in the xor ax,ax ; Moore neighbourhood calculation, just zero mov cx,HSIZE/2 ; out the borders for a slightly smaller image rep stosw ; Upper border, mov di,FSIZE-HSIZE mov cx,HSIZE/2 rep stosw ; lower border, mov di,HSIZE-5 ; right border. mov cx,VSIZE-1 .bordr: stosb add di,HSIZE-1 loop .bordr jmp disp ; and update the display. .tree: mov ax,[si-HSIZE-2] ; Load Moore neighbourhood or al,[si-HSIZE] or ax,[si-2] or al,[si] or ax,[si+HSIZE-2] or al,[si+HSIZE] or al,ah test al,FIRE ; Are any of the trees on fire? jnz .tburn ; Then set this tree on fire too call rand16 ; Otherwise, spontaneous combustion? cmp ax,probF jc .tburn mov al,TREE ; If not, the tree remains a tree stosb jmp .cnext .tburn: mov al,FIRE ; Set the tree on fire stosb jmp .cnext ;;; Get a random word in AX rand16: call random xchg al,ah ;;; Get a random byte in AL. BX and DX destroyed. random: mov bx,[cs:rnddat] ; BL=X BH=A mov dx,[cs:rnddat+2] ; DL=B DH=C inc bl ; X++ xor bh,dh ; A ^= C xor bh,bl ; A ^= X add dl,bh ; B += A mov al,dl ; C' = B shr al,1 ; C' >>= 1 add al,dh ; C' += C xor al,bh ; C' ^= A mov dh,al ; C = C' mov [cs:rnddat+2],dx ; Update RNG state mov [cs:rnddat],bx ret section .data errcga: db 'CGA mode not supported.\$' errmem: db 'Not enough memory.\$' section .bss rnddat: resb 4 ; RNG state stack: resw 128 ; Stack space .top: equ \$</lang>

procedure Forest_Fire is

```  type Cell is (Empty, Tree, Fire);
type Board is array (Positive range <>, Positive range <>) of Cell;
procedure Step (S : in out Board; P, F : Float; Dice : Generator) is
function "+" (Left : Boolean; Right : Cell) return Boolean is
begin
return Left or else Right = Fire;
end "+";
function "+" (Left, Right : Cell) return Boolean is
begin
return Left = Fire or else Right = Fire;
end "+";
Above : array (S'Range (2)) of Cell := (others => Empty);
Left_Up, Up, Left : Cell;
begin
for Row in S'First (1) + 1..S'Last (1) - 1 loop
Left_Up := Empty;
Up      := Empty;
Left    := Empty;
for Column in S'First (2) + 1..S'Last (2) - 1 loop
Left_Up := Up;
Up      := Above (Column);
Above (Column) := S (Row, Column);
case S (Row, Column) is
when Empty =>
if Random (Dice) < P then
S (Row, Column) := Tree;
end if;
when Tree =>
if Left_Up                 + Up                  +      Above (Column + 1) +
Left                    + S (Row,     Column) + S (Row,     Column + 1) +
S (Row + 1, Column - 1) + S (Row + 1, Column) + S (Row + 1, Column + 1)
or else Random (Dice) < F then
S (Row, Column) := Fire;
end if;
when Fire =>
S (Row, Column) := Empty;
end case;
Left := Above (Column);
end loop;
end loop;
end Step;
procedure Put (S : Board) is
begin
for Row in S'First (1) + 1..S'Last (1) - 1 loop
for Column in S'First (2) + 1..S'Last (2) - 1 loop
case S (Row, Column) is
when Empty => Put (' ');
when Tree  => Put ('Y');
when Fire  => Put ('#');
end case;
end loop;
New_Line;
end loop;
end Put;

Dice   : Generator;
Forest : Board := (1..10 => (1..40 => Empty));
```

begin

```  Reset (Dice);
for I in 1..10 loop
Step (Forest, 0.3, 0.1, Dice);
Put_Line ("-------------" & Integer'Image (I) & " -------------");
Put (Forest);
end loop;
```

end Forest_Fire;</lang> Sample output:

```------------- 1 -------------
Y  Y Y        Y YY   Y Y Y  Y        Y
Y Y  YYY   YY  Y      Y  Y  Y     Y
Y     YY Y  Y Y Y  Y   Y   Y   Y YY
Y          Y Y     Y  YY
Y         YY YYY  Y Y        Y   Y   Y
Y Y         YY  Y    Y        Y    Y
Y  Y    Y Y          Y Y Y Y
Y   Y  Y     YYY  Y  Y  Y   Y  Y
------------- 2 -------------
Y  Y Y   YYYYY# YYY  Y Y Y  YYY  Y Y Y
YY#  YYY   YY  Y Y Y  Y  #Y Y    YY  Y
YYY   YY Y  YY# Y  YY  Y Y Y   Y YY
Y Y     YY   Y  Y YYYY   Y Y YYY  YY
Y    Y   Y#Y YYY YYYY       YYY  Y Y Y
Y Y Y    Y YYY Y#    Y Y Y    Y    Y
Y  Y   Y# Y   Y  Y Y Y YYY Y
YY YY  Y  Y  YYY  YYYYY Y   Y YY  Y
------------- 3 -------------
YY # Y   YYYY#  YY#  Y Y #  YYY Y# Y Y
Y# Y YYYYY Y#  # YYY YYY  #YY Y  YY  Y
Y##  Y#Y Y  Y#  YY YY YY # Y   Y YYY
# Y    Y##   #  YYYYYY YYY YYYYYY YY
Y Y YY   # # YY# #YYYYYY  YYYYY  YY# Y
YYY YYY Y# #YYY#     YYY Y    YY   Y
Y  YY Y   # Y# Y YY YYY Y YYYYY
YY #Y YYY Y  ###  YYYY# YY YYYYY YY
------------- 4 -------------
##   Y   YY## Y ## Y YYY  Y YYY #  Y Y
# Y# ###YYY#  Y  ### YYYY  #Y Y Y##  Y
#    # # #  #   #YYYY Y#  Y# YYYYYYYY
Y   YY YY#   YY Y ##YYYY ##Y YYYYY#Y#Y
YY#YYY  Y Y  Y# Y #YYYYYY YYYYY  Y#  Y
YY#YYY#Y#   ### Y YY #YY Y    YY   # Y
#Y ## #    Y#  YYY# ##Y Y YYYYY  Y
YYY  #YYY# YYY     YYY#  YYYYY#YY YY
------------- 5 -------------
Y  #   Y#   Y    #YYYYY #Y#YYY  Y# Y
Y# Y   ###   Y      Y###Y  # Y #    Y
Y    Y Y Y      #### #   #  #YY#####
#   ## ##   Y##Y#   #Y##Y  # YYYY# # #
Y# #Y#YY#Y#Y # YY  ####Y# ##YYYY #   #
Y# ### #   Y    # ##Y ##Y#    YY  Y  Y
Y #         #   Y##    # Y ###Y#  Y
Y##   ###  YYY  Y  Y##   #YYY# #Y YYY
------------- 6 -------------
Y#   YY #    Y  Y  #####Y # #Y#Y #  Y
# Y#Y      Y YY  YYY#   #Y   #Y  Y  #
#    # # #   Y               ##
Y#  #   Y #  # Y  ####
# Y # ## # #Y  ## Y    # Y  #YYY   Y
#         Y#YYYY    #   #   Y ##YY#  #
Y #    Y  Y Y    Y#        Y    # Y Y
#  Y     Y YY# YY Y#      #Y# Y #Y#YY
------------- 7 -------------
Y# Y  YY      Y  Y       #  Y # #Y  Y#
# # YY   # YY YY##  Y  #Y   #Y #Y
Y Y    Y Y    #Y  Y  YY     Y     Y
Y   Y    # Y  Y YY     YYY         Y
YY        #    YY   Y  #   ###Y  #
Y        # ####YY       YY #   ##
Y#    Y Y  # #  Y #    YY  Y#Y     # #
Y #     Y Y# YYYY#     Y  #  YY # #Y
------------- 8 -------------
#  #  #Y Y  Y YYYY Y   Y    Y    #  #
YYY    YY Y   ## Y#  Y Y Y #  Y #Y #Y
Y #Y  Y#YY     #Y #  #Y  Y  YY    #Y
Y   Y      #  YYYYYY  Y##Y Y   Y   Y
YYYY   Y  Y  Y  YYY   Y Y Y Y   #   YY
# YY  YY  Y    ##Y   YYY##Y YYY
#   Y Y Y       #Y   YY#Y  # # Y YY
#Y Y YYY# # YY###      Y    YYY    #
------------- 9 -------------
Y # YY YY####Y# YYYYYY #      Y
###    ## # Y    #   # Y Y    YY #  #
Y  #Y # #Y Y  Y #     # Y#  #Y Y   # Y
#   # YYYY    ######YY#  # Y  Y#  YY
###Y  YY YYY #  ###   YY# # YY      YY
YYY  YY  Y Y    # Y ###  # ### Y YY
Y Y Y  Y   Y #Y  Y# #Y     Y Y#
# Y YY#    Y#         # Y  #Y#  YY
------------- 10 -------------
YYYY   ## Y#    #  ##YYYYY      Y#
Y        Y       Y Y# #    YYY YY
#Y  #    # #  Y   Y  Y  # Y  # YYYY Y#
Y   Y###Y          ##  Y Y# Y#   #Y
#  ## YYY         Y##    ## YY   YY
##Y  YY YYY#      Y           Y# #Y
# Y #  Y Y #  #  #   #     # #
Y   YYY#     #           YY Y #   #Y
```

## ALGOL 68

### Textual version

Translation of: D
Note: This specimen retains the original D coding style.
Works with: ALGOL 68 version Revision 1 - no extensions to language used.
Works with: ALGOL 68G version Any - tested with release 1.18.0-9h.tiny.

<lang algol68>LONG REAL tree prob = 0.55, # original tree probability #

```         f prob =    0.01, # new combustion probability #
p prob =    0.01; # tree creation probability #
```

MODE CELL = CHAR; CELL empty=" ", tree="T", burning="#"; MODE WORLD = [6, 65]CELL;

PROC has burning neighbours = (WORLD world, INT r, c)BOOL:(

``` FOR row shift FROM -1 TO 1 DO
FOR col shift FROM -1 TO 1 DO
INT rs = r + row shift, cs = c + col shift;
IF rs >= LWB world AND rs <= UPB world AND
cs >= 2 LWB world AND cs <= 2 UPB world THEN
IF world[rs, cs] = burning THEN true exit FI
FI
OD
OD;
FALSE EXIT
true exit: TRUE
```

);

PROC next state = (REF WORLD world, REF WORLD next world)VOID:(

``` FOR r FROM LWB world TO UPB world DO
REF[]CELL row = world[r, ];
FOR c FROM LWB row TO UPB row DO
REF CELL elem = row[c];
next world[r, c] :=
IF elem = empty THEN
IF random<p prob THEN tree ELSE empty FI
ELIF elem = tree THEN
IF has burning neighbours(world, r, c) THEN
burning
ELSE
IF random<f prob THEN burning ELSE tree FI
FI
ELIF elem = burning THEN
empty
FI
OD
OD;
world := next world
```

);

main:(

``` WORLD world; # create world #
FOR r FROM LWB world TO UPB world DO
REF []CELL row = world[r, ];
FOR i FROM LWB row TO UPB row DO
REF CELL el = row[i];
el := IF random < tree prob THEN tree ELSE empty FI
OD
OD;
```
``` WORLD next world;
FOR i FROM 0 TO 4 DO
next state(world, next world);
printf((\$n(2 UPB world)(a)l\$, world)); # show world #
printf((\$gl\$, 2 UPB world * "-"))
OD
```

)</lang> Output:

```TTTT T TTTT TT  T T TTT TT TTT  TT TTT T TT T  T    TTT TT T   TT
TTT TTTTT  T T    T TTTT T   T TTT  TT  T  T TT T   T T TTT  T T
T   T T T TT    T    #  T T   TTT T T  T  TTTTT T  TTT  TTTT TTTT
TT     T  TT TTTTTTTTT TT  TT  T T  TT  T TT TTT TTT TTTT TT  TTT
TT    TTTTTT  T  T  T T T T TT TT      TT  #T TTT  TT #TTTTTTTT
TT  TTT TTTTTTTTTT TT TTTTTT  TT T TT T TTT T TT T  TT #  T   T
-----------------------------------------------------------------
TTTT T TTTT TT  T T TTT TT TTT  TT TTT T TT T  T    TTT TT T   TT
TTT TTTTT  T T    T ##TT T   T TTT  TT  T  T TT T   T T TTT  T T
T   T T T TT    T       T T   TTT T T  T  TTTTT T  TTT  TTTT TTTT
TT     T  T# TTTTTTT## TT  TT  T T  TT  T T# #TT TTT T### TT  TTT
TT    TTTTTT  T  T  T T T T TT TT      TTT  # TTT  TT  #TTTTTTT
TT  TTT TTTTTTTTTT TT TTTTTT  TT T TT T TTT # TT T  TT    T   T
-----------------------------------------------------------------
TTTT T TTTT TT  T T ### TT TTT  TT TTT T TT T  T    TTT TT T   TT
TTT TTTTT  T T    T   #T T   T TTT  TT  T  T TT T   T T TT#  T T
T   T T T ##    T       T T   TTT T T  T  ##### T  TT#  ##TT TTTT
TT     T  #  TTTTTT#   TT  TT  T T  TT TT #   #T TTT #    TT  TTT
TT    T#T###  T  T  # T T T TT TT      TT#    TTT  T#   #TTTTTT
TT  TTT TTTTTTTTTT TT TTTTTT  TT T TT T TTT   #T T  TTT   T   T
-----------------------------------------------------------------
TTTT T TTTT TT  T T     #T TTT  TT TTT T TT T  T    TTT TT #   TT
TTT TTTT#  # T    #    # T   T TTT  TT  #  # ## T   # # ##   T T
T   T T T       T       # T   TTT T T  T        T  T#     ## TTTT
TT     #     #TTTT#    TT  TT  T T  TT TT      # TTT      #T  TTT
TT    # #     T  #    T T T TT TT      T#     #TT  #     #TTTTT
TT  TTT ######TTTT T# #TTTTT  TT T TT T T##    # T  ###   #   T
-----------------------------------------------------------------
#TTT T T### ##  T #      # TTT  TT TTT T ## #  #    ### ##     TT
TTT TTT#     T           T   T TTT  TT          T            T T
T   T # #       T         T   TTT T T  T       T#  #         TTTT
TT            #TT#     ##  TT  T T  TT T#        TT#       #  TTT
TT            T       # T T TT TT      #       #T         #TTTT
TT  TT#       #TT# #   #TTTT  TT T TT T #        T            T
-----------------------------------------------------------------
```

## AutoHotkey

This implementation uses AutoHotkey's pseudo-arrays to contain each cell. The size of the (square) map, probabilities, and characters which correspond to burning, tree, or empty can be edited at the beginning of the script. <lang AutoHotkey>

The array Frame1%x%_%y% holds the current frame. frame2%x%_%y%
is then calculated from this, and printed. frame2 is then copied to frame1.
Two arrays are necessary so that each cell advances at the same time
T=Tree, #=Fire, O=Empty cell
Size holds the width and height of the map and is used as the # of iterations in loops
This will save the map as forest_fire.txt in its working directory
======================================================================================

Size := 10 Generation := 0 Tree := "T" Fire := "#" Cell := "O"

--Define probabilities--
```   New_Tree := 5
; 20 percent chance (1 in 5). A random number will be generated from 1 to New_tree. If this number is 1,
; A tree will be created in the current cell
```
```   Spontaneous := 10
; 10 percent chance (1 in 10). A random number will be generated from 1 to Spontaneous. If this number is 1,
; and the current cell contains a tree, the tree in the current cell will become fire.
```

GoSub, Generate

----------------------Main Loop------------------------------

loop {

```   Generation++
GoSub, Calculate
GoSub, Copy
GoSub, Display
msgbox, 4, Forest Fire, At Generation %generation%. Continue?
IfMsgbox, No
ExitApp
```

} return

-------------------------------------------------------------

Generate:  ; Randomly initializes the map. loop % size  ; % forces expression mode. { x := A_Index Loop % size { Y := A_Index Random, IsTree, 1, 2 ; -- Roughly half of the spaces will contain trees If ( IsTree = 1 ) Frame1%x%_%y% := Tree Else Frame1%x%_%y% := Cell } } return

Calculate: Loop % size { x := A_Index Loop % size { Y := A_Index If ( Frame1%x%_%y% = Cell ) { Random, tmp, 1, New_Tree If ( tmp = 1 ) Frame2%x%_%y% := tree Else Frame2%x%_%y% := Cell } Else If ( Frame1%x%_%y% = Tree ) { BoolCatch := PredictFire(x,y) If (BoolCatch) Frame2%x%_%y% := Fire Else Frame2%x%_%y% := Tree } Else If ( Frame1%x%_%y% = Fire ) Frame2%x%_%y% := Cell Else { contents := Frame1%x%_%y% Msgbox Error! Cell %x% , %y% contains %contents% ; This has never happened ExitApp } } } return

Copy: Loop % size { x := A_Index Loop % size { y := A_Index frame1%x%_%y% := Frame2%x%_%y% } } return

Display: ToPrint := "" ToPrint .= "=====Generation " . Generation . "=====`n" Loop % size { x := A_Index Loop % size { y := A_Index ToPrint .= Frame1%x%_%y% } ToPrint .= "`n" } FileAppend, %ToPrint%, Forest_Fire.txt Return

PredictFire(p_x,p_y){

```   Global ; allows access to all frame1*_* variables (the pseudo-array)
A := p_x-1
B := p_y-1
C := p_x+1
D := p_y+1
If ( Frame1%A%_%p_Y% = fire )
return 1
If ( Frame1%p_X%_%B% = fire )
return 1
If ( Frame1%C%_%p_Y% = fire )
return 1
If ( Frame1%p_X%_%D% = fire )
return 1
```
```   If ( Frame1%A%_%B% = Fire )
return 1
If ( Frame1%A%_%D% = fire )
return 1
If ( Frame1%C%_%B% = fire )
return 1
If ( Frame1%C%_%D% = Fire )
return 1
```
```   Random, tmp, 1, spontaneous
if ( tmp = 1 )
return 1
return 0
```

} </lang> Sample Output using the default settings:

```=====Generation 1=====
OTTTOOTOOT
OTOOTTTTOT
TTOOOTTTO#
TOOTOTOOTT
OTTOTOOTTO
TOTTTTOOTO
TOTTT#OOOT
OT#OOTOOTT
TTO#TOOTTT
O#OOOTOTTT
=====Generation 2=====
OTTTOOTOOT
OTTOTTT#O#
TTOOOTTTOO
TOOTTTOT##
OTTOTTO##O
TOTT##OTTO
TO###OOOOT
T#OOO#OOTT
##TO#OOTTT
TOTOOTOTTT
=====Generation 3=====
OTT#OO#TO#
OTTOTT#OTO
TTOOOT##OO
TOOTTTT#OO
OTTO##OOOO
TO##OOO##O
#OOOOOOOOT
#OOOOOOOTT
OO#OOTOTTT
#O#TT#OTTT
=====Generation 4=====
OT#OOOO#OO
OT#O##OO#T
T#TOT#OOOO
TOO####OOT
O##OOOOOOO
#OOOOOOOOO
OOOOOOOOO#
OTOOOOOOTT
OOOOO#TTTT
OTO##OO#TT
=====Generation 5=====
O#OOOTOOOT
O#OOOOOOO#
#O#O#OOTOT
#OOOOOOOOT
OOOOOOOOOO
OTOOOOOOOO
TTOOOTOTTO
TTOOOTOO##
OOTTOO###T
OTOOOOOO#T
```

## BASIC

### Applesoft BASIC

Translation of: 6502 Assembly

<lang gwbasic> 100 FOR I = 17239 TO 17493

```110      READ B
120  NEXT
130  CALL 17239
140  END
150  DATA 162,23,138,32,71,248,165,38,157,60,3,165,39,157,84,3,202,16,239,162,96
160  DATA 134,249,134,1,160,0,132,0,152,145,0,200,208,251,232,134,1,224,128,208
170  DATA 244,44,86,192,44,82,192,44,84,192,44,80,192,32,50,248,162,0,134,0,169
180  DATA 41,133,2,133,254,169,83,133,4,165,249,133,1,133,3,133,5,73,16,133,255
190  DATA 133,249,138,134,45,74,168,169,15,144,2,105,224,133,46,185,60,3,133,38
200  DATA 185,84,3,133,39,160,1,132,44,177,2,145,254,240,79,16,93,169,0,164,44
210  DATA 145,254,136,81,38,37,46,81,38,145,38,164,44,200,192,41,208,224,165,2
220  DATA 133,0,165,3,133,1,165,4,133,2,133,254,24,105,42,133,4,165,5,73,16
230  DATA 133,255,73,16,133,3,105,0,133,5,166,45,232,224,48,208,159,44,0,192
240  DATA 48,3,76,144,67,44,16,192,44,81,192,96,198,8,208,190,169,101,133,8,169
250  DATA 68,208,169,169,153,208,165,198,6,208,14,198,7,208,10,169,23,133,6,169
260  DATA 39,133,7,208,234,177,0,17,4,136,17,0,17,2,17,4,200,200,17,0,17,2,17,4
270  DATA 48,213,16,137,41</lang>
```

### BASIC256

<lang basic256>N = 150 : M = 150 : P = 0.03 : F = 0.00003

dim f(N+2,M+2) # 1 tree, 0 empty, 2 fire dim fn(N+2,M+2) graphsize N,M fastgraphics

for x = 1 to N for y = 1 to M if rand<0.5 then f[x,y] = 1 next y next x

while True for x = 1 to N for y = 1 to M if not f[x,y] and rand<P then fn[x,y]=1 if f[x,y]=2 then fn[x,y]=0 if f[x,y]=1 then fn[x,y] = 1 if f[x-1,y-1]=2 or f[x,y-1]=2 or f[x+1,y-1]=2 then fn[x,y]=2 if f[x-1,y]=2 or f[x+1,y]=2 or rand<F then fn[x,y]=2 if f[x-1,y+1]=2 or f[x,y+1]=2 or f[x+1,y+1]=2 then fn[x,y]=2 end if # Draw if fn[x,y]=0 then color black if fn[x,y]=1 then color green if fn[x,y]=2 then color yellow plot x-1,y-1 next y next x refresh for x = 1 to N for y = 1 to M f[x,y] = fn[x,y] next y next x end while</lang>

### BBC BASIC

<lang bbcbasic> VDU 23,22,400;400;16,16,16,128

```     OFF

DIM old&(200,200), new&(200,200)
p = 0.01
f = 0.0001

REM 0 = empty, 1 = tree, 2 = burning
REPEAT
WAIT 10
FOR x% = 1 TO 199
FOR y% = 1 TO 199
CASE old&(x%,y%) OF
WHEN 0:
IF p > RND(1) THEN
new&(x%,y%) = 1
GCOL 2
PLOT 4*x%,4*y%
ENDIF
WHEN 1:
IF f > RND(1) OR old&(x%-1,y%)=2 OR old&(x%+1,y%)=2 OR \
\ old&(x%-1,y%-1)=2 OR old&(x%,y%-1)=2 OR old&(x%+1,y%-1)=2 OR \
\ old&(x%-1,y%+1)=2 OR old&(x%,y%+1)=2 OR old&(x%+1,y%+1)=2 THEN
new&(x%,y%) = 2
GCOL 1
PLOT 4*x%,4*y%
ENDIF
WHEN 2:
new&(x%,y%) = 0
GCOL 15
PLOT 4*x%,4*y%
ENDCASE
NEXT
NEXT x%
old&() = new&()
UNTIL FALSE</lang>
```

Output:

### FreeBASIC

<lang freebasic>'[RC] Forest Fire 'written for FreeBASIC 'Program code based on BASIC256 from Rosettacode website 'http://rosettacode.org/wiki/Forest_fire#BASIC256 '06-10-2016 updated/tweaked the code 'compile with fbc -s gui

1. Define M 400
2. Define N 640

Dim As Double p = 0.003 Dim As Double fire = 0.00003 'Dim As Double number1 Dim As Integer gen, x, y Dim As String press

'f0() and fn() use memory from the memory pool Dim As UByte f0(), fn() ReDim f0(-1 To N +2, -1 To M +2) ReDim fn(-1 To N +2, -1 To M +2)

Dim As UByte white = 15 'color 15 is white Dim As UByte yellow = 14 'color 14 is yellow Dim As UByte black = 0 'color 0 is black Dim As UByte green = 2 'color 2 is green Dim As UByte red = 4 'color 4 is red

Screen 18 'Resolution 640x480 with at least 256 colors Randomize Timer

Locate 28,1 Beep Print " Welcome to Forest Fire" Locate 29,1 Print " press any key to start" Sleep 'Locate 28,1 'Print " Welcome to Forest Fire" Locate 29,1 Print " "

' 1 tree, 0 empty, 2 fire Color green ' this is green color for trees For x = 1 To N

``` For y = 1 To M
If Rnd < 0.5 Then 'populate original tree density
f0(x,y) = 1
PSet (x,y)
End If
Next y
```

Next x

Color white Locate 29,1 Print " Press any key to continue " Sleep Locate 29,1 Print " Press 'space bar' to continue/pause, ESC to stop "

Do

``` press = InKey
ScreenLock
For x = 1 To N
For y = 1 To M
If Not f0(x,y) And Rnd<P Then fn(x,y)=1
If f0(x,y)=2 Then fn(x,y)=0
If f0(x,y)=1 Then
fn(x,y) = 1
If f0(x-1,y-1)=2 OrElse f0(x,y-1)=2 OrElse f0(x+1,y-1)=2 Then fn(x,y)=2
If f0(x-1,y)=2 OrElse f0(x+1,y)=2 OrElse Rnd<fire Then fn(x,y)=2
If f0(x-1,y+1)=2 OrElse f0(x,y+1)=2 OrElse f0(x+1,y+1)=2 Then fn(x,y)=2
End If
'set up color and drawing
'0 empty (black),  1 tree (green), 2 fire (white)
If fn(x,y)=0 Then Color black 'empty
If fn(x,y)=1 Then Color green 'tree
If fn(x,y)=2 Then Color red   'fire
'plot x-1,y-1
PSet (x-1,y-1)
Next y
Next x
'print generation number
gen = gen + 1
Locate 28,1
Color white 'this is white color
Print " Generation number # ";gen
'transfer new generation to current generation
For x = 1 To N
For y = 1 To M
f0(x,y) = fn(x,y)
Next y
Next x
ScreenUnlock
```
``` ' amount for sleep is in milliseconds, 1 = ignore key press
Sleep 50, 1  ' slow down a little ... goes too fast otherwise
If press = " " Then Sleep : press = InKey
If press = "s" Then Sleep
' return to do loop up top until "esc" key is pressed.
' clicking close windows "X", closes the window immediately
```

Loop Until press = Chr(27) OrElse press = Chr(255)+"k" If press = Chr(255) + "k" Then End

Locate 28,1 Color white Print " You entered ESC - goodbye " Print " Press any key to exit " Sleep</lang>

### GFA Basic

<lang basic> width%=80 height%=50 DIM world%(width%+2,height%+2,2) clock%=0 ' empty%=0 ! some mnemonic codes for the different states burning%=1 tree%=2 ' f=0.0003 p=0.03 max_clock%=100 ' @open_window @setup_world DO

``` clock%=clock%+1
EXIT IF clock%>max_clock%
@display_world
@update_world
```

LOOP @close_window ' ' Setup the world ' PROCEDURE setup_world

``` LOCAL i%,j%
'
RANDOMIZE 0
ARRAYFILL world%(),empty%
' with Probability 0.5, create tree in cells
FOR i%=1 TO width%
FOR j%=1 TO height%
IF RND>0.5
world%(i%,j%,0)=tree%
ENDIF
NEXT j%
NEXT i%
'
cur%=0
new%=1
```

RETURN ' ' Display world on window ' PROCEDURE display_world

``` LOCAL size%,i%,j%,offsetx%,offsety%,x%,y%
'
size%=5
offsetx%=10
offsety%=20
'
VSETCOLOR 0,15,15,15 ! colour for empty
VSETCOLOR 1,15,0,0 ! colour for burning
VSETCOLOR 2,0,15,0 ! colour for tree
VSETCOLOR 3,0,0,0 ! colour for text
DEFTEXT 3
PRINT AT(1,1);"Clock: ";clock%
'
FOR i%=1 TO width%
FOR j%=1 TO height%
x%=offsetx%+size%*i%
y%=offsety%+size%*j%
SELECT world%(i%,j%,cur%)
CASE empty%
DEFFILL 0
CASE tree%
DEFFILL 2
CASE burning%
DEFFILL 1
ENDSELECT
PBOX x%,y%,x%+size%,y%+size%
NEXT j%
NEXT i%
```

RETURN ' ' Check if a neighbour is burning ' FUNCTION neighbour_burning(i%,j%)

``` LOCAL x%
'
IF world%(i%,j%-1,cur%)=burning%
RETURN TRUE
ENDIF
IF world%(i%,j%+1,cur%)=burning%
RETURN TRUE
ENDIF
FOR x%=-1 TO 1
IF world%(i%-1,j%+x%,cur%)=burning% OR world%(i%+1,j%+x%,cur%)=burning%
RETURN TRUE
ENDIF
NEXT x%
RETURN FALSE
```

ENDFUNC ' ' Update the world state ' PROCEDURE update_world

``` LOCAL i%,j%
'
FOR i%=1 TO width%
FOR j%=1 TO height%
world%(i%,j%,new%)=world%(i%,j%,cur%)
SELECT world%(i%,j%,cur%)
CASE empty%
IF RND>1-p
world%(i%,j%,new%)=tree%
ENDIF
CASE tree%
IF @neighbour_burning(i%,j%) OR RND>1-f
world%(i%,j%,new%)=burning%
ENDIF
CASE burning%
world%(i%,j%,new%)=empty%
ENDSELECT
NEXT j%
NEXT i%
'
cur%=1-cur%
new%=1-new%
```

RETURN ' ' open and clear window ' PROCEDURE open_window

``` OPENW 1
CLEARW 1
VSETCOLOR 4,8,8,0
DEFFILL 4
PBOX 0,0,500,400
```

RETURN ' ' close the window after keypress ' PROCEDURE close_window

``` ~INP(2)
CLOSEW 1
```

RETURN </lang>

### PureBasic

<lang PureBasic>; Some systems reports high CPU-load while running this code.

This may likely be due to the graphic driver used in the
2D-function Plot().
If experiencing this problem, please reduce the #Width & #Height
or activate the parameter #UnLoadCPU below with a parameter 1 or 2.
This code should work with the demo version of PureBasic on both PC & Linux
General parameters for the world
1. f = 1e-6
2. p = 1e-2
3. SeedATree = 0.005
4. Width = 400
5. Height = 400
Setting up colours
1. Fire = \$080CF7
2. BackGround = \$BFD5D3
3. YoungTree = \$00E300
4. NormalTree = \$00AC00
5. MatureTree = \$009500
6. OldTree = \$007600
7. Black = \$000000
1 = Only active about every second frame
2 = '1' & release the CPU after each horizontal line.

Enumeration

``` #Empty  =0
#Ignited
#Burning
#Tree
#Old=#Tree+20
```

EndEnumeration

Global Dim Forest.i(#Width, #Height) Global Title\$="Forest fire in PureBasic" Global Cnt

Macro Rnd()

``` (Random(2147483647)/2147483647.0)
```

EndMacro

Procedure Limit(n, min, max)

``` If n<min
n=min
ElseIf n>max
n=max
EndIf
ProcedureReturn n
```

EndProcedure

``` Protected cnt=0, i, j
For i=Limit(x-1, 0, #Width) To Limit(x+1, 0, #Width)
For j=Limit(y-1, 0, #Height) To Limit(y+1, 0, #Height)
If Forest(i,j)>=#Tree
Forest(i,j)=#Ignited
EndIf
Next
Next
```

EndProcedure

Procedure InitMap()

``` Protected x, y, type
For y=1 To #Height
For x=1 To #Width
If Rnd()<=#SeedATree
type=#Tree
Else
type=#Empty
EndIf
Forest(x,y)=type
Next
Next
```

EndProcedure

Procedure UpdateMap()

``` Protected x, y
For y=1 To #Height
For x=1 To #Width
Select Forest(x,y)
Case #Burning
Forest(x,y)=#Empty
Case #Ignited
Forest(x,y)=#Burning
Case #Empty
If Rnd()<=#p
Forest(x,y)=#Tree
EndIf
Default
If Rnd()<=#f
Forest(x,y)=#Burning
Else
Forest(x,y)+1
EndIf
EndSelect
Next
Next
```

EndProcedure

Procedure PresentMap()

``` Protected x, y, c
cnt+1
SetWindowTitle(0,Title\$+", time frame="+Str(cnt))
StartDrawing(ImageOutput(1))
For y=0 To OutputHeight()-1
For x=0 To OutputWidth()-1
Select Forest(x,y)
Case #Empty
c=#BackGround
Case #Burning, #Ignited
c=#Fire
Default
If Forest(x,y)<#Tree+#Old
c=#YoungTree
ElseIf Forest(x,y)<#Tree+2*#Old
c=#NormalTree
ElseIf Forest(x,y)<#Tree+3*#Old
c=#MatureTree
ElseIf Forest(x,y)<#Tree+4*#Old
c=#OldTree
Else ; Tree died of old age
Forest(x,y)=#Empty
c=#Black
EndIf
EndSelect
Plot(x,y,c)
Next
Delay(1)
CompilerEndIf
Next
StopDrawing()
ImageGadget(1, 0, 0, #Width, #Height, ImageID(1))
```

EndProcedure

If OpenWindow(0, 10, 30, #Width, #Height, Title\$, #PB_Window_MinimizeGadget)

``` SmartWindowRefresh(0, 1)
If CreateImage(1, #Width, #Height)
Define Event, freq
If ExamineDesktops() And DesktopFrequency(0)
freq=DesktopFrequency(0)
Else
freq=60
EndIf
InitMap()
Repeat
Event = WaitWindowEvent()
Select Event
Case #PB_Event_CloseWindow
End
Case #PB_Event_Timer
Delay(25)
CompilerEndIf
UpdateMap()
PresentMap()
EndSelect
ForEver
EndIf
```

EndIf</lang>

### REALbasic

This example puts all of the forestry logic into a Thread class. This allows the UI to remain responsive while the Thread does all the work in the background. We create a Thread by subclassing the Thread object in the IDE, in this case creating forestfire as a subclass of the Thread object and put the following code in its Run() event: <lang realbasic> Sub Run()

``` //Handy named constants
Const empty = 0
Const tree = 1
Const fire = 2
Const ablaze = &cFF0000    //Using the &c numeric operator to indicate a color in hex
Const alive = &c00FF00

//Our forest
Dim worldPic As New Picture(480, 480, 32)
Dim newWorld(120, 120) As Integer
Dim oldWorld(120, 120) As Integer

//Initialize forest
Dim rand As New Random
For x as Integer = 0 to 119
For y as Integer = 0 to 119
if rand.InRange(0, 2) = 0 Or x = 119 or y = 119 or x = 0 or y = 0 Then
newWorld(x, y) = empty
worldPic.Graphics.FillRect(x*4, y*4, 4, 4)
Else
newWorld(x, y) = tree
worldPic.Graphics.ForeColor = alive
worldPic.Graphics.FillRect(x*4, y*4, 4, 4)
end if
Next
Next
oldWorld = newWorld

//Burn, baby burn!
While Window1.stop = False
For x as Integer = 0 To 119
For y As Integer = 0 to 119
Dim willBurn As Integer = rand.InRange(0, Window1.burnProb.Value)
Dim willGrow As Integer = rand.InRange(0, Window1.growProb.Value)
if x = 119 or y = 119 or x = 0 or y = 0 Then
Continue
end if
Select Case oldWorld(x, y)
Case empty
If willGrow = (Window1.growProb.Value) Then
newWorld(x, y) = tree
worldPic.Graphics.ForeColor = alive
worldPic.Graphics.FillRect(x*4, y*4, 4, 4)
end if
Case tree
if oldWorld(x - 1, y) = fire Or oldWorld(x, y - 1) = fire Or oldWorld(x + 1, y) = fire Or oldWorld(x, y + 1) = fire Or oldWorld(x + 1, y + 1) = fire Or oldWorld(x - 1, y - 1) = fire Or oldWorld(x - 1, y + 1) = fire Or oldWorld(x + 1, y - 1) = fire Or willBurn = (Window1.burnProb.Value) Then
newWorld(x, y) = fire
worldPic.Graphics.ForeColor = ablaze
worldPic.Graphics.FillRect(x*4, y*4, 4, 4)
end if
Case fire
newWorld(x, y) = empty
worldPic.Graphics.FillRect(x*4, y*4, 4, 4)
End Select
Next
Next
Window1.Canvas1.Graphics.DrawPicture(worldPic, 0, 0)
oldWorld = newWorld
me.Sleep(Window1.speed.Value)
Wend
```

End Sub </lang> As you can see, this Thread is expecting a Window object called Window1 with several other objects within it. The IDE will automatically create a Window object called Window1 when a new GUI application is created. Our Window1 has 5 objects (widgets) in it: a Canvas (for displaying graphics), three sliders, and a pushbutton. <lang realbasic> Sub Open()

``` //First method to run on the creation of a new Window. We instantiate an instance of our forestFire thread and run it.
Dim fire As New forestFire
fire.Run()
```

End Sub

stop As Boolean //a globally accessible property of Window1. Boolean properties default to False.

Sub Pushbutton1.Action()

``` stop = True
```

End Sub </lang>

### Run BASIC

<lang runbasic>graphic #g, 200,200 dim preGen(200,200) dim newGen(200,200)

for gen = 1 to 200

``` for x = 1 to 199
for y = 1 to 199
select case preGen(x,y)
case 0
if rnd(0) > .99 then newGen(x,y) = 1  : #g "color green ; set "; x; " "; y
case 2
newGen(x,y) = 0                       : #g "color brown ; set "; x; " "; y
case 1
if preGen(x-1,y-1) = 2 or preGen(x-1,y)   = 2 or preGen(x-1,y+1) = 2 _
or preGen(x,y-1)   = 2 or preGen(x,y+1)   = 2 or preGen(x+1,y-1) = 2 _
or preGen(x+1,y)   = 2 or preGen(x+1,y+1) = 2 or rnd(0) > .999 then
#g "color red ; set "; x; " "; y
newGen(x,y) = 2
end if
end select
preGen(x-1,y-1) = newGen(x-1,y-1)
next y
next x
```

next gen render #g</lang>

### Sinclair ZX81 BASIC

Requires 16k of RAM.

In essence this is an enhanced version of my ZX Spectrum implementation (see below). The main improvement is that this version shows the ages of the trees: the age is represented using `0` to `9`, then `A` to `Z`, followed theoretically by the special characters `£\$:?()><=+-*/;,.` (in that order) and only then cycling back to `0`. Realistically, no tree is likely to live that long.

The subroutine at line 1000 takes a number `N` and returns its inverse-video string representation as `I\$`.

A couple of other notes on the listing:

(1) some characters need to be entered in `G`raphics mode, which is accessed using `SHIFT``9`. I have represented this using square brackets: so if the listing says `[ROSETTA CODE]`, you need to go into `G` mode and type `ROSETTA CODE` (which will be displayed on the ZX81 screen in inverse video). As a special case, `[a]` means for you to go into `G` mode and then type `SHIFT``A`. The ZX81 character set does not include either square brackets or lower-case letters, so I hope this convention will not lead to too much confusion.

(2) this program differs from most BASIC examples on Rosetta Code, but resembles most real BASIC programs of more than about 20 lines, in that the line numbers do not always go up smoothly in multiples of ten. <lang basic> 10 DIM F\$(20,30)

``` 20 DIM N\$(20,30)
30 LET INIT=.5
40 LET F=.02
50 LET P=.05
60 PRINT AT 0,1;"[FOREST FIRE   FOR ROSETTA CODE]"
70 FOR I=0 TO 21
80 PRINT AT I,0;"[ ]"
90 PRINT AT I,31;"[ ]"
100 NEXT I
110 FOR I=1 TO 30
120 PRINT AT 21,I;"[ ]"
130 NEXT I
140 LET G=0
150 LET T=0
160 PRINT AT 21,1;"[GENERATION 0]"
170 PRINT AT 21,20;"[COVER]"
180 FOR I=1 TO 20
190 FOR J=1 TO 30
200 IF RND>=INIT THEN GOTO 240
210 PRINT AT I,J;"0"
220 LET F\$(I,J)="0"
230 LET T=T+1
240 NEXT J
250 NEXT I
300 PRINT AT 21,26;"[      ]"
310 LET N=INT (.5+T/6)
320 GOSUB 1000
330 PRINT AT 21,26;I\$;"[ PC]"
340 FOR I=1 TO 20
350 PRINT AT I,0;"[>]"
360 FOR J=1 TO 30
380 IF F\$(I,J)<>"[a]" THEN GOTO 410
390 LET N\$(I,J)=" "
400 GOTO 530
410 IF F\$(I,J)<>" " THEN GOTO 433
420 IF RND<=P THEN LET N\$(I,J)="0"
430 GOTO 530
433 LET N\$(I,J)=CHR\$ (1+CODE F\$(I,J))
437 IF N\$(I,J)>"Z" THEN LET N\$(I,J)="£"
440 FOR K=I-1 TO I+1
450 FOR L=J-1 TO J+1
460 IF K=0 OR L=0 OR K=21 OR L=21 THEN GOTO 480
470 IF F\$(K,L)="[a]" THEN GOTO 510
480 NEXT L
490 NEXT K
500 GOTO 520
510 LET N\$(I,J)="[a]"
520 IF RND<=F THEN LET N\$(I,J)="[a]"
530 NEXT J
540 PRINT AT I,0;"[ ]"
550 NEXT I
552 LET G=G+1
554 LET N=G
556 GOSUB 1000
558 PRINT AT 21,12;I\$
560 LET T=0
570 FOR I=1 TO 20
575 PRINT AT I,31;"[<]"
580 FOR J=1 TO 30
590 IF N\$(I,J)<>"[a]" AND N\$(I,J)<>" " THEN LET T=T+1
600 NEXT J
610 LET F\$(I)=N\$(I)
620 PRINT AT I,1;F\$(I)
625 PRINT AT I,31;"[ ]"
630 GOTO 300
```

1000 LET S\$=STR\$ N 1010 LET I\$="" 1020 FOR K=1 TO LEN S\$ 1030 LET I\$=I\$+CHR\$ (128+CODE S\$(K)) 1040 NEXT K 1050 RETURN</lang>

Output:

Screenshot here.

### Visual Basic .NET

This program sits behind a Windows form with fixed borders, the only component of which is a timer (named Timer1, set to something like 50 or 100ms depending on the speed the user wants to see it). Other constant values (the probabilities and the window dimensions) can be set at the top of the code.

<lang vbnet>Public Class ForestFire

```   Private _forest(,) As ForestState
Private _isBuilding As Boolean
Private _bm As Bitmap
Private _gen As Integer
Private _sw As Stopwatch
```
```   Private Const _treeStart As Double = 0.5
Private Const _f As Double = 0.00001
Private Const _p As Double = 0.001
```
```   Private Const _winWidth As Integer = 300
Private Const _winHeight As Integer = 300
```
```   Private Enum ForestState
Empty
Burning
Tree
End Enum
```
```   Private Sub ForestFire_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
Me.ClientSize = New Size(_winWidth, _winHeight)
ReDim _forest(_winWidth, _winHeight)
```
```       Dim rnd As New Random()
For i As Integer = 0 To _winHeight - 1
For j As Integer = 0 To _winWidth - 1
_forest(j, i) = IIf(rnd.NextDouble <= _treeStart, ForestState.Tree, ForestState.Empty)
Next
Next
```
```       _sw = New Stopwatch
_sw.Start()
DrawForest()
Timer1.Start()
End Sub
```
```   Private Sub Timer1_Tick(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Timer1.Tick
If _isBuilding Then Exit Sub
```
```       _isBuilding = True
GetNextGeneration()
```
```       DrawForest()
_isBuilding = False
End Sub
```
```   Private Sub GetNextGeneration()
Dim forestCache(_winWidth, _winHeight) As ForestState
Dim rnd As New Random()
```
```       For i As Integer = 0 To _winHeight - 1
For j As Integer = 0 To _winWidth - 1
Select Case _forest(j, i)
Case ForestState.Tree
If forestCache(j, i) <> ForestState.Burning Then
forestCache(j, i) = IIf(rnd.NextDouble <= _f, ForestState.Burning, ForestState.Tree)
End If
```
```                   Case ForestState.Burning
For i2 As Integer = i - 1 To i + 1
If i2 = -1 OrElse i2 >= _winHeight Then Continue For
For j2 As Integer = j - 1 To j + 1
If j2 = -1 OrElse i2 >= _winWidth Then Continue For
If _forest(j2, i2) = ForestState.Tree Then forestCache(j2, i2) = ForestState.Burning
Next
Next
forestCache(j, i) = ForestState.Empty
```
```                   Case Else
forestCache(j, i) = IIf(rnd.NextDouble <= _p, ForestState.Tree, ForestState.Empty)
End Select
Next
Next
```
```       _forest = forestCache
_gen += 1
End Sub
```
```   Private Sub DrawForest()
Dim bmCache As New Bitmap(_winWidth, _winHeight)
```
```       For i As Integer = 0 To _winHeight - 1
For j As Integer = 0 To _winWidth - 1
Select Case _forest(j, i)
Case ForestState.Tree
bmCache.SetPixel(j, i, Color.Green)
```
```                   Case ForestState.Burning
bmCache.SetPixel(j, i, Color.Red)
End Select
Next
Next
```
```       _bm = bmCache
Me.Refresh()
End Sub
```
```   Private Sub ForestFire_Paint(ByVal sender As System.Object, ByVal e As System.Windows.Forms.PaintEventArgs) Handles MyBase.Paint
e.Graphics.DrawImage(_bm, 0, 0)
```
```       Me.Text = "Gen " & _gen.ToString() & " @ " & (_gen / (_sw.ElapsedMilliseconds / 1000)).ToString("F02") & " FPS: Forest Fire"
End Sub
```

End Class</lang>

### ZX Spectrum Basic

This isn't a graphical implementation, but it uses a bit of colour to make the display clearer. It runs very slowly. The variable init defines the initial likelihood that each square will hold a tree, and can take values between 0 (no trees) and 1 (a tree in every square) inclusive. This can be used to check that the program is running correctly, and using a value of 1 is probably the most dramatic: but it only makes a difference in the short term. After a few generations, any starting configuration using these values of ${\displaystyle f}$ and ${\displaystyle p}$ will end up fluctuating around 20% tree cover—sparse woodland, perhaps, rather than true forest.

A screenshot of the program running can be found here. <lang zxbasic> 10 PAPER 6: CLS

```20 DIM n\$(20,30)
30 LET init=.5
40 LET f=.02
50 LET p=.05
60 PAPER 0
70 FOR i=0 TO 31
80 PRINT AT 0,i;" "
90 PRINT AT 21,i;" "
```

100 NEXT i 110 FOR i=0 TO 21 120 PRINT AT i,0;" " 130 PRINT AT i,31;" " 140 NEXT i 150 INK 7 160 PRINT AT 0,1;"FOREST FIRE for Rosetta Code" 170 LET generation=0 180 PRINT AT 21,1;"Generation 0" 190 LET trees=0 200 PRINT AT 21,22;"Cover" 210 FOR i=1 TO 20 220 FOR j=1 TO 30 230 IF RND<init THEN PAPER 4: INK 7: PRINT AT i,j;"T": LET trees=trees+1 240 NEXT j 250 NEXT i 260 LET generation=generation+1 270 INK 7 280 PAPER 0 290 PRINT AT 21,12;generation 300 PRINT AT 21,28;" " 310 PRINT AT 21,28;INT (trees/6+.5);"%" 320 FOR i=1 TO 20 330 FOR j=1 TO 30 340 LET n\$(i,j)=SCREEN\$ (i,j) 350 IF SCREEN\$ (i,j)="B" THEN LET n\$(i,j)=" ": GO TO 450 360 IF SCREEN\$ (i,j)="T" THEN GO TO 390 370 IF RND<=p THEN LET n\$(i,j)="T" 380 GO TO 450 390 FOR k=i-1 TO i+1 400 FOR l=j-1 TO j+1 410 IF SCREEN\$ (k,l)="B" THEN LET n\$(i,j)="B": LET k=i+2: LET l=j+2 420 NEXT l 430 NEXT k 440 IF RND<=f THEN LET n\$(i,j)="B" 450 NEXT j 460 NEXT i 470 LET trees=0 480 FOR i=1 TO 20 490 FOR j=1 TO 30 500 IF n\$(i,j)="T" THEN INK 7: PAPER 4: PRINT AT i,j;"T": LET trees=trees+1: GO TO 540 510 IF n\$(i,j)="B" THEN INK 6: PAPER 2: PRINT AT i,j;"B": GO TO 540 520 PAPER 6 530 PRINT AT i,j;" " 540 NEXT j 550 NEXT i 560 GO TO 260</lang>

## Batch File

Accepts command line arguments in the form of `m p f i`
Where:

```m - length and width of the array
p - probability of a tree growing
f - probability of a tree catching on fire
i - iterations to output
```

Default is ` 10 50 5 5 ` <lang dos> @echo off setlocal enabledelayedexpansion

if "%1"=="" (

``` call:default
```

) else (

``` call:setargs %*
```

)

call:createarray call:fillarray call:display echo. echo ------------------- echo.

for /l %%i in (1,1,%i%) do (

``` echo.
echo  -------------------
echo.
call:evolve
call:display
```

) pause>nul

default

set m=10 set n=11 set p=50 set f=5 set i=5 exit /b

setargs

set m=%1 set n=%m%+1 set p=%2 set f=%3 set i=%4 exit /b

createarray

for /l %%m in (0,1,%n%) do (

``` for /l %%n in (0,1,%n%) do (
set a%%m%%n=0
)
```

) exit /b

fillarray

for /l %%m in (1,1,%m%) do (

``` for /l %%n in (1,1,%m%) do (
set /a treerandom=!random! %% 101
if !treerandom! leq %p% set a%%m%%n=T
)
```

) exit /b

display

for /l %%m in (1,1,%m%) do (

``` set "line%%m="
for /l %%n in (1,1,%m%) do (
set line%%m=!line%%m! !a%%m%%n!
)
set line%%m=!line%%m:0= !
echo.!line%%m!
```

) exit /b

evolve

for /l %%m in (1,1,%m%) do (

``` for /l %%n in (1,1,%m%) do (
call:nexttick !a%%m%%n! %%m %%n
set newa%%m%%n=!errorlevel!
)
```

) call:update exit /b

nexttick

if %1==0 (

``` set /a treerandom=!random! %% 101
if !treerandom! leq %p% exit /b 1
exit /b 0
```

)

if %1==T (

``` set /a lowerm=%2-1
set /a upperm=%2+1
set /a lowern=%3-1
set /a uppern=%3+1
set burn=0
for /l %%m in (!lowerm!,1,!upperm!) do (
for /l %%n in (!lowern!,1,!uppern!) do (
if !a%%m%%n!==# set burn=1
)
)
if !burn!==1 exit /b 2

set /a burnrandom=!random! %% 101
if !burnrandom! leq %f% exit /b 2
exit /b 1
```

)

if %1==# exit /b 0

update

for /l %%m in (1,1,%m%) do (

``` for /l %%n in (1,1,%m%) do (
if !newa%%m%%n!==1 set newa%%m%%n=T
if !newa%%m%%n!==2 set newa%%m%%n=#
set a%%m%%n=!newa%%m%%n!
)
```

) exit /b </lang>

Output:

Sample Default Output

```     T T           T
T T T   T       T
T T   T
T T T T T T   T
T   T       T T
T     T T T T T T
T   T     T T   T
T T       T     T T
T   T T T   T   T
T     T T   T   T

-------------------

-------------------

T T # T     T   T #
T T T T   T   T T T
T T T   T T T
T T T T T T   T T T
T T T   T       T T
T T T T T T T T T T
T T T T T T T T T
T T     T T     T T
T T T T T T T T   #
T     T T T T T T

-------------------

T #   #     #   #
T # # # T T T T # #
T T T   T T T
T T T T T T   T T T
T T T T T T     T T
T T T T T # T T T T
T T T T T T T T #
T T T   T T   T # #
T T T T # T T T
#     T T T T T #

-------------------

#   T             T
#       # # # #
T # # # T # # #
T T T T T T T T T T
T T T T # # T   T T
T T T T #   # T # #
T T T T # # # # #
T T T   # #   #
# # T #   # T # T T
T   # # # T #   T

-------------------

T T T T T T   T
T
#       #
T # # # # # # # # #
T # T #     # T # #
T # T #       #
T T T #
# # # T           T
#       #   # T
T #         #     T

-------------------

T T T T T T T   T
T     T T T T
T     T           T
#
#   #   T     #
#   #   T T
# # #       T T   T
#   T       #
T     T T T       #
#   T T         T #
```

## C

Works with: POSIX
Library: SDL

<lang c>#include <stdio.h>

1. include <stdlib.h>
2. include <stdint.h>
3. include <stdbool.h>
4. include <string.h>
1. include <SDL.h>

// defaults

1. define PROB_TREE 0.55
2. define PROB_F 0.00001
3. define PROB_P 0.001
1. define TIMERFREQ 100
1. ifndef WIDTH
2. define WIDTH 640
3. endif
4. ifndef HEIGHT
5. define HEIGHT 480
6. endif
7. ifndef BPP
8. define BPP 32
9. endif
1. if BPP != 32
``` #warning This program could not work with BPP different from 32
```
1. endif

uint8_t *field[2], swapu; double prob_f = PROB_F, prob_p = PROB_P, prob_tree = PROB_TREE;

enum cell_state {

``` VOID, TREE, BURNING
```

};

// simplistic random func to give [0, 1) double prand() {

``` return (double)rand() / (RAND_MAX + 1.0);
```

}

// initialize the field void init_field(void) {

``` int i, j;
swapu = 0;
for(i = 0; i < WIDTH; i++)
{
for(j = 0; j < HEIGHT; j++)
{
*(field[0] + j*WIDTH + i) = prand() > prob_tree ? VOID : TREE;
}
}
```

}

// the "core" of the task: the "forest-fire CA" bool burning_neighbor(int, int); pthread_mutex_t synclock = PTHREAD_MUTEX_INITIALIZER; static uint32_t simulate(uint32_t iv, void *p) {

``` int i, j;
```
``` /*
Since this is called by SDL, "likely"(*) in a separated
thread, we try to avoid corrupted updating of the display
(done by the show() func): show needs the "right" swapu
i.e. the right complete field. (*) what if it is not so?
The following is an attempt to avoid unpleasant updates.
*/
```
``` for(i = 0; i < WIDTH; i++) {
for(j = 0; j < HEIGHT; j++) {
enum cell_state s = *(field[swapu] + j*WIDTH + i);
switch(s)
{
case BURNING:
```

*(field[swapu^1] + j*WIDTH + i) = VOID; break;

```     case VOID:
```

*(field[swapu^1] + j*WIDTH + i) = prand() > prob_p ? VOID : TREE; break;

```     case TREE:
```

if (burning_neighbor(i, j)) *(field[swapu^1] + j*WIDTH + i) = BURNING; else *(field[swapu^1] + j*WIDTH + i) = prand() > prob_f ? TREE : BURNING; break;

```     default:
```

fprintf(stderr, "corrupted field\n"); break;

```     }
}
}
swapu ^= 1;
return iv;
```

}

// the field is a "part" of an infinite "void" region

1. define NB(I,J) (((I)<WIDTH)&&((I)>=0)&&((J)<HEIGHT)&&((J)>=0) \

? (*(field[swapu] + (J)*WIDTH + (I)) == BURNING) : false) bool burning_neighbor(int i, int j) {

``` return NB(i-1,j-1) || NB(i-1, j) || NB(i-1, j+1) ||
NB(i, j-1) || NB(i, j+1) ||
NB(i+1, j-1) || NB(i+1, j) || NB(i+1, j+1);
```

}

// "map" the field into gfx mem // burning trees are red // trees are green // "voids" are black; void show(SDL_Surface *s) {

``` int i, j;
uint8_t *pixels = (uint8_t *)s->pixels;
uint32_t color;
SDL_PixelFormat *f = s->format;
```
``` pthread_mutex_lock(&synclock);
for(i = 0; i < WIDTH; i++) {
for(j = 0; j < HEIGHT; j++) {
switch(*(field[swapu] + j*WIDTH + i)) {
case VOID:
```

color = SDL_MapRGBA(f, 0,0,0,255); break;

```     case TREE:
```

color = SDL_MapRGBA(f, 0,255,0,255); break;

```     case BURNING:
```

color = SDL_MapRGBA(f, 255,0,0,255); break;

```     }
*(uint32_t*)(pixels + j*s->pitch + i*(BPP>>3)) = color;
}
}
```

}

int main(int argc, char **argv) {

``` SDL_Surface *scr = NULL;
SDL_Event event[1];
bool quit = false, running = false;
SDL_TimerID tid;
```
``` // add variability to the simulation
srand(time(NULL));
```
``` // we can change prob_f and prob_p
// prob_f prob of spontaneous ignition
// prob_p prob of birth of a tree
double *p;
for(argv++, argc--; argc > 0; argc--, argv++)
{
if ( strcmp(*argv, "prob_f") == 0 && argc > 1 )
{
p = &prob_f;
} else if ( strcmp(*argv, "prob_p") == 0 && argc > 1 ) {
p = &prob_p;
} else if ( strcmp(*argv, "prob_tree") == 0 && argc > 1 ) {
p = &prob_tree;
} else  continue;
```

```   argv++; argc--;
char *s = NULL;
double t = strtod(*argv, &s);
if (s != *argv) *p = t;
}
```
``` printf("prob_f %lf\nprob_p %lf\nratio %lf\nprob_tree %lf\n",
```

prob_f, prob_p, prob_p/prob_f, prob_tree);

``` if ( SDL_Init(SDL_INIT_VIDEO|SDL_INIT_TIMER) != 0 ) return EXIT_FAILURE;
atexit(SDL_Quit);
```
``` field[0] = malloc(WIDTH*HEIGHT);
if (field[0] == NULL) exit(EXIT_FAILURE);
field[1] = malloc(WIDTH*HEIGHT);
if (field[1] == NULL) { free(field[0]); exit(EXIT_FAILURE); }
```
``` scr = SDL_SetVideoMode(WIDTH, HEIGHT, BPP, SDL_HWSURFACE|SDL_DOUBLEBUF);
if (scr == NULL) {
fprintf(stderr, "SDL_SetVideoMode: %s\n", SDL_GetError());
free(field[0]); free(field[1]);
exit(EXIT_FAILURE);
}
```
``` init_field();
```
``` tid = SDL_AddTimer(TIMERFREQ, simulate, NULL); // suppose success
running = true;
```
``` event->type = SDL_VIDEOEXPOSE;
SDL_PushEvent(event);
```
``` while(SDL_WaitEvent(event) && !quit)
{
switch(event->type)
{
case SDL_VIDEOEXPOSE:
while(SDL_LockSurface(scr) != 0) SDL_Delay(1);
show(scr);
SDL_UnlockSurface(scr);
SDL_Flip(scr);
event->type = SDL_VIDEOEXPOSE;
SDL_PushEvent(event);
break;
case SDL_KEYDOWN:
switch(event->key.keysym.sym)
{
case SDLK_q:
```

quit = true; break;

```     case SDLK_p:
```

if (running) { running = false; pthread_mutex_lock(&synclock); SDL_RemoveTimer(tid); // ignore failure... pthread_mutex_unlock(&synclock); } else { running = true; tid = SDL_AddTimer(TIMERFREQ, simulate, NULL); // suppose success... } break;

```     }
case SDL_QUIT:
quit = true;
break;
}
}
```
``` if (running) {
SDL_RemoveTimer(tid);
}
free(field[0]); free(field[1]);
exit(EXIT_SUCCESS);
```

}</lang>

### Console version

C99. Uncomment srand() for variaty, usleep() for slower speed. <lang C>#include <stdio.h>

1. include <stdlib.h>
2. include <unistd.h>
3. include <time.h> // For time

enum { empty = 0, tree = 1, fire = 2 }; const char *disp[] = {" ", "\033[32m/\\\033[m", "\033[07;31m/\\\033[m"}; double tree_prob = 0.01, burn_prob = 0.0001;

1. define for_x for (int x = 0; x < w; x++)
2. define for_y for (int y = 0; y < h; y++)
3. define for_yx for_y for_x
4. define chance(x) (rand() < RAND_MAX * x)

void evolve(int w, int h) { unsigned univ[h][w], new[h][w]; for_yx new[y][x] = univ[y][x] = chance(tree_prob) ? tree : empty;

show: printf("\033[H"); for_y { for_x printf("%s",disp[univ[y][x]]); printf("\033[E"); } fflush(stdout);

for_yx { switch (univ[y][x]) { case fire: new[y][x] = empty; break; case empty: if (chance(tree_prob)) new[y][x] = tree; break; default: for (int y1 = y - 1; y1 <= y + 1; y1++) { if (y1 < 0 || y1 >= h) continue; for (int x1 = x - 1; x1 <= x + 1; x1++) { if (x1 < 0 || x1 >= w) continue; if (univ[y1][x1] != fire) continue;

new[y][x] = fire; goto burn; } }

burn: if (new[y][x] == tree && chance(burn_prob)) new[y][x] = fire; } }

for_yx { univ[y][x] = new[y][x]; } //usleep(100000); goto show; }

int main(int c, char **v) { //srand(time(0)); int w = 0, h = 0;

if (c > 1) w = atoi(v[1]); if (c > 2) h = atoi(v[2]); if (w <= 0) w = 30; if (h <= 0) h = 30;

evolve(w, h); }</lang>

## C#

<lang csharp>using System; using System.Drawing; using System.Drawing.Drawing2D; using System.Threading; using System.Windows.Forms;

namespace ForestFire {

```   class Program : Form
{
private static readonly Random rand = new Random();
private Bitmap img;
```
```       public Program(int w, int h, int f, int p)
{
Size = new Size(w, h);
StartPosition = FormStartPosition.CenterScreen;
```
```           Thread t = new Thread(() => fire(f, p));
t.Start();
```
```           FormClosing += (object sender, FormClosingEventArgs e) => { t.Abort(); t = null; };
}
```
```       private void fire(int f, int p)
{
int clientWidth = ClientRectangle.Width;
int clientHeight = ClientRectangle.Height;
int cellSize = 10;
```
```           img = new Bitmap(clientWidth, clientHeight);
Graphics g = Graphics.FromImage(img);
```
```           CellState[,] state = InitializeForestFire(clientWidth, clientHeight);
```
```           uint generation = 0;
```
```           do
{
g.FillRectangle(Brushes.White, 0, 0, img.Width, img.Height);
state = StepForestFire(state, f, p);
```
```               for (int y = 0; y < clientHeight - cellSize; y += cellSize)
{
for (int x = 0; x < clientWidth - cellSize; x += cellSize)
{
switch (state[y, x])
{
case CellState.Empty:
break;
case CellState.Tree:
g.FillRectangle(Brushes.DarkGreen, x, y, cellSize, cellSize);
break;
case CellState.Burning:
g.FillRectangle(Brushes.DarkRed, x, y, cellSize, cellSize);
break;
}
}
}
```
```               Thread.Sleep(500);
```
```               Invoke((MethodInvoker)Refresh);
```
```           } while (generation < uint.MaxValue);
```
```           g.Dispose();
}
```
```       private CellState[,] InitializeForestFire(int width, int height)
{
// Create our state array, initialize all indices as Empty, and return it.
var state = new CellState[height, width];
state.Initialize();
return state;
}
```
```       private enum CellState : byte
{
Empty = 0,
Tree = 1,
Burning = 2
}
```
```       private CellState[,] StepForestFire(CellState[,] state, int f, int p)
{
/* Clone our old state, so we can write to our new state
* without changing any values in the old state. */
var newState = (CellState[,])state.Clone();
```
```           int numRows = state.GetLength(0);
int numCols = state.GetLength(1);
```
```           for (int r = 1; r < numRows - 1; r++)
{
for (int c = 1; c < numCols - 1; c++)
{
/*
* Check the current cell.
*
* If it's empty, give it a 1/p chance of becoming a tree.
*
* If it's a tree, check to see if any neighbors are burning.
* If so, set the cell's state to burning, otherwise give it
* a 1/f chance of combusting.
*
* If it's burning, set it to empty.
*/
switch (state[r, c])
{
case CellState.Empty:
if (rand.Next(0, p) == 0)
newState[r, c] = CellState.Tree;
break;
```
```                       case CellState.Tree:
if (NeighborHasState(state, r, c, CellState.Burning) || rand.Next(0, f) == 0)
newState[r, c] = CellState.Burning;
break;
```
```                       case CellState.Burning:
newState[r, c] = CellState.Empty;
break;
}
}
}
```
```           return newState;
}
```
```       private bool NeighborHasState(CellState[,] state, int x, int y, CellState value)
{
// Check each cell within a 1 cell radius for the specified value.
for (int r = -1; r <= 1; r++)
{
for (int c = -1; c <= 1; c++)
{
if (r == 0 && c == 0)
continue;
```
```                   if (state[x + r, y + c] == value)
return true;
}
}
```
```           return false;
}
```
```       protected override void OnPaint(PaintEventArgs e)
{
base.OnPaint(e);
e.Graphics.DrawImage(img, 0, 0);
}
```
```       [STAThread]
static void Main(string[] args)
{
Application.Run(new Program(w: 500, h: 500, f: 2, p: 5));
}
}
```

}</lang>

## C++

<lang cpp>

1. include <windows.h>
2. include <string>

//-------------------------------------------------------------------------------------------------- using namespace std;

//-------------------------------------------------------------------------------------------------- enum states { NONE, TREE, FIRE }; const int MAX_SIDE = 500;

//-------------------------------------------------------------------------------------------------- class myBitmap { public:

```   myBitmap() : pen( NULL ) {}
~myBitmap()
{
```

DeleteObject( pen ); DeleteDC( hdc ); DeleteObject( bmp );

```   }
```
```   bool create( int w, int h )
{
```

BITMAPINFO bi; ZeroMemory( &bi, sizeof( bi ) );

HDC dc = GetDC( GetConsoleWindow() ); bmp = CreateDIBSection( dc, &bi, DIB_RGB_COLORS, &pBits, NULL, 0 ); if( !bmp ) return false;

hdc = CreateCompatibleDC( dc ); SelectObject( hdc, bmp ); ReleaseDC( GetConsoleWindow(), dc );

width = w; height = h;

return true;

```   }
```
```   void clear()
{
```

ZeroMemory( pBits, width * height * sizeof( DWORD ) );

```   }
```
```   void setPenColor( DWORD clr )
{
```

if( pen ) DeleteObject( pen ); pen = CreatePen( PS_SOLID, 1, clr ); SelectObject( hdc, pen );

```   }
```
```   void saveBitmap( string path )
{
```

GetObject( bmp, sizeof( bitmap ), &bitmap );

DWORD* dwpBits = new DWORD[bitmap.bmWidth * bitmap.bmHeight]; ZeroMemory( dwpBits, bitmap.bmWidth * bitmap.bmHeight * sizeof( DWORD ) ); ZeroMemory( &infoheader, sizeof( BITMAPINFO ) ); ZeroMemory( &fileheader, sizeof( BITMAPFILEHEADER ) );

GetDIBits( hdc, bmp, 0, height, ( LPVOID )dwpBits, &infoheader, DIB_RGB_COLORS );

HANDLE file = CreateFile( path.c_str(), GENERIC_WRITE, 0, NULL, CREATE_ALWAYS, FILE_ATTRIBUTE_NORMAL, NULL ); WriteFile( file, &fileheader, sizeof( BITMAPFILEHEADER ), &wb, NULL ); WriteFile( file, &infoheader.bmiHeader, sizeof( infoheader.bmiHeader ), &wb, NULL ); WriteFile( file, dwpBits, bitmap.bmWidth * bitmap.bmHeight * 4, &wb, NULL ); CloseHandle( file );

delete [] dwpBits;

```   }
```
```   HDC getDC() const     { return hdc; }
int getWidth() const  { return width; }
int getHeight() const { return height; }
```

private:

```   HBITMAP bmp;
HDC	    hdc;
HPEN    pen;
void	*pBits;
int	    width, height;
```

}; //-------------------------------------------------------------------------------------------------- class forest { public:

```   forest()
{
```

_bmp.create( MAX_SIDE, MAX_SIDE ); initForest( 0.05f, 0.005f );

```   }
```
```   void initForest( float p, float f )
{
```

_p = p; _f = f; seedForest();

```   }
```
```   void mainLoop()
{
```

display(); simulate();

```   }
```
```   void setHWND( HWND hwnd ) { _hwnd = hwnd; }
```

private:

```   float probRand() { return ( float )rand() / 32768.0f; }
```
```   void display()
{
```

HDC bdc = _bmp.getDC(); DWORD clr;

for( int y = 0; y < MAX_SIDE; y++ ) { for( int x = 0; x < MAX_SIDE; x++ ) { switch( _forest[x][y] ) { case FIRE: clr = 255; break; case TREE: clr = RGB( 0, 255, 0 ); break; default: clr = 0; }

SetPixel( bdc, x, y, clr ); } }

HDC dc = GetDC( _hwnd ); BitBlt( dc, 0, 0, MAX_SIDE, MAX_SIDE, _bmp.getDC(), 0, 0, SRCCOPY ); ReleaseDC( _hwnd, dc );

```   }
```
```   void seedForest()
{
```

ZeroMemory( _forestT, sizeof( _forestT ) ); ZeroMemory( _forest, sizeof( _forest ) ); for( int y = 0; y < MAX_SIDE; y++ ) for( int x = 0; x < MAX_SIDE; x++ ) if( probRand() < _p ) _forest[x][y] = TREE;

```   }
```
```   bool getNeighbors( int x, int y )
{
```

int a, b; for( int yy = -1; yy < 2; yy++ ) for( int xx = -1; xx < 2; xx++ ) { if( !xx && !yy ) continue; a = x + xx; b = y + yy; if( a < MAX_SIDE && b < MAX_SIDE && a > -1 && b > -1 ) if( _forest[a][b] == FIRE ) return true; }

return false;

```   }
```
```   void simulate()
{
```

for( int y = 0; y < MAX_SIDE; y++ ) { for( int x = 0; x < MAX_SIDE; x++ ) { switch( _forest[x][y] ) { case FIRE: _forestT[x][y] = NONE; break; case NONE: if( probRand() < _p ) _forestT[x][y] = TREE; break; case TREE: if( getNeighbors( x, y ) || probRand() < _f ) _forestT[x][y] = FIRE; } } }

for( int y = 0; y < MAX_SIDE; y++ ) for( int x = 0; x < MAX_SIDE; x++ ) _forest[x][y] = _forestT[x][y];

```   }
```
```   myBitmap _bmp;
HWND     _hwnd;
BYTE     _forest[MAX_SIDE][MAX_SIDE], _forestT[MAX_SIDE][MAX_SIDE];
float    _p, _f;
```

}; //-------------------------------------------------------------------------------------------------- class wnd { public:

```   int wnd::Run( HINSTANCE hInst )
{
```

_hInst = hInst; _hwnd = InitAll();

_ff.setHWND( _hwnd ); _ff.initForest( 0.02f, 0.001f );

ShowWindow( _hwnd, SW_SHOW ); UpdateWindow( _hwnd );

MSG msg; ZeroMemory( &msg, sizeof( msg ) ); while( msg.message != WM_QUIT ) { if( PeekMessage( &msg, NULL, 0, 0, PM_REMOVE ) != 0 ) { TranslateMessage( &msg ); DispatchMessage( &msg ); } else { _ff.mainLoop(); } } return UnregisterClass( "_FOREST_FIRE_", _hInst );

```   }
```

private:

```   static int WINAPI wnd::WndProc( HWND hWnd, UINT msg, WPARAM wParam, LPARAM lParam )
{
```

switch( msg ) { case WM_DESTROY: PostQuitMessage( 0 ); break; default: return DefWindowProc( hWnd, msg, wParam, lParam ); } return 0;

```   }
```
```   HWND InitAll()
{
```

WNDCLASSEX wcex; ZeroMemory( &wcex, sizeof( wcex ) ); wcex.cbSize = sizeof( WNDCLASSEX ); wcex.style = CS_HREDRAW | CS_VREDRAW; wcex.lpfnWndProc = ( WNDPROC )WndProc; wcex.hInstance = _hInst; wcex.hCursor = LoadCursor( NULL, IDC_ARROW ); wcex.hbrBackground = ( HBRUSH )( COLOR_WINDOW + 1 ); wcex.lpszClassName = "_FOREST_FIRE_";

RegisterClassEx( &wcex );

return CreateWindow( "_FOREST_FIRE_", ".: Forest Fire -- PJorente :.", WS_SYSMENU, CW_USEDEFAULT, 0, MAX_SIDE, MAX_SIDE, NULL, NULL, _hInst, NULL );

```   }
```
```   HINSTANCE _hInst;
HWND      _hwnd;
forest    _ff;
```

}; //-------------------------------------------------------------------------------------------------- int APIENTRY _tWinMain( HINSTANCE hInstance, HINSTANCE hPrevInstance, LPTSTR lpCmdLine, int nCmdShow ) {

```   srand( GetTickCount() );
wnd myWnd;
return myWnd.Run( hInstance );
```

} //-------------------------------------------------------------------------------------------------- </lang>

## Ceylon

<lang ceylon>import ceylon.random { DefaultRandom }

abstract class Cell() of tree | dirt | burning {} object tree extends Cell() { string => "A"; } object dirt extends Cell() { string => " "; } object burning extends Cell() { string => "#"; }

class Forest(Integer width, Integer height, Float f, Float p) {

```   value random = DefaultRandom();
function chance(Float probability) => random.nextFloat() < probability;
value sparked => chance(f);
value sprouted => chance(p);
```
```   alias Point => Integer[2];
interface Row => {Cell*};
```
```   object doubleBufferedGrid satisfies
Correspondence<Point, Cell> &
KeyedCorrespondenceMutator<Point, Cell> {
```
```       value grids = [
Array {
for (j in 0:height)
Array {
for (i in 0:width)
chance(0.5) then tree else dirt
}
},
Array {
for (j in 0:height)
Array.ofSize(width, dirt)
}
];
```
```       variable value showFirst = true;
value currentState => showFirst then grids.first else grids.last;
value nextState => showFirst then grids.last else grids.first;
```
```       shared void swapStates() => showFirst = !showFirst;
```
```       shared {Row*} rows => currentState;
```
```       shared actual Boolean defines(Point key) =>
let (x = key[0], y = key[1])
0 <= x < width && 0 <= y < height;
shared actual Cell? get(Point key) =>
let (x = key[0], y = key[1])
currentState.get(y)?.get(x);
```
```       shared actual void put(Point key, Cell cell) {
value [x, y] = key;
nextState.get(y)?.set(x, cell);
}
}
```
```   variable value evolutions = 0;
shared Integer generation => evolutions + 1;
```
```   shared void evolve() {
```
```       evolutions++;
```
```       function firesNearby(Integer x, Integer y) => {
for (j in y - 1 : 3)
for (i in x - 1 : 3)
doubleBufferedGridi, j
}.coalesced.any(burning.equals);
```
```       for(j->row in doubleBufferedGrid.rows.indexed) {
for(i->cell in row.indexed) {
switch (cell)
case (burning) {
doubleBufferedGridi, j = dirt;
}
case (dirt) {
doubleBufferedGridi, j = sprouted then tree else dirt;
}
case (tree) {
doubleBufferedGridi, j =
firesNearby(i, j) || sparked
then burning else tree;
}
}
}
```
```       doubleBufferedGrid.swapStates();
}
```
```   shared void display() {
```
```       void drawLine() => print("-".repeat(width + 2));
```
```       drawLine();
for (row in doubleBufferedGrid.rows) {
process.write("|");
for (cell in row) {
process.write(cell.string);
}
print("|");
}
drawLine();
}
```

}

shared void run() {

```   value forest = Forest(78, 38, 0.02, 0.03);
```
```   while (true) {
```
```       forest.display();
```
```       print("Generation ``forest.generation``");
print("Press enter for next generation or q and then enter to quit");
```
```       value input = process.readLine();
if (exists input, input.trimmed.lowercased == "q") {
return;
}
```
```       forest.evolve();
}
```

}</lang>

## Clojure

<lang Clojure> (def burn-prob 0.1) (def new-tree-prob 0.5)

(defn grow-new-tree? [] (> new-tree-prob (rand))) (defn burn-tree? [] (> burn-prob (rand))) (defn tree-maker [] (if (grow-new-tree?) :tree :grass))

(defn make-forest

``` ([] (make-forest 5))
([size]
(take size (repeatedly #(take size (repeatedly tree-maker))))))
```

(defn tree-at [forest row col] (try (-> forest

```                                  (nth row)
(nth col))
(catch Exception _ false)))
```

(defn neighbores-burning? [forest row col]

``` (letfn [(burnt? [row col] (= :burnt (tree-at forest row col)))]
(or
(burnt? (inc row) col)
(burnt? (dec row) col)
(burnt? row (inc col))
(burnt? row (dec col)))))
```

(defn lightning-strike [forest]

``` (map (fn [forest-row]
(map #(if (and (= % :tree) (burn-tree?))
:fire!
%)
forest-row)
)
forest))
```

(defn burn-out-trees [forest]

``` (map (fn [forest-row]
(map #(case %
:burnt :grass
:fire! :burnt
%)
forest-row))
forest))
```

(defn burn-neighbores [forest]

``` (let [forest-size (count forest)
indicies (partition forest-size (for [row (range forest-size) col (range forest-size)] (cons row (list col))))]
(map (fn [forest-row indicies-row]
(map #(if (and
(= :tree %)
(neighbores-burning? forest (first %2) (second %2)))
:fire!
%)
forest-row indicies-row))
forest indicies)))

```

(defn grow-new-trees [forest] (map (fn [forest-row]

```                                    (map #(if (= % :grass)
(tree-maker)
%)
forest-row))
forest))
```

(defn forest-fire

``` ([] (forest-fire 5))
([forest-size]
(loop
[forest (make-forest forest-size)]
(pprint forest)
(-> forest
(burn-out-trees)
(lightning-strike)
(burn-neighbores)
(grow-new-trees)
(recur)))))
```

(forest-fire)

</lang>

example output

```((:tree :tree :grass :tree :tree)
(:tree :grass :tree :tree :tree)
(:fire! :tree :tree :grass :tree)
(:fire! :fire! :tree :tree :tree)
(:burnt :tree :tree :fire! :grass))

((:tree :tree :grass :tree :tree)
(:fire! :tree :tree :fire! :tree)
(:burnt :fire! :tree :grass :tree)
(:burnt :burnt :fire! :fire! :tree)
(:grass :fire! :fire! :burnt :tree))
```

## COBOL

Works with: OpenCOBOL

<lang cobol> IDENTIFICATION DIVISION.

```      PROGRAM-ID. forest-fire.
```
```      DATA DIVISION.
WORKING-STORAGE SECTION.
*> Probability represents a fraction of 10000.
*> For instance, IGNITE-PROB means a tree has a 1 in 10000 chance
*> of igniting.
78  IGNITE-PROB                 VALUE 1.
78  NEW-TREE-PROB               VALUE 100.
```
```      78  EMPTY-PROB                  VALUE 3333.
```
```      78  AREA-SIZE                   VALUE 40.
```
```      01  sim-table.
03  sim-row OCCURS AREA-SIZE TIMES INDEXED BY row-index.
05  sim-area OCCURS AREA-SIZE TIMES
INDEXED BY col-index.
07  current-status  PIC 9.
*> The flags correspond to the colours they will
*> be displayed as.
88  empty       VALUE 0. *> Black
88  tree        VALUE 2. *> Green
88  burning     VALUE 4. *> Red

07  next-status     PIC 9.
88  empty       VALUE 0.
88  tree        VALUE 2.
88  burning     VALUE 4.

01  rand-num                    PIC 9999.

01  next-row                    PIC 9(4).
01  next-col                    PIC 9(4).
```
```      01  neighbours-row              PIC 9(4).
01  neighbours-col              PIC 9(4).
```
```      PROCEDURE DIVISION.
main-line.
*> Seed RANDOM with current time.
MOVE FUNCTION RANDOM(FUNCTION CURRENT-DATE (9:8)) TO rand-num
```
```          PERFORM initialise-table
PERFORM FOREVER
PERFORM show-simulation
PERFORM step-simulation
END-PERFORM
```
```          GOBACK
.
```
```      initialise-table.
PERFORM VARYING row-index FROM 1 BY 1
UNTIL AREA-SIZE < row-index
AFTER col-index FROM 1 BY 1
UNTIL AREA-SIZE < col-index
PERFORM get-rand-num
IF rand-num <= EMPTY-PROB
SET empty OF current-status (row-index, col-index)
TO TRUE
SET empty OF next-status (row-index, col-index)
TO TRUE
ELSE
SET tree OF current-status (row-index, col-index)
TO TRUE
SET tree OF next-status (row-index, col-index)
TO TRUE
END-IF
END-PERFORM
.
```
```      show-simulation.
PERFORM VARYING row-index FROM 1 BY 1
UNTIL AREA-SIZE < row-index
AFTER col-index FROM 1 BY 1
UNTIL AREA-SIZE < col-index
DISPLAY SPACE AT LINE row-index COLUMN col-index
WITH BACKGROUND-COLOR
current-status (row-index, col-index)
END-PERFORM
.
```
```      *> Updates the simulation.
step-simulation.
PERFORM VARYING row-index FROM 1 BY 1
UNTIL AREA-SIZE < row-index
AFTER col-index FROM 1 BY 1
UNTIL AREA-SIZE < col-index
EVALUATE TRUE
WHEN empty OF current-status (row-index, col-index)
PERFORM get-rand-num
IF rand-num <= NEW-TREE-PROB
SET tree OF next-status
(row-index, col-index) TO TRUE
END-IF
```
```                   WHEN tree OF current-status (row-index, col-index)
PERFORM simulate-tree
```
```                   WHEN burning OF current-status
(row-index, col-index)
SET empty OF next-status (row-index, col-index)
TO TRUE
END-EVALUATE
END-PERFORM
```
```           PERFORM update-statuses.
.
```
```      *> Updates a tree tile, assuming row-index and col-index are at
*> a tree area.
simulate-tree.
*> Find the row and column of the bottom-right neighbour.
COMPUTE next-row = FUNCTION MIN(row-index + 1, AREA-SIZE)
COMPUTE next-col = FUNCTION MIN(col-index + 1, AREA-SIZE)

COMPUTE neighbours-row = FUNCTION MAX(row-index - 1, 1)
COMPUTE neighbours-col = FUNCTION MAX(col-index - 1, 1)
```
```          *> If a neighbour is burning, catch fire.
PERFORM VARYING neighbours-row FROM neighbours-row BY 1
UNTIL next-row < neighbours-row
*> Check if neighbours in a row are on fire.
PERFORM VARYING neighbours-col FROM neighbours-col BY 1
UNTIL next-col < neighbours-col
IF neighbours-row = row-index
AND neighbours-col = col-index
EXIT PERFORM CYCLE
END-IF

IF burning OF current-status
(neighbours-row, neighbours-col)
SET burning OF next-status (row-index, col-index)
TO TRUE
EXIT PARAGRAPH
END-IF
END-PERFORM
```
```              *> Move neighbours-col back to starting position
COMPUTE neighbours-col =
FUNCTION MAX(neighbours-col - 3, 1)
END-PERFORM
```
```          *> Otherwise, there is a random chance of
*> catching fire.
PERFORM get-rand-num
IF rand-num <= IGNITE-PROB
SET burning OF next-status (row-index, col-index) TO TRUE
END-IF
.
```
```      update-statuses.
PERFORM VARYING row-index FROM 1 BY 1
UNTIL AREA-SIZE < row-index
AFTER col-index FROM 1 BY 1
UNTIL AREA-SIZE < col-index
MOVE next-status (row-index, col-index)
TO current-status (row-index, col-index)
END-PERFORM
.
```
```      *> Puts a random value between 0 and 9999 in rand-num.
get-rand-num.
COMPUTE rand-num =
FUNCTION MOD(FUNCTION RANDOM * 100000, 10000)
.</lang>
```

## Common Lisp

<lang lisp>(defvar *dims* '(10 10)) (defvar *prob-t* 0.5) (defvar *prob-f* 0.1) (defvar *prob-p* 0.01)

(defmacro with-gensyms (names &body body)

``` `(let ,(mapcar (lambda (n) (list n '(gensym))) names)
```

,@body))

(defmacro traverse-grid (grid rowvar colvar (&rest after-cols) &body body)

``` (with-gensyms (dims rows cols)
```

`(let* ((,dims (array-dimensions ,grid)) (,rows (car ,dims)) (,cols (cadr ,dims))) (dotimes (,rowvar ,rows ,grid) (dotimes (,colvar ,cols ,after-cols) ,@body)))))

(defun make-new-forest (&optional (dims *dims*))

``` (let ((forest (make-array dims :element-type 'symbol :initial-element 'void)))
```

(traverse-grid forest row col nil (if (<= (random 1.0) *prob-t*) (setf (aref forest row col) 'tree)))))

(defun print-forest (forest)

``` (traverse-grid forest row col (terpri)
```

(ecase (aref forest row col) ((void) (write-char #\space)) ((tree) (write-char #\T)) ((fire) (write-char #\#))))

``` (values))
```

(defvar *neighboring* '((-1 . -1) (-1 . 0) (-1 . 1) (0 . -1) (0 . 1) (1 . -1) (1 . 0) (1 . 1)))

(defun neighbors (forest row col)

``` (loop for n in *neighboring*
```

for nrow = (+ row (car n))

```       for ncol = (+ col (cdr n))
```

when (array-in-bounds-p forest nrow ncol) collect (aref forest nrow ncol)))

(defun evolve-tree (forest row col)

``` (let ((tree (aref forest row col)))
```

(cond ((eq tree 'fire) ;; if the tree was on fire, it's dead Jim 'void) ((and (eq tree 'tree) ;; if a neighbor is on fire, it's on fire too (find 'fire (neighbors forest row col) :test #'eq)) 'fire) ((and (eq tree 'tree) ;; random chance of fire happening (<= (random 1.0) *prob-f*)) 'fire) ((and (eq tree 'void) ;; random chance of empty space becoming a tree (<= (random 1.0) *prob-p*)) 'tree) (t tree))))

(defun evolve-forest (forest)

``` (let* ((dims (array-dimensions forest))
```

(new (make-array dims :element-type 'symbol :initial-element 'void))) (traverse-grid forest row col nil (setf (aref new row col) (evolve-tree forest row col))) new))

(defun simulate (forest n &optional (print-all t))

``` (format t "------ Initial forest ------~%")
(print-forest forest)
(dotimes (i n)
(setf forest (evolve-forest forest))
(when print-all
(progn (format t "~%------ Generation ~d ------~%" (1+ i))
(print-forest forest)))))
```

</lang> Example results: <lang lisp>CL-USER>(defparameter *forest* (make-new-forest)) CL-USER>(simulate *forest* 5)

Initial forest ------

TTTTT TT

```  TTT  TT
TT T  T
TTTT T TT
```

T TT T T

```   T  TTT
TTTT TTT
T
T T T T
```

TTT TTT T

Generation 1 ------

TTTTT TT

```  TTT  TT
TT T  T
TTTT T TT
```

T TT T T

```   T  TTT
TTTT TTT
T
T T T T
```

TTT TTT T

Generation 2 ------

TTTTT TT

```  TTT  TT
TT T  T
TTTT T TT
```

TTTT T T

```   T  TTT
TTT# TTT
T
T T T T
```

TTT TTT T

Generation 3 ------

TTTTT TT

```  TTT  TT
TT T  T
TTTT T TT
```

TTTT T T

```   #  TTT
TT#  TTT
T
T T T T
```

TTT TTT T

Generation 4 ------

TTTTT TT

```  TTT  TT
TT T  TT
TTTT T TT
```

TTT# T T

```      TTT
T#   TTT
T
T T T T
```

TTT TTT T

Generation 5 ------

TTTTT TT

```  TTT  TT
TT T  TT
T### T TT
```

TT# T T

```      TTT
#    TTT
T
T T T T
```

TTT TTT T NIL </lang>

## D

### Textual Version

<lang d>import std.stdio, std.random, std.string, std.algorithm;

enum treeProb = 0.55; // Original tree probability. enum fProb = 0.01; // Auto combustion probability. enum cProb = 0.01; // Tree creation probability.

enum Cell : char { empty=' ', tree='T', fire='#' } alias World = Cell[][];

bool hasBurningNeighbours(in World world, in ulong r, in ulong c) pure nothrow @safe @nogc {

```   foreach (immutable rowShift; -1 .. 2)
foreach (immutable colShift; -1 .. 2)
if ((r + rowShift) >= 0 && (r + rowShift) < world.length &&
(c + colShift) >= 0 && (c + colShift) < world[0].length &&
world[r + rowShift][c + colShift] == Cell.fire)
return true;
return false;
```

}

void nextState(in World world, World nextWorld) /*nothrow*/ @safe /*@nogc*/ {

```   foreach (r, row; world)
foreach (c, elem; row)
final switch (elem) with (Cell) {
case empty:
nextWorld[r][c]= (uniform01 < cProb) ? tree : empty;
break;
```
```               case tree:
if (world.hasBurningNeighbours(r, c))
nextWorld[r][c] = fire;
else
nextWorld[r][c] = (uniform01 < fProb) ? fire : tree;
break;
```
```               case fire:
nextWorld[r][c] = empty;
break;
}
```

}

void main() @safe {

```   auto world = new World(8, 65);
foreach (row; world)
foreach (ref el; row)
el = (uniform01 < treeProb) ? Cell.tree : Cell.empty;
auto nextWorld = new World(world.length, world[0].length);
```
```   foreach (immutable i; 0 .. 4) {
nextState(world, nextWorld);
writefln("%(%(%c%)\n%)\n", nextWorld);
world.swap(nextWorld);
}
```

}</lang>

Output:
```  T    T T#TT  T   TT  TT TTTT TT TTT T TT T# T T TT TT     TTTTT
T TT  TT T    TTTTTTTTTT T TTT T T    T    TT    TTTTTTTT TTTT #T
TT  T  TTTTTT TTTTT       TTT TTTT TTTT TTT T  T T T T  TT T TT
T TT T TT T TT T  TTTT   T T TT TTT    T  TT     T T   T TT    T
TTT   T  TTTT  T#  T T T  TTT  TT  TTTTT T      T  TT  T  T TT T
TT TTTT  TTT  TTTTT T T T  T  TT  T TTT   T  T T   TT    TTT T T
T  TTT T TT   T TTT#TT  T TT  TTTTTTTT  TTTT  TTTTT TTTT TTT
TT TTTTT TTTTTT TT  TT T TT T   TT  T   TT T TT TT  TTTT   TTTTT

T    T # #T  T   TT  TT TTTT TT TTT T TT #  T T TT TT     TT###
T TT  TT #    TTTTTTTTTT T TTT T T    T    ##    TTTTTTTT TTTT  #
TT  T  TTTTTT TTTTT       TTT TTTT TTTT TTT #  T T T T  TT T T#
T TT T TT T TT T  #TTT   T T TT TTT    T  TT     T T   T TTT   T
TTT   T  TTTT  #   T T T  TTT  TT  TTTTT T      T  TT  T  T TT T
TT TTTT  TTT  T#### # T T  T  TT  T TTT   T  T T   TT    TTT T T
T  TTT T TT   T TT# #T  T TT  TTTTTTTT  TTTT  TTTTT TTTT TTT
TT TTTTT TTTTTT TT  ## T TT T   TT  T   TT T TT TT  TTTT   TTTTT

T    T    #  T   TT  TT TTTT TT TTT T TT    T T TT TT     T#
T TT  TT      TTTTTTTTTT T TTT T T    T          TTTTTTTT TTT#
TT  T  T###TT TTT##       TTT TTTT TTTT TT#    T T T T  #T T #
T TT T TT T TT #   #TT   T T TT TTT    T  T#     T T   T TTT   #
TTT   T  TTTT      # # T  TTT  TT  TTTTT T      T  TT  T  T TT T
TT TTTT  TTT  #       T T  #  TT  T TTT   T  T T   TT    TTT T T
T  TTT T TT   # ##   #  T TT  TTTTTTTT  TTTT  TTTTT TTTT TTT
TT TTTTT TT#TTT TT     T TT T   TT  T   TT T TT TT  TTTT   TTTTT

T    T       T   TT  TT TTTT TT TTT T TT    T T TT TT     #
T TT  T#      TT####TTTT T TTT T T    T          TTTTTT## TT#
TT  T  #   #T ###         TTT TTTT TTTT T#     T T T T   # T
T TT T ## # TT      ##   T T TT TTT    T  #      T T   # #TT
TTT   T  TTTT          T  ###  TT  TTTTT #      T  TT  T  T T# #
TT TTTT  TTT          # T     TT  T TTT   T  T T   TT    TTT T T
T  TTT T ##             T ##  TTTTTTTT  TTTT  TTTTT TTTT TTT
TT TTTTT T# #T# ##     # TT T   TT  T   TT T TT TT  TTTT   TTTTT
```

### Graphical Version

Library: simpledisplay

<lang d>import std.stdio, std.random, std.algorithm, std.typetuple,

```      simpledisplay;
```

enum double TREE_PROB = 0.55; // Original tree probability. enum double F_PROB = 0.01; // Auto combustion probability. enum double P_PROB = 0.01; // Tree creation probability. enum worldSide = 600;

enum Cell : ubyte { empty, tree, burning } alias World = Cell[worldSide][];

immutable white = Color(255, 255, 255),

```         red = Color(255, 0, 0),
green = Color(0, 255, 0);
```

void nextState(ref World world, ref World nextWorld,

```              ref Xorshift rnd, Image img) {
immutable nr = world.length;
immutable nc = world[0].length;
foreach (immutable r, const row; world)
foreach (immutable c, immutable elem; row)
START: final switch (elem) with (Cell) {
case empty:
img.putPixel(c, r, white);
nextWorld[r][c] = rnd.uniform01 < P_PROB ? tree : empty;
break;
```
```       case tree:
img.putPixel(c, r, green);
```
```         foreach (immutable rowShift; TypeTuple!(-1, 0, 1))
foreach (immutable colShift; TypeTuple!(-1, 0, 1))
if ((r + rowShift) >= 0 && (r + rowShift) < nr &&
(c + colShift) >= 0 && (c + colShift) < nc &&
world[r + rowShift][c + colShift] == Cell.burning) {
nextWorld[r][c] = Cell.burning;
break START;
}
```
```         nextWorld[r][c]= rnd.uniform01 < F_PROB ? burning : tree;
break;
```
```       case burning:
img.putPixel(c, r, red);
nextWorld[r][c] = empty;
break;
}
```
``` swap(world, nextWorld);
```

}

void main() {

``` auto rnd = Xorshift(1);
auto world = new World(worldSide);
foreach (ref row; world)
foreach (ref el; row)
el = rnd.uniform01 < TREE_PROB ? Cell.tree : Cell.empty;
auto nextWorld = new World(world[0].length);
```
``` auto w= new SimpleWindow(world.length,world[0].length,"ForestFire");
auto img = new Image(w.width, w.height);
```
``` w.eventLoop(1, {
auto painter = w.draw;
nextState(world, nextWorld, rnd, img);
painter.drawImage(Point(0, 0), img);
});
```

}</lang>

## Déjà Vu

<lang dejavu>#chance of empty->tree set :p 0.004

1. chance of spontaneous tree combustion

set :f 0.001

1. chance of tree in initial state

set :s 0.5

1. height of world

set :H 10

1. width of world

set :W 20

has-burning-neigbour state pos: for i range -- swap ++ dup &< pos: for j range -- swap ++ dup &> pos: & i j try: state! catch value-error: :empty if = :burning: return true false

evolve state pos: state! pos if = :tree dup: if has-burning-neigbour state pos: :burning drop elseif chance f: :burning drop elseif = :burning: :empty else: if chance p: :tree else: :empty

step state: local :next {} for k in keys state: set-to next k evolve state k next

local :(c) { :tree "T" :burning "B" :empty "." } print-state state: for j range 0 H: for i range 0 W: !print\ (c)! state! & i j !print ""

init-state: local :first {} for j range 0 H: for i range 0 W: if chance s: :tree else: :empty set-to first & i j first

run: init-state while true: print-state dup !print "" step

run-slowly: init-state while true: print-state dup drop !prompt "Continue." step

run</lang>

Output:
```T.T.T...T..T..TT.T.T.
.TT.T...T..T....TTTTT
......T.TTT.TTTTT....
..TTT...T.T..T..TTT..
....T.....TTT...TTTTT
..TTT..TTTTTTTTT....T
T....T..TT.TT.T...T..
TTT.TT.T..TT.TTT.TT..
.TT.TT.T...T.T..T.TTT
..TTTTT...TTTTTT..T.T
TT..T....T..T..TTTT..

TTT.T...T..T.TTT.T.T.
.TT.T...T..T..T.TTTTT
......T.TTT.TTTTT....
..TTT...T.T..T..TTT..
....TT....TTB...TTTTT
..TTT..TTTTTTTTT...TT
T....T.TTT.TT.T...T..
TTT.TT.T..TB.TTT.TT..
.TT.TT.T...T.T..T.TTT
..TTTTB...TTTTTT..T.T
TT..T....T..T..TTTT..

TTT.T...T..T.TTT.T.T.
.TTTT...T..T..T.TTTTT
......T.TTTTTTTTT....
..TTT...T.T..B..TTT..
....TT....TB....TTTTT
..TTT..TTTTBBBTT...TT
T....T.TTT.BB.T...T..
TTT.TT.T..B..TTT.TT..
.TTTTB.B...B.T..T.TTT
..TTTB....TTTTTT..T.T
TT..T....T..T..TTTT..```

## EasyLang

<lang>p_fire = 0.00002 p_tree = 0.002

len f[] 102 * 102 len p[] len f[] background 100 clear for r range 100

``` for c range 100
i = r * 102 + c + 103
if randomf < 0.5
f[i] = 1
.
.
```

. timer 0

subr show

``` for r range 100
for c range 100
i = r * 102 + c + 103
h = f[i]
if h <> p[i]
move c + 0.5 r + 0.5
if h = 0
color 100
circle 0.6
elif h = 1
color 151
circle 0.5
else
color 9 * 100 + (18 - 2 * h) * 10
circle 0.5
.
.
.
.
```

. subr update

``` swap f[] p[]
for r range 100
for c range 100
i = r * 102 + c + 103
if p[i] = 0
f[i] = 0
if randomf < p_tree
f[i] = 1
.
elif p[i] = 1
f[i] = 1
s = p[i - 103] + p[i - 102] + p[i - 101]
s += p[i - 1] + p[i + 1]
s += p[i + 101] + p[i + 102] + p[i + 103]
if s >= 9 or randomf < p_fire
f[i] = 9
.
elif p[i] = 4
f[i] = 0
else
f[i] = p[i] - 1
.
.
.
```

. on timer

``` call show
call update
timer 0.2
```

.</lang>

## Emacs Lisp

<lang lisp>#!/usr/bin/env emacs -script

-*- lexical-binding
t -*-
run
./forest-fire forest-fire.config

(require 'cl-lib)

(setq debug-on-error t)

(defmacro swap (a b)

``` `(setq ,b (prog1 ,a (setq ,a ,b))))
```

(defconst burning ?B) (defconst tree ?t)

(cl-defstruct world rows cols data)

(defun new-world (rows cols)

``` ;; When allocating the vector add padding so the border will always be empty.
(make-world :rows rows :cols cols :data (make-vector (* (1+ rows) (1+ cols)) nil)))
```

(defmacro world--rows (w)

``` `(1+ (world-rows ,w)))
```

(defmacro world--cols (w)

``` `(1+ (world-cols ,w)))
```

(defmacro world-pt (w r c)

``` `(+ (* (mod ,r (world--rows ,w)) (world--cols ,w))
(mod ,c (world--cols ,w))))
```

(defmacro world-ref (w r c)

``` `(aref (world-data ,w) (world-pt ,w ,r ,c)))
```

(defun print-world (world)

``` (dotimes (r (world-rows world))
(dotimes (c (world-cols world))
(let ((cell (world-ref world r c)))
(princ (format "%c" (if (not (null cell))
cell
?.)))))
(terpri)))
```

(defun random-probability ()

``` (/ (float (random 1000000)) 1000000))
```

(defun initialize-world (world p)

``` (dotimes (r (world-rows world))
(dotimes (c (world-cols world))
(setf (world-ref world r c) (if (<= (random-probability) p) tree nil)))))
```

(defun neighbors-burning (world row col)

``` (let ((n 0))
(dolist (offset '((1 . 1) (1 . 0) (1 . -1) (0 . 1) (0 . -1) (-1 . 1) (-1 . 0) (-1 . -1)))
(when (eq (world-ref world (+ row (car offset)) (+ col (cdr offset))) burning)
(setq n (1+ n))))
(> n 0)))
```

(defun advance (old new p f)

``` (dotimes (r (world-rows old))
(dotimes (c (world-cols old))
(cond
((eq (world-ref old r c) burning)
(setf (world-ref new r c) nil))
((null (world-ref old r c))
(setf (world-ref new r c) (if (<= (random-probability) p) tree nil)))
((eq (world-ref old r c) tree)
(setf (world-ref new r c) (if (or (neighbors-burning old r c)
(<= (random-probability) f))
burning
tree)))))))
```

``` (with-temp-buffer
(insert-file-contents-literally file-name)
```

(defun get-config (key config)

``` (let ((val (assoc key config)))
(if (null val)
(error (format "missing value for %s" key))
(cdr val))))
```

(defun simulate-forest (file-name)

``` (let* ((config (read-config file-name))
(rows (get-config 'rows config))
(cols (get-config 'cols config))
(skip (get-config 'skip config))
(a (new-world rows cols))
(b (new-world rows cols)))
(initialize-world a (get-config 'tree config))
(dotimes (time (get-config 'time config))
(when (or (and (> skip 0) (= (mod time skip) 0))
(<= skip 0))
(princ (format "* time %d\n" time))
(print-world a))
(advance a b (get-config 'p config) (get-config 'f config))
(swap a b))))
```

(simulate-forest (elt command-line-args-left 0)) </lang>

The configuration file controls the simulation. <lang lisp>((rows . 10)

```(cols . 45)
(time . 100)
(skip . 10)
(f . 0.001)   ;; probability tree ignites
(p . 0.01)    ;; probability empty space fills with a tree
(tree . 0.5)) ;; initial probability of tree in a new world</lang>
```
Output:
```* time 0
.t...t..t.t.t...ttt...tttt..tt...t.t.t.t.t..t
.t.t.t..t.ttt.tt.tttt.tt....t.t.tt.t.t.tt.ttt
t..t.tttt..t..tt..tt.t.t.tt.....t..t..tt.tt.t
.tt.t.ttt.t...t...tt..t....tttttt.t..tt.tt.tt
.t..t..t.tt.t...tt...t.t.tt.t.t..ttttt.t..ttt
.tt.ttttt..t.t....tttt.t.t..tttttt.tt.t.t.t.t
ttt.....t.tttttttt.tt....ttt.t.....t.ttt..ttt
.tt..tt.tt.ttt...tt.t..ttt.t.tt.tt....tttt...
t.tt...tttt...t.t.tt.tt..ttt...t.tt.t.tttttt.
...t......t.t...tttt...ttttt.tttt..t..t.tttt.
* time 10
......................tttt..tt...t.B........B
....................B.tt...tt.t.tt..........B
.....................t.t.tt.....B...........B
...........t..........t...tttttB............B
.............t..tB...t.t.tt.t.tB.........t..B
.........t.......ttttt.t.tt.tttB.............
................Btttt....ttttt...........t...
t....B...t.......tt.t..ttt.t.tt.BB...........
.....B..........t.ttttt..ttt..tt.tt.t...t....
................tttt...ttttt.tttt..t.........
* time 20
..........t.....t.t................t........t
.....t...........t.t.........................
.........................t..............t....
..........tttt..........................t....
.t.........t.t...........................t...
....t....t......................t............
..t.tt.....t..............t........t.t...t...
tt.......t...................................
..t...t.........................t....t..t.t..
.....t.......................................
* time 30
......t...t.....t.t......t.........t.......tt
.....t.........t.t.t...............t...t.....
...........tt.........t..t..t......t....t....
..........tttt.......t.....t.........t..t....
.t.........t.t...t.tt..........t.........t...
....t....t......t.tt.t..........t.......t....
..t.tt.....t..t.....t.t...t..tB....t.t...t...
tt..t....t.......t..................t........
..t...t....t...........t........t....t..t.t..
.....t...t....t..t....tt.t.....t...........t.
* time 40
......t...t.....t.t......t......t..t.......tt
.....t.........t.t.tt..............tt..t.....
...........tt............t..t......t....tt...
t...t.....tttt.............tt.t.t....t..t....
.t.........t.t......t..........t.........t...
....t....t...t........t.t.......t.t..t..t....
..t.tt.....t..B....t......t....t...t.t...t...
tt..t....t.t.....tt.................t........
..t...t....t..t........tt.t.....t....t..t.t..
..t..t...t....t..t....tt.t.....t......t....t.
* time 50
......t...t.....t.t......t.....tt.t...t....tt
..t.tt.........t.t.tt.t......t.t...t...t.....
.........................t..t..t..t.....tt...
t...t......................tt.t.t....t..t...t
.t..................t.........tt.........t..t
....t....t..........t.t.t.......t.t..t..t....
..tttt...t.t.......t......t....t...ttt...tt.t
tt..t.t..t.t.....tt.................t........
..t...t....t..t....t...tt.t.....t....tt.t.t..
..t..t...t....t..t....tt.t.t...t....t.t....t.
* time 60
......t...t.t...t.t.t....t.....tt.t...t....tt
..t.tt.......t.t.t.tt.t......t.t...t...t..t.t
......t.t...............tt.tt..t..t.....tt...
t...t.t.............t......tt.t.t....t..t...t
tt...............tttt.........tt.........t..t
....tt.ttt..t.......t.t.t.t.....t.t..t..t....
..tttt...ttt.......t......t....t...ttt..ttt.t
tt..t.t.tt.t...t.tt.................t....t...
..tt..t....t..t..t.t...B........t....tt.t.t..
..t..t...t....t..t..t.tB...Bt..t...tt.t....t.
* time 70
......tt..t.t...t.t.t.t..t.....tt.t...t....tt
t.t.tt.......t.t.t.tt.t.....tttt...t...t..t.t
.t....t.t............t..tt.tt..t..t....ttt...
t...t.tt..t.....t...t...t..tt.t.tt...t..t.t.t
tt.....t.........tttt.........tt..t......tt.t
....ttttttt.t...t...t.t.t.t.....t.t..t..t.t..
..tttt...ttt..t....t......t...tt...ttt..ttt.t
ttt.t.t.tttt...t.tt....t.......t....tt..tt...
..tt..ttt.tt..t..ttt.....t......t...ttt.t.t..
..t..tt..t....t.tt..t..........t.t.tt.t...tt.
* time 80
....t.tt.tt.t...t.t.t.t..t....ttt.t.........B
t.t.tt.......t.t.t.tt.t.....ttttt..t........B
.t....t.t............t..tt.tt..t..t..........
t...t.ttt.t.....t...t...t..tt.tttt...t......t
tt.....t.......tttttt....t....ttt.ttt.......t
....ttttttt.t..tt..tt.t.t.t.....t.t..t.......
..tttt...ttt..tt...t......t...tt...ttt......t
ttt.t.t.tttt...t.tt....t......ttt...tt..BB...
..ttt.ttt.tt..t..tttt....tt.....t...ttt.t.t..
..t..tt..t....tttt.tt..........t.t.tt.t...tt.
* time 90
....t.tt.tt.t...t.t.t.t..t........B..........
t.t.tt.......t.ttt.tt.t.............B........
tt....t.t.t.......t..t..tt...................
t...t.ttt.t.....t.t.t.t.t............t..t...t
tt.tt.tt.......tttttt....t..........B...t...t
....ttttttt.t..ttt.tt.ttt.t..........t.....t.
..tttt...ttt..tt.t.t......t........Btt..t.t.t
ttt.t.t.tttt...t.tt..t.t...........ttt.......
..ttt.ttt.tt..t..tttt.t..tt.....BB..ttt......
..t..tt..t....tttt.tt.......t..t.t.tt.t......
```

## Erlang

Not even text graphics. Notice the use of random:seed/1 when creating a tree. Without it all calls to random:uniform/1 gave the same result for each tree.

<lang Erlang> -module( forest_fire ).

-record( state, {neighbours=[], position, probability_burn, probability_grow, tree} ).

```      erlang:spawn( fun() ->
Pid_positions = forest_create( 5, 5, 0.5, 0.3, 0.2 ),
Pids = [X || {X, _} <- Pid_positions],
[X ! {tree_pid_positions, Pid_positions} || X <- Pids],
Start = forest_status( Pids ),
Histories = [Start | [forest_step( Pids ) || _X <- lists:seq(1, 2)]],
[io:fwrite("~p~n~n", [X]) || X <- Histories]
end ).
```

forest_create( X_max, Y_max, Init, Grow, Burn ) ->

```      [{tree_create(tree_init(Init, random:uniform()), X, Y, Grow, Burn), {X,Y}} || X <- lists:seq(1, X_max), Y<- lists:seq(1, Y_ma\
```

x)].

forest_status( Pids ) ->

```      [X ! {status_request, erlang:self()} || X <- Pids],
[receive {status, Tree, Position, X} -> {Tree, Position} end || X <- Pids].
```

forest_step( Pids ) ->

```      [X ! {step} || X <- Pids],
forest_status( Pids ).
```

is_neighbour({X, Y}, {X, Y} ) -> false; % Myself is_neighbour({Xn, Yn}, {X, Y} ) when abs(Xn - X) =< 1, abs(Yn - Y) =< 1 -> true; is_neighbour( _Position_neighbour, _Position ) -> false.

loop( State ) ->

```       receive
{tree_pid_positions, Pid_positions} ->
loop( loop_neighbour(Pid_positions, State) );
{step} ->
[X ! {tree, State#state.tree, erlang:self()} || X <- State#state.neighbours],
loop( loop_step(State) );
{status_request, Pid} ->
Pid ! {status, State#state.tree, State#state.position, erlang:self()},
loop( State )
end.
```

loop_neighbour( Pid_positions, State ) -> My_position = State#state.position,

```       State#state{neighbours=[Pid || {Pid, Position} <- Pid_positions, is_neighbour( Position, My_position)]}.
```

loop_step( State ) ->

```       Is_burning = lists:any( fun loop_step_burning/1, [loop_step_receive(X) || X <- State#state.neighbours] ),
Tree = loop_step_next( Is_burning, random:uniform(), State ),
State#state{tree=Tree}.
```

loop_step_burning( Tree ) -> Tree =:= burning.

loop_step_next( _Is_burning, Probablility, #state{tree=empty, probability_grow=Grow} ) when Grow > Probablility -> tree; loop_step_next( _Is_burning, _Probablility, #state{tree=empty} ) -> empty; loop_step_next( _Is_burning, _Probablility, #state{tree=burning} ) -> empty; loop_step_next( true, _Probablility, #state{tree=tree} ) -> burning; loop_step_next( false, Probablility, #state{tree=tree, probability_burn=Burn} ) when Burn > Probablility -> burning; loop_step_next( false, _Probablility, #state{tree=tree} ) -> tree.

tree_create( Tree, X, Y, Grow, Burn ) ->

```       State = #state{position={X, Y}, probability_burn=Burn, probability_grow=Grow, tree=Tree},
erlang:spawn_link( fun() -> random:seed( X, Y, 0 ), loop( State ) end ).
```

tree_init( Tree_probalility, Random ) when Tree_probalility > Random -> tree; tree_init( _Tree_probalility, _Random ) -> empty. </lang>

Output:

```[{tree,{1,1}},
{empty,{1,2}},
{empty,{1,3}},
{empty,{1,4}},
{tree,{1,5}},
{empty,{2,1}},
{empty,{2,2}},
{empty,{2,3}},
{tree,{2,4}},
{empty,{2,5}},
{tree,{3,1}},
{tree,{3,2}},
{empty,{3,3}},
{tree,{3,4}},
{empty,{3,5}},
{tree,{4,1}},
{tree,{4,2}},
{tree,{4,3}},
{tree,{4,4}},
{empty,{4,5}},
{tree,{5,1}},
{tree,{5,2}},
{tree,{5,3}},
{tree,{5,4}},
{empty,{5,5}}]

[{burning,{1,1}},
{tree,{1,2}},
{tree,{1,3}},
{tree,{1,4}},
{burning,{1,5}},
{tree,{2,1}},
{tree,{2,2}},
{tree,{2,3}},
{burning,{2,4}},
{tree,{2,5}},
{burning,{3,1}},
{burning,{3,2}},
{tree,{3,3}},
{burning,{3,4}},
{tree,{3,5}},
{burning,{4,1}},
{burning,{4,2}},
{burning,{4,3}},
{burning,{4,4}},
{tree,{4,5}},
{burning,{5,1}},
{burning,{5,2}},
{burning,{5,3}},
{burning,{5,4}},
{tree,{5,5}}]

[{empty,{1,1}},
{burning,{1,2}},
{burning,{1,3}},
{burning,{1,4}},
{empty,{1,5}},
{burning,{2,1}},
{burning,{2,2}},
{burning,{2,3}},
{empty,{2,4}},
{burning,{2,5}},
{empty,{3,1}},
{empty,{3,2}},
{burning,{3,3}},
{empty,{3,4}},
{burning,{3,5}},
{empty,{4,1}},
{empty,{4,2}},
{empty,{4,3}},
{empty,{4,4}},
{burning,{4,5}},
{empty,{5,1}},
{empty,{5,2}},
{empty,{5,3}},
{empty,{5,4}},
{burning,{5,5}}]
```

## F#

This implementation can be compiled or run in the interactive F# shell. <lang fsharp>open System open System.Diagnostics open System.Drawing open System.Drawing.Imaging open System.Runtime.InteropServices open System.Windows.Forms

module ForestFire =

```   type Cell = Empty | Tree | Fire
```
```   let rnd = new System.Random()
let initial_factor = 0.35
let ignition_factor = 1e-5 // rate of lightning strikes (f)
let growth_factor = 2e-3   // rate of regrowth (p)
let width = 640            // width of the forest region
let height = 480           // height of the forest region
```
```   let make_forest =
Array2D.init height width
(fun _ _ -> if rnd.NextDouble() < initial_factor then Tree else Empty)

let count (forest:Cell[,]) row col =
let mutable n = 0
let h,w = forest.GetLength 0, forest.GetLength 1
for r in row-1 .. row+1 do
for c in col-1 .. col+1 do
if r >= 0 && r < h && c >= 0 && c < w && forest.[r,c] = Fire then
n <- n + 1
if forest.[row,col] = Fire then n-1 else n
```
```   let burn (forest:Cell[,]) r c =
match forest.[r,c] with
| Fire -> Empty
| Tree -> if rnd.NextDouble() < ignition_factor then Fire
else if (count forest r c) > 0 then Fire else Tree
| Empty -> if rnd.NextDouble() < growth_factor then Tree else Empty
```
```   // All the functions below this point are drawing the generated images to screen.
let make_image (pixels:int[]) =
let bmp = new Bitmap(width, height)
let bits = bmp.LockBits(Rectangle(0,0,width,height), ImageLockMode.WriteOnly, PixelFormat.Format32bppArgb)
Marshal.Copy(pixels, 0, bits.Scan0, bits.Height*bits.Width) |> ignore
bmp.UnlockBits(bits)
bmp
```
```   // This function is run asynchronously to avoid blocking the main GUI thread.
let run (box:PictureBox) (label:Label) = async {
let timer = new Stopwatch()
let forest = make_forest |> ref
let pixel = Array.create (height*width) (Color.Black.ToArgb())
let rec update gen =
timer.Start()
forest := burn !forest |> Array2D.init height width
for y in 0..height-1 do
for x in 0..width-1 do
pixel.[x+y*width] <- match (!forest).[y,x] with
| Empty -> Color.Gray.ToArgb()
| Tree -> Color.Green.ToArgb()
| Fire -> Color.Red.ToArgb()
let img = make_image pixel
box.Invoke(MethodInvoker(fun () -> box.Image <- img)) |> ignore
let msg = sprintf "generation %d @ %.1f fps" gen (1000./timer.Elapsed.TotalMilliseconds)
label.Invoke(MethodInvoker(fun () -> label.Text <- msg )) |> ignore
timer.Reset()
update (gen + 1)
update 0 }
```
```   let main args =
let form = new Form(AutoSize=true,
Size=new Size(800,600),
Text="Forest fire cellular automata")
let box = new PictureBox(Dock=DockStyle.Fill,Location=new Point(0,0),SizeMode=PictureBoxSizeMode.StretchImage)
let label = new Label(Dock=DockStyle.Bottom, Text="Ready")
Application.Exit())
run box label |> Async.Start
form.Show()
Application.Run()
0
```
1. if INTERACTIVE

ForestFire.main [|""|]

1. else

[<System.STAThread>] [<EntryPoint>] let main args = ForestFire.main args

1. endif</lang>

## Factor

Works with: Factor version 0.99 Development version 2019-07-10

<lang factor>USING: combinators grouping kernel literals math math.matrices math.vectors prettyprint random raylib.ffi sequences ; IN: rosetta-code.forest-fire

! The following private vocab builds up to a useful combinator, ! matrix-map-neighbors, which takes a matrix, a quotation, and ! inside the quotation makes available each element of the ! matrix as well as its neighbors, mapping the result of the ! quotation to a new matrix.

<PRIVATE

CONSTANT: neighbors {

```   { -1 -1 } { -1  0 } { -1  1 }
{  0 -1 }           {  0  1 }
{  1 -1 } {  1  0 } {  1  1 }
```

}

?i,j ( i j matrix -- elt/f ) swapd ?nth ?nth ;
?i,jths ( seq matrix -- newseq )
```   [ [ first2 ] dip ?i,j ] curry map ;
```
neighbor-coords ( loc -- seq )
```   [ neighbors ] dip [ v+ ] curry map ;
```
get-neighbors ( loc matrix -- seq )
```   [ neighbor-coords ] dip ?i,jths ;
```
matrix>neighbors ( matrix -- seq )
```   dup dim matrix-coordinates concat
[ swap get-neighbors sift ] with map ;
```
matrix-map-neighbors ( ... matrix quot: ( ... neighbors elt -- ... newelt ) -- ... newmatrix )
```   [ [ dim first ] [ matrix>neighbors ] [ concat ] tri ] dip
2map swap group ; inline
```

PRIVATE>

! ##### Simulation code #####

! In our forest, ! 0 = empty ! 1 = tree ! 2 = fire

CONSTANT: ignite-probability 1/12000 CONSTANT: grow-probability 1/100

make-forest ( m n probability -- matrix )
```   [ random-unit > 1 0 ? ] curry make-matrix ;
```
?ignite ( -- 1/2 ) ignite-probability random-unit > 2 1 ? ;
?grow ( -- 0/1 ) grow-probability random-unit > 1 0 ? ;
next-plot ( neighbors elt -- n )
```   {
{ [ dup 2 = ] [ 2drop 0 ] }
{ [ 2dup [ [ 2 = ] any? ] [ 1 = ] bi* and ] [ 2drop 2 ] }
{ [ 1 = ] [ drop ?ignite ] }
[ drop ?grow ]
} cond ;
```
next-forest ( forest -- newforest )
```   [ next-plot ] matrix-map-neighbors ;
```

! ##### Display code #####

CONSTANT: colors \${ GRAY GREEN RED }

draw-forest ( matrix -- )
```   dup dim matrix-coordinates [ concat ] bi@ swap [
[ first2 [ 5 * ] bi@ 5 5 ] dip colors nth draw-rectangle
] 2each ;
```

500 500 "Forest Fire" init-window 100 100 1/2 make-forest 60 set-target-fps [ window-should-close ] [

```   begin-drawing
BLACK clear-background dup draw-forest
end-drawing
next-forest
```

] until drop close-window</lang>

Output:

## Forth

Works with: Gforth version 0.7.3

<lang forth>30 CONSTANT WIDTH 30 CONSTANT HEIGHT WIDTH HEIGHT * CONSTANT SIZE

1 VALUE SEED

(RAND) ( -- u) \ xorshift generator
```  SEED DUP 13 LSHIFT XOR
DUP 17 RSHIFT XOR
DUP  5 LSHIFT XOR
DUP TO SEED ;
```

10000 CONSTANT RANGE 100 CONSTANT GROW 1 CONSTANT BURN

RAND ( -- u) (RAND) RANGE MOD ;

\ Create buffers for world state CREATE A SIZE ALLOT A SIZE ERASE CREATE B SIZE ALLOT B SIZE ERASE

0 CONSTANT NONE 1 CONSTANT TREE 2 CONSTANT FIRE

NEARBY-FIRE? ( addr u -- t|f)
```  2 -1 DO
2 -1 DO
J WIDTH * I + OVER +  \ calculate an offset
DUP 0> OVER SIZE < AND IF
>R OVER R> + C@     \ fetch state of the offset cell
FIRE = IF UNLOOP UNLOOP DROP DROP TRUE EXIT THEN
ELSE DROP THEN
LOOP
LOOP  DROP DROP FALSE ;
```
GROW? RAND GROW <= ; \ spontaneously sprout?
BURN? RAND BURN <= ; \ spontaneously combust?
STEP ( prev next --) \ Given state in PREV, put next in NEXT
```  >R 0 BEGIN DUP SIZE <
WHILE
2DUP + C@ CASE
FIRE OF NONE ENDOF
TREE OF 2DUP NEARBY-FIRE? BURN? OR IF FIRE ELSE TREE THEN ENDOF
NONE OF GROW? IF TREE ELSE NONE THEN ENDOF
ENDCASE
( i next-cell-state) OVER R@ + C!        \ commit to next
1+ REPEAT  R> DROP DROP DROP ;
```
(ESCAPE) 27 EMIT [CHAR] [ EMIT ;
ESCAPE" POSTPONE (ESCAPE) POSTPONE S" POSTPONE TYPE ; IMMEDIATE
CLEAR ESCAPE" H" ;
RETURN ESCAPE" E" ;
RESET ESCAPE" m" ;
```  HEIGHT 0 DO
WIDTH 0 DO
DUP C@ CASE
NONE OF SPACE ENDOF
TREE OF ESCAPE" 32m" [CHAR] T EMIT RESET ENDOF
FIRE OF ESCAPE" 31m" [CHAR] # EMIT RESET ENDOF
ENDCASE  1+
LOOP  RETURN
LOOP RESET DROP ;
```
(GO) ( buffer buffer' -- buffer' buffer)
```  2DUP STEP    \ step the simulation
DUP .FOREST  \ print the current state
SWAP ;       \ prepare for next iteration
```
GO A B BEGIN (GO) AGAIN ;</lang>

## Fortran

Works with: Fortran version 95 and later

<lang fortran>module ForestFireModel

``` implicit none
```
``` type :: forestfire
integer, dimension(:,:,:), allocatable :: field
integer :: width, height
integer :: swapu
real :: prob_tree, prob_f, prob_p
end type forestfire
```
``` integer, parameter :: &
empty = 0, &
tree = 1, &
burning = 2
```
``` private :: bcheck, set, oget, burning_neighbor ! cset, get
```

contains

``` ! create and initialize the field(s)
function forestfire_new(w, h, pt, pf, pp) result(res)
type(forestfire) :: res
integer, intent(in) :: w, h
real, intent(in), optional :: pt, pf, pp
```
```   integer :: i, j
real :: r
```
```   allocate(res%field(2,w,h)) ! no error check
res%prob_tree = 0.5
res%prob_f = 0.00001
res%prob_p = 0.001
if ( present(pt) ) res%prob_tree = pt
if ( present(pf) ) res%prob_f = pf
if ( present(pp) ) res%prob_p = pp
```
```   res%width = w
res%height = h
res%swapu = 0
```
```   res%field = empty
```
```   do i = 1,w
do j = 1,h
call random_number(r)
if ( r <= res%prob_tree ) call cset(res, i, j, tree)
end do
end do

end function forestfire_new

! destroy the field(s)
subroutine forestfire_destroy(f)
type(forestfire), intent(inout) :: f
```
```   if ( allocated(f%field) ) deallocate(f%field)

end subroutine forestfire_destroy
```
``` ! evolution
subroutine forestfire_evolve(f)
type(forestfire), intent(inout) :: f
```
```   integer :: i, j
real :: r
```
```   do i = 1, f%width
do j = 1, f%height
select case ( get(f, i, j) )
case (burning)
call set(f, i, j, empty)
case (empty)
call random_number(r)
if ( r > f%prob_p ) then
call set(f, i, j, empty)
else
call set(f, i, j, tree)
end if
case (tree)
if ( burning_neighbor(f, i, j) ) then
call set(f, i, j, burning)
else
call random_number(r)
if ( r > f%prob_f ) then
call set(f, i, j, tree)
else
call set(f, i, j, burning)
end if
end if
end select
end do
end do
f%swapu = ieor(f%swapu, 1)
end subroutine forestfire_evolve
```
``` ! helper funcs/subs
subroutine set(f, i, j, t)
type(forestfire), intent(inout) :: f
integer, intent(in) :: i, j, t
```
```   if ( bcheck(f, i, j) ) then
f%field(ieor(f%swapu,1), i, j) = t
end if
end subroutine set
```
``` subroutine cset(f, i, j, t)
type(forestfire), intent(inout) :: f
integer, intent(in) :: i, j, t
```
```   if ( bcheck(f, i, j) ) then
f%field(f%swapu, i, j) = t
end if
end subroutine cset
```
``` function bcheck(f, i, j)
logical :: bcheck
type(forestfire), intent(in) :: f
integer, intent(in) :: i, j

bcheck = .false.
if ( (i >= 1) .and. (i <= f%width) .and. &
(j >= 1) .and. (j <= f%height) ) bcheck = .true.

end function bcheck

```
``` function get(f, i, j) result(r)
integer :: r
type(forestfire), intent(in) :: f
integer, intent(in) :: i, j

if ( .not. bcheck(f, i, j) ) then
r = empty
else
r = f%field(f%swapu, i, j)
end if
end function get
```
``` function oget(f, i, j) result(r)
integer :: r
type(forestfire), intent(in) :: f
integer, intent(in) :: i, j

if ( .not. bcheck(f, i, j) ) then
r = empty
else
r = f%field(ieor(f%swapu,1), i, j)
end if
end function oget
```
``` function burning_neighbor(f, i, j) result(r)
logical :: r
type(forestfire), intent(in) :: f
integer, intent(in) :: i, j
```
```   integer, dimension(3,3) :: s

s = f%field(f%swapu, i-1:i+1, j-1:j+1)
s(2,2) = empty
r = any(s == burning)
end function burning_neighbor
```
``` subroutine forestfire_print(f)
type(forestfire), intent(in) :: f
```
```   integer :: i, j
```
```   do j = 1, f%height
do i = 1, f%width
select case(get(f, i, j))
case (empty)
case (tree)
case (burning)
end select
end do
write(*,*)
end do
end subroutine forestfire_print
```

end module ForestFireModel</lang>

<lang fortran>program ForestFireTest

``` use ForestFireModel
implicit none
```
``` type(forestfire) :: f
integer :: i
```
``` f = forestfire_new(74, 40)
```
``` do i = 1, 1001
write(*,'(A)', advance='no') achar(z'1b') // '[H' // achar(z'1b') // '[2J'
call forestfire_print(f)
call forestfire_evolve(f)
end do

call forestfire_destroy(f)
```

end program ForestFireTest</lang>

## Go

Text. The program prints the configuration, waits for the Enter key, and prints the next. It makes a pretty good animation to just hold down the Enter key. <lang go>package main

import (

```   "fmt"
"math/rand"
"strings"
```

)

const (

```   rows = 20
cols = 30
p    = .01
f    = .001
```

)

const rx = rows + 2 const cx = cols + 2

func main() {

```   odd := make([]byte, rx*cx)
even := make([]byte, rx*cx)
for r := 1; r <= rows; r++ {
for c := 1; c <= cols; c++ {
if rand.Intn(2) == 1 {
odd[r*cx+c] = 'T'
}
}
}
for {
print(odd)
step(even, odd)
fmt.Scanln()
```
```       print(even)
step(odd, even)
fmt.Scanln()
}
```

}

func print(model []byte) {

```   fmt.Println(strings.Repeat("__", cols))
fmt.Println()
for r := 1; r <= rows; r++ {
for c := 1; c <= cols; c++ {
if model[r*cx+c] == 0 {
fmt.Print("  ")
} else {
fmt.Printf(" %c", model[r*cx+c])
}
}
fmt.Println()
}
```

}

func step(dst, src []byte) {

```   for r := 1; r <= rows; r++ {
for c := 1; c <= cols; c++ {
x := r*cx + c
dst[x] = src[x]
switch dst[x] {
case '#':
// rule 1. A burning cell turns into an empty cell
dst[x] = 0
case 'T':
// rule 2. A tree will burn if at least one neighbor is burning
if src[x-cx-1]=='#'  || src[x-cx]=='#' || src[x-cx+1]=='#' ||
src[x-1] == '#'  ||                   src[x+1] == '#'  ||
src[x+cx-1]=='#' || src[x+cx]=='#' || src[x+cx+1] == '#' {
dst[x] = '#'
```
```                   // rule 3. A tree ignites with probability f
// even if no neighbor is burning
} else if rand.Float64() < f {
dst[x] = '#'
}
default:
// rule 4. An empty space fills with a tree with probability p
if rand.Float64() < p {
dst[x] = 'T'
}
}
}
}
```

}</lang>

<lang haskell>import Control.Monad (replicateM, unless) import Data.List (tails, transpose) import System.Random (randomRIO)

data Cell

``` = Empty
| Tree
| Fire
deriving (Eq)

```

instance Show Cell where

``` show Empty = " "
show Tree = "T"
show Fire = "\$"

```

randomCell :: IO Cell randomCell = fmap ([Empty, Tree] !!) (randomRIO (0, 1) :: IO Int)

randomChance :: IO Double randomChance = randomRIO (0, 1.0) :: IO Double

rim :: a -> a -> a rim b = fmap (fb b) . (fb =<< rb)

``` where
fb = (.) <\$> (:) <*> (flip (++) . return)
rb = fst . unzip . zip (repeat b) . head

```

take3x3 :: a -> [[[a]]] take3x3 = concatMap (transpose . fmap take3) . take3

``` where
take3 = init . init . takeWhile (not . null) . fmap (take 3) . tails

```

list2Mat :: Int -> [a] -> a list2Mat n = takeWhile (not . null) . fmap (take n) . iterate (drop n)

evolveForest :: Int -> Int -> Int -> IO () evolveForest m n k = do

``` let s = m * n
fs <- replicateM s randomCell
let nextState xs = do
ts <- replicateM s randomChance
vs <- replicateM s randomChance
let rv [r1, [l, c, r], r3] newTree fire
| c == Fire = Empty
| c == Tree && Fire `elem` concat [r1, [l, r], r3] = Fire
| c == Tree && 0.01 >= fire = Fire
| c == Empty && 0.1 >= newTree = Tree
| otherwise = c
return \$ zipWith3 rv xs ts vs
evolve i xs =
unless (i > k) \$
do let nfs = nextState \$ take3x3 \$ rim Empty \$ list2Mat n xs
putStrLn ("\n>>>>>> " ++ show i ++ ":")
mapM_ (putStrLn . concatMap show) \$ list2Mat n xs
nfs >>= evolve (i + 1)
evolve 1 fs

```

main :: IO () main = evolveForest 6 50 3</lang>

Output:
Sample
```>>>>>> 1:
TTT  TT TT     TTT T TTT  T   TT  T  TT  TTTT
TTTT  T T TT T      T  TTTTTTT T    T  TT T TT  TT
TTTT TT   T TTTT T TT  T  TTTT T TT TT TT  T T TTT
T  TT TTTT TTT TTT TT TT   TTTTTT  TTTT  T TTT TTT
T T  TTT  T T T TT T    TT     TT  TT   T TTT  TT
T T TTT TT TT     T  TT  TTTTT  TT  TT  T

>>>>>> 2:
TTT  TT TT     TTT T TTT  T T TT  T  T\$  TTTT
TTTT  T T TTTT    T T  TTTTTTT T   TT  TT T TTT TT
TTTT TT   T TTTT T TT  T  TTTT TTT\$ TT TT TT T TTT
T  TTTTTTT TTT TTTTTT TT   TTTTTTT TTTT  TTTTT TTT
TTT TTTT TT T T TT T    TT     TT  TT   T TTT  TT
T      T T TTT TT TT     T  TT  TTTTT  TT TTT  T
>>>>>> 3:
TTT  TT TT     TTT T TTT  T T TT  T  \$ TTTTTT
TTTT  T T TTTT    T TT TTTTTTTTT T \$T  T\$T\$ TTT TT
TTTT TT   T TTTT T TT  T  TTTT TT\$  TT TT TT T TTT
T TTTTTTTT TTT TTTTTT TT   TTTTTT\$ \$TTT  TTTTT TTT
TTT TTTT TT T T TT TT T TT     TT  TT   T TTT  TT
T      T T TTT TT TT   T T  TT  TTTTTT TT TTT  T ```

## Icon and Unicon

\$define EDGE 0 \$define EMPTY 1 \$define TREE 2 \$define FIRE 3

global Colours,Width,Height,ProbTree,ProbFire,ProbInitialTree,Forest,oldForest

procedure main() # forest fire

```   Height := 400            # Window height
Width := 400             # Window width
ProbInitialTree := .10   # intial probability of trees
ProbTree := .01          # ongoing probability of trees
ProbFire := ProbTree/50. # probability of fire
Rounds := 500            # rounds to evolve

setup_forest()
every 1 to Rounds do {
show_forest()
evolve_forest()
}
printf("Forest fire %d x %d rounds=%d p.initial=%r p/f=%r/%r fps=%r\n",
Width,Height,Rounds,ProbInitialTree,ProbTree,ProbFire,
Rounds/(&time/1000.))  # stats
WDone()
```

end

procedure setup_forest() #: setup the forest

```   Colours := table()       # define colours
Colours[EDGE]  := "black"
Colours[EMPTY] := "grey"
Colours[TREE]  := "green"
Colours[FIRE]  := "red"

WOpen("label=Forest Fire", "bg=black",
"size=" || Width+2 || "," || Height+2) | # add for border
stop("Unable to open Window")
every !(Forest := list(Height)) := list(Width,EMPTY)  # default
every ( Forest[1,1 to Width]  | Forest[Height,1 to Width] |
Forest[1 to Height,1] | Forest[1 to Height,Width] ) := EDGE
every r := 2 to Height-1 & c := 2 to Width-1 do
if probability(ProbInitialTree) then Forest[r,c] := TREE
```

end

procedure show_forest() #: show Forest - drawn changes only

```  every r := 2 to *Forest-1 & c := 2 to *Forest[r]-1 do
if /oldForest | oldForest[r,c] ~= Forest[r,c] then {
WAttrib("fg=" || Colours[Forest[r,c]])
DrawPoint(r,c)
}
```

end

procedure evolve_forest() #: evolve forest

```   old := oldForest := list(*Forest)     # freeze copy
every old[i := 1 to *Forest] := copy(Forest[i])  # deep copy
```
```   every r := 2 to *Forest-1 & c := 2 to *Forest[r]-1 do
Forest[r,c] := case old[r,c] of {   # apply rules
FIRE : EMPTY
TREE : if probability(ProbFire) |
( old[r-1, c-1 to c+1] |
old[r,c-1|c+1] |
old[r+1,c-1 to c+1] ) = FIRE then FIRE
EMPTY: if probability(ProbTree) then TREE
}
```

end

procedure probability(P) #: succeed with probability P if ?0 <= P then return end</lang>

## J

<lang j>NB. states: 0 empty, 1 tree, _1 fire dims =:10 10

``` tessellate=: 0,0,~0,.0,.~ 3 3 >./@,;._3 ]
chance=: 1 :'(> ? bind (dims\$0)) bind (mask*m)'
```

start=: 0.5 chance grow =: 0.01 chance fire =: 0.001 chance

``` spread=: [: tessellate 0&>
```
``` step=: grow [`]@.(|@])"0 >.&0 * _1 ^ fire +. spread
```
``` run=:3 :0
forest=. start
for.i.y do.
smoutput ' #o' {~ forest=. step forest
end.
)</lang>
```

Example use:

<lang j> run 2

```##### #
# #
### ####
# # # #
##### #
##   # #
#  #
o##   #

##### #
# #
### ####
# # # #
##### #
##   # #
o  #
o#   # </lang>
```

Note that I have used an artificially small grid here, and that I ran this several times until I could find one that had a fire from the start. Also, the current revision of this code does not show the starting state, though that would be easily changed.

Also, currently the parameters defining the size of the forest, and the probabilities are hard coded into the program and you need to rerun the program's script when they change.

Finally note that the grid size includes the one cell "border" which are blank. If the border cells are meant to be outside of the represented dimensions, you can add 2 to them (or change the code to do so).

## JAMES II/Rule-based Cellular Automata

<lang j2carules>@caversion 1;

dimensions 2;

state EMPTY, TREE, BURNING;

// an empty cell grows a tree with a chance of p = 5 % rule{EMPTY} [0.05] : -> TREE;

// a burning cell turns to a burned cell rule{BURNING}: -> EMPTY;

// a tree starts burning if there is at least one neighbor burning rule{TREE} : BURNING{1,} -> BURNING;

// a tree is hit by lightning with a change of f = 0.006 % rule{TREE} [0.00006] : -> BURNING;</lang> The starting configuration cannot be given in the modeling language since the concepts of the model and its parameters (which includes the starting configuration) are separate in JAMES II.

## Java

Works with: Java version 1.5+

### Text

<lang java5>import java.util.Arrays; import java.util.LinkedList; import java.util.List;

public class Fire { private static final char BURNING = 'w'; //w looks like fire, right? private static final char TREE = 'T'; private static final char EMPTY = '.'; private static final double F = 0.2; private static final double P = 0.4; private static final double TREE_PROB = 0.5;

private static List<String> process(List<String> land){ List<String> newLand = new LinkedList<String>(); for(int i = 0; i < land.size(); i++){ String rowAbove, thisRow = land.get(i), rowBelow; if(i == 0){//first row rowAbove = null; rowBelow = land.get(i + 1); }else if(i == land.size() - 1){//last row rowBelow = null; rowAbove = land.get(i - 1); }else{//middle rowBelow = land.get(i + 1); rowAbove = land.get(i - 1); } newLand.add(processRows(rowAbove, thisRow, rowBelow)); } return newLand; }

private static String processRows(String rowAbove, String thisRow, String rowBelow){ String newRow = ""; for(int i = 0; i < thisRow.length();i++){ switch(thisRow.charAt(i)){ case BURNING: newRow+= EMPTY; break; case EMPTY: newRow+= Math.random() < P ? TREE : EMPTY; break; case TREE: String neighbors = ""; if(i == 0){//first char neighbors+= rowAbove == null ? "" : rowAbove.substring(i, i + 2); neighbors+= thisRow.charAt(i + 1); neighbors+= rowBelow == null ? "" : rowBelow.substring(i, i + 2); if(neighbors.contains(Character.toString(BURNING))){ newRow+= BURNING; break; } }else if(i == thisRow.length() - 1){//last char neighbors+= rowAbove == null ? "" : rowAbove.substring(i - 1, i + 1); neighbors+= thisRow.charAt(i - 1); neighbors+= rowBelow == null ? "" : rowBelow.substring(i - 1, i + 1); if(neighbors.contains(Character.toString(BURNING))){ newRow+= BURNING; break; } }else{//middle neighbors+= rowAbove == null ? "" : rowAbove.substring(i - 1, i + 2); neighbors+= thisRow.charAt(i + 1); neighbors+= thisRow.charAt(i - 1); neighbors+= rowBelow == null ? "" : rowBelow.substring(i - 1, i + 2); if(neighbors.contains(Character.toString(BURNING))){ newRow+= BURNING; break; } } newRow+= Math.random() < F ? BURNING : TREE; } } return newRow; }

public static List<String> populate(int width, int height){ List<String> land = new LinkedList<String>(); for(;height > 0; height--){//height is just a copy anyway StringBuilder line = new StringBuilder(width); for(int i = width; i > 0; i--){ line.append((Math.random() < TREE_PROB) ? TREE : EMPTY); } land.add(line.toString()); } return land; }

//process the land n times public static void processN(List<String> land, int n){ for(int i = 0;i < n; i++){ land = process(land); } }

//process the land n times and print each step along the way public static void processNPrint(List<String> land, int n){ for(int i = 0;i < n; i++){ land = process(land); print(land); } }

//print the land public static void print(List<String> land){ for(String row: land){ System.out.println(row); } System.out.println(); }

public static void main(String[] args){ List<String> land = Arrays.asList(".TTT.T.T.TTTT.T", "T.T.T.TT..T.T..", "TT.TTTT...T.TT.", "TTT..TTTTT.T..T", ".T.TTT....TT.TT", "...T..TTT.TT.T.", ".TT.TT...TT..TT", ".TT.T.T..T.T.T.", "..TTT.TT.T..T..", ".T....T.....TTT", "T..TTT..T..T...", "TTT....TTTTTT.T", "......TwTTT...T", "..T....TTTTTTTT", ".T.T.T....TT..."); print(land); processNPrint(land, 10);

System.out.println("Random land test:");

land = populate(10, 10); print(land); processNPrint(land, 10); } }</lang>

## JavaScript

### JavaScript Node

Functional approach using lodash

<lang javascript>"use strict"

const _ = require('lodash');

const WIDTH_ARGUMENT_POSITION = 2; const HEIGHT_ARGUMENT_POSITION = 3; const TREE_PROBABILITY = 0.5; const NEW_TREE_PROBABILITY = 0.01; const BURN_PROBABILITY = 0.0001; const CONSOLE_RED = '\x1b[31m'; const CONSOLE_GREEN = '\x1b[32m'; const CONSOLE_COLOR_CLOSE = '\x1b[91m'; const CONSOLE_CLEAR = '\u001B[2J\u001B[0;0f'; const NEIGHBOURS = [

```   [-1, -1],
[-1,  0],
[-1,  1],
[ 0, -1],
[ 0,  1],
[ 1, -1],
[ 1,  0],
[ 1,  1]
```

]; const PRINT_DECODE = {

```   ' ': ' ',
'T': `\${CONSOLE_GREEN}T\${CONSOLE_COLOR_CLOSE}`,
'B': `\${CONSOLE_RED}T\${CONSOLE_COLOR_CLOSE}`,
```

}; const CONDITIONS = {

```   'T': (forest, y, x) => Math.random() < BURN_PROBABILITY || burningNeighbour(forest, y, x) ? 'B' : 'T',
' ':  () => Math.random() < NEW_TREE_PROBABILITY ? 'T' : ' ',
'B':  () => ' '
```

};

const WIDTH = process.argv[WIDTH_ARGUMENT_POSITION] || 20; const HEIGHT = process.argv[HEIGHT_ARGUMENT_POSITION] || 10;

const update = forest => {

```   return _.map(forest, (c, ci) => {
return _.map(c, (r, ri) => {
return CONDITIONS[r](forest, ci, ri);
});
});
```

}

const printForest = forest => {

```   process.stdout.write(CONSOLE_CLEAR);
_.each(forest, c => {
_.each(c, r => {
process.stdout.write(PRINT_DECODE[r]);
});
process.stdout.write('\n');
})
```

}

const burningNeighbour = (forest, y, x) => {

```   return _(NEIGHBOURS)
.map(n => _.isUndefined(forest[y + n[0]]) ? null : forest[y + n[0]][x + n[1]])
.any(_.partial(_.isEqual, 'B'));
```

};

let forest = _.times(HEIGHT, () => _.times(WIDTH, () => Math.random() < TREE_PROBABILITY ? 'T' : ' '));

setInterval(() => {

```   forest = update(forest);
printForest(forest)
```

}, 20);

</lang>

### JavaScript

<lang javascript>var forest = {

```   X: 50,
Y: 50,
propTree: 0.5,
propTree2: 0.01,
propBurn: 0.0001,
t: [],
c: ['rgb(255,255,255)', 'rgb(0,255,0)', 'rgb(255,0,0)']
```

};

for(var i = 0; i < forest.Y; i++) {

```   forest.t[i] = [];
for(var j = 0; j < forest.Y; j++) {
forest.t[i][j] = Math.random() < forest.propTree ? 1 : 0;
}
```

}

```   var canvas = document.getElementById('canvas');
var c = canvas.getContext('2d');
for(var i = 0; i < forest.X; i++) {
for(var j = 0; j < forest.Y; j++) {
c.fillStyle = forest.c[forest.t[i][j]];
c.fillRect(10*j, 10*i, 10*j+9, 10*i+9);
}
}
```

}

function doStep(forest) {

```   var to = [];
for(var i = 0; i < forest.Y; i++) {
to[i] = forest.t[i].slice(0);
}
```
```   //indices outside the array are undefined; which converts to 0=empty on forced typecast
for(var i = 0; i < forest.Y; i++) {
for(var j = 0; j < forest.Y; j++) {
if(0 == to[i][j]) {
forest.t[i][j] = Math.random() < forest.propTree2 ? 1 : 0;
} else if(1 == to[i][j]) {
if(
((i>0) && (2 == to[i-1][j])) ||
((i<forest.Y-1) && (2 == to[i+1][j])) ||
((j>0) && (2 == to[i][j-1])) ||
((j<forest.X-1) && (2 == to[i][j+1]))
) {
forest.t[i][j] = 2;
} else {
forest.t[i][j] = Math.random() < forest.propBurn ? 2 : 1;
}
} else if(2 == to[i][j]) {
//If it burns, it gets empty ...
forest.t[i][j] = 0;
}
}
}
```

}

window.setInterval(function(){

```   doStep(forest);
```

}, 100); </lang>

To actually see it work we need a small demo page with HTML5 compliant code:

<lang html5><!DOCTYPE html> <html> <head> <title>Forest Fire</title> </head> <body> <canvas id="canvas" width="500" height="500"> Your browser doesn't support HTML5 Canvas. </canvas> <script language="JavaScript">//<![CDATA[ HERE COMES THE SCRIPT FROM ABOVE <-- //-->]]></script> </body> </html> </lang>

The output is a (mostly fluent) animation of the area.

## Julia

<lang julia>using Printf

@enum State empty tree fire

function evolution(nepoch::Int=100, init::Matrix{State}=fill(tree, 30, 50))

```   # Single evolution
function evolve!(forest::Matrix{State}; f::Float64=0.12, p::Float64=0.5)
dir = [-1 -1; -1 0; -1 1; 0 -1; 0 1; 1 -1; 1 0; 1 1]
# A tree will burn if at least one neighbor is burning
for i in 1:size(forest, 1), j in 1:size(forest, 2)
for k in 1:size(dir, 1)
if checkbounds(Bool, forest, i + dir[k, 1], j + dir[k, 2]) &&
get(forest, i + dir[k, 1], j + dir[k, 2]) == fire
forest[i, j] = fire
break
end
end
end
for i in LinearIndices(forest)
# A burning cell turns into an empty cell
if forest[i] == fire forest[i] = empty end
# A tree ignites with probability f even if no neighbor is burning
if forest[i] == tree && rand() < f forest[i] = fire end
# An empty space fills with a tree with probability p
if forest[i] == empty && rand() < p forest[i] = tree end
end
end
```
```   # Print functions
function printforest(f::Matrix{State})
for i in 1:size(f, 1)
for j in 1:size(f, 2)
print(f[i, j] == empty ? ' ' : f[i, j] == tree ? '🌲' : '🔥')
end
println()
end
end
function printstats(f::Matrix{State})
tot = length(f)
nt  = count(x -> x in (tree, fire), f)
nb  = count(x -> x == fire, f)
@printf("\n%6i cell(s), %6i tree(s), %6i currently burning (%6.2f%%, %6.2f%%)\n",
tot, nt, nb, nt / tot * 100, nb / nt * 100)
end
```
```   # Main
printforest(init)
printstats(init)
for i in 1:nepoch
# println("\33[2J")
evolve!(init)
# printforest(init)
# printstats(init)
# sleep(1)
end
printforest(init)
printstats(init)
```

end

evolution()</lang>

Output:

Final output (epoch 100):

```🌲🌲🔥🌲 🌲🌲🌲🌲 🔥🌲🌲🔥🌲🌲🌲🌲🌲🔥🌲🌲🌲 🌲🌲🌲🌲🌲🌲🌲🌲🌲🌲🌲 🌲 🌲🌲🌲🔥 🌲🌲🌲🌲🔥🌲🌲
🌲🌲🌲🌲🌲🌲🌲🌲🌲🌲🌲🌲🌲🌲🌲🌲🌲🌲🌲🌲🌲🌲🌲🌲🌲 🌲🌲🌲🌲 🔥🌲🌲 🌲🌲🔥🔥🌲🌲 🌲🌲🌲 🌲🌲🌲🌲
🌲🌲🌲🌲🌲🔥🔥🌲   🌲🌲🌲 🔥🔥🌲🌲🌲 🌲  🌲🌲🌲🌲🌲🌲🌲🌲🔥🌲 🌲🌲 🌲🌲🌲 🌲🌲🌲🌲🌲🌲🌲
🌲🔥🌲 🌲🌲 🌲 🌲🌲🌲🌲 🌲🌲   🌲 🌲🌲🌲 🌲🌲 🌲 🌲🔥🌲🌲🌲🔥🔥🔥🌲🌲🌲🌲🌲🌲🌲🌲🌲🔥🌲🌲
🌲🌲🌲 🔥🌲🌲🌲🌲🌲🌲🌲🌲🌲🌲🌲🌲🌲🔥🌲🌲🌲🌲🌲 🌲🌲🌲🌲🌲🌲🌲🌲🌲🔥🌲🌲🌲🌲🌲🌲 🌲🌲🌲  🌲🌲
🌲 🌲🌲🌲🌲🌲🌲🌲🌲🌲🌲 🌲🌲🌲🌲🌲🌲🌲🌲🌲🌲🌲🌲 🌲 🌲🌲🌲🌲🌲🌲🌲🔥🌲🌲🌲🌲🌲🌲🌲🌲 🌲🌲 🌲🌲
🌲🌲🌲 🌲🌲🌲🌲 🌲🌲 🌲🌲 🌲🌲🌲🌲🌲🌲 🌲🌲🌲🌲🌲🌲🔥🌲 🌲🌲🌲🌲🌲🌲 🌲🌲🌲 🌲 🔥🌲🌲🌲🌲🌲
🌲🌲🔥🔥🌲🌲🌲🌲🌲🌲🌲🌲🌲🌲 🌲🌲🌲🌲 🌲🌲🌲 🌲🌲 🌲🌲🌲 🌲🌲🌲🌲🌲🌲🌲🌲 🌲🌲🌲🌲🌲🔥🌲🌲🌲🌲
🌲🌲🌲🌲🌲🌲🌲🌲 🌲🌲🌲🌲🌲🌲🌲🔥 🌲🌲🌲🌲 🌲🌲🌲🌲🌲 🌲🌲🌲🌲🌲🌲🌲🌲🌲🌲🌲🌲🌲🌲🌲🌲🌲🌲🌲🌲🌲
🌲🌲🌲🌲🌲🌲🌲🌲🌲🌲🌲🌲 🌲🌲   🌲🌲🌲🌲🌲🌲🌲🌲🌲🌲🌲🌲🔥  🔥🌲🔥🌲🌲 🌲🌲🌲🌲🌲🌲🌲 🌲🌲🌲
🌲 🔥 🌲🌲🌲🌲🌲🌲🌲🌲 🌲🌲 🌲🌲🌲🌲🌲🔥🌲 🌲 🌲🌲🌲 🌲🔥 🔥🔥🌲🌲🌲🌲🌲🌲🌲🌲🌲🌲🌲🌲🌲🌲
🌲🌲🌲🔥🌲🌲🌲🌲🌲🌲🌲🔥🌲🌲🌲🌲🌲🌲🌲🌲🌲 🌲🌲🌲🌲🌲🌲🌲🌲🌲🌲🌲🌲🌲🔥🌲🌲🔥🌲🌲 🌲 🌲🌲🌲🌲🌲🌲
🌲🌲🔥🌲🌲🌲 🌲 🔥🌲 🌲 🌲 🌲🌲🌲🔥🌲🌲🔥🌲🌲🌲🌲🔥🌲🌲🌲🌲🌲🌲🌲🌲 🌲🌲🌲🌲  🌲🌲🌲🌲🌲🌲
🌲 🌲🌲 🌲🌲🌲🌲  🌲 🔥🔥🌲🌲🌲🔥 🌲🌲 🌲🌲🌲🌲🌲🌲🌲🌲🌲🌲🌲🌲🌲🌲🌲🌲🌲🌲🌲🌲🌲🌲🌲🔥 🌲🌲
🌲🌲🌲🔥 🌲🌲🌲🌲🔥🌲🔥🌲 🌲🌲🌲🌲🌲🌲🌲🔥🌲🌲🌲🌲🌲🌲🌲🌲🌲🌲🌲🌲🌲🌲🌲🌲🌲🌲 🌲🌲🌲🌲🌲🌲🔥🌲🌲
🌲🌲🌲🌲🌲 🌲🌲🌲🌲🌲🌲 🌲🌲🌲 🌲🌲🌲🌲🌲🌲🌲🌲🌲🌲🌲🔥🌲🔥 🌲🌲🌲🌲🌲🌲🔥   🌲🌲🌲  🔥🔥
🌲 🌲🌲🌲🌲🌲🌲🌲🔥 🌲🌲🌲🌲 🌲🌲 🌲🌲🔥🌲🌲  🌲 🌲🌲🌲🌲🌲🌲🌲🌲🌲🌲🌲🌲🌲🔥🌲  🔥🌲🔥🌲
🌲🌲🌲 🌲🌲🔥 🌲🌲🌲🌲🌲🌲🌲🌲🔥🌲🌲  🌲🔥 🌲🌲  🌲🌲🌲🔥🌲🌲🔥🌲 🔥🌲 🌲🌲🌲🌲🌲🌲🌲🌲 🌲
🌲🌲🌲 🔥🌲🌲🌲🌲  🌲🌲 🌲 🌲🌲🌲 🌲🌲🌲🌲🌲 🌲🌲 🌲🌲🌲🌲🌲🌲🌲🌲🌲🌲🌲 🌲 🌲🌲🌲🌲🌲🌲🌲
🌲 🌲 🌲🌲  🌲🌲 🌲🌲  🌲 🌲🌲🌲🌲🌲🌲🌲  🌲  🌲  🌲🌲🌲 🌲🌲 🌲🌲🌲🌲 🌲 🌲
🌲🌲  🌲 🌲🌲🌲 🌲🌲    🌲  🌲🌲🌲🌲🌲 🌲🌲 🌲🌲  🌲🌲 🌲🌲 🌲🌲   🌲 🌲🌲🌲
🌲🌲  🌲🌲 🌲🌲 🌲🌲  🌲🌲 🌲🌲🌲🌲🌲🌲🌲🌲🌲🌲  🌲  🌲   🌲🌲🌲 🌲
🌲🌲🌲  🌲🌲🌲🌲  🌲 🌲  🌲 🌲🌲🌲🌲🌲   🌲🌲 🌲   🌲 🌲🌲  🌲🌲 🌲 🌲🌲  🌲🌲
🌲🌲 🌲🌲🌲 🌲🌲🌲  🌲  🌲    🌲  🌲 🌲🌲   🌲  🌲🌲      🌲 🌲 🌲 🌲🌲
🌲🌲 🌲      🌲🌲🌲🌲 🌲   🌲🌲  🌲🌲🌲🌲 🌲   🌲🌲🌲🌲  🌲    🌲🌲🌲🌲
🌲🌲  🌲🌲 🌲🌲🌲🌲🌲 🌲 🌲🌲 🌲🌲🌲🌲🌲  🌲 🌲 🌲🌲🌲 🌲🌲🌲   🌲 🌲🌲 🌲 🌲
🌲 🌲🌲 🌲🌲   🌲   🌲🌲🌲🌲  🌲🌲 🌲 🌲🌲🌲 🌲🌲   🌲🌲🌲      🌲
🌲🌲 🌲🌲  🌲    🌲  🌲🌲🌲🌲🌲 🌲🌲 🌲   🌲 🌲 🌲🌲 🌲  🌲🌲🌲🌲🌲🌲    🌲🌲
🌲   🌲  🌲🌲 🌲🌲   🌲 🌲🌲 🌲🌲🌲 🌲    🌲 🌲   🌲  🌲🌲🌲🌲      🌲
🌲🌲🌲🌲🌲 🌲 🌲🌲   🌲  🌲 🌲🌲🌲   🌲🌲🌲     🌲 🌲🌲 🌲🌲 🌲 🌲🌲🌲🌲

1500 cell(s),   1089 tree(s),     73 currently burning ( 72.60%,   6.70%)```

## Lua

This program uses the Lua Curses library for graphics, although changing the code to avoid such dependency is easy. <lang Lua> -- ForestFire automaton implementation -- Rules: at each step: -- 1) a burning tree disappears -- 2) a non-burning tree starts burning if any of its neighbours is -- 3) an empty spot may generate a tree with prob P -- 4) a non-burning tree may ignite with prob F

local socket = require 'socket' -- needed for socket.sleep local curses = require 'curses'

local p_spawn, p_ignite = 0.005, 0.0002 local naptime = 0.03 -- seconds local forest_x, forest_y = 60, 30

local forest = (function (x, y) local wrl = {} for i = 1, y do wrl[i] = {} for j = 1, x do local rand = math.random() wrl[i][j] = (rand < 0.5) and 1 or 0 end end return wrl end)(forest_x, forest_y)

math.randomseed(os.time())

forest.step = function (self) for i = 1, #self do for j = 1, #self[i] do if self[i][j] == 0 then if math.random() < p_spawn then self[i][j] = 1 end elseif self[i][j] == 1 then if self:ignite(i, j) or math.random() < p_ignite then self[i][j] = 2 end elseif self[i][j] == 2 then self[i][j] = 0 else error("Error: forest[" .. i .. "][" .. j .. "] is " .. self[i][j] .. "!") end end end end

forest.draw = function (self) for i = 1, #self do for j = 1, #self[i] do if self[i][j] == 0 then win:mvaddch(i,j," ") elseif self[i][j] == 1 then win:attron(curses.color_pair(1)) win:mvaddch(i,j,"Y") win:attroff(curses.color_pair(1)) elseif self[i][j] == 2 then win:attron(curses.color_pair(2)) win:mvaddch(i,j,"#") win:attroff(curses.color_pair(2)) else error("self[" .. i .. "][" .. j .. "] is " .. self[i][j] .. "!") end end end end

forest.ignite = function (self, i, j) for k = i - 1, i + 1 do if k < 1 or k > #self then goto continue1 end for l = j - 1, j + 1 do if l < 1 or l > #self[i] or math.abs((k - i) + (l - j)) ~= 1 then goto continue2 end if self[k][l] == 2 then return true end ::continue2:: end ::continue1:: end return false end

local it = 1 curses.initscr() curses.start_color() curses.echo(false) curses.init_pair(1, curses.COLOR_GREEN, curses.COLOR_BLACK) curses.init_pair(2, curses.COLOR_RED, curses.COLOR_BLACK) win = curses.newwin(forest_y + 2, forest_x, 0, 0) win:clear() win:mvaddstr(forest_y + 1, 0, "p_spawn = " .. p_spawn .. ", p_ignite = " .. p_ignite) repeat forest:draw() win:move(forest_y, 0) win:clrtoeol() win:addstr("Iteration: " .. it .. ", nap = " .. naptime*1000 .. "ms") win:refresh() forest:step() it = it + 1 socket.sleep(naptime) until false </lang>

## Mathematica / Wolfram Language

Mathematica is good at working with cellular automata -- especially 2-color 1-dimensional cellular automata. The automaton function is awkward yet very powerful. This code implements a 3-color 2-dimensional cellular automaton with 9-cell neighbourhoods using a custom cell evolution function. There is probably a rule number specification that can replace the custom evolution function and make this simpler and faster. But this works well enough. The last line of code plots the state of the forest after the 300th step.

<lang Mathematica>evolve[nbhd_List, k_] := 0 /; nbhd2, 2 == 2 (*burning->empty*) evolve[nbhd_List, k_] := 2 /; nbhd2, 2 == 1 && Max@nbhd == 2 (*near_burning&nonempty->burning*) evolve[nbhd_List, k_] := RandomChoice[{f, 1 - f} -> {2, nbhd2, 2}] /; nbhd2, 2 == 1 && Max@nbhd < 2 (*spontaneously combusting tree*) evolve[nbhd_List, k_] := RandomChoice[{p, 1 - p} -> {1, nbhd2, 2}] /; nbhd2, 2 == 0 (*random tree growth*)

r = 100; c = 100; p = 10^-2; f = 10^-4; init = RandomInteger[BernoulliDistribution[0.05], {r, c}]; MatrixPlot[CellularAutomaton[{evolve, {}, {1, 1}}, {init, 0}, {{{300}}}], ColorRules -> {0 -> White, 1 -> Green, 2 -> Red}, Frame -> False]</lang>

## MATLAB / Octave

<lang MATLAB>function forest_fire(f,p,N,M) % Forest fire if nargin<4; M=200; end if nargin<3; N=200; end if nargin<2; p=.03; end if nargin<1; f=p*.0001; end

% initialize; F = (rand(M,N) < p)+1;  % tree with probability p S = ones(3); S(2,2)=0;  % surrounding

textmap = ' T#'; colormap([.5,.5,.5;0,1,0;1,0,0]); while(1) image(F); pause(.1)  % uncomment for graphical output % disp(textmap(F)); pause;  % uncomment for textual output G = ((F==1).*((rand(M,N)<p)+1));  % grow tree G = G + (F==2) .* ((filter2(S,F==3)>0) + (rand(M,N)<f) + 2);  % burn tree if neighbor is burning or by chance f G = G + (F==3);  % empty after burn F = G; end; </lang>

## Nim

Translation of: C

<lang nim>import random, os, sequtils, strutils

randomize()

type State {.pure.} = enum Empty, Tree, Fire

const

``` Disp: array[State, string] = ["  ", "\e[32m/\\\e[m", "\e[07;31m/\\\e[m"]
TreeProb = 0.01
BurnProb = 0.001
```

proc chance(prob: float): bool {.inline.} = rand(1.0) < prob

1. Set the size

var w, h: int if paramCount() >= 2:

``` w = paramStr(1).parseInt
h = paramStr(2).parseInt
```

if w <= 0: w = 30 if h <= 0: h = 30

iterator fields(a = (0, 0), b = (h-1, w-1)): tuple[y, x: int] =

``` ## Iterate over fields in the universe
for y in max(a[0], 0) .. min(b[0], h-1):
for x in max(a[1], 0) .. min(b[1], w-1):
yield (y, x)
```
1. Initialize

var univ, univNew = newSeqWith(h, newSeq[State](w))

while true:

``` # Show.
stdout.write "\e[H"
for y, x in fields():
stdout.write Disp[univ[y][x]]
if x == 0: stdout.write "\e[E"
stdout.flushFile
```
``` # Evolve.
for y, x in fields():
case univ[y][x]
of Fire:
univNew[y][x] = Empty
of Empty:
if chance(TreeProb): univNew[y][x] = Tree
of Tree:
for y1, x1 in fields((y-1, x-1), (y+1, x+1)):
if univ[y1][x1] == Fire:
univNew[y][x] = Fire
break
if chance(BurnProb): univNew[y][x] = Fire
univ = univNew
sleep 200</lang>
```

## OCaml

Library: curses

This example uses a curses display (with the ocaml-curses bindings).

<lang ocaml>open Curses

let ignite_prob = 0.02 let sprout_prob = 0.01

type cell = Empty | Burning | Tree

let get w x y =

``` try w.(x).(y)
with Invalid_argument _ -> Empty
```

let neighborhood_burning w x y =

``` try
for _x = pred x to succ x do
for _y = pred y to succ y do
if get w _x _y = Burning then raise Exit
done
done
; false
with Exit -> true
```

let evolves w x y =

``` match w.(x).(y) with
| Burning -> Empty
| Tree ->
if neighborhood_burning w x y
then Burning
else begin
if (Random.float 1.0) < ignite_prob
then Burning
else Tree
end
| Empty ->
if (Random.float 1.0) < sprout_prob
then Tree
else Empty
```

let step width height w =

``` for x = 0 to pred width do
for y = 0 to pred height do
w.(x).(y) <- evolves w x y
done
done
```

let i = int_of_char let repr = function

``` | Empty -> i ' ' | Burning -> i '#' | Tree -> i 't'
```

let draw width height w =

``` for x = 0 to pred width do
for y = 0 to pred height do
ignore(move y x);
ignore(delch ());
ignore(insch (repr w.(x).(y)));
done;
done;
ignore(refresh ())
```

let () =

``` Random.self_init ();
let wnd = initscr () in
ignore(cbreak ());
ignore(noecho ());
let height, width = getmaxyx wnd in
let w = Array.make_matrix width height Empty in
clear ();
ignore(refresh ());
while true do
draw width height w;
step width height w;
Unix.sleep 1;
done;
endwin()</lang>
```

You can execute this script with:

```\$ ocaml unix.cma -I +curses curses.cma forest.ml
```

## Ol

<lang scheme> (import (lib gl)) (import (otus random!))

(define WIDTH 170) (define HEIGHT 96)

probabilities

(define p 20) (define f 1000)

(gl:set-window-title "Drossel and Schwabl 'forest-fire'") (import (OpenGL version-1-0))

```  (glShadeModel GL_SMOOTH)
(glClearColor 0.11 0.11 0.11 1)
(glOrtho 0 WIDTH 0 HEIGHT 0 1)
```

(gl:set-userdata (make-vector (map (lambda (-) (make-vector (map (lambda (-) (rand! 2)) (iota WIDTH)))) (iota HEIGHT))))

(gl:set-renderer (lambda (mouse)

```  (let ((forest (gl:get-userdata))
(step (make-vector (map (lambda (-) (make-vector (repeat 0 WIDTH))) (iota HEIGHT)))))
(glClear GL_COLOR_BUFFER_BIT)
```
```     (glPointSize (/ 854 WIDTH))
(glBegin GL_POINTS)
(for-each (lambda (y)
(for-each (lambda (x)
(case (ref (ref forest y) x)
(0 ; An empty space fills with a tree with probability "p"
(if (zero? (rand! p))
(set-ref! (ref step y) x 1)))
(1
(glColor3f 0.2 0.7 0.2)
(glVertex2f x y)
; A tree will burn if at least one neighbor is burning
; A tree ignites with probability "f" even if no neighbor is burning
(if (or (eq? (ref (ref forest (- y 1)) (- x 1)) 2)  (eq? (ref (ref forest (- y 1))    x)    2)  (eq? (ref (ref forest (- y 1)) (+ x 1)) 2)
(eq? (ref (ref forest    y   ) (- x 1)) 2)                                              (eq? (ref (ref forest    y   ) (+ x 1)) 2)
(eq? (ref (ref forest (+ y 1)) (- x 1)) 2)  (eq? (ref (ref forest (+ y 1))    x)    2)  (eq? (ref (ref forest (+ y 1)) (+ x 1)) 2)
(zero? (rand! f)))
(set-ref! (ref step y) x 2)
(set-ref! (ref step y) x 1)))
(2
(glColor3f 0.7 0.7 0.1)
(glVertex2f x y))
; A burning cell turns into an empty cell
(set-ref! (ref step y) x 0)))
(iota WIDTH)))
(iota HEIGHT))
(glEnd)
(gl:set-userdata step))))
```

</lang>

## PARI/GP

<lang parigp>step(M,p,f)={ my(m=matsize(M)[1],n=matsize(M)[2]); matrix(m,n,i,j, if(M[i,j]=="*", " " , if(M[i,j]=="t", my(nbr="t"); for(x=max(1,i-1),min(m,i+1), for(y=max(1,j-1),min(n,j+1), if(M[x,y]=="*",nbr="*";break(2)) ) ); if(random(1.)<f,"*",nbr) , if(random(1.)<p,"t"," ") ) ) ) }; burn(n,p,f)={ my(M=matrix(n,n,i,j,if(random(2)," ","t")),N); while(1,print(M=step(M,p,f))) }; burn(5,.1,.03)</lang>

## Perl

Requires terminal that understands ANSI escape sequences:<lang Perl> use 5.10.0;

my \$w = `tput cols` - 1; my \$h = `tput lines` - 1; my \$r = "\033[H";

my (\$green, \$red, \$yellow, \$norm) = ("\033[32m", "\033[31m", "\033[33m", "\033[m");

my \$tree_prob = .05; my \$burn_prob = .0002;

my @forest = map([ map((rand(1) < \$tree_prob) ? 1 : 0, 1 .. \$w) ], 1 .. \$h);

sub iterate { my @new = map([ map(0, 1 .. \$w) ], 1 .. \$h); for my \$i (0 .. \$h - 1) { for my \$j (0 .. \$w - 1) { \$new[\$i][\$j] = \$forest[\$i][\$j]; if (\$forest[\$i][\$j] == 2) { \$new[\$i][\$j] = 3; next; } elsif (\$forest[\$i][\$j] == 1) { if (rand() < \$burn_prob) { \$new[\$i][\$j] = 2; next; } for ( [-1, -1], [-1, 0], [-1, 1], [ 0, -1], [ 0, 1], [ 1, -1], [ 1, 0], [ 1, 1] ) { my \$y = \$_->[0] + \$i; next if \$y < 0 || \$y >= \$h; my \$x = \$_->[1] + \$j; next if \$x < 0 || \$x >= \$w; if (\$forest[\$y][\$x] == 2) { \$new[\$i][\$j] = 2; last; } } } elsif (rand() < \$tree_prob) { \$new[\$i][\$j] = 1; } elsif (\$forest[\$i][\$j] == 3) { \$new[\$i][\$j] = 0; } }} @forest = @new; }

sub forest { print \$r; for (@forest) { for (@\$_) { when(0) { print " "; } when(1) { print "\${green}*"} when(2) { print "\${red}&" } when(3) { print "\${yellow}&" } } print "\033[E\033[1G"; } iterate; }

forest while (1);</lang>

### Alternate Perl Solution

<lang Perl>#!/usr/bin/perl

use strict; # http://www.rosettacode.org/wiki/Forest_fire use warnings;

my \$p = 0.01; # probability of empty -> tree my \$f = 0.0001; # probability of tree -> burning

my (\$high, \$wide) = split ' ', qx(stty size); # 135 174 tiny font in xterm my \$mask = 0 x \$wide . (0 . 7 x (\$wide - 2) . 0) x (\$high - 5) . 0 x \$wide; my \$forest = \$mask =~ s/7/ rand() < 0.5 ? 2 : 1 /ger;

for( 1 .. 1e3 )

``` {                                         # 0=border 1=empty 2=tree 3=burning
print "\e[H", \$forest =~ tr/0123/  ^#/r, "\n"; # ^=tree  #=burning tree
my \$n = \$forest =~ tr/123/004/r;          # 4=a neighbor is burning
\$forest |= 0 x \$_ . \$n | substr \$n, \$_ for 1, \$wide - 1 .. \$wide + 1;
\$forest &= \$mask;                         # clear borders and trim
\$forest =~ tr/1-7/et10e31/;               # step to next generation
\$forest =~ s/t/ rand() < \$f ? 3 : 2 /ge;  # rule 3) tree cell to burning
\$forest =~ s/e/ rand() < \$p ? 2 : 1 /ge;  # rule 4) empty cell to tree
select undef, undef, undef, 0.1;          # comment out for full speed
}</lang>
```

## Phix

Library: Phix/pGUI
```--
-- demo\rosetta\Forest_fire.exw
-- ============================
--
--  A burning cell turns into an empty cell
--  A tree will burn if at least one neighbor is burning
--  A tree ignites with probability F even if no neighbor is burning
--  An empty space fills with a tree with probability P
--
--  Draws bigger "pixels" when it feels the need to.
--
with javascript_semantics
include pGUI.e
Ihandle dlg, canvas, hTimer
cdCanvas cddbuffer, cdcanvas

constant TITLE = "Forest Fire",
P = 0.03,      -- probability of new tree growing
F = 0.00003    -- probability of new fire starting

enum EMPTY,TREE,FIRE    -- (1,2,3)
constant colours = {CD_BLACK,CD_GREEN,CD_YELLOW}

sequence f = {}     -- the forest

function randomf()
return rand(1000000)/1000000    -- returns 0.000001..1.000000
end function

function redraw_cb(Ihandle /*ih*/)
integer {width, height} = IupGetIntInt(canvas, "DRAWSIZE"),
-- limit to 40K cells, otherwise it gets too slow.
-- n here is the cell size in pixels (min of 1x1)
-- Note you still get some setTimeout violations
-- in js even with the limit reduced to just 5K..
n = ceil(sqrt(width*height/40000)),
w = floor(width/n)+2, -- (see cx below)
h = floor(height/n)+2

cdCanvasActivate(cddbuffer)
if length(f)!=w
or length(f[1])!=h then
f = sq_rand(repeat(repeat(2,h),w))  -- (EMPTY or TREE)
end if
sequence fn = deep_copy(f)
--
-- There is a "dead border" of 1 cell all around the edge of f (& fn) which
-- we never display or update. If we have got this right/an exact fit, then
-- w*n should be exactly 2n too wide, whereas in the worst case there is an
-- (2n-1) pixel border, which we split between left and right, ditto cy.
--
integer cx = n+floor((width-w*n)/2)
for x=2 to w-1 do
integer cy = n+floor((height-h*n)/2)
for y=2 to h-1 do
integer fnxy
switch f[x,y] do
case EMPTY:
fnxy = EMPTY+(randomf()<P)  -- (EMPTY or TREE)
case TREE:
fnxy = TREE
if f[x-1,y-1]=FIRE or f[x,y-1]=FIRE or f[x+1,y-1]=FIRE
or f[x-1,y  ]=FIRE or (randomf()<F) or f[x+1,y  ]=FIRE
or f[x-1,y+1]=FIRE or f[x,y+1]=FIRE or f[x+1,y+1]=FIRE then
fnxy = FIRE
end if
case FIRE:
fnxy = EMPTY
end switch
fn[x,y] = fnxy
cdCanvasSetForeground(cddbuffer,colours[fnxy])
cdCanvasBox(cddbuffer, cx, cx+n-1, cy, cy+n-1)
cy += n
end for
cx += n
end for
f = fn
cdCanvasFlush(cddbuffer)
return IUP_DEFAULT
end function

function map_cb(Ihandle ih)
cdcanvas = cdCreateCanvas(CD_IUP, ih)
cddbuffer = cdCreateCanvas(CD_DBUFFER, cdcanvas)
return IUP_DEFAULT
end function

function timer_cb(Ihandle /*ih*/)
IupUpdate(canvas)
return IUP_IGNORE
end function

procedure main()
IupOpen()
canvas = IupCanvas("RASTERSIZE=225x100")
IupSetCallbacks(canvas, {"MAP_CB", Icallback("map_cb"),
"ACTION", Icallback("redraw_cb")})
dlg = IupDialog(canvas, `TITLE="%s", MINSIZE=245x140`, {TITLE})
-- (above MINSIZE prevents the title from getting squished)
IupShow(dlg)
hTimer = IupTimer(Icallback("timer_cb"), 100)   -- (10 fps)
if platform()!=JS then
IupMainLoop()
IupClose()
end if
end procedure

main()
```

## PHP

<lang PHP><?php

define('WIDTH', 10); define('HEIGHT', 10);

define('GEN_CNT', 10); define('PAUSE', 250000);

define('TREE_PROB', 50); define('GROW_PROB', 5); define('FIRE_PROB', 1);

define('BARE', ' '); define('TREE', 'A'); define('BURN', '/');

\$forest = makeNewForest();

for (\$i = 0; \$i < GEN_CNT; \$i++) {

```   displayForest(\$forest, \$i);
\$forest = getNextForest(\$forest);
```

}

displayForest(\$forest, 'done'); exit;

function makeNewForest() {

```   return mapForest([
'func' => function(){
return isProb(TREE_PROB) ? TREE : BARE;
}
]);
```

}

function displayForest(\$forest, \$generationNum) {

```   system("clear");
echo PHP_EOL . "Generation: \$generationNum" . PHP_EOL;
mapForest(['forest' => \$forest, 'func' => function(\$f, \$x, \$y){
echo \$f[\$y][\$x] . (\$x == WIDTH - 1 ? PHP_EOL : );
}
]);
echo PHP_EOL;
usleep(PAUSE);
```

}

function getNextForest(\$oldForest) {

```   return mapForest(['forest' => \$oldForest, 'func' => function(\$f, \$x, \$y){
switch (\$f[\$y][\$x]) {
case BURN:
return BARE;
case BARE:
return isProb(GROW_PROB) ? TREE : BARE;
case TREE:
\$caughtFire = isProb(FIRE_PROB);
\$ablaze = \$caughtFire ? true : getNumBurningNeighbors(\$f, \$x, \$y) > 0;
return \$ablaze ? BURN : TREE;
}
}
]);
```

}

function getNumBurningNeighbors(\$forest, \$x, \$y) {

```   \$burningNeighbors = mapForest([
'forest' => \$forest,
'x1' => \$x - 1, 'x2' => \$x + 2,
'y1' => \$y - 1, 'y2' => \$y + 2,
'default' => 0,
'func' => function(\$f, \$x, \$y){
return \$f[\$y][\$x] == BURN ? 1 : 0;
}
]);

\$numOnFire = 0;
foreach (\$burningNeighbors as \$row) {
\$numOnFire += array_sum(\$row);
}
return \$numOnFire;
```

}

function mapForest(\$params) {

```   \$p = array_merge([
'forest' => [],
'func' => function(){echo "default\n";},
'x1' => 0,
'x2' => WIDTH,
'y1' => 0,
'y2' => HEIGHT,
'default' => BARE
], \$params);

\$newForest = [];
for (\$y = \$p['y1']; \$y < \$p['y2']; \$y++) {
\$newRow = [];
for (\$x = \$p['x1']; \$x < \$p['x2']; \$x++) {
\$inBounds = (\$x >= 0 && \$x < WIDTH && \$y >= 0 && \$y < HEIGHT);
\$newRow[] = (\$inBounds ? \$p['func'](\$p['forest'], \$x, \$y) : \$p['default']);
}
\$newForest[] = \$newRow;
}
return \$newForest;
```

}

function isProb(\$prob) {

```   return rand(0, 100) < \$prob;
```

} </lang>

## PicoLisp

(scl 3)

(de forestFire (Dim ProbT ProbP ProbF)

```  (let Grid (grid Dim Dim)
(for Col Grid
(for This Col
(=: tree (> ProbT (rand 0 1.0))) ) )
(loop
(disp Grid NIL
'((This)
(cond
((: burn) "# ")
((: tree) "T ")
(T ". ") ) ) )
(wait 1000)
(for Col Grid
(for This Col
(=: next
(cond
((: burn) NIL)
((: tree)
(if
(or
(find  # Neighbor burning?
'((Dir) (get (Dir This) 'burn))
(quote
west east south north
((X) (south (west X)))
((X) (north (west X)))
((X) (south (east X)))
((X) (north (east X))) ) )
(> ProbF (rand 0 1.0)) )
'burn
'tree ) )
(T (and (> ProbP (rand 0 1.0)) 'tree)) ) ) ) )
(for Col Grid
(for This Col
(if (: next)
(put This @ T)
(=: burn)
(=: tree) ) ) ) ) ) )</lang>
```

Use:

`(forestFire 26 0.5 0.01 0.001)`

## PostScript

<lang PostScript>%!PS-Adobe-3.0 %%BoundingBox: 0 0 400 400

/size 400 def

/rand1 { rand 2147483647 div } def

/m { moveto } bind def /l { rlineto} bind def /drawforest {

```       0 1 n 1 sub { /y exch def
0 1 n 1 sub { /x exch def
forest x get y get dup 0 eq { pop } {
1 eq { 0 1 0 } { 1 0 0 } ifelse setrgbcolor
x c mul y c mul m
c 0 l 0 c l c neg 0 l closepath fill
} ifelse
} for
} for
```

} def

/r1n { dup 0 ge exch n lt and } def

/neighbors { /y exch def /x exch def /cnt 0 def

```       [
y 1 sub 1 y 1 add { /y1 exch def
y1 r1n {
x 1 sub 1 x 1 add { /x1 exch def
x1 r1n { forest x1 get y1 get } if
} for
} if
} for]
```

} def

/iter {

```       /nf [ n {[ n {0} repeat]} repeat ] def
0 1 n 1 sub { /x exch def
0 1 n 1 sub { /y exch def
nf x get y
forest x get y get dup
0 eq { pop rand1 treeprob le {1}{0} ifelse
} {
1 eq {  /fire false def
x y neighbors {
-1 eq { /fire true def } if
} forall
fire {-1}{
rand1 burnprob lt {-1}{1} ifelse
} ifelse
}{0} ifelse
} ifelse
put
} for } for
/forest nf def
```

} def

/n 200 def /treeprob .05 def /burnprob .0001 def /c size n div def /forest [ n {[ n { rand1 treeprob le {1}{0} ifelse } repeat]} repeat ] def

1000 { drawforest showpage iter } repeat %%EOF</lang>

## Python

Just hit return to advance the simulation, or enter an integer to advance that integer amount of 'frames'. Entering 'p' will print the grid, and 'q' will quit. A summary of the grids status is printed before each prompt for input. <lang python> Forest-Fire Cellular automation

```See: http://en.wikipedia.org/wiki/Forest-fire_model
```

L = 15

1. d = 2 # Fixed

initial_trees = 0.55 p = 0.01 f = 0.001

try:

```   raw_input
```

except:

```   raw_input = input

```

import random

tree, burning, space = 'TB.' hood = ((-1,-1), (-1,0), (-1,1),

```       (0,-1),          (0, 1),
(1,-1),  (1,0),  (1,1))
```

def initialise():

```   grid = {(x,y): (tree if random.random()<= initial_trees else space)
for x in range(L)
for y in range(L) }
return grid
```

def gprint(grid):

```   txt = '\n'.join(.join(grid[(x,y)] for x in range(L))
for y in range(L))
print(txt)
```

def quickprint(grid):

```   t = b = 0
ll = L * L
for x in range(L):
for y in range(L):
if grid[(x,y)] in (tree, burning):
t += 1
if grid[(x,y)] == burning:
b += 1
print(('Of %6i cells, %6i are trees of which %6i are currently burning.'
+ ' (%6.3f%%, %6.3f%%)')
% (ll, t, b, 100. * t / ll, 100. * b / ll))

```

def gnew(grid):

```   newgrid = {}
for x in range(L):
for y in range(L):
if grid[(x,y)] == burning:
newgrid[(x,y)] = space
elif grid[(x,y)] == space:
newgrid[(x,y)] = tree if random.random()<= p else space
elif grid[(x,y)] == tree:
newgrid[(x,y)] = (burning
if any(grid.get((x+dx,y+dy),space) == burning
for dx,dy in hood)
or random.random()<= f
else tree)
return newgrid
```

if __name__ == '__main__':

```   grid = initialise()
iter = 0
while True:
quickprint(grid)
inp = raw_input('Print/Quit/<int>/<return> %6i: ' % iter).lower().strip()
if inp:
if inp[0] == 'p':
gprint(grid)
elif inp.isdigit():
for i in range(int(inp)):
iter +=1
grid = gnew(grid)
quickprint(grid)
elif inp[0] == 'q':
break
grid = gnew(grid)
iter +=1</lang>
```

Sample output

```Of    225 cells,    108 are trees of which      0 are currently burning. (48.000%,  0.000%)
Print/Quit/<int>/<return>      0:
Of    225 cells,    114 are trees of which      1 are currently burning. (50.667%,  0.444%)
Print/Quit/<int>/<return>      1: p
.TTT.T.T.TTTT.T
T.T.T.TT..T.T..
TT.TTTT...T.TT.
TTT..TTTTT.T..T
.T.TTT....TT.TT
...T..TTT.TT.T.
.TT.TT...TT..TT
.TT.T.T..T.T.T.
..TTT.TT.T..T..
.T....T.....TTT
T..TTT..T..T...
TTT....TTTTTT.T
......TBTTT...T
..T....TTTTTTTT
.T.T.T....TT...
Of    225 cells,    115 are trees of which      6 are currently burning. (51.111%,  2.667%)
Print/Quit/<int>/<return>      2: p
.TTT.TTT.TTTT.T
T.T.T.TT..T.T..
TT.TTTT...T.TT.
TTT..TTTTT.T..T
.T.TTT....TT.TT
...T..TTT.TT.T.
.TT.TT...TT..TT
.TT.T.T..T.T.T.
..TTT.TT.T..T..
.T....T.....TTT
T..TTT..T..T...
TTT....BBTTTT.T
....T.B.BTT...T
..T....BBTTTTTT
.T.T.T....TT...
Of    225 cells,    113 are trees of which      4 are currently burning. (50.222%,  1.778%)
Print/Quit/<int>/<return>      3: p
.TTT.TTT.TTTT.T
T.T.T.TT..T.T..
TT.TTTT...T.TT.
TTT..TTTTT.T..T
.T.TTT...TTT.TT
...T..TTT.TTTTT
.TT.TT...TT..TT
.TT.T.T..T.T.T.
..TTT.TT.T..T..
.T.T..T.....TTT
T..TTT..B..T...
TTT......BTTT.T
....T....BT...T
..T......BTTTTT
.T.T.T....TT...
Of    225 cells,    110 are trees of which      4 are currently burning. (48.889%,  1.778%)
Print/Quit/<int>/<return>      4: ```

## Racket

<lang racket>#lang racket (require 2htdp/universe) (require 2htdp/image)

(define (initial-forest w p-tree)

``` (for/vector #:length w ((rw w))
(for/vector #:length w ((cl w))
(if (< (random) p-tree) #\T #\_))))
```

(define (has-burning-neighbour? forest r# c# w)

``` ;; note, this will check r# c#, too but it's not
;; worth checking that r=r# and c=c# each time in
;; this case
(for*/first
((r (in-range (- r# 1) (+ r# 2)))
#:when (< 0 r w)
(c (in-range (- c# 1) (+ c# 2)))
#:when (< 0 c w)
#:when (equal? #\* (vector-ref (vector-ref forest r) c)))
#t))
```

(define (fire-tick forest p-sprout f-combust w)

``` (for/vector #:length w ((rw forest) (r# (in-naturals)))
(for/vector #:length w ((cl rw) (c# (in-naturals)))
(case cl
((#\_) (if (< (random) p-sprout) #\T #\_))
((#\*) #\_)
((#\T)
(cond
[(has-burning-neighbour? forest r# c# w) #\*]
[(< (random) f-combust) #\*]
[else #\T]))))))
```

(define (render-forest state)

``` (for/fold
((scn (empty-scene
(* (vector-length state) 8)
(* (vector-length (vector-ref state 0)) 8)
'black)))

((rw state) (r# (in-naturals)))
(for/fold
((scn scn))
((cl rw) (c# (in-naturals)))
(place-image (circle 4 'solid
(case cl
((#\_) 'brown)
((#\T) 'green)
((#\*) 'red)))
(+ 4 (* c# 8)) (+ 4 (* r# 8)) scn))))
```

(define (forest-fire p-tree p-sprout f-combust w)

``` (big-bang
(initial-forest w p-tree) ;; initial state
[on-tick (lambda (state)
;(displayln state)
(fire-tick state p-sprout f-combust w))]
[to-draw render-forest]))
```

(forest-fire 0 1/8 1/1024 50)</lang>

I'll tweak with the parameters for a bit, and when I have some nice photos I'll post them!

## Raku

(formerly Perl 6)

### ANSI graphics

Works with: rakudo version 2015-10-04

This version saves a lot of looking around by using four states instead of three; the Heating state does a lookahead to track trees that are being heated up by burning trees, so we only ever have to traverse the neighbors of burning trees, not all trees. Also, by only checking the list of burning trees, we can avoid copying the entire forest each iteration, since real forests are mutable. <lang perl6>my \$RED = "\e[1;31m"; my \$YELLOW = "\e[1;33m"; my \$GREEN = "\e[1;32m"; my \$CLEAR = "\e[0m";

enum Cell-State <Empty Tree Heating Burning>; my @pix = ' ', \$GREEN ~ '木', \$YELLOW ~ '木', \$RED ~ '木';

class Forest {

```   has Rat \$.p = 0.01;
has Rat \$.f = 0.001;
has Int \$!height;
has Int \$!width;
has @!coords;
has @!spot;
has @!neighbors;
```
```   method BUILD (Int :\$!height, Int :\$!width) {
```

@!coords = ^\$!height X ^\$!width; @!spot = [ (Bool.pick ?? Tree !! Empty) xx \$!width ] xx \$!height;

```       self!init-neighbors;
}

method !init-neighbors {
for @!coords -> (\$i, \$j) {
@!neighbors[\$i][\$j] = eager gather for
[-1,-1],[+0,-1],[+1,-1],
[-1,+0],        [+1,+0],
[-1,+1],[+0,+1],[+1,+1]
```

{ take-rw @!spot[\$i + .[0]][\$j + .[1]] // next; } }

```   }

method step {
```

my @heat;

```       for @!coords -> (\$i, \$j) {
given @!spot[\$i][\$j] {
when Empty   { \$_ = Tree if rand < \$!p }
when Tree    { \$_ = Heating if rand < \$!f }
when Heating { \$_ = Burning; push @heat, (\$i, \$j); }
when Burning { \$_ = Empty }
}
}
```

for @heat -> (\$i,\$j) { \$_ = Heating for @!neighbors[\$i][\$j].grep(Tree); }

```   }

method show {
for ^\$!height -> \$i {
say @pix[@!spot[\$i].list].join;
}
}
```

}

my (\$ROWS, \$COLS) = qx/stty size/.words;

signal(SIGINT).act: { print "\e[H\e[2J"; exit }

sub MAIN (Int \$height = \$ROWS - 2, Int \$width = +\$COLS div 2 - 1) {

```   my Forest \$forest .= new(:\$height, :\$width);
print "\e[2J";      # ANSI clear screen
loop {
```

print "\e[H"; # ANSI home say \$++; \$forest.show; \$forest.step;

```   }
```

}</lang>

### SDL2 Animation

An alternate version implemented in SDL2.

<lang perl6>use NativeCall; use SDL2::Raw;

my (\$width, \$height) = 900, 900;

SDL_Init(VIDEO); my SDL_Window \$window = SDL_CreateWindow(

```   "Forest Fire - Raku",
\$width, \$height,
RESIZABLE
```

); my SDL_Renderer \$renderer = SDL_CreateRenderer( \$window, -1, ACCELERATED +| PRESENTVSYNC );

SDL_ClearError();

my int (\$w, \$h) = 200, 200;

my \$forest_texture = SDL_CreateTexture(\$renderer, %PIXELFORMAT<RGB332>, STREAMING, \$w, \$h);

my \$pixdatabuf = CArray[int64].new(0, \$w, \$h, \$w); my \$work-buffer = CArray[int64].new(0, \$w, \$h, \$w);

my int \$bare = 0; # Black my int \$tree = 8; # Green my int \$heating = -120; # Orange ( 132 but it's being passed into an int8 ) my int \$burning = 128; # Red my int \$buf = \$w * \$h; my \$humidity = .7; # Chance that a tree next to a burning tree will resist catching fire my \$tree-spawn = .75; # Initial probability that a space will contain a tree. Probability

```                      # will be adjusted (way down) once rendering starts.
```

sub render {

```   # work-around to pass the pointer-pointer.
my \$pixdata = nativecast(Pointer[int64], \$pixdatabuf);
SDL_LockTexture(\$forest_texture, SDL_Rect, \$pixdata, my int \$pitch);
```
```   \$pixdata = nativecast(CArray[int8], Pointer.new(\$pixdatabuf[0]));
```
```   loop (my int \$row; \$row < \$h; \$row = \$row + 1) {
my int \$rs = \$row * \$w; # row start
my int \$re = \$rs  + \$w; # row end
loop (my int \$idx = \$rs; \$idx < \$re; \$idx = \$idx + 1) {
# Skip it if it is a tree
next if \$pixdata[\$idx] == \$tree;
if \$pixdata[\$idx] == \$bare {
# Maybe spawn a tree on bare ground
\$work-buffer[\$idx] = rand < \$tree-spawn ?? \$tree !! \$bare;
} elsif \$pixdata[\$idx] == \$heating {
# Check if there are trees around a hot spot and light them if humidity is low enough
\$work-buffer[\$idx - \$w - 1] = \$heating if rand > \$humidity && \$pixdata[\$idx - \$w - 1] && \$row > 0;
\$work-buffer[\$idx - \$w    ] = \$heating if rand > \$humidity && \$pixdata[\$idx - \$w    ] && \$row > 0;
\$work-buffer[\$idx - \$w + 1] = \$heating if rand > \$humidity && \$pixdata[\$idx - \$w + 1] && \$row > 0;
\$work-buffer[\$idx - 1     ] = \$heating if rand > \$humidity && \$pixdata[\$idx -  1    ];
\$work-buffer[\$idx + \$w - 1] = \$heating if rand > \$humidity && \$pixdata[\$idx + \$w - 1];
\$work-buffer[\$idx + \$w    ] = \$heating if rand > \$humidity && \$pixdata[\$idx + \$w    ];
\$work-buffer[\$idx + \$w + 1] = \$heating if rand > \$humidity && \$pixdata[\$idx + \$w + 1];
\$work-buffer[\$idx + 1     ] = \$heating if rand > \$humidity && \$pixdata[\$idx +  1    ];
```
```               # Hotspot becomes a flame
\$work-buffer[\$idx] = \$burning
} else {
# Extinguish a flame after fuel is gone
\$work-buffer[\$idx] = \$bare;
}
}
}
# copy working buffer to main texture buffer
loop (my int \$i; \$i < \$buf; \$i = \$i + 1) { \$pixdata[\$i] = \$work-buffer[\$i] }
```
```   # start a fire maybe
\$pixdata[\$buf.rand] = \$heating if rand < .1;
```
```   SDL_UnlockTexture(\$forest_texture);
```
```   SDL_RenderCopy(\$renderer, \$forest_texture, SDL_Rect, SDL_Rect.new(:x(0), :y(0), :w(\$width), :h(\$height)));
SDL_RenderPresent(\$renderer);
once \$tree-spawn = .005;
```

}

my \$event = SDL_Event.new;

enum KEY_CODES ( K_Q => 20 );

main: loop {

```   while SDL_PollEvent(\$event) {
my \$casted_event = SDL_CastEvent(\$event);
```
```       given \$casted_event {
when *.type == QUIT {
last main;
}
when *.type == KEYDOWN {
if KEY_CODES(.scancode) -> \$comm {
given \$comm {
when 'K_Q'      { last main }
}
}
}
when *.type == WINDOWEVENT {
if .event == RESIZED {
\$width  = .data1;
\$height = .data2;
}
}
}
}
render();
print fps;
```

} say ;

sub fps {

```   state \$fps-frames = 0;
state \$fps-now    = now;
state \$fps        = ;
\$fps-frames++;
if now - \$fps-now >= 1 {
\$fps = [~] "\b" x 40, ' ' x 20, "\b" x 20 ,
sprintf "FPS: %5.2f  ", (\$fps-frames / (now - \$fps-now)).round(.01);
\$fps-frames = 0;
\$fps-now = now;
}
\$fps
```

}</lang>

## REXX

This version has been elided,   otherwise the size of the program (with all it's options and optional formatting) would
probably be on the big side for general viewing, and maybe a wee bit complex to demonstrate how to program for this task.

If repeatable results are desired, the   randSeed   variable can be set to a non-negative integer.

Glyphs were chosen in an attempt to pictorialize a tree   ()   and also a fire   ().

The choice of glyphs within the code page 437   (DOS and/or under Windows) is rather limited.

There is one (OS) dependency:   use of the   CLS   (DOS) command which is used to clear the screen   (the original
version examined the host environment and used the correct command to clear the terminal screen).

```             ┌───────────────────────────elided version──────────────────────────┐
├─── original version has many more options & enhanced displays. ───┤
└───────────────────────────────────────────────────────────────────┘
```

<lang rexx>/*REXX program grows and displays a forest (with growth and fires caused by lightning).*/ parse value scrSize() with sd sw . /*the size of the terminal display. */ parse arg generations birth lightning rSeed . /*obtain the optional arguments from CL*/ if datatype(rSeed,'W') then call random ,,rSeed /*do we want RANDOM BIF repeatability?*/ generations = p(generations 100) /*maybe use one hundred generations. */

```     birth = p(strip(birth    , ,'%') 50 ) *100 /*calculate the percentage for births. */
lightning = p(strip(lightning, ,'%') 1/8) *100 /*    "      "       "      " lightning*/
bare! = ' '                                /*the glyph used to show a bare place. */
fire! = '▒'                                /*glyph is close to a conflagration.   */
tree! = '↑'                                /*this is an up─arrow [↑] glyph (tree).*/
rows = max(12, sd-2)                      /*shrink the usable screen rows by two.*/
cols = max(79, sw-1)                      /*   "    "     "      "   cols  " one.*/
every = 999999999                          /*shows a snapshot every Nth generation*/
field = min(100000, rows*cols)             /*the size of the forest area (field). */
```

\$.=bare! /*forest: it is now a treeless field. */ @.=\$. /*ditto, for the "shadow" forest. */ gens=abs(generations) /*use this for convenience. */ signal on halt /*handle any forest life interruptus. */

```             /*▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒observe the forest grow and/or burn. */
do  life=1  for gens                           /*simulate a forest's life cycle.      */
do   r=1  for rows;     rank=bare!           /*start a forest rank as being bare.   */
do c=2  for cols;     ?=substr(\$.r, c, 1);              ??=?
select                                   /*select the most likeliest choice 1st.*/
when ?==tree!  then  if ignite?()                then ??=fire!     /*on fire ?  */
when ?==bare!  then  if random(1, field)<=birth  then ??=tree!     /*new growth.*/
otherwise                                             ??=bare!     /*it's barren*/
end   /*select*/                         /* [↑]  when (↑)  if  ≡  short circuit.*/
rank=rank || ??                            /*build rank:  1 forest "row" at a time*/
@.r=rank                                     /*and assign rank to alternate forest. */
end       /*r*/                              /* [↓]  ··· and, later, yet back again.*/
```
```     do r=1  for rows;   \$.r=@.r;   end  /*r*/  /*assign alternate cells ──► real cells*/
if \(life//every==0 | generations>0 | life==gens)   then iterate
'CLS'                                          /* ◄─── change this command for your OS*/
do r=rows  by -1  for rows;   say strip(substr(\$.r, 2), 'T')    /*a row of trees*/
end   /*r*/                              /* [↑]  display forest to the terminal.*/
say right(copies('▒', cols)life, cols)         /*show and tell for a stand of trees.  */
end         /*life*/
/*▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒stop observing the forest evolve.    */
```

halt: if life-1\==gens then say 'Forest simulation interrupted.' /*was this pgm HALTed?*/ exit /*stick a fork in it, we're all done. */ /*──────────────────────────────────────────────────────────────────────────────────────*/ ignite?: if substr(\$.r, c+1, 1) == fire! then return 1 /*is east on fire? */

```        cm=c-1;   if substr(\$.r, cm , 1) == fire!  then return 1   /* "  west  "   "   */
rm=r-1;            rp=r+1           /*test north & south*/
if pos(fire!, substr(\$.rm, cm, 3)substr(\$.rp, cm, 3)) \== 0   then return 1
return  random(1, field) <= lightning                      /*lightning ignition*/
```

/*──────────────────────────────────────────────────────────────────────────────────────*/ p: return word(arg(1), 1) /*pick─a─word: first or second word.*/</lang> This REXX program makes use of   scrSize   REXX program (or BIF)   which is used to determine the screen size of the terminal (console).
The   SCRSIZE.REX   REXX program is included here   ──►    SCRSIZE.REX.

output   when using the defaults of:

•   generations = 100
•   rows = 48
•   lightning rate = 12.5%
•   new growth rate = 50%
•   bare character = (a true blank)
•   fire character = ▒
•   tree character =

Shown below is the 10th generation   (out of 100).

```↑↑↑↑↑↑↑↑▒▒▒▒▒▒▒▒▒ ↑↑↑↑↑↑  ▒↑↑↑↑▒     ▒↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑▒     ▒↑↑↑↑↑↑↑↑↑↑↑↑↑▒▒▒↑↑↑
↑↑↑↑↑↑↑↑▒         ↑↑↑↑↑↑↑ ▒↑↑↑↑▒ ↑↑  ▒↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑▒ ↑   ▒↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑
↑↑↑↑↑↑↑↑▒ ↑ ↑     ↑↑↑↑↑↑  ▒↑↑↑↑▒     ▒↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑▒ ↑↑↑ ▒↑↑▒▒▒▒▒▒▒▒▒▒▒▒▒▒↑↑↑
↑↑↑↑↑↑↑↑▒  ↑↑↑↑  ↑↑  ↑↑↑↑ ▒↑↑↑↑▒ ↑↑↑ ▒↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑▒ ↑   ▒▒▒▒            ▒↑↑↑
↑↑↑↑↑↑↑↑▒  ↑↑↑↑↑↑ ↑       ▒↑↑↑↑▒     ▒↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑▒            ↑↑   ↑   ▒↑↑↑
↑↑↑↑↑↑↑↑▒ ↑↑↑↑↑↑↑↑↑ ▒▒▒▒▒▒▒↑↑↑↑▒▒▒▒▒▒▒↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑▒▒  ↑↑  ↑↑ ↑↑↑↑▒   ↑  ▒▒↑↑
↑↑↑↑↑↑↑↑▒   ↑↑↑↑↑↑↑ ▒↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑▒▒▒▒▒▒▒▒▒▒▒▒  ↑↑↑↑↑↑↑   ↑▒ ▒↑↑↑  ▒↑↑
↑↑↑↑↑↑↑↑▒ ↑↑↑↑↑↑↑↑  ▒↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑▒            ↑↑↑↑↑↑ ↑ ↑ ↑▒  ▒↑↑↑ ▒↑↑
↑↑↑↑↑↑↑↑▒ ↑↑↑↑↑↑↑↑  ▒↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑▒ ↑  ↑↑↑↑↑↑  ↑↑↑↑↑↑ ↑↑▒▒▒ ↑   ↑↑ ▒↑↑
↑↑↑↑↑↑↑↑▒  ↑↑▒▒▒↑↑↑ ▒↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑▒ ↑↑↑↑↑  ↑ ↑↑ ↑↑↑↑↑ ↑↑▒  ▒▒▒  ↑  ▒▒▒
↑↑▒↑↑↑↑↑▒  ▒▒▒ ▒ ↑  ▒↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑▒  ↑  ▒▒▒↑▒↑▒↑ ↑↑ ↑ ↑ ▒   ↑  ↑ ↑
↑↑↑↑↑↑↑↑▒    ▒↑↑ ▒↑ ▒↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑▒ ↑↑▒  ↑    ▒ ↑  ↑↑ ↑↑▒     ▒↑   ↑
▒▒▒▒▒▒▒▒▒  ↑▒▒  ▒↑↑ ▒▒▒▒▒▒▒▒↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑▒     ▒↑  ↑ ▒↑       ↑   ↑   ↑↑↑↑ ↑↑
↑ ▒▒▒▒↑         ▒↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑▒  ▒ ↑↑ ▒▒  ▒   ▒▒   ▒▒      ↑ ↑↑↑↑↑
↑ ↑↑  ↑  ↑↑▒ ↑↑↑↑↑↑↑↑↑↑↑  ▒↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑▒  ▒▒ ▒↑   ▒ ↑↑ ▒▒  ▒ ▒ ▒▒↑▒▒↑↑↑ ↑↑↑
↑↑↑↑↑↑      ↑↑ ↑↑  ↑↑  ↑ ↑ ▒↑↑↑↑↑↑↑↑ ↑↑↑↑↑↑▒  ↑↑ ↑↑   ▒↑↑↑ ▒▒  ▒▒ ↑▒↑↑ ↑↑↑↑↑↑↑↑
↑ ↑↑↑▒ ▒  ↑↑▒▒▒ ▒↑↑↑↑↑↑    ▒↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑▒  ↑▒   ▒▒▒▒↑↑↑ ▒▒   ↑↑ ▒↑↑↑ ↑↑↑↑↑↑↑
↑▒▒ ↑  ↑↑ ▒ ↑▒ ▒▒▒↑       ▒↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑▒  ↑▒▒▒↑▒↑↑ ↑↑  ▒▒   ↑↑▒▒↑↑↑ ↑↑↑↑↑↑↑
↑ ▒ ↑▒ ▒↑↑ ▒   ↑  ▒ ▒↑↑ ▒▒▒▒↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑▒ ↑↑ ↑↑↑↑↑↑↑↑↑  ▒▒▒ ↑↑  ▒↑↑↑↑↑↑↑↑↑↑
▒  ↑ ▒↑↑↑↑   ↑↑↑ ▒ ↑  ▒↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑▒  ↑↑↑↑↑ ↑ ↑↑↑  ▒↑▒  ↑▒ ↑↑↑↑↑↑↑
↑↑↑▒   ▒↑↑↑▒▒  ▒▒       ▒↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑▒  ↑↑↑ ↑↑↑ ↑↑↑  ▒↑▒  ↑↑↑↑↑↑↑↑↑
↑↑↑▒▒▒▒↑↑  ↑▒ ↑↑ ▒↑  ↑  ▒↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑▒              ▒▒↑▒  ↑ ↑↑ ↑↑↑↑  ▒▒▒▒
↑↑↑↑↑↑↑↑ ↑↑↑     ↑↑  ↑  ▒↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒↑↑▒ ↑↑↑↑↑↑↑↑↑↑  ▒↑↑↑
↑↑↑↑↑↑ ↑ ↑↑↑▒▒▒ ▒↑  ▒   ▒↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑▒ ↑  ↑↑↑ ↑↑↑  ▒↑↑↑
↑↑↑↑↑↑↑↑↑  ↑↑↑▒ ↑ ↑▒ ↑  ▒▒▒▒↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑▒      ↑↑   ↑ ▒↑↑↑
↑↑↑↑↑↑    ↑ ↑↑↑▒ ▒ ↑↑ ↑    ▒↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑▒▒            ▒↑↑↑
↑↑↑↑↑   ↑      ↑   ↑       ▒↑↑▒▒▒↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑▒▒▒▒▒▒▒▒▒▒▒▒▒▒↑↑↑
↑↑↑↑ ↑  ↑↑↑            ▒   ▒↑↑▒ ▒↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑
↑↑ ↑↑↑      ▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒↑↑▒▒▒↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑
↑ ↑↑       ▒↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑ ↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑
▒▒▒▒▒▒↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑▒▒▒↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑
▒▒▒▒▒▒▒▒↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑▒ ▒↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑
↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒↑↑↑↑↑▒▒▒↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑▒▒▒▒▒▒▒↑↑↑↑↑↑↑↑↑↑
↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑▒                    ▒▒↑↑↑↑↑↑↑↑↑↑↑▒▒▒▒▒▒▒↑↑↑↑↑↑▒     ▒↑↑↑↑↑↑↑↑↑↑
↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑▒ ↑↑↑    ↑↑↑↑  ↑↑ ↑   ▒↑↑↑↑↑↑↑↑↑↑↑▒     ▒▒▒▒▒▒▒▒ ↑   ▒↑↑↑↑↑↑↑↑↑↑
▒▒▒▒▒▒▒▒↑↑↑↑↑↑↑▒  ↑↑↑↑↑ ↑ ↑↑  ↑↑↑▒   ▒↑↑↑↑↑↑↑↑↑↑↑▒  ↑           ↑↑  ▒↑↑↑↑↑↑↑↑↑↑
▒↑↑↑↑↑↑↑▒  ↑↑↑   ↑↑↑↑    ↑↑▒↑ ▒↑↑↑↑↑↑↑↑↑↑↑▒ ↑↑↑    ↑  ↑  ↑↑  ▒↑▒▒▒▒▒▒▒↑↑
↑↑ ↑  ▒↑↑↑↑↑↑↑▒  ↑↑↑↑↑↑↑↑↑   ↑↑↑↑↑  ▒↑↑↑↑↑↑↑↑↑↑↑▒ ↑  ↑ ↑↑↑ ↑ ↑↑↑   ▒↑▒     ▒↑↑
↑ ↑↑ ▒↑↑↑↑↑↑↑▒ ↑↑  ↑ ↑  ↑   ↑↑↑↑↑↑ ▒↑↑↑↑↑↑↑↑↑↑↑▒     ↑ ↑↑↑↑↑↑↑  ▒▒▒↑▒↑  ↑ ▒↑↑
↑ ↑  ▒▒▒▒↑↑↑↑▒ ↑↑↑ ↑↑      ↑↑↑ ↑↑  ▒↑↑↑↑↑↑↑↑↑↑↑▒▒▒▒   ↑↑ ↑↑↑↑↑  ▒↑↑↑▒ ↑↑↑ ▒↑↑
↑↑↑↑     ▒↑↑↑↑▒  ↑↑↑  ↑ ▒▒▒ ↑   ↑↑↑ ▒↑↑↑↑↑↑↑↑↑↑↑↑↑↑▒   ↑ ↑↑↑↑↑↑  ▒↑↑↑▒  ↑  ▒↑↑
↑↑↑      ▒↑↑↑↑▒         ▒↑▒         ▒↑↑↑↑↑↑↑↑↑↑↑↑↑↑▒▒▒  ↑↑↑↑↑↑↑  ▒↑↑↑▒     ▒↑↑
▒↑↑↑↑▒▒▒▒▒▒▒▒▒▒▒↑▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒▒↑↑↑↑↑↑↑↑↑▒  ↑ ↑↑↑↑ ↑ ▒↑↑↑▒▒▒▒▒▒▒↑↑
▒▒▒▒▒▒▒▒▒▒▒↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑▒     ▒↑▒▒▒↑↑↑↑↑▒   ↑ ↑↑↑↑  ▒↑↑↑↑↑↑↑↑↑↑↑↑
↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑▒  ↑  ▒↑▒ ▒↑↑↑↑↑▒ ↑↑  ↑ ↑   ▒↑↑↑ ↑↑↑↑↑↑↑↑
↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑↑▒ ↑   ▒↑▒▒▒↑↑↑↑↑▒           ▒↑↑↑↑↑↑↑↑↑↑↑↑
═════════════════════════════════════════════════════════════════════════════10
```

## Ring

<lang ring>

1. Project : Forest fire

paint = null

new qapp

```       {
win1 = new qwidget() {
setwindowtitle("Forest fire")
setgeometry(100,100,500,600)
label1 = new qlabel(win1) {
setgeometry(10,10,400,400)
settext("")
}
new qpushbutton(win1) {
setgeometry(150,500,100,30)
settext("draw")
setclickevent("draw()")
}
show()
}
exec()
}
```

func draw

```       p1 = new qpicture()
color = new qcolor() {
setrgb(0,0,255,255)
}
pen = new qpen() {
setcolor(color)
setwidth(1)
}
paint = new qpainter() {
begin(p1)
setpen(pen)
```

pregen = newlist(200,200) newgen = newlist(200,200)

```for gen = 1 to 20
see "gen = " + gen + nl
for x = 1 to 199
for y = 1 to 199
switch pregen[x][y]
on 0
if random(9)/10 > 0.099
newgen[x][y] = 1
color = new qcolor()
color.setrgb(0,128,0,255)
pen.setcolor(color)
setpen(pen)
drawpoint(x,y)
ok
on 2
newgen[x][y] = 0
color = new qcolor()
color.setrgb(165,42,42,255)
pen.setcolor(color)
setpen(pen)
drawpoint(x,y)
on 1
if pregen[x][y] = 2 or pregen[x][y]   = 2 or pregen[x][y+1] = 2 or
pregen[x][y]   = 2 or pregen[x][y+1]   = 2 or pregen[x+1][y] = 2 or
pregen[x+1][y]   = 2 or pregen[x+1][y+1] = 2 or random(9)/10 > 0.0999
color = new qcolor()
color.setrgb(255,0,0,255)
pen.setcolor(color)
setpen(pen)
drawpoint(x,y)
newgen[x][y] = 2
ok
off
pregen[x][y] = newgen[x][y]
next
next
```

next

```       endpaint()
}
label1 { setpicture(p1) show() }
return
```

</lang> Output:

## Ruby

<lang ruby>class Forest_Fire

``` Neighborhood = [-1,0,1].product([-1,0,1]) - [0,0]
States = {empty:" ", tree:"T", fire:"#"}

def initialize(xsize, ysize=xsize, p=0.5, f=0.01)
@xsize, @ysize, @p, @f = xsize, ysize, p, f
@field = Array.new(xsize+1) {|i| Array.new(ysize+1, :empty)}
@generation = 0
end

def evolve
@generation += 1
work = @field.map{|row| row.map{|cell| cell}}
for i in 0...@xsize
for j in 0...@ysize
case cell=@field[i][j]
when :empty
cell = :tree  if rand < @p
when :tree
cell = :fire  if fire?(i,j)
else
cell = :empty
end
work[i][j] = cell
end
end
@field = work
end

def fire?(i,j)
rand < @f or Neighborhood.any? {|di,dj| @field[i+di][j+dj] == :fire}
end

def display
puts "Generation : #@generation"
puts @xsize.times.map{|i| @ysize.times.map{|j| States[@field[i][j]]}.join}
end
```

end

forest = Forest_Fire.new(10,30) 10.times do |i|

``` forest.evolve
forest.display
```

end</lang> Sample Output:

```Generation : 1
TT TTTT  TT    TT  T T  T TTT
T TTT    T   TTT T  T T T  T
TT   T TTT T T   T    T TTT T
T  TT T     T   TT   TTT T T
TTTT    TTTTTTT      TT   T
T  T  T  TT   T        TTT TT
TT TT TTT   TT TTT     T T
T   TTTTT   TT  TT T TTT   TT
T TTT    T T  T T T      TT  T
TTTTT T  TT    TTT TT T T   T
Generation : 2
TTTTTTTT TTTT TTTTTTTTT  TTTTT
T# TTTTTTTTT  TTTTTT T T T  TT
TT   # TTTTT T T TTTTTTTTTT TT
T  TTTTT T TT TTTTTT TTT TTT
TTTTTTT TTTTTTTT  T   TTT  TTT
TTTT  T  TTT TTT   TT  TTTTTTT
TT TT TTTT TTT TTTT TTTT TT T
T T TTTTTT TTTTTTT T TTTTTTTTT
TTTTT TTTTTT  T T T TT TTTT TT
TTTTTTT  TTTTT TTTTTT T T  TT
Generation : 3
###TTTTT TTTT TTTTTTTTTTTTTTTT
#  T####TTTTT TTTTTT TTTTTT TT
##TT   TTTTTTT TTTTTTTTTTTT TT
TT T###T T TTTTTTTTTTTTTTTTT
TTTTTTTTTTTTTTTTTTTT TTTTTTTTT
TTTTT T  TTTTTTT TTTT  TTTTTTT
TT TTTTTTT TTT TTTT TTTTTTT T
TTTTTTTTTTTTTTTTTTTTTTTTTTTTTT
TTTTT TTTTTT  T TTTTTTTT#TTTTT
TTTTTTTT  TTTTTT#TTTTT TTTT TT
Generation : 4
##### TTTT TTTTTTTTTTTTTTTT
T #    #TTTT TTTTTTTTTTTTT TT
##   ##TTTTTTTTTTTTTTTTTTTTT
## #   # T TTTTTTTTTTTTTTTTTTT
TTT#####TTTTTTTTTTTT TTTTTTTTT
TTTTTTT TTTTTTTTTTTTT TTTTTTTT
TTTTTTTTTTTTTTTTTTT TTTTTTTTT
TTTTTTTTTTTTTTTTTTTTTTT###TTTT
TTTTTTTTTTTTTTTT##TTTTT# #TTTT
TTTTTTTT  TTTTT# #TTTT ###TTTT
Generation : 5
T#TTTTTTTTTTTTTTTTTTTT
#T TTTT #TTT TTTTTTTTTTTTT TT
T    T  #TTTTTTTTTTTTTTTTTTTT
T    #TTTTT#TTTTTT#TTTTTTT
###     #TTTTTTTTTTT TTTTTTTTT
TT##### #TTTTTTTTTTTTTTTTTTTTT
TTTTTTTTTTTTTTTTTTTTTT#####TTT
TTTTTTTTTTTTTTT####TTT#   #TTT
TTTTTTTTTTTTTT##  #TTT# T #TTT
TTTTTTTT  TTTT# T #TTT    #TTT
Generation : 6
T T  # ##TTTTTTTTTTTTTTTTTT
T #TTTTT  #TT TTTTTTTTTTTTT TT
T#TT  TTT #TTT###TTTT###TTTTTT
TTTTTT  T #TTT# #TTTT# #TTTTTT
TTT   ##TTT###TTTT###TTTTTT
##       #TTTTTTTTTTT#######TT
T#########TTT#######T#     #TT
TTTTTTTTTTTTT##    #T#   T #TT
TTTTTTTTTTTTT#  TT #T# TTT #TT
TTTTTTTT  TTT#  #T #T#T    #TT
Generation : 7
TT # T   T  #TTTTTTTTTTTTTTTTT
#T #TTT# T ## ####TT#####TTTTT
# ##TTTTTT #T#   #TT#   #TTTTT
###TTTTT#  #T# T #TT# T #TTTTT
TTTT T  #T#   #TT#   #####T
T TTT T ###########       #T
#         #T#       # T TTT #T
###########T#   TT  #    T  #T
TTTTTTTTTTTT# TT##T #  TTT  #T
TTTTTT#T TTT#    #T # #T TT #T
Generation : 8
##  TT   T   #############TTTT
#  #T# TT   T    ##     #TTTT
T  #T####  #  T  ##   T #TTTT
##TT#  T #  TT ## TTT #####
T#TTTT#TT # TT  ## TT      #
T T TTTTT            TTT T   #
TT   TTTT #  TTT T   T TTT  #
#    ##T   TTTT T #
############  T#  #T   #TTTT #
TTTTT# #TTT# TT   #T T # TT  #
Generation : 9
TT##T  TTT              #TTT
T TT #  ##TTT#T       TTT #TTT
#T  #    T    TTT   TTT  ####
T  ##  T#T  TTTT  TTTT
TT# #### #T   TT    TTT T T T
T # #TT## T    TTT T TTT TT T
TTT TTTTT  T T## #T  T TTT
TT    T TT    #TTT###TTT
T# T  #TT  #TTTT
#####   ###  T#T   # TT TTT
Generation : 10
T#  # T##T  TTTT TTT     #TT
#T##T     #T# #TTTTT  TTT  ###
T # T TTTT#T  TTTT TTTTTTT
# T  T # #T TTTT  TTTTT
T# T    T #TT TTT   TT# TTT T
T    ##   #TT  ###T#TTTTTTTTTT
T### #####TTTT#  T #T # ##T TT
TTTTTTTTTT#TTT  ###   #TT
TTTT  TTTT T # TT T ## T #TTT
T      # # TT  TT ##TTT
```

## Rust

Inspired by the Raku implementation, this runs in the terminal, printing a colored ASCII rendition of the forest (and it's fires!). You can configure the size of the forest, frame delay, and various probabilities.

Library: rand
Library: ansi_term

<lang rust>extern crate rand; extern crate ansi_term;

1. [derive(Copy, Clone, PartialEq)]

enum Tile {

```   Empty,
Tree,
Burning,
Heating,
```

}

impl fmt::Display for Tile {

```   fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
let output = match *self {
Empty => Black.paint(" "),
Tree => Green.bold().paint("T"),
Burning => Red.bold().paint("B"),
Heating => Yellow.bold().paint("T"),
};
write!(f, "{}", output)
}
```

}

// This has been added to the nightly rust build as of March 24, 2016 // Remove when in stable branch! trait Contains<T> {

```   fn contains(&self, T) -> bool;
```

}

impl<T: PartialOrd> Contains<T> for std::ops::Range<T> {

```   fn contains(&self, elt: T) -> bool {
self.start <= elt && elt < self.end
}
```

}

const NEW_TREE_PROB: f32 = 0.01; const INITIAL_TREE_PROB: f32 = 0.5; const FIRE_PROB: f32 = 0.001;

const FOREST_WIDTH: usize = 60; const FOREST_HEIGHT: usize = 30;

const SLEEP_MILLIS: u64 = 25;

use std::fmt; use std::io; use std::io::prelude::*; use std::io::BufWriter; use std::io::Stdout; use std::process::Command; use std::time::Duration; use rand::Rng; use ansi_term::Colour::*;

use Tile::{Empty, Tree, Burning, Heating};

fn main() {

```   let sleep_duration = Duration::from_millis(SLEEP_MILLIS);
let mut forest = [[Tile::Empty; FOREST_WIDTH]; FOREST_HEIGHT];
```
```   prepopulate_forest(&mut forest);
print_forest(forest, 0);
```
```   std::thread::sleep(sleep_duration);
```
```   for generation in 1.. {
```
```       for row in forest.iter_mut() {
for tile in row.iter_mut() {
update_tile(tile);
}
}
```
```       for y in 0..FOREST_HEIGHT {
for x in 0..FOREST_WIDTH {
if forest[y][x] == Burning {
heat_neighbors(&mut forest, y, x);
}
}
}
```
```       print_forest(forest, generation);
```
```       std::thread::sleep(sleep_duration);
}
```

}

fn prepopulate_forest(forest: &mut [[Tile; FOREST_WIDTH]; FOREST_HEIGHT]) {

```   for row in forest.iter_mut() {
for tile in row.iter_mut() {
*tile = if prob_check(INITIAL_TREE_PROB) {
Tree
} else {
Empty
};
}
}
```

}

fn update_tile(tile: &mut Tile) {

```   *tile = match *tile {
Empty => {
if prob_check(NEW_TREE_PROB) == true {
Tree
} else {
Empty
}
}
Tree => {
if prob_check(FIRE_PROB) == true {
Burning
} else {
Tree
}
}
Burning => Empty,
Heating => Burning,
}
```

}

fn heat_neighbors(forest: &mut [[Tile; FOREST_WIDTH]; FOREST_HEIGHT], y: usize, x: usize) {

```   let neighbors = [(-1, -1), (-1, 0), (-1, 1), (0, -1), (0, 1), (1, -1), (1, 0), (1, 1)];
```
```   for &(xoff, yoff) in neighbors.iter() {
let nx: i32 = (x as i32) + xoff;
let ny: i32 = (y as i32) + yoff;
if (0..FOREST_WIDTH as i32).contains(nx) && (0..FOREST_HEIGHT as i32).contains(ny) &&
forest[ny as usize][nx as usize] == Tree {
forest[ny as usize][nx as usize] = Heating
}
}
```

}

fn prob_check(chance: f32) -> bool {

```   let roll = rand::thread_rng().gen::<f32>();
if chance - roll > 0.0 {
true
} else {
false
}
```

}

fn print_forest(forest: [[Tile; FOREST_WIDTH]; FOREST_HEIGHT], generation: u32) {

```   let mut writer = BufWriter::new(io::stdout());
clear_screen(&mut writer);
writeln!(writer, "Generation: {}", generation + 1).unwrap();
for row in forest.iter() {
for tree in row.iter() {
write!(writer, "{}", tree).unwrap();
}
writer.write(b"\n").unwrap();
}
```

}

fn clear_screen(writer: &mut BufWriter<Stdout>) {

```   let output = Command::new("clear").output().unwrap();
write!(writer, "{}", String::from_utf8_lossy(&output.stdout)).unwrap();
```

} </lang>

## Sather

<lang sather>class FORESTFIRE is

``` private attr fields:ARRAY{ARRAY{INT}};
private attr swapu:INT;
private attr rnd:RND;
private attr verbose:BOOL;
private attr generation:INT;
const empty:INT := 0;
const tree:INT := 1;
const burning:INT := 2;
```
``` attr prob_tree, prob_p, prob_f :FLT;
```
``` create(w, h:INT, v:BOOL):SAME is
res:FORESTFIRE := new;
res.fields := #(2);
res.fields[0] := #(w*h);
res.fields[1] := #(w*h);
res.width := w; res.height := h;
res.swapu := 0;
res.prob_tree := 0.55;
res.prob_p := 0.001;
res.prob_f := 0.00001;
res.rnd := #RND;
res.verbose := v;
res.generation := 0;
res.initfield;
return res;
end;
```
``` -- to give variability
seed(i:INT) is
rnd.seed(i);
end;
```
``` create(w, h:INT):SAME is
res ::= create(w, h, false);
return res;
end;
```
``` initfield is
n ::= 0;
swapu := 0;
if verbose and generation > 0 then
#ERR + "Previous generation " + generation + "\n";
end;
generation := 0;
loop i ::= 0.upto!(width-1);
loop j ::= 0.upto!(height-1);
if rnd.uniform > prob_tree.fltd then
cset(i, j, empty);
else
```

n := n + 1;

```         cset(i, j, tree);
end;
end;
end;
if verbose then
#ERR + #FMT("Field size is %dx%d (%d)", width, height, size) + "\n";
#ERR + "There are " + n + " trees (" + (100.0*n.flt/size.flt) + "%)\n";
#ERR + "prob_tree = " + prob_tree + "\n";
#ERR + "prob_f = " + prob_f + "\n";
#ERR + "prob_p = " + prob_p + "\n";
#ERR + "ratio = " + prob_p/prob_f + "\n";
end;
end;
```
``` field:ARRAY{INT} is
return fields[swapu];
end;
```
``` ofield:ARRAY{INT} is
return fields[swapu.bxor(1)];
end;

size:INT is
return width*height;
end;
```
``` set(i, j, t:INT)
pre bcheck(i, j)
is
ofield[j*width + i] := t;
end;
```
``` cset(i, j, t:INT)
pre bcheck(i, j)
is
field[j*width + i] := t;
end;
```
``` private bcheck(i, j:INT):BOOL is
if i.is_between(0, width-1) and j.is_between(0, height-1) then
return true; -- is inside
else
return false; -- is outside
end;
end;
```
``` get(i, j:INT):INT is
if ~bcheck(i, j) then
return empty;
end;
return field[j*width + i];
end;
```
``` oget(i, j:INT):INT is
if ~bcheck(i, j) then
return empty;
end;
return ofield[j*width + i];
end;
```
``` burning_neighbor(i, j:INT):BOOL is
loop x ::= (-1).upto!(1);
loop y ::= (-1).upto!(1);
if x /= y then
if get(i+x, j+y) = burning then return true; end;
end;
end;
end;
return false;
end;
```
``` evolve is
bp ::= 0;
loop i ::= 0.upto!(width-1);
loop j ::= 0.upto!(height-1);
```

case get(i, j)

```       when burning then set(i, j, empty); bp := bp + 1;
when empty then
if rnd.uniform > prob_p.fltd then
set(i, j, empty);
else
set(i, j, tree);
end;
when tree then
if burning_neighbor(i, j) then
set(i, j, burning);
else
if rnd.uniform > prob_f.fltd then
set(i, j, tree);
else
set(i, j, burning);
end;
end;
else
#ERR + "corrupted field\n";
end;
end;
end;
generation := generation + 1;
if verbose then
if bp > 0 then
#ERR + #FMT("Burning at gen %d: %d\n", generation-1, bp);
end;
end;
swapu := swapu.bxor(1);
end;
```
``` str:STR is
s ::= "";
loop j ::= 0.upto!(height -1);
loop i ::= 0.upto!(width -1);
case get(i, j)
when empty then s := s + ".";
when tree then s := s + "Y";
when burning then s := s + "*";
end;
end;
s := s + "\n";
end;
s := s + "\n";
return s;
end;

```

end;

class MAIN is

``` main is
forestfire ::= #FORESTFIRE(74, 40);
-- #FORESTFIRE(74, 40, true) to have some extra info
-- (redirecting stderr to a file is a good idea!)
```
```   #OUT + forestfire.str;
-- evolve 1000 times
loop i ::= 1000.times!;
forestfire.evolve;
-- ANSI clear screen sequence
#OUT + 0x1b.char + "[H" + 0x1b.char + "[2J";
#OUT + forestfire.str;
end;
end;
```

end;</lang>

## Scala

<lang scala>import scala.util.Random

class Forest(matrix:Array[Array[Char]]){

``` import Forest._
val f=0.01;	 // auto combustion probability
val p=0.1;	 // tree creation probability
val rows=matrix.size
val cols=matrix(0).size
```
``` def evolve():Forest=new Forest(Array.tabulate(rows, cols){(y,x)=>
matrix(y)(x) match {
case EMPTY => if (Random.nextDouble<p) TREE else EMPTY
case BURNING => EMPTY
case TREE => if (neighbours(x, y).exists(_==BURNING)) BURNING
else if (Random.nextDouble<f) BURNING else TREE
}
})

def neighbours(x:Int, y:Int)=matrix slice(y-1, y+2) map(_.slice(x-1, x+2)) flatten
override def toString()=matrix map (_.mkString("")) mkString "\n"
```

}

object Forest{

``` val TREE='T'
val BURNING='#'
val EMPTY='.'
def apply(x:Int=30, y:Int=15)=new Forest(Array.tabulate(y, x)((y,x)=> if (Random.nextDouble<0.5) TREE else EMPTY))
```

}</lang>

<lang scala>object ForestFire{

``` def main(args: Array[String]): Unit = {
var l=Forest()
for(i <- 0 until 20){
println(l+"\n-----------------------")
l=l.evolve
}
}
```

}</lang> Sample output:

```.T..TTT.TT    .T..TTT.TT    TT..TTT.TT    TT..TTTTTT    TT..TTTTTT
TTT.TTTT..    TTT.TTTTT.    TTT.TTTTT.    TTT.TTTTT.    TTT.TTTTT.
.T...T..T.    .TT..T..T.    .TT..T.TT.    .TT.TT.TTT    .TT.##.TTT
T...TT.T.T    T...TT.T.T    T...TT.T.T    T.TT##.T.T    T.T#...T.T
.T..TTTTTT    .T..TTTTTT    .T..#TTTTT    .T...#TTTT    .T....#TTT
TTT..TTTT.    TTT..TTTT.    TTT..TTTT.    TTT..#TTT.    ###...##T.
TT.TTTTTTT    TT.TTTTTTT    TT.TTTTTTT    ##.TTT#TTT    ...###.#TT
......TT..    T.....TT..    #.T.TTTT..    .T#.TTTT..    .#..####..
.TTT.TTTTT    .#TT.TTTTT    ..#T.TTTTT    ...#.TTTTT    .....TTTTT
T.T.TTT.T.    TTT.TTT.T.    ###.TTT.T.    ...TTTT.T.    T..##TT.T.```

## Sidef

Translation of: Perl

<lang ruby>define w = `tput cols`.to_i-1 define h = `tput lines`.to_i-1 define r = "\033[H"

define red = "\033[31m" define green = "\033[32m" define yellow = "\033[33m"

define chars = [' ', green+'*', yellow+'&', red+'&']

define tree_prob = 0.05 define burn_prob = 0.0002

enum |Empty, Tree, Heating, Burning|

define dirs = [

```   %n(-1 -1), %n(-1 0), %n(-1 1), %n(0 -1),
%n(0   1), %n(1 -1), %n(1  0), %n(1  1),
```

]

var forest = h.of { w.of { 1.rand < tree_prob ? Tree : Empty } }

var range_h = h.range var range_w = w.range

func iterate {

```   var new = h.of{ w.of(0) }
for i in range_h {
for j in range_w {
given (new[i][j] = forest[i][j]) {
when (Tree) {
1.rand < burn_prob && (new[i][j] = Heating; next)
dirs.each { |pair|
var y = pair[0]+i
range_h.contains(y) || next
var x = pair[1]+j
range_w.contains(x) || next
forest[y][x] == Heating && (new[i][j] = Heating; break)
}
}
when (Heating)            { new[i][j] = Burning }
when (Burning)            { new[i][j] = Empty   }
case (1.rand < tree_prob) { new[i][j] = Tree    }
}
}
}
forest = new
```

}

STDOUT.autoflush(true)

func init_forest {

```   print r
forest.each { |row|
print chars[row]
print "\033[E\033[1G"
}
iterate()
```

}

loop { init_forest() }</lang>

Translation of: Raku

OO approach: <lang ruby>define RED = "\e[1;31m" define YELLOW = "\e[1;33m" define GREEN = "\e[1;32m"   define DIRS = [

```   [-1, -1], [0, -1], [1, -1],
[-1,  0],          [1,  0],
[-1,  1], [0,  1], [1,  1],
```

]   enum (Empty, Tree, Heating, Burning) define pix = [' ', GREEN + "*", YELLOW + "*", RED + "*"]   class Forest(p=0.01, f=0.001, height, width) {

```   has coords = []
has spot = []
has neighbors = []
```

```   method init {
coords = (0..height ~X 0..width)
spot = height.of { width.of { [true, false].pick ? Tree : Empty } }
self.init_neighbors
}
```

```   method init_neighbors {
for i,j in coords {
neighbors[i][j] = gather {
for dir in DIRS {
take(\(spot[i + dir[0]][j + dir[1]] \\ next))
}
}
}
}
```

```   method step {
var heat = []
```

```       for i,j in coords {
given (spot[i][j]) {
when Empty   { spot[i][j] = Tree    if (1.rand < p) }
when Tree    { spot[i][j] = Heating if (1.rand < f) }
when Heating { spot[i][j] = Burning; heat << [i, j] }
when Burning { spot[i][j] = Empty }
}
}
```

```       for i,j in heat {
neighbors[i][j].each { |ref|
*ref = Heating if (*ref == Tree)
}
}
}
```

```   method show {
for i in ^height {
say pix[spot[i]]
}
}
```

}

STDOUT.autoflush(true) var(height, width) = `stty size`.nums.map{.dec}...   var forest = Forest(height: height, width: width) print "\e[2J"

loop {

```   print "\e[H"
forest.show
forest.step
```

}</lang>

## Tcl

<lang tcl>package require Tcl 8.5

1. Build a grid

proc makeGrid {w h {treeProbability 0.5}} {

```   global grid gridW gridH
set gridW \$w
set gridH \$h
set grid [lrepeat \$h [lrepeat \$w " "]]
for {set x 0} {\$x < \$w} {incr x} {
```

for {set y 0} {\$y < \$h} {incr y} { if {rand() < \$treeProbability} { lset grid \$y \$x "#" } }

```   }
```

}

1. Evolve the grid (builds a copy, then overwrites)

proc evolveGrid {{fireProbability 0.01} {plantProbability 0.05}} {

```   global grid gridW gridH
set newGrid {}
for {set y 0} {\$y < \$gridH} {incr y} {
```

set row {} for {set x 0} {\$x < \$gridW} {incr x} { switch -exact -- [set s [lindex \$grid \$y \$x]] { " " { if {rand() < \$plantProbability} { set s "#" } } "#" { if {[burningNeighbour? \$x \$y] || rand() < \$fireProbability} { set s "o" } } "o" { set s " " } } lappend row \$s } lappend newGrid \$row

```   }
set grid \$newGrid
```

}

1. We supply the neighbourhood model as an optional parameter (not used...)

proc burningNeighbour? {

```   x y
{neighbourhoodModel {-1 -1  -1 0  -1 1  0 -1  0 1  1 -1  1 0  1 1}}
```

} {

```   global grid gridW gridH
foreach {dx dy} \$neighbourhoodModel {
```

set i [expr {\$x + \$dx}] if {\$i < 0 || \$i >= \$gridW} continue set j [expr {\$y + \$dy}] if {\$j < 0 || \$j >= \$gridH} continue if {[lindex \$grid \$j \$i] eq "o"} { return 1 }

```   }
return 0
```

}

proc printGrid {} {

```   global grid
foreach row \$grid {
```

puts [join \$row ""]

```   }
```

}

1. Simple main loop; press Return for the next step or send an EOF to stop

makeGrid 70 8 while 1 {

```   evolveGrid
printGrid
if {[gets stdin line] < 0} break
```

}</lang> Sample output:

```###  #     ####### ##  #  ## #####     # # # ###   ## #
#  #      ##   #   ##### # ## #   #   ##   o ###  #  # #### # # #### #
# #######  ###   #####  ###  ####  #######  ###   ##  ## ####  # ##
# ###   ## ####       #     ##  #        #  #### # ### #  # ##  #####
# #    ##  #     ##### ###  # ## # ##    ######    # ####     ## # #
### ### #   #####  # ###  ## # ### # ####### #### # # # #   #  #
# # # # #  ####  ### #  ##  ##  ### #  ## # #   # #    # ## #   ## ##
#####    ## ## #  #  # # ##   # ##  ###   # # #   ### ##    ## # ### #

#  ### # ### #####  #  #  ####### ##  #  #o o####     # # # ###   ## #
#  #  #   #o   #   ##### # ## ##  #   ##     ###  #  # #### # # #### #
# #######  ###   #####  ###  ####  #####oo  ###   ### ## ####  # ##
# ###   ## ####       #     ##  #        #  #### # ### #  # ##  #####
# #    ##  #     ##### ###  # ## # ##    ######    # #o##     ## # #
### ### #   ###### # ###  ## # ### # ####### #### # # # #   #  #
# # # # #  ####  ### #  ##  ##  ### #  ## # #   # #    # ## #   ## ##
o####    ## ## #  #  # # ##   # ##  ###   # # #   ### ##  # ## # ### #

#  ### # #oo o####  #  # ######## ##  #  o   o###    ## # # #o#   ## #
#  #  #   o    #   ##### # ## ##  #   ##     o##  #  # #### # # ##o# #
# ######o  ###   #####  #### ####  ####o    ### # ### ## #### ## ##
#####   ## ####       #     ##  #     #  o  o### # ### o  # ##  #####
# #    ##  ##    ##### ###  # ## # ##    ######    # o o#     ## # #
### #####   ###### # ###  ## # ### # ####### #### o o # # # o  #
o # # # #  ####  #####  ## ###  ### #  ## # #   # #    # ## #   ## ##
o###    ## ## #  #  # # ##   # ##  ###   # ###   ### ##  # ## # #o# #

#  ### # o    o###  #  # ######## ##  #       o##    ## # # o o   oo##
#  #  # #   #  #   ##### # ## ##  #   ##      o#  #  # #### o o #o o #
# #####o   ###   #####  #### ####  ###o     o## ####o o# #### #o o#
#####   #o o###       #    ###  #     #      o## # ##o    # ##  ######
# #    ##  ##    ##### ###  # ## # ##    oooo##    #    o     oo # #
### #####   ###### #####  ## # ### # ####### ####     # # o    #
# # # #  ####  #####  ## ###  ### #  ## # #   # #    o### #   oo ##
o##    ## ## #  #  # # ##   # o#  ###   # ###   ######  # ## # o o #

# #### #       o##  #  # ######## ##  #        o#    ## # #     #   o#
#  #  # o   #  o   ##### # ## ##  #   #o       o  #  o ooo#     o #  #
# ####o    ###   #####  o### ####  ##o     # o# ##oo   o oooo#o   o#
######  o   o##    #  #    ###  #     #       oo # #o     o ##  ooooo#
# #    oo  o# #  ##### ###  # ## # ##        o#   #o   #         # #
### #####   ###### #####  ## # ### # oooooo# ####     o #    # o
o # # #  ####  #####  ## ###  o## #  ## # #   # #     o## o#    #o#
o#    ## ## #  #  # # ##  ##  o  ###   # ### # #####o  # ## #     #
```

## uBasic/4tH

It's a small forest, since it's a small interpreter. <lang>B = 1 ' A burning tree E = 16 ' An empty space T = 256 ' A living tree

Input "%Chance a tree will burn: ";F ' Enter chance of combustion Input "%Chance a tree will grow: ";P ' Enter chance of a new tree

Proc _CreateForest ' Now create a new forest

Do

``` Proc _PrintForest                    ' Print the current forest
Input "Press '1' to continue, '0' to quit: ";A
Proc _BurnForest                     ' See what happens
Proc _UpdateForest                   ' Update from buffer
While A                              ' Until the user has enough
```

Loop ' and answers with zero

End

_CreateForest ' Create an entire new forest

``` Local(1)
```
``` For a@ = 0 to 120                    ' For each main cell determine
If RND(100) < P Then               ' if a tree will grow here
@(a@) = T                        ' Ok, we got a tree
Else                               ' Otherwise it remains empty
@(a@) = E
EndIf
Next
```

Return

_BurnForest ' Now the forest starts to burn

``` Local(2)
```
``` For a@ = 0 To 10                     ' Loop vertical
For b@ = 0 To 10                   ' Loop horizontal
If @((a@ * 11) + b@) = B Then @((a@ * 11) + b@ + 121) = E
' A tree has been burned flat
If @((a@ * 11) + b@) = E Then    ' For each open space determine
If RND(100) < P Then           ' if a tree will grow here
@((a@ * 11) + b@ + 121) = T
Else                           ' Otherwise it remains an empty space
@((a@ * 11) + b@ + 121) = E
EndIf
EndIf
```
```     If @((a@ * 11) + b@) = T Then    ' A tree grows here
If RND(100) < F Then           ' See if it will spontaneously combust
@((a@ * 11) + b@ + 121) = B
Else                           ' No, then see if it got any burning
@((a@ * 11) + b@ + 121) = FUNC(_BurningTrees(a@, b@))
EndIf                          ' neighbors that will set it ablaze
EndIf
```
```   Next
Next
```

Return

_UpdateForest ' Update the main buffer

``` Local(1)
```
``` For a@ = 0 To 120                    ' Move from temporary buffer to main
@(a@) = @(a@+121)
Next
```

Return

_PrintForest ' Print the forest on screen

``` Local(2)
Print                                ' Let's make a little space
```
``` For a@ = 0 To 10                     ' Loop vertical
For b@ = 0 To 10                   ' Loop horizontal
If @((a@ * 11) + b@) = B Then    ' This is a burning tree
Print " *";
Else                             ' Otherwise..
If @((a@ * 11) + b@) = E Then  ' It may be an empty space
Print "  ";
Else                           ' Otherwise
Print " @";                  ' It has to be a tree
EndIf
EndIf
Next
Print                              ' Terminate row
Next
```
``` Print                                ' Terminate map
```

Return

_BurningTrees Param(2) ' Check the trees environment

``` Local(2)
```
``` For c@ = a@-1 To a@+1                ' Loop vertical -1/+1
Until c@ > 10                        ' End at bottom edge
For d@ = b@-1 To b@+1              ' Loop horizontal -1/+1
If d@ < 0 Then Continue          ' Skip left edge
Until d@ > 10                      ' End at right edge
If @((c@ * 11) + d@) = B Then Unloop : Unloop : Return (B)
Next                               ' We found a burning tree, exit!
Next                                 ' Try next row
```

Return (T) ' No burning trees found</lang>

Output:
```   @ @   @       @
@ @   @   @   @ @
@ @           @ @
@ @ @
@         @ @ @   @
@
@             @
@ *           *
*
*       @       @

Press '1' to continue, '0' to quit: 1

@ @   @       @
@ @   @   @   @ @
@ @           @ @
@ @ @
@         @ @ @   @
@     @
*             *
*         @
@
@     @ @
@

Press '1' to continue, '0' to quit: 0

0 OK, 0:1236```

## Vedit macro language

This macro shows an example of using search in columnar block. Instead of checking all the 8 neighboring cells separately, a search in 3x3 character block is performed to check if there is fire.

Note: In order to display the graphics characters correctly, use DOS (OEM) font such as "Terminal". <lang vedit>#1 = 25 // height of the grid

1. 2 = 60 // width of the grid
2. 3 = 2 // probability of random fire, per 1000
3. 4 = 40 // probability of new tree, per 1000
1. 5 = #2+2+Newline_Chars // total length of a line
2. 90 = Time_Tick // seed for random number generator
3. 91 = 1000 // get random numbers in range 0 to 999

// Fill the grid and draw border Buf_Switch(Buf_Free) Ins_Char('-', COUNT, #2+2) Ins_Newline for (#11=0; #11<#1; #11++) {

```   Ins_Char('|')
for (#12=0; #12<#2; #12++) {
Call("RANDOM")
if (Return_Value < 500) {               // 50% propability for a tree
Ins_Char('♠')
} else {
Ins_Char(' ')
}
}
Ins_Char('|')
Ins_Newline
```

} Ins_Char('-', COUNT, #2+2)

1. 8=1

Repeat(10) {

```   BOF
Update()
// calculate one generation
for (#11=1; #11<#1+2; #11++) {
Goto_Line(#11)
for (#12=1; #12<#2+2; #12++) {
Goto_Col(#12)
#14=Cur_Pos
Call("RANDOM")
#10 = Return_Value
if (Cur_Char == '♠') {                      // tree?
if (#10 < #3) {
Ins_Char('*', OVERWRITE)            // random combustion
} else {
if (Search_Block("░", CP-#5-1, CP+#5+2, COLUMN+BEGIN+NOERR)) {
Goto_Pos(#14)
Ins_Char('*', OVERWRITE)        // combustion
}
}
} else {
if (Cur_Char == ' ') {                  // empty space?
if (#10 < #4) {
Ins_Char('+', OVERWRITE)        // new tree
}
}
}
}
}
// convert tmp symbols
Replace("░"," ", BEGIN+ALL+NOERR)           // old fire goes out
Replace("*","░", BEGIN+ALL+NOERR)           // new fire
Replace("+","♠", BEGIN+ALL+NOERR)           // new tree
```

} Return

//-------------------------------------------------------------- // Generate random numbers in range 0 <= Return_Value < #91 // #90 = Seed (0 to 0x7fffffff) // #91 = Scaling (0 to 0xffff)

RANDOM:
1. 92 = 0x7fffffff / 48271
2. 93 = 0x7fffffff % 48271
3. 90 = (48271 * (#90 % #92) - #93 * (#90 / #92)) & 0x7fffffff

return ((#90 & 0xffff) * #91 / 0x10000)</lang>

Sample output, 10th generation:

```--------------------------------------------------------------
|       ♠♠♠♠ ♠♠ ♠ ♠♠♠♠        ♠    ♠♠♠♠♠♠ ♠♠♠♠♠ ♠♠♠♠ ♠♠♠♠ ♠♠♠|
|         ░♠♠♠ ♠   ♠♠          ♠  ░♠♠♠♠ ♠   ♠   ♠ ♠♠♠  ♠ ♠♠░♠|
|♠  ♠     ░ ♠    ♠♠ ♠ ♠♠           ♠   ♠♠♠ ♠ ♠ ♠♠♠ ♠♠♠♠♠♠♠♠ ♠|
|    ♠    ░♠♠♠  ♠  ♠  ♠░       ♠ ░░♠♠♠♠♠  ♠♠♠♠ ♠ ♠♠♠♠♠  ♠♠♠♠♠|
|    ♠    ░♠♠♠ ♠♠  ♠  ♠ ░       ░♠ ♠ ♠░░░░░░░░ ♠  ♠♠♠♠♠♠♠♠♠♠ |
|          ♠♠ ♠ ♠♠♠ ♠♠♠        ░ ♠ ♠♠ ░        ♠♠  ♠ ♠♠♠♠♠♠♠♠|
|♠        ░♠♠♠♠♠♠♠♠ ♠♠ ♠♠♠░ ░░░ ░░░░ ♠            ░ ░ ░░ ░  ♠|
|    ♠    ░       ♠  ♠ ♠   ♠♠♠♠░             ░               |
|         ░♠ ♠♠♠♠♠♠♠♠♠ ♠ ♠♠♠  ♠   ♠      ♠                   |
|  ♠    ♠ ░♠ ♠♠ ♠♠♠♠♠♠♠♠♠♠  ░░ ░                             |
|    ♠    ░♠♠♠      ♠♠ ░░░    ♠░ ░          ♠♠♠   ░░░░   ♠   |
|        ░░♠♠♠    ♠  ♠░        ♠   ♠   ♠ ♠ ♠      ♠ ░        |
|     ♠ ♠♠♠♠♠♠  ♠♠ ♠♠♠░         ♠                  ░ ♠       |
|░ ░   ♠ ♠♠ ♠ ♠ ♠  ♠♠♠               ♠ ♠♠                    |
|  ♠ ♠♠  ░░░░♠  ♠♠ ♠♠♠░♠       ♠ ♠      ♠             ░     ░|
|♠♠♠    ♠   ░ ♠♠♠♠  ♠         ♠        ♠♠            ░♠░    ♠|
|♠  ♠♠♠♠░     ♠♠  ♠♠♠ ░        ♠         ♠  ♠         ░ ░    |
|♠ ♠♠♠♠♠░    ♠♠ ♠ ♠ ♠♠      ♠        ♠  ♠             ░♠♠♠  ♠|
|♠♠♠♠♠ ♠ ░░░░♠♠♠♠♠  ♠♠░    ♠                    ♠      ♠♠ ♠ ♠|
|      ♠♠♠♠♠♠♠  ♠ ♠♠ ♠░  ♠   ♠ ♠                      ░♠♠♠ ♠ |
| ♠ ♠♠♠♠♠ ♠♠ ♠    ♠ ♠♠              ♠    ♠            ░♠♠  ♠ |
|♠♠♠ ♠♠♠♠♠♠  ♠  ♠♠♠  ♠░                  ░            ░♠♠ ♠♠♠|
| ♠♠♠♠♠ ♠♠♠♠♠  ♠♠♠ ♠♠ ♠░ ♠          ♠  ░♠   ░  ♠      ░♠ ♠ ♠♠|
| ♠ ♠♠ ♠ ♠♠  ♠♠♠♠ ♠♠♠♠♠░          ░♠♠ ♠♠♠♠♠♠░     ♠      ♠♠  |
|  ♠ ♠ ♠♠♠♠♠♠♠    ♠♠♠ ♠░░ ░░ ♠░ ░░░♠♠♠   ♠  ♠♠ ♠♠ ♠    ♠♠ ♠  |
--------------------------------------------------------------
```

## Vlang

Text. The program prints the configuration, waits for enter key, and prints the next. It makes a pretty good animation to just hold down the enter key.

Translation of: go

<lang vlang>import rand import strings import os

const (

```   rows = 20
cols = 30
p    = .01
f    = .001
```

)

const rx = rows + 2 const cx = cols + 2

fn main() {

```   mut odd := []string{len: rx*cx}
mut even := []string{len: rx*cx}
for r := 1; r <= rows; r++ {
for c := 1; c <= cols; c++ {
if rand.intn(2) or {1} == 1 {
odd[r*cx+c] = 'T'
}
}
}
mut _ :=
for {
print_row(odd)
step(mut even, odd)
_ = os.input()

print_row(even)
step(mut odd, even)
_ = os.input()
}
```

}

fn print_row(model []string) {

```   println(strings.repeat_string("__", cols))
println()
for r := 1; r <= rows; r++ {
for c := 1; c <= cols; c++ {
if model[r*cx+c] == '0' {
print("  ")
} else {
print(" \${model[r*cx+c]}")
}
}
println()
}
```

}

fn step(mut dst []string, src []string) {

```   for r := 1; r <= rows; r++ {
for c := 1; c <= cols; c++ {
x := r*cx + c
dst[x] = src[x]
match dst[x] {
'#' {
// rule 1. A burning cell turns into an empty cell
dst[x] = '0'
}
'T' {
// rule 2. A tree will burn if at least one neighbor is burning
if src[x-cx-1]=='#'  || src[x-cx]=='#' || src[x-cx+1]=='#' ||
src[x-1] == '#'  ||                   src[x+1] == '#'  ||
src[x+cx-1]=='#' || src[x+cx]=='#' || src[x+cx+1] == '#' {
dst[x] = '#'
```
```                   // rule 3. A tree ignites with probability f
// even if no neighbor is burning
} else if rand.f64() < f {
dst[x] = '#'
}
}
else {
// rule 4. An empty space fills with a tree with probability p
if rand.f64() < p {
dst[x] = 'T'
}
}
}
}
}
```

}</lang>

## Wren

Translation of: Go

<lang ecmascript>import "random" for Random import "io" for Stdin

var rand = Random.new() var rows = 20 var cols = 30 var p = 0.01 var f = 0.001 var rx = rows + 2 var cx = cols + 2

var step = Fn.new { |dst, src|

```   for (r in 1..rows) {
for (c in 1..cols) {
var x = r*cx + c
dst[x] = src[x]
if (dst[x] == "#") {
// rule 1. A burning cell turns into an empty cell
dst[x] = " "
} else if(dst[x] == "T") {
// rule 2. A tree will burn if at least one neighbor is burning
if (src[x-cx-1] == "#"  || src[x-cx] == "#" || src[x-cx+1] == "#" ||
src[x-1] == "#"     || src[x+1] == "#"  ||
src[x+cx-1] == "#"  || src[x+cx] == "#" || src[x+cx+1] == "#") {
dst[x] = "#"
// rule 3. A tree ignites with probability f
// even if no neighbor is burning
} else if (rand.float() < f) {
dst[x] = "#"
}
} else {
// rule 4. An empty space fills with a tree with probability p
if (rand.float() < p) dst[x] = "T"
}
}
}
```

}

var print = Fn.new { |model|

```   System.print("__" * cols)
System.print()
for (r in 1..rows) {
for (c in 1..cols) System.write(" %(model[r*cx+c])")
System.print()
}
```

}

var odd = List.filled(rx*cx, " ") var even = List.filled(rx*cx, " ") for (r in 1 ..rows) {

```   for (c in 1..cols) {
if (rand.int(2) == 1) odd[r*cx+c] = "T"
}
```

} while (true) {

```   print.call(odd)
step.call(even, odd)
```   print.call(even)