Imperative programs like to jump around, but some languages restrict these jumps. Many structured languages restrict their conditional structures and loops to local jumps within a function. Some assembly languages limit certain jumps or branches to a small range.

Task
Jump anywhere
You are encouraged to solve this task according to the task description, using any language you may know.

This task is to demonstrate a local jump and a global jump and the various other types of jumps that the language supports. For the purpose of this task, the jumps need not be used for a single purpose and you have the freedom to use these jumps for different purposes. You may also defer to more specific tasks, like Exceptions or Generator. This task provides a "grab bag" for several types of jumps. There are non-local jumps across function calls, or long jumps to anywhere within a program. Anywhere means not only to the tops of functions!

  • Some languages can go to any global label in a program.
  • Some languages can break multiple function calls, also known as unwinding the call stack.
  • Some languages can save a continuation. The program can later continue from the same place. So you can jump anywhere, but only if you have a previous visit there (to save the continuation).


These jumps are not all alike. A simple goto never touches the call stack. A continuation saves the call stack, so you can continue a function call after it ends.


Task

Use your language to demonstrate the various types of jumps that it supports.

Because the possibilities vary by language, this task is not specific. You have the freedom to use these jumps for different purposes. You may also defer to more specific tasks, like Exceptions or Generator.

360 Assembly

The unconditionnal branch instruction B is the jump anywhere of the S/360 assembler.

		 ...
         B      ANYWHERE           branch
 		 ...
ANYWHERE EQU *                     label
		 ...

6502 Assembly

Assembly languages in general do not restrict where or how you can jump. 6502 Assembly in particular does not have any sort of W^X protection so the entire address space is a valid jump target. The question is, what address does your code reside in after it is assembled? Most assemblers allow you to define labels, which get converted to the address of the instruction just after the label. This way you don't have to manually calculate the address yourself.

Direct Jump

This is strictly a one-way trip, just like GOTO in BASIC. The program counter will be set to the specified address or label. This technique is limited to constants. In other words, a direct jump cannot be altered at runtime (self-modifying code notwithstanding)

JMP PrintChar ; jump to the label "PrintChar" where a routine to print a letter to the screen is located.

Indirect Jump

This method is a form of the "computed GOTO" and lets you jump to an address stored in a pair of memory addresses. The least effective way to do this is as follows:

lda #<PrintChar ;load into A the low byte of the address that PrintChar references.
sta $00 
lda #>PrintChar ;load into A the high byte of the address that PrintChar references.
sta $01 ;these need to be stored low then high because the 6502 is a little-endian cpu
JMP ($00) ;dereferences to JMP PrintChar

The above example is just the same as a direct jump but more complicated for no added benefit. To actually use an indirect jump correctly, the input needs to be variable. Here's one way to do that:

JumpTable_Lo: db <PrintChar, <WaitChar, <ReadKeys, <MoveMouse ;each is the low byte of a memory address
JumpTable_Hi: db >PrintChar, >WaitChar, >ReadKeys, >MoveMouse ;each is the high byte of a memory address

lda JumpTable_Lo,x
sta $10
lda JumpTable_Hi,x
sta $11
JMP ($0010)

Depending on the value of x, you will be taken to a different procedure. Once again, this is a one-way jump and you can't return.

Another way to do this is with a "jump block."

.org $8000
JMP PrintChar
JMP WaitChar
JMP ReadKeys
JMP MoveMouse

Each jump instruction on the 6502 takes up 3 bytes: one for the JMP command itself, and two for the destination. Knowing this, we can use a variable that is a multiple of 3 to take us to the desired location. Let's pretend X is such a variable, and this routine lets us JMP to the "next" routine.

lda $80
sta $21
txa
clc
adc #$03
sta $20
JMP ($0020)

If X was 0, the JMP takes us to WaitChar.

If X was 3, the JMP takes us to ReadKeys.

If X was 6, the JMP takes us to MoveMouse.

If X isn't a multiple of 3, or is too large, the JMP will take you... somewhere. This isn't good, so make sure you have a way to bounds check.

The 65c02, which was used in the Apple II and the Atari Lynx, can perform an indirect jump offset by X. This can be used to perform the above technique with much less setup.

JumpTable:
word PrintChar
word PrintString
word MoveMouse

ldx #$02
JMP (JumpTable,x) ;dereferences to JMP PrintString

Your index needs to be a multiple of 2 for this to work, most of the time you'll use ASL A then TAXto double your index prior to performing the indirect jump.

Indirect JSR

Make sure you read Indirect Jump before reading this, it won't make much sense otherwise.

Unfortunately, you cannot simply replace "JMP" in the above example with "JSR" as that is not a valid command. What you have to do instead is a bit trickier. One way to accomplish this is with a "Return Table." Let's rewrite JumpTable_Lo and JumpTable_Hi in that format.

ReturnTable: dw PrintChar-1,WaitChar-1,ReadKeys-1,MoveMouse-1

For this example, assume that all of those labels are subroutines that end in an RTS instruction. This method won't work otherwise. Once your return table is defined, you need some sort of variable that allows you to index into that table (i.e. select a subroutine to use). We'll assume for the code below that the accumulator contains such a variable right now.

 
;execution is currently here
JSR UseReturnTable ;the address just after this label is pushed onto the stack.
;the chosen subroutine's RTS will bring you here.


UseReturnTable:     ;pretend this is somewhere far away from where execution is, its distance doesn't matter.
ASL                 ;double the value of the variable, because this is a table of words.
TAX
LDA ReturnTable+1,x ;load the chosen subroutine's high byte into the accumulator
PHA                 ;push it onto the stack
LDA ReturnTable,x   ;load the chosen subroutine's low byte into the accumulator
PHA                 ;push it onto the stack.
RTS                 ;this "RTS" actually takes you to the desired subroutine. 
                    ;The top two bytes of the stack are popped, the low byte is incremented by 1, 
                    ;and this value becomes the new program counter.

Now all of that was a bit confusing wasn't it? Essentially this "abuses" the following concepts:

  • The JSR instruction automatically pushes the current address + 1 onto the stack.
  • The RTS instruction pulls the top two bytes off the stack, subtracts 1 from the low byte, and sets the program counter to that value.

Finally, and most importantly:

  • The RTS instruction assumes that the top two bytes of the stack are the correct place to return to, and goes there without any way of knowing if the address is "correct."

With this knowledge in mind, we can take a value equal to the address of the desired subroutine, minus 1, push it onto the stack, then "return" to that subroutine (even if we've never been there!)

This is all very complicated, and luckily if you're programming for the 16-bit 65816 you don't have to do this. The 65816 (which was used in the Super Nintendo) has a special command just for doing this. JSR ($####,x) can be used for selecting from a list of functions to call.

Long Jump

This is only available on the 65816 thanks to its extended 24-bit address space. A standard JMP on the 65816 is confined to $nn0000-$nnFFFF. To break free of this limitation, you'll need to use JML $xxxxxx to go to a different bank. JSL $xxxxxx can call a subroutine in a different bank, and you'll need to use RTL to safely return from a JSL.

68000 Assembly

Local Jumps

The 68000's branching syntax is nearly identical to that of the 6502. One key difference is that after a comparison, carry set is less than, and carry clear is greater than or equal. Thankfully, the equivalent BGE and BLT can take the place of BCC and BCS for unsigned comparisons, respectively, which makes the code easier to read.

In addition, for nearby subroutines, BSR can be used in place of JSR to save data. There is also BRA (branch always) for unconditional local jumping, which the original 6502 didn't have. 
bra foo
nop ;execution will never reach here
foo:

CMP.L D0,D1
BGE D1_Is_Greater_Than_Or_Equal_To_D0 
   ; your code for what happens when D1 is less than D0 goes here
D1_Is_Greater_Than_Or_Equal_To_D0:

Absolute Jumps

The 68000 has JMP and JSR for absolute jumping and function calls, respectively. When you JSR, the next RTS you encounter will return the program counter to just after the JSR statement you came from, provided that the return address is still on top of the stack when the RTS is executed. The CPU assumes that the top 4 bytes of the stack are the correct return address, and has no way of knowing if it's wrong. A sequence like this will likely result in a crash or otherwise undefined behavior:

JSR foo:

; this is somewhere far away from the JSR above
foo:
MOVE.L D0,(SP)+
RTS                ;the CPU will "return" to the value that was in D0, not the actual return address.

This can be abused for our benefit, allowing the programmer to select a subroutine from a list of functions. This trick goes by many names, some of the more common ones are "RTS Trick" or "Ret-poline" (a portmanteau of x86's RET and trampoline. RET is called RTS on the 6502 and 68000)

;For this example, we want to execute "ReadJoystick"
MOVE.W D0,#1
JSR Retpoline
;;;;; ReadJoystick's RTS will return the program counter to here
; rest of program


;assume this is somewhere far away from the JSR above, and that execution won't fall through to here.
Retpoline:         ;uses D0 as the index into the table.
LEA A0,SubroutineTable
LSL.B #2,D0        ;multiply D0 by 4 since this is a table of 32-bit memory addresses
MOVE.L (A0,D0),A0  ;offset and deference A0, now A0 contains the address of ReadJoystick
PEA A0             ;push the address of A0 onto the stack
RTS                ;now we'll "return" to ReadJoystick. If it ends in an RTS, that RTS shall return to the area specified above.

SubroutineTable:
DC.L MoveMouse, DC.L ReadJoystick, DC.L ReadKeyboard, DC.L PrintString

Indirect Jumps

In addition to a fixed memory address, you can also JMP to the value stored in an address register (effectively MOVE.L An,PC if such a thing existed), or you can dereference the pointer stored in an address register and jump to that instead.

8086 Assembly

The 8086 has the unconditional JMP, as well as conditional variants JZ,JNZ, etc. There are also a few special jump types:

JCXZ will jump only if the CX register equals 0. This is useful for skipping a loop if CX (the loop counter) is already zero.

JCXZ bar
foo:
LOOP foo      ;subtract 1 from CX, and if CX is still nonzero jump back to foo
bar:

LOOP label is the equivalent of DEC CX JNZ label and, as the name implies, is used for looping. You might have heard that DEC CX JNZ label should always be used over LOOP label for better performance. This is only true on later x86-based CPUs - the reasons for LOOP's poor performance weren't present on the 8086, and as such it's better to use there.


Although JMP was referred to as "unconditional" before, it does not have access to the entire address space of the CPU, unlike the 6502, Z80, and 68000. The 8086 uses a segmented memory model, where it uses 20-bit addresses despite being a 16-bit CPU. The other 4 bits are the "segment," and a JMP or CALL cannot exit that segment.

AArch64 Assembly

Works with: as version Raspberry Pi 3B version Buster 64 bits
or android 64 bits with application Termux
/* ARM assembly AARCH64 Raspberry PI 3B */
/*  program julpanaywhere64.s   */

/************************************/
/* Constantes                       */
/************************************/
/* for this file see task include a file in language AArch64 assembly*/
.include "../includeConstantesARM64.inc" 

/*********************************/
/* Initialized data              */
/*********************************/
.data
szMessResult:         .asciz "loop indice : "
szMessage1:           .asciz "Display to routine call by register\n"
szMessage2:           .asciz "Equal to zero.\n"
szMessage3:           .asciz "Not equal to zero.\n"
szMessage4:           .asciz "loop start\n"
szMessage5:           .asciz "No executed.\n"
szMessResult1:        .asciz ","
szMessResult2:        .asciz "]\n"
szMessStart:          .asciz "Program 64 bits start.\n"
szCarriageReturn:     .asciz "\n"


/*********************************/
/* UnInitialized data            */
/*********************************/
.bss
sZoneConv:             .skip 24
/*********************************/
/*  code section                 */
/*********************************/
.text
.global main 
main:                            // entry of program 
    ldr x0,qAdrszMessStart
    bl affichageMess             // branch and link to routine
                                 // return here after routine execution
    b label1                     // branch unconditional to label
    ldr x0,qAdrszMessage5        // this instruction is never executed
    bl affichageMess             // and this
label1:
    ldr x0,qAdrszMessage4
    bl affichageMess       
    mov x20,0
1:
    mov x0,x20
    ldr x1,qAdrsZoneConv
    bl conversion10              // decimal conversion
    strb wzr,[x1,x0]
    mov x0,#3                   // number string to display
    ldr x1,qAdrszMessResult
    ldr x2,qAdrsZoneConv         // insert conversion in message
    ldr x3,qAdrszCarriageReturn
    bl displayStrings            // display message
    add x20,x20,1                    // increment indice
    cmp x20,5
    blt 1b                       // branch for loop if lower
    
    mov x0,0
    cbz x0,2f                    // jump to label 2 if x0 = 0
    
2:
    adr x1,affichageMess         // load routine address in register
    ldr x0,qAdrszMessage1
    blr x1
    
    mov x4,4
    cmp x4,10
    bgt 3f                       // branch if higter
    mov x0,x4
3:
    mov x0,0b100                 // 1 -> bit 2
    tbz x0,2,labzero             // if bit 2 equal 0 jump to label
    ldr x0,qAdrszMessage3        // bit 2 <> 0
    bl affichageMess
    b endtest                    // jump end if else
labzero:                         // display if bit equal to 0
    ldr x0,qAdrszMessage2
    bl affichageMess
endtest:
    mov x0,0b000                  // 0 -> bit 2
    tbnz x0,2,4f                  // if bit 2 <> 0 jump to label
    ldr x0,qAdrszMessage2         // bit 2 = 0
    bl affichageMess
    b 5f                          // jump end test
4:                                // display if bit equal to 1
    ldr x0,qAdrszMessage3
    bl affichageMess
5:

100:                              // standard end of the program 
    mov x0, #0                    // return code
    mov x8,EXIT 
    svc #0                        // perform the system call
qAdrszCarriageReturn:        .quad szCarriageReturn
qAdrsZoneConv:               .quad sZoneConv
qAdrszMessResult:            .quad szMessResult
qAdrszMessage1:              .quad szMessage1
qAdrszMessage2:              .quad szMessage2
qAdrszMessage3:              .quad szMessage3
qAdrszMessage4:              .quad szMessage4
qAdrszMessage5:              .quad szMessage5
qAdrszMessStart:             .quad szMessStart

/***************************************************/
/*   display multi strings                    */
/***************************************************/
/* x0  contains number strings address */
/* x1 address string1 */
/* x2 address string2 */
/* x3 address string3 */
/* other address on the stack */
/* thinck to add  number other address * 4 to add to the stack */
displayStrings:            // INFO:  displayStrings
    stp x1,lr,[sp,-16]!          // save  registers 
    stp x2,x3,[sp,-16]!          // save  registers 
    stp x4,x5,[sp,-16]!          // save  registers 
    add fp,sp,#48          // save paraméters address (6 registers saved * 8 bytes)
    mov x4,x0              // save strings number
    cmp x4,#0              // 0 string -> end
    ble 100f               // branch to equal or smaller
    mov x0,x1              // string 1
    bl affichageMess
    cmp x4,#1              // number > 1
    ble 100f
    mov x0,x2
    bl affichageMess
    cmp x4,#2
    ble 100f
    mov x0,x3
    bl affichageMess
    cmp x4,#3
    ble 100f
    mov x3,#3
    sub x2,x4,#4
1:                         // loop extract address string on stack
    ldr x0,[fp,x2,lsl #3]
    bl affichageMess
    subs x2,x2,#1
    bge 1b
100:
    ldp x4,x5,[sp],16        // restaur  registers 
    ldp x2,x3,[sp],16        // restaur  registers 
    ldp x1,lr,[sp],16        // restaur  registers
    ret                      // return to addtress stored in lr

/***************************************************/
/*      ROUTINES INCLUDE                           */
/***************************************************/
/* for this file see task include a file in language AArch64 assembly */
.include "../includeARM64.inc"
Output:
Program 64 bits start.
loop start
loop indice : 0
loop indice : 1
loop indice : 2
loop indice : 3
loop indice : 4
Display to routine call by register
Not equal to zero.
Equal to zero.

Ada

procedure Goto_Test is
begin

   Stuff;
   goto The_Mother_Ship; -- You can do this if you really must!
   Stuff;
   if condition then
      Stuff;
   <<Jail>>
      Stuff;
   end if;
   Stuff;

   -- Ada does not permit any of the following
   goto Jail; 
   goto The_Sewer; 
   goto The_Morgue;

   Stuff;
   case condition is
      when Arm1 =>
         Stuff;
         goto The_Gutter; -- Cant do this either
         Stuff;
      when Arm2 =>
         Stuff;
      <<The_Gutter>>
         Stuff;
      <<The_Sewer>>
         Stuff;
   end case;

   Stuff;
   for I in Something'Range loop
      Stuff;
   <<The_Morgue>>
      if You_Are_In_Trouble then
         goto The_Mother_Ship;
         -- This is the usual use of a goto.
      end if;
      Stuff;
   end loop;

   Stuff;
<<The_Mother_Ship>>
   Stuff;

end Goto_Test;

ARM Assembly

The ARM's branching syntax is similar to the 6502 and the 68000. Branches can be given a condition, and if the condition is not met no jump will take place, and execution simply "falls through" to the instruction below.

  • B is an unconditional branch. The operand is a specified label, which the assembler will calculate the necessary offset to adjust the program counter (PC/R15) by. Branches have a limit on how far forward or back you can go (on ARM v4 it was 4096 bytes) but this limit is incredibly generous so you're not likely to encounter it.


  • Like most instructions, a condition code can be added to a branch. The zero, carry, and overflow flags can all be used to branch.


  • BL will branch to the specified label, and will MOV LR,PCbefore the branch. This is the equivalent of CALL on x86 Assembly. Nested subroutines will require that the link register is caller-preserved so that once the inner subroutine returns, the outer one knows where to return to. Returning from a subroutine can be done with BX LR or MOV PC,LR. (The former is preferred because it can switch to THUMB mode and back, which will be explained next.)


  • BX takes another register as its operand and will set PC to that register's value. In addition, if the least significant digit of the register's value is 1, the CPU will enter THUMB mode, which uses a more limited instruction set, but each instruction only takes up 16 bits instead of 32. This is often used to save memory when writing firmware for embedded systems. To switch back to 32-bit ARM mode, you'll need to use BX again, with a register whose value is a multiple of 4. In addition, BLX (a combination of BL and BX) can also be used.


ARM is very unique in that the program counter can be directly loaded as well as influenced by branching. You need to be very careful when doing this, because loading a value into PC that isn't a multiple of 4 will crash the CPU.

MOV PC,R0   ;loads the program counter with the value in R0. (Any register can be used for this)
LDR PC,[R0] ;loads the program counter with the 32-bit value at the memory location specified by R0

This sequence of commands can store registers onto the stack, retrieve them, and return all at once. For this to work properly the only difference in the choice of registers can be that you push LR and pop PC.

PUSH {R0-R12,LR}
POP {R0-R12,PC}

If you don't have access to unified syntax, the above will only work in THUMB mode. For 32-bit ARM, you may have to use

STMFD sp!,{r0-r12,lr}
LDMFD sp!,{r0-r12,pc}

Arturo

Arturo has no GOTO equivalent and no labels.

Apart from exceptions handling (with try and try?), Arturo has continue (to continue to next iteration - within a loop) and break (to leave a loop).

AutoHotkey

; Define a function.
function()
{
	MsgBox, Start
	gosub jump
	
	free:
	MsgBox, Success
}

; Call the function.
function()
goto next
return

jump:
MsgBox, Suspended
return

next:
Loop, 3
{
	gosub jump
}
return

/*
Output (in Message Box):

Start
Suspended
Success
Suspended
Suspended
Suspended

*/

BASIC

10 GOTO 100: REM jump to a specific line
20 RUN 200: REM start the program running from a specific line

Some versions of basic allow line labels to be used. Here we jump to a label:

Works with: BaCon
Works with: QuickBASIC
GOTO mylabel

Applesoft BASIC

caveat: http://www.u.arizona.edu/~rubinson/copyright_violations/Go_To_Considered_Harmful.html

  0 REM GOTO
100 GOTO 110 : REM JUMP TO A SPECIFIC LINE
110 RUN 120 : REM START THE PROGRAM RUNNING FROM A SPECIFIC LINE
120 IF 1 GOTO 130 : REM CONDITIONAL JUMP
130 IF 1 THEN 140 : REM THEN ALSO WORKS IN PLACE OF GOTO
140 IF 1 THEN GOTO 150 : REM BE VERBOSE BY USING THEN GOTO
150 ON A GOTO 170, 180, 190 : REM JUMP A SPECIFIC LINE NUMBER IN THE LIST INDEXED BY THE VALUE OF A STARTING AT 1, IF A IS OUT OF RANGE DO NOT JUMP
160 ON ERR GOTO 270 : REM WHEN AN ERROR OCCURS JUMP TO A SPECIFIC LINE
170 GOSUB 180 : REM JUMP TO LINE 180, PUSHING THE CURRENT PLACE ON THE STACK
180 POP : REM POP THE CURRENT PLACE FROM THE STACK, EFFECTIVELY MAKING THE PREVIOUS LINE A JUMP
190 CALL -151 : REM CALL ANY MACHINE LANGUAGE SUBROUTINE, IT MIGHT RETURN, IT MIGHT NOT
200 & : REM CALL THE USER-DEFINED AMPERSAND ROUTINE, IT MIGHT RETURN, IT MIGHT NOT
210 ? USR(0) : REM CALL THE USER-DEFINED FUNCTION, IT MIGHT RETURN, IT MIGHT NOT
220 S = 6 : ?CHR$(4)"PR#"S : REM CALL THE ROM ROUTINE IN SLOT S
230 S = 6 : ?CHR$(4)"IN#"S : REM CALL THE ROM ROUTINE IN SLOT S
240 ?CHR$(4)"RUN PROGRAM" : REM RUN A BASIC PROGRAM FROM DISK
250 ?CHR$(4)"BRUN BINARY PROGRAM": REM RUN A MACHINE LANGUAGE BINARY PROGRAM FROM DISK
260 ?CHR$(4)"EXEC PROGRAM.EX" : REM EXECUTE THE TEXT THAT IS CONTAINED IN THE FILE PROGRAM.EX
270 RESUME : REM JUMP BACK TO THE STATEMENT THAT CAUSED THE ERROR
280 STOP : REM BREAK THE PROGRAM
290 END : REM END THE PROGRAM
300 GOTO : REM NO LINE NUMBER, JUMPS TO LINE 0
CONT : REM CONTINUE, JUMP BACK TO WHERE THE PROGRAM STOPPED

BASIC256

BASIC256 supports both goto and gosub.

Works with: QBasic
Works with: Yabasic
print "First line."
gosub sub1
print "Fifth line."
goto Ending

sub1:
print "Second line."
gosub sub2
print "Fourth line."
return

Ending:
print "We're just about done..."
goto Finished

sub2:
print "Third line."
return

Finished:
print "... with goto and gosub, thankfully."
end
Output:
Igual que la entrada de FutureBasic.

Chipmunk Basic

Chipmunk Basic supports both goto and gosub.

Works with: Chipmunk Basic version 3.6.4
Works with: QBasic
100 CLS
110 PRINT "First line."
120 GOSUB sub1
130 PRINT "Fifth line."
140 GOTO Ending
150 sub1:
160 PRINT "Second line."
170 GOSUB sub2
180 PRINT "Fourth line."
190 RETURN
200 Ending:
210 PRINT "We're just about done..."
220 GOTO Finished
230 sub2:
240 PRINT "Third line."
250 RETURN
260 Finished:
270 PRINT "... with goto and gosub, thankfully."
280 END
Output:
Same as FutureBasic entry.

GW-BASIC

GW-BASIC supports both goto and gosub.

Works with: Applesoft BASIC
Works with: BASICA
Works with: Chipmunk Basic
Works with: Minimal BASIC
Works with: MSX BASIC version any
Works with: PC-BASIC version any
Works with: QBasic
Works with: Quite BASIC
100 PRINT "First line."
110 GOSUB 140
120 PRINT "Fifth line."
130 GOTO 190
140 REM sub1:
150 PRINT "Second line."
160 GOSUB 220
170 PRINT "Fourth line."
180 RETURN
190 REM Ending:
200 PRINT "We're just about done..."
210 GOTO 250
220 REM sub2:
230 PRINT "Third line."
240 RETURN
250 REM Finished:
260 PRINT "... with goto and gosub, thankfully."
270 END

IS-BASIC

10 GOTO 100 ! jump to a specific line
20 RUN 200 ! start the program running from a specific line

Minimal BASIC

The GW-BASIC solution works without any changes.

MSX Basic

The GW-BASIC solution works without any changes.

Quite BASIC

The GW-BASIC solution works without any changes.

Run BASIC

for i = 1 to 10
 if i = 5 then goto [label5]
next i
end

[label5]
print i
while i < 10
 if i = 6 then  goto [label6]
i = i + 1
wend
end

[label6]
print i
if i = 6 then goto [finish]
print "Why am I here"

[finish]
 print "done"

True BASIC

True BASIC supports both goto and gosub.

100 ! Jump anywhere
110 CLEAR
120 PRINT "First line."
130 GOSUB 160
140 PRINT "Fifth line."
150 GOTO 210
160 ! sub1:
170 PRINT "Second line."
180 GOSUB 250
190 PRINT "Fourth line."
200 RETURN
210 ! Ending:
220 PRINT "We're just about done..."
230 GOTO 270
240 ! sub2:
250 PRINT "Third line."
260 RETURN
270 ! Finished:
280 PRINT "... with goto and gosub, thankfully."
290 END
Output:
Same as FutureBasic entry.

Tiny BASIC

The GW-BASIC solution works without any changes.

BQN

Jumping anywhere (akin to APL's `→`) is not possible in BQN, and BQN does not have labels either. The main forms of jumping are within blocks.

Block predicates

These constitute conditional jumps. If the value is 0, the section following it is skipped.

   { 0 ? "Will not execute"; "Will execute" }
"Will execute"

Function calls

You can call a function from a block, temporarily jumping over to the function's body, and coming back.

 F{𝕩⊣•Out"In Second"}
{
  •Out "First"
  F@
  •Out "Last"
}
 First
In Second
Last

C

C has goto LABEL keyword.

	if (x > 0) goto positive;
	else goto negative;

positive:
	printf("pos\n"); goto both;

negative:
	printf("neg\n");

both:
	...

The label must be literal, not computed at run time. This won't work:

goto (x > 0 ? positive : negative);
You can goto almost anywhere inside the same function, but can't go across function boundaries. It's sometimes used to break out of nested loops:
for (i = 0; ...) {
	for (j = 0; ...) {
		if (condition_met) goto finish;
	}
}
although you can (not that you should) jump into a loop, too:
	goto danger;
	for (i = 0; i < 10; i++) {
danger: /* unless you jumped here with i set to a proper value */
		printf("%d\n", i);
	}

For unwrapping call stack and go back up to a caller, see longjmp example; more powerful, but more expensive and complicated, is POSIX ucontext. The best application for goto is error handling, this simplifies the resource clean up of a large function. This is used in the linux kernel.


  char *str;
  int *array;
  FILE *fp;

   str = (char *) malloc(100);
   if(str == NULL) {
     return;
   }
    
   
   fp=fopen("c:\\test.csv", "r");
   if(fp== NULL) {
     free(str );
     return;
   }
   
   array = (int *) malloc(15);
   if(array==NULL)   if(fp== NULL) {
     free(str );
     fclose(fp);
     return;
   }
     
   ...// read in the csv file and convert to integers


  char *str;
  int *array;
  FILE *fp;

   str = (char *) malloc(100);
   if(str == NULL) 
    goto:  exit;
   
   fp=fopen("c:\\test.csv", "r");
   if(fp== NULL) 
      goto:  clean_up_str;
   
   array = (int *) malloc(15);
   if(array==NULL)
     goto: clean_up_file;
   ...// read in the csv file and convert to integers

   clean_up_array:
     free(array);
   clean_up_file:
     fclose(fp);
   clean_up_str:
     free(str );
   exit:
   return;

C#

Like C, C# also has a goto LABEL keyword. This section is partly copied from the section on C, since both languages share common syntax.

if (x > 0) goto positive;
else goto negative;

positive:
    Console.WriteLine("pos\n"); goto both;

negative:
    Console.WriteLine("neg\n");

both:
    ...

The label must be literal, not computed at run time. This won't work:

goto (x > 0 ? positive : negative);

You can goto almost anywhere inside the same method, but can't go across method boundaries. It's sometimes used to break out of nested loops:

for (i = 0; ...) {
    for (j = 0; ...) {
        if (condition_met) goto finish;
    }
}

The label must be in scope, so you cannot jump into a loop. This will not compile:

goto danger;
for (i = 0; i < 10; i++) {
    danger:
    Console.WriteLine(i);
}

In C#, you can also goto a label from within any section of a try .. catch block. However, it is not permitted to jump out of a finally block.

int i = 0;
tryAgain:
try {
    i++;
    if (i < 10) goto tryAgain;
}
catch {
    goto tryAgain;
}
finally {
    //goto end; //Error
}

Another usage of goto is to jump between case labels inside a switch statement:

public int M(int n) {
    int result = 0;
    switch (n) {
        case 1:
            cost += 25;
            break;
        case 2:
            cost += 25;
            goto case 1;
        case 3:
            cost += 50;
            goto case 1;
    }
    return result;
}

C++

Like C, C++ also has a goto LABEL statement which can be used to jump within a function.

#include <iostream>
#include <utility>

using namespace std;

int main(void) 
{
    cout << "Find a solution to i = 2 * j - 7\n";
    pair<int, int> answer;
    for(int i = 0; true; i++)
    {
        for(int j = 0; j < i; j++)
        {
            if( i == 2 * j - 7)
            {
                // use brute force and run until a solution is found
                answer = make_pair(i, j);
                goto loopexit;
            }
        }
    }
    
loopexit:
    cout << answer.first << " = 2 * " << answer.second << " - 7\n\n"; 
    
    // jumping out of nested loops is the main usage of goto in
    // C++.  goto can be used in other places but there is usually
    // a better construct.  goto is not allowed to jump across
    // initialized variables which limits where it can be used.
    // this is case where C++ is more restrictive than C.

    goto spagetti;
        
    int k;
    k = 9;  // this is assignment, can be jumped over
    
    /* The line below won't compile because a goto is not allowed
     * to jump over an initialized value.
    int j = 9;
    */

spagetti:
    
    cout << "k = " << k << "\n";  // k was never initialized, accessing it is undefined behavior
    
}
Output:
Find a solution to i = 2 * j - 7
9 = 2 * 8 - 7

k = 0

C++ also inherited std::longjmp from C which can jump out of functions but it is almost never used. See the C longjmp example.

Clipper

Clipper has no labels and goto statements. The exit statements allows leave the current loop and doesn't contain any label where to go.

COBOL

 IDENTIFICATION DIVISION.
 PROGRAM-ID. jumps-program.
* Nobody writes like this, of course; but...

 PROCEDURE DIVISION.

* You can jump anywhere you like.
 start-paragraph.
     GO TO an-arbitrary-paragraph.

 yet-another-paragraph.
     ALTER start-paragraph TO PROCEED TO a-paragraph-somewhere.
* That's right, folks: we don't just have GO TOs, we have GO TOs whose
* destinations can be changed at will, from anywhere in the program,
* at run time.
     GO TO start-paragraph.
* But bear in mind: once you get there, the GO TO no longer goes to
* where it says it goes to.

 a-paragraph-somewhere.
     DISPLAY 'Never heard of him.'
     STOP RUN.

 some-other-paragraph.
* You think that's bad? You ain't seen nothing.
     GO TO yet-another-paragraph.

 an-arbitrary-paragraph.
     DISPLAY 'Edsger who now?'
     GO TO some-other-paragraph.

 END PROGRAM jumps-program.
Output:
Edsger who now?
Never heard of him.

COBOL also supports computed go to phrases, given a list of labels (paragraph names) and an integer index into that list.

 DATA DIVISION.
 WORKING-STORAGE SECTION.
 01 province PICTURE IS 99 VALUE IS 2.

 PROCEDURE DIVISION.
     GO TO quebec, ontario, manitoba DEPENDING ON province.
*    Jumps to section or paragraph named 'ontario'.

Common Lisp

In Common Lisp you can jump anywhere inside a tagbody.

(tagbody
  beginning
    (format t "I am in the beginning~%")
    (sleep 1)
    (go end)
  middle
    (format t "I am in the middle~%")
    (sleep 1)
    (go beginning)
  end
    (format t "I am in the end~%")
    (sleep 1)
    (go middle))
Output:
I am in the beginning
I am in the end
I am in the middle
I am in the beginning
I am in the end
I am in the middle
I am in the beginning
...

Computer/zero Assembly

A JMP (jump) instruction can transfer control to any point in memory. Its target can be modified at run time, if required, by using instruction arithmetic:

        LDA  goto
        SUB  somewhere
        ADD  somewhereElse
        STA  goto
goto:   JMP  somewhere

By the time execution reaches the instruction labelled goto, that instruction has become JMP somewhereElse. (This kind of coding does not, however, necessarily make the flow of control easier to follow.)

D

Apart from exception handling, D has the break and continue statements that can jump to a label in the current scope. The goto statement can jump to any label inside the current function.

DCL

$ return  ! ignored since we haven't done a gosub yet
$
$ if p1 .eqs. "" then $ goto main
$ inner:
$ exit
$
$ main:
$ goto label  ! if label hasn't been read yet then DCL will read forward to find label
$ label:
$ write sys$output "after first occurrence of label"
$
$ on control_y then $ goto continue1  ! we will use this to get out of the loop that's coming up
$
$ label:  ! duplicate labels *are* allowed, the most recently read is the one that will be the target
$  write sys$output "after second occurrence of label"
$  wait 0::2  ! since we are in a loop this will slow things down
$  goto label  ! hit ctrl-y to break out
$
$ continue1:  ! the previous "on control_y" remains in force despite having been triggered
$
$ label = "jump"
$ goto 'label  ! target can be a variable; talk about handy
$ jump:
$ write sys$output "after first occurrence of jump"
$
$ first_time = "true"
$ continue_label = "continue2"
$ 'continue_label:  ! even the label can be a variable (but only backwards); talk about handy
$ if first_time then $ goto skip
$ break = "true"
$ return
$
$ skip:
$ first_time = "false"
$
$ on control_y then $ gosub 'continue_label  ! setup a new on control_y to get out the next loop coming up
$
$ break = "false"
$ 'label:
$  write sys$output "after second occurrence of jump"
$  wait 0::2
$  if .not. break then $ goto 'label
$
$ gosub sub1  ! no new scope or parameters
$ label = "sub1"
$ gosub 'label
$
$ call sub4 a1 b2 c3  ! new scope and parameters
$
$ @nl:  ! new scope and parameters in another file but same process
$
$ procedure_filename = f$environment( "procedure " )  ! what is our own filename?
$ @'procedure_filename inner
$
$ exit  ! exiting outermost scope exits the command procedure altogether, i.e. back to shell
$
$ sub1:
$ return
$
$ sub2:
$ goto break  ! structurally disorganized but allowed
$
$ sub3:
$ return
$
$ break:
$ return
$
$ sub4: subroutine
$ exit
$ endsubroutine
Output:
$ @jump_anywhere
after first occurrence of label
after second occurrence of label
after second occurrence of label
 Interrupt

after first occurrence of jump
after second occurrence of jump
after second occurrence of jump
 Interrupt

$ 

Same thing but with verify (tracing) on

Output:
$ @jump_anywhere
$ return  ! ignored since we haven't done a gosub yet
$
$ if p1 .eqs. "" then $ goto main
$ main:
$ goto label  ! if label hasn't been read yet then DCL will read forward to find label
$ label:
$ write sys$output "after first occurrence of label"
after first occurrence of label
$
$ on control_y then $ goto continue1  ! we will use this to get out of the loop that's coming up
$
$ label:  ! duplicate labels *are* allowed, the most recently read is the one that will be the target
$  write sys$output "after second occurrence of label"
after second occurrence of label
$  wait 0::2  ! since we are in a loop this will slow things down
$  goto label  ! hit ctrl-y to break out
$ label:  ! duplicate labels *are* allowed, the most recently read is the one that will be the target
$  write sys$output "after second occurrence of label"
after second occurrence of label
$  wait 0::2  ! since we are in a loop this will slow things down
 Interrupt

$ continue1:  ! the previous "on control_y" remains in force despite having been triggered
$
$ label = "jump"
$ goto jump  ! target can be a variable; talk about handy
$ jump:
$ write sys$output "after first occurrence of jump"
after first occurrence of jump
$
$ first_time = "true"
$ continue_label = "continue2"
$ continue2:
$ if first_time then $ goto skip
$ skip:
$ first_time = "false"
$
$ on control_y then $ gosub continue2  ! setup a new on control_y to get out the next loop coming up
$
$ break = "false"
$ jump:  ! even the target can be a variable (but only backwards); talk about handy
$  write sys$output "after second occurrence of jump"
after second occurrence of jump
$  wait 0::2
$  if .not. break then $ goto jump
$ jump:  ! even the target can be a variable (but only backwards); talk about handy
$  write sys$output "after second occurrence of jump"
after second occurrence of jump
$  wait 0::2
 Interrupt

$ continue2:
$ if first_time then $ goto skip
$ break = "true"
$ return
$  if .not. break then $ goto jump
$
$ gosub sub1  ! no new scope or parameters
$ sub1:
$ return
$ label = "sub1"
$ gosub sub1
$ sub1:
$ return
$
$ call sub4 a1 b2 c3  ! new scope and parameters
$ sub4: subroutine
$ exit
$
$ @nl:  ! new scope and parameters in another file but same process
$
$ procedure_filename = f$environment( "procedure " )  ! what is our own filename?
$ @DSVE_PAA_ROOT:[NG25957]JUMP_ANYWHERE.COM;1 inner
$ return  ! ignored since we haven't done a gosub yet
$
$ if p1 .eqs. "" then $ goto main
$ inner:
$ exit
$
$ exit  ! exiting outermost scope exits the command procedure altogether, i.e. back to shell

Déjà Vu

Déjà Vu supports continuations:

example:
    !print "First part"
    yield
    !print "Second part"

local :continue example
!print "Interrupted"
continue
Output:
First part
Interrupted
Second part

The byte-code language supports jumping to arbitrary positions in the same file.

Delphi

Delphi has a goto LABEL keyword. Labels must be declared outside function body scope. Every function/procedure must have your own labels, globals labels won't work in local functions. The label must be literal, not computed at run time.

var
  x: Integer = 5;

label
  positive, negative, both;

begin
  if (x > 0) then
    goto positive
  else
    goto negative;

positive:
  writeln('pos');
  goto both;

negative:
  writeln('neg');
both:
  readln;
end.

Although you can (not that you should) jump into a loop, too. If you use a loop variable, it will start with its value. If the loop variable has a value out range loop limits, then you cause a intinity loop.

label
  inloop, outloop;

begin
  x := 2;
  if x > 0 then
    goto inloop;

  for x := -10 to 10 do
  begin
inloop:
    Writeln(x);
    if x = 8 then
      goto outloop;
  end;
outloop:
  readln;
end.
Output:
2
3
4
5
6
7
8

In Delphi you can't goto a label from within any section of a try .. except or finally block. This won't work.

 
label
  tryAgain, finished;

begin
  x := 0;

  try
    Writeln(x);
    inc(x);
    if (x < 10) then
      goto tryAgain;
  finally
    goto finished
  end;
finished:
  readln;
end.

EMal

^|EMal has no goto statement.
 |The closes statements are break, continue, return, exit
 |and exceptions management.
 |^
fun sample = void by block
  for int i = 1; i < 10; ++i
    if i == 1 do continue end # jumps to next iteration when 'i' equals 1
    writeLine("i = " + i)
    if i > 4 do break end # exits the loop when 'i' exceeds 4
  end
  for int j = 1; j < 10; ++j
    writeLine("j = " + j)
    if j == 3 do return end # returns from the function when 'j' exceeds 3
  end
end
sample()
type StateMachine
^|this code shows how to selectevely jump to specific code
 |to simulate a state machine as decribed here:
 |https://wiki.tcl-lang.org/page/A+tiny+state+machine
 |Functions return the next state.
 |^
int n = -1
Map stateMachine = int%fun[
  0 => int by block
    if Runtime.args.length == 1
      n = when(n == -1, int!Runtime.args[0], 0)
    else
      n = ask(int, "hello - how often? ")
    end
    return when(n == 0, 2, 1)
  end,
  1 => int by block
    if n == 0 do return 0 end
    writeLine(n + " Hello")
    n--
    return 1
  end,
  2 => int by block
    writeLine("Thank you, bye")
    return -1
  end]
int next = 0
for ever
  next = stateMachine[next]()
  if next == -1 do break end
end
Output:
emal.exe Org\RosettaCode\JumpAnywhere.emal 2
i = 2
i = 3
i = 4
i = 5
j = 1
j = 2
j = 3
2 Hello
1 Hello
Thank you, bye

Erlang

Jumps are limited to Exceptions.

ERRE

ERRE has a GOTO statement in the form GOTO <label>. <label> is a numercic string and must be declared. ERRE GOTO is local only: you can jump only within the same procedure or within the main program. In the following example there are two errors:

PROGRAM GOTO_ERR

LABEL 99,100

PROCEDURE P1
   INPUT(I)
   IF I=0 THEN GOTO 99 END IF
END PROCEDURE

PROCEDURE P2
99: PRINT("I'm in procdedure P2")
END PROCEDURE

BEGIN
100:
    INPUT(J)
    IF J=1 THEN GOTO 99 END IF
    IF J<>0 THEN GOTO 100 END IF
END PROGRAM

You can't jump from procedure P1 to procedure P2 or from main to procedure P2 (label 99). Jump to label 100 is allowed (within main program).

Factor

A lot of things that seem like jumps in Factor are really just tail recursion or quotation manipulation. For instance, breaking out of iteration early with find consists of satisfying the base case of a recursive combinator. do simply makes a copy of the body quotation and calls it before proceeding to while.

For everything else, Factor has continuations. Exception handling, co-operative threads, backtracking, and break (called return in Factor) are implemented with continuations.

A continuation is conceptually simple in Factor. It is a tuple consisting of slots for the five stacks that make up the entire execution context: data stack, call stack, retain stack, name stack, and catch stack. To create a continuation from the current execution context, use current-continuation.

USING: continuations prettyprint ;

current-continuation short.
Output:
T{ continuation f ~array~ ~callstack~ ~array~ ~vector~ ~vector~...

Following is a simple example where we reify a continuation before attempting to divide 1 by 0. Note the current execution context (a continuation object) is placed on the top of the data stack inside the callcc0 quotation which continue then reifies.

USING: continuations math prettyprint ;

[ 10 2 / . continue 1 0 / . ] callcc0
Output:
5

We can even reify a continuation while taking an object back with us.

USING: continuations kernel math ;

[ 10 2 / swap continue-with 1 0 / ] callcc1
Output:
--- Data stack:
5

FBSL

FBSL's BASIC supports labels (jump targets) and the corresponding GoTo and GoSub/Return commands. However, they are considered obsolete and have been superceded in everyday practice by more modern structured programming methods - subprocedures (Subs and Functions), block constructs, loops, and OOP.

FBSL's BASIC labels are denoted with colon prefixes:

:label ' this is a label named "label"
GOTO label ' this is a jump to the label named "label"

and belong to the global namespace. This means they are accessible for the GoTo and GoSub commands from anywhere throughout the script regardless of whether they are defined locally (in a subprocedure) or globally (outside all subprocedures). Consequently, a label's name must be unique throughout the script. Duplicate label names generate a compile-time exception.

FBSL's DynAsm labels may be named or nameless (automatic):

@label ; this is a label named "label"
JMP label ; this is a jump to the label named "label"
@@ ; this is an automatic label
JMP @F ; this is a jump to the nearest @@ label ahead
JMP @B ; this is a jump to the nearest @@ label behind
@@ ; this is another automatic label

and are local to the block they are defined in.

FBSL's DynC labels are denoted with colon postfixes and follow the ANSI C scoping rules:

label: // this is a label named "label"
goto label; // this is a jump to the label named "label"

Forth

\ this prints five lines containing elements from the two
\ words 'proc1' and 'proc2'. gotos are used here to jump
\ into and out of the two words at various points, as well
\ as to create a loop. this functions with ficl, pfe,
\ gforth, bigforth, swiftforth, iforth, and vfxforth; it
\ may work with other forths as well.

create goto1 1 cells allot create goto2 1 cells allot
create goto3 1 cells allot create goto4 1 cells allot
create goto5 1 cells allot create goto6 1 cells allot
create goto7 1 cells allot create goto8 1 cells allot
create goto9 1 cells allot create goto10 1 cells allot

: proc1
[ here goto1 ! ] s" item1 " type goto7 @ >r exit
[ here goto2 ! ] s" item2 " type goto8 @ >r exit
[ here goto3 ! ] s" item3 " type goto9 @ >r exit
[ here goto4 ! ] s" item4 " type goto10 @ >r exit
[ here goto5 ! ] s" item5" type cr 2dup = if 2drop exit then 1+ goto6 @ >r ;

: proc2
[ here goto6 ! ] s" line " type dup . s" --> item6 " type goto1 @ >r exit
[ here goto7 ! ] s" item7 " type goto2 @ >r exit
[ here goto8 ! ] s" item8 " type goto3 @ >r exit
[ here goto9 ! ] s" item9 " type goto4 @ >r exit
[ here goto10 ! ] s" item10 " type goto5 @ >r ;

5 1 proc2
bye

Output:

line 1 --> item6 item1 item7 item2 item8 item3 item9 item4 item10 item5
line 2 --> item6 item1 item7 item2 item8 item3 item9 item4 item10 item5
line 3 --> item6 item1 item7 item2 item8 item3 item9 item4 item10 item5
line 4 --> item6 item1 item7 item2 item8 item3 item9 item4 item10 item5
line 5 --> item6 item1 item7 item2 item8 item3 item9 item4 item10 item5


\ this is congruent to the previous demonstration, employing
\ a data structure to store goto/jump addresses instead of
\ separate variables, and two additional words 'mark_goto' and
\ 'goto'. works with ficl, pfe, gforth, bigforth, and vfxforth.
\ swiftforth and iforth crash.

create gotos 10 cells allot  \ data structure for storing goto/jump addresses
: mark_goto here swap 1- cells gotos + ! ; immediate  \ save addresses for jumping
: goto  r> drop 1- cells gotos + @ >r ;

\ designations for commands are immaterial when using goto's,
\ since the commands are not referenced by name, and are instead
\ jumped into by means of the goto marker.

: command1
[ 1 ] mark_goto s" item1 " type 7 goto
[ 2 ] mark_goto s" item2 " type 8 goto
[ 3 ] mark_goto s" item3 " type 9 goto
[ 4 ] mark_goto s" item4 " type 10 goto
[ 5 ] mark_goto s" item5 " type cr 2dup = if 2drop exit then 1+ 6 goto ;

: command2
[ 6 ] mark_goto s" line " type dup . s" --> item6 " type 1 goto
[ 7 ] mark_goto s" item7 " type 2 goto
[ 8 ] mark_goto s" item8 " type 3 goto
[ 9 ] mark_goto s" item9 " type 4 goto
[ 10 ] mark_goto s" item10 " type 5 goto ;

: go 5 1 6 goto ; go
bye

Output:

line 1 --> item6 item1 item7 item2 item8 item3 item9 item4 item10 item5
line 2 --> item6 item1 item7 item2 item8 item3 item9 item4 item10 item5
line 3 --> item6 item1 item7 item2 item8 item3 item9 item4 item10 item5
line 4 --> item6 item1 item7 item2 item8 item3 item9 item4 item10 item5
line 5 --> item6 item1 item7 item2 item8 item3 item9 item4 item10 item5


\ works with ficl, pfe, gforth, bigforth, and vfx.
\ swiftforth may crash, iforth does not function.

: create_goto create 4 allot does> r> drop @ >r ;
: mark_goto here ' >body ! ; immediate

create_goto goto1
create_goto goto2
create_goto goto3
create_goto goto4
create_goto goto5
create_goto goto6
create_goto goto7
create_goto goto8
create_goto goto9
create_goto stop_here

:noname
mark_goto goto1   s" iteration " type dup . s" --> " type
                  s" goto1 " type   goto3
mark_goto goto2   s" goto2 " type   goto4
mark_goto goto3   s" goto3 " type   goto5
mark_goto goto4   s" goto4 " type   goto6
mark_goto goto5   s" goto5 " type   goto7
mark_goto goto6   s" goto6 " type   goto8
mark_goto goto7   s" goto7 " type   goto9
mark_goto goto8   s" goto8 " type   stop_here
mark_goto goto9   s" goto9 " type   goto2 ; drop

:noname  mark_goto stop_here
  cr 2dup = if 2drop exit then 1+ goto1
\ cr 2dup = if 2drop bye  then 1+ goto1  \ for swiftforth
; drop

: go goto1 ;
5 1 go

bye

Output:

iteration 1 --> goto1 goto3 goto5 goto7 goto9 goto2 goto4 goto6 goto8
iteration 2 --> goto1 goto3 goto5 goto7 goto9 goto2 goto4 goto6 goto8
iteration 3 --> goto1 goto3 goto5 goto7 goto9 goto2 goto4 goto6 goto8
iteration 4 --> goto1 goto3 goto5 goto7 goto9 goto2 goto4 goto6 goto8
iteration 5 --> goto1 goto3 goto5 goto7 goto9 goto2 goto4 goto6 goto8


Minimal Option
Although Forth was designed to be a structured programming language it is simple to add a generic jump anywhere. The Forth dictionary of WORDs is essentially a linked list of labels. We can find the execution token for any label in the dictionary with the ['] operator and jump to it with the keyword EXECUTE.

: GOTO     [']  EXECUTE ;

TEST

: WORLD ." World!" ;
: HELLO ." Hello" ;

GOTO CR GOTO HELLO GOTO SPACE GOTO WORLD
Hello World!

Fortran

Fortran programmers have long been condemned for their usage of GO TO label (a label being an integer only: no text) which can be to any labelled statement in a program unit. That is, within a subroutine (or function) or within the main line. There is no provision for referencing labels outside a program unit, as with jumping from one subroutine into another. Even when F90 introduced the ability to nest routines whereby a routine is defined within another and the inner routine can reference the containing routine's variables, it is not allowed to reference its labels - purely as an intended restriction and despite this being allowed in Algol and PL/I. However, the "alternate return" protocol can be used, whereby a routine is invoked with additional parameters that are not numbers but labels within the calling routine. The called routine can then execute a normal RETURN statement, or say RETURN 2 to return not to the calling location but to the second nominated label in the invocation. By this means, the called routine can jump to some location in the calling routine, in the same way that in READ (IN,*,ERR = 666) X provides an alternate return for error conditions.

Early Fortran was devised without much worry over "structured" constructions, so it was quite possible to jump into the scope of a DO-loop (perhaps after jumping out) and subsequent results would depend on the method used by the compiler to control the number of iterations that are made. With F77 and the IF ... THEN ... ELSE ... ENDIF constructions, possibly nested, came the chance to jump from one clause to another - say from the ELSE clause to part-way into the THEN clause. As with the DO-loop violation, this behaviour gathered opprobrium and although allowed by the syntax is likely deemed to be an error by later compilers.

As for "Jump Anywhere", some implementations of the computed-GO TO statement really did do a calculate-offset-and-jump so that GO TO (665,666,667), HOP would produce an array of three addresses indexed by the value of HOP, and if HOP was outside the range of one to three, whatever was found at the indexed location would be taken as the address to jump to... Even worse opportunities might be exercised via the ASSIGN statement, which "assigns" a label to an integer variable as in ASSIGN 666 TO THENCE - effectively, storing the machine address associated with label 666 to variable THENCE. Such a variable is open to adjustment and might be available via a COMMON storage area to other routines, whose execution of GO TO THENCE is sure to prove interesting.

FreeBASIC

The default and most modern dialect of FreeBASIC (-lang fb) supports the 'Goto' keyword either on its own or within the following constructs:

  • On (Local) Error Goto (requires compilation with -e, -ex or -exx switch)
  • On ... Goto
  • If ... Goto (deprecated)


'Goto' is always followed by a label which must be a valid identifier and can only jump to locations at the same level (either within the same procedure or within module-level code).

However, a compiler error or warning is issued if 'Goto' skips a variable definition but not the end of the variable's scope. This is intended to prevent potential accesses to unconstructed or uninitialized variables and ensures that automatic destruction never happens to such variables.

'On (Local) Error Goto' can be used for error handling at module level or procedure level. In theory, the 'Local' keyword should restrict error handling to procedure level but currently is ignored by the compiler. It still works with the 'Error' statement, which forces an error to be generated, even if the above compiler switches are not used

'On ... Goto' allows one to define a 'jump table' which jumps to a specific label depending on the value of a variable or expression. A value of 1 will jump to the first label, a value of 2 to the second label and so on.

'If ... Goto' is shorthand for 'If ... Then Goto' in a single line 'If' statement. It's an old construct which is now deprecated but still works.

In the other dialects of FreeBASIC, 'Goto' behaves in a similar fashion except that:

  • In the -lang qb dialect, labels can still be line numbers for compatibility with old QuickBasic code.
  • 'Goto' is allowed to skip uninitialized variables in the -lang qb and -lang fblite dialects because these dialects do not support nested scopes and all local variable declarations are moved to the top of their procedures.
  • The -lang qb dialect also supports the 'Gosub' and 'On ... Gosub' constructs which (on execution of the 'Return' statement) return to the location from which they were called. In the -lang fblite dialect these constructs are disabled by default - you have to use the 'Option Gosub' statement to turn them on or 'Option NoGosub' statement to turn them off again.
  • The -lang qb and -lang fblite dialects also support the 'Resume' and 'Resume Next' statements in conjunction with the 'On (Local) Error Goto' statement (requires compilation with -ex or -exx switch). These statements resume execution at the current or next line, respectively, following the execution of the error handling routine.


None of the FreeBASIC dialects support jumping out of multiple procedures or continuations. However, you can leave procedures prematurely (and rejoin the calling procedure or module-level code) using the 'Exit ... ' or 'Return ...' statements.

The following program demonstrate the use of the various 'Goto' constructs in the -lang fb dialect only:

' FB 1.05.0 Win64

' compiled with -lang fb (the default) and -e switches

Sub MySub()
  Goto localLabel
  Dim a As Integer = 10  '' compiler warning that this variable definition is being skipped
  localLabel:
  Print "localLabel reached"
  Print "a = "; a  '' prints garbage as 'a' is uninitialized
End Sub

Sub MySub2()
  On Error Goto handler
  Open "zzz.zz" For Input As #1 '' this file doesn't exist!
  On Error Goto 0 '' turns off error handling
  End

  handler:
  Dim e As Integer = Err '' cache error number before printing message
  Print "Error number"; e; " occurred - file not found"
End Sub

Sub MySub3()
  Dim b As Integer = 2
  On b Goto label1, label2 '' jumps to label2

  label1:
  Print "Label1 reached"
  Return '' premature return from Sub

  label2:
  Print "Label2 reached"
End Sub

Sub MySub4()
  Dim c As Integer = 3
  If c = 3 Goto localLabel2 '' better to use If ... Then Goto ... in new code
  Print "This won't be seen"
  localLabel2:
  Print "localLabel2 reached"
End Sub

MySub
MySub2
MySub3
MySub4
Print
Print "Pres any key to quit"
Print
Output:
localLabel reached
a =  5
Error number 2 occurred - file not found
Label2 reached
localLabel2 reached

FutureBasic

FB supports both goto and gosub.

The goto statement causes program execution to continue at the statement at the indicated line number or statement label. The target statement must be within the same "scope" as the goto statement (i.e., they must both be within the "main" part of the program, or they must both be within the same local function). Also, you should not use goto to jump into the middle of any "block" statement structures (such as for...next, select...end select, long if...end if, etc.).

The gosub statement should include a return statement; return causes execution to continue at the statement following the gosub statement.

All that said, don't use spaghetti code -- use functions. You can still by spark plugs for a 1985 Yugo, but why?

window 1

print "First line."
gosub "sub1"
print "Fifth line."
goto "Almost over"
"sub1"
print "Second line."
gosub "sub2"
print "Fourth line."
return
"Almost over"
print "We're just about done..."
goto "Outa here"
"sub2"
print "Third line."
return
"Outa here"
print "... with goto and gosub, thankfully."

HandleEvents

Output:

First line.
Second line.
Third line.
Fourth line.
Fifth line.
We're just about done...
... with goto and gosub, thankfully.

Go

Go has labelled 'break' and 'continue' statements which enable one to easily break out of a nested loop or continue with a containing loop.

Go also has a 'goto' statement which allows one to jump to a label in the same function. However, 'goto' is not allowed to jump over the creation of new variables or to jump to a label inside a block from outside that block.

For example:

package main

import "fmt"

func main() {
    outer:
    for i := 0; i < 4; i++ {
        for j := 0; j < 4; j++ {
            if i + j == 4 { continue outer }
            if i + j == 5 { break outer }
            fmt.Println(i + j)
        }
    }

    k := 3
    if k == 3 { goto later }
    fmt.Println(k)  // never executed
    later:
    k++
    fmt.Println(k)
}
Output:
0
1
2
3
1
2
3
2
3
3
4
package main

import "fmt"

func main() {
	// defer run last
	defer fmt.Println("World")
	fmt.Println("Hello")
	// goto 
	i := 0
Here:
	if i < 5 {
		fmt.Println(i)
		i++
		goto Here
	} else {
		fmt.Println("i is less than 5")
	}
	// break & continue
	number := 0
	for {
		number++
		if number > 3 {
			break
		}
		if number == 2 {
			continue
		}
		fmt.Printf("%v\n", number)
	}
}
// init
func init() {
	fmt.Println("run first")
}

Harbour

Harbour has no labels and goto statements. The exit statements allows leave the current loop and doesn't contain any label where to go.

Haskell

Haskell being pure functional language doesn't need labels or goto's. However it is flexible and powerful enough to implement imperative constructions using monads. Hackage has a library GoToT-transformers. This module provides a Goto monad and corresponding monad transformer that allow the user to transfer the flow of execution from an arbitrary point of a monadic computation to another monadic computation. It works with any monad, not only with IO.

We show possible implementation of goto, given here, with some simplifications.

First some boilerplate, where we define labels and goto "operator".

import Control.Monad.Cont

data LabelT r m = LabelT (ContT r m ())

label :: ContT r m (LabelT r m)
label = callCC subprog
  where subprog lbl = let l = LabelT (lbl l) in return l

goto :: LabelT r m -> ContT r m b
goto (LabelT l) = const undefined <$> l

runProgram :: Monad m => ContT r m r -> m r
runProgram program = runContT program return

Here is example of using labels in IO:

main = runProgram $
  do
    start <- label
    lift $ putStrLn "Enter your name, please"
    name <- lift $ getLine
    if name == ""
      then do lift $ putStrLn "Name can't be empty!"
              goto start
      else lift $ putStrLn ("Hello, " ++ name)
Output:
λ> main
Enter your name, please

Name can't be empty!
Enter your name, please
John
Hello, John

We can build tiny EDSL to get rid of explicit lifting and to add refferences:

import Data.IORef

readInt = lift $ readLn >>= newIORef
get ref = lift $ readIORef ref
set ref expr = lift $ modifyIORef ref (const expr)
output expr = lift $ putStrLn expr

and implement famous Euclid's algorithm as an imperative program:

gcdProg = runProgram $ callCC $ \exit ->          -- <--------+
  do                                              --          |
    start <- label                                -- <-----+  |
    output "Enter two integers, or zero to exit"  --       |  | 
    nr <- readInt                                 --       |  | 
    n <- get nr                                   --       |  | 
    when (n == 0) $                               --       |  | 
      do output "Exiting"                         --       |  | 
         exit ()                                  -- ---------+
    mr <- readInt                                 --       |
    loop <- label                                 -- <--+  | 
    n <- get nr                                   --    |  | 
    m <- get mr                                   --    |  | 
    when (n == m) $                               --    |  | 
      do output ("GCD: " ++ show n)               --    |  | 
         goto start                               -- ------+
    when (n > m) $ set nr (n - m)                 --    | 
    when (m > n) $ set mr (m - n)                 --    | 
    goto loop                                     -- ---+
Output:
λ> gcdProg
Enter two integer numbers, or zero to exit
12
15
GCD: 3
Enter two integer numbers, or zero to exit
0
Exiting

In native Haskell such flow jumps are done by function calls:

gcdFProg = start
  where
    start = do
      putStrLn "Enter two integers, or zero to exit"
      n <- readLn
      if n == 0
        then
          putStrLn "Exiting"
        else do
          m <- readLn
          putStrLn $ "GCD: " ++ show (loop n m)
          start

loop n m 
  | n == m = n
  | n < m  = loop n (m-n)
  | n > m  = loop (n-m) m

Or without explicit recursion and branching:

import Control.Applicative
import Control.Monad.Trans.Maybe

gcdFProg2 = forever mainLoop <|> putStrLn "Exiting"
  where
    mainLoop = putStrLn "Enter two integers, or zero to exit" >>
               runMaybeT process >>=
               maybe empty (\r -> putStrLn ("GCD: " ++ show r))

    process = gcd <$> (lift readLn >>= exitOn 0) <*> lift readLn

    exitOn n x = if x == n then empty else pure x

i

//'i' does not have goto statements, instead control flow is the only legal way to navigate the program.
concept there() {
	print("Hello there")
	return //The return statement goes back to where the function was called.
	print("Not here")
}

software {
	loop {
		break //This breaks the loop, the code after the loop block will be executed next.
		
		print("This will never print")
	}
	
	loop {
		loop {
			loop {
				break //This breaks out of 1 loop.
			}
			print("This will print")
			break 2 //This breaks out of 2 loops.
		}
		print("This will not print")
	}
	
	
	//Move to the code contained in the 'there' function.
	there() 
}

J

J allows control to be passed to any named verb at any time. When the verb completes, control returns to the caller, unless an unhandled exception was raised (or unless a handled exception was raised, where the handler is outside the caller).

For example:

F=: verb define
  smoutput 'Now we are in F'
  G''
  smoutput 'Now we are back in F'
)

G=: verb define
  smoutput 'Now we are in G'
  throw.
)

   F''
Now we are in F
Now we are in G

J also supports jumps to labels within a definition (but makes them a bit tedious to express, which has been rather successful at discouraging their use):

H=: verb define
  smoutput 'a'
  label_b.
  smoutput 'c'
  goto_f.
  label_d.
  smoutput 'e' return.
  label_f.
  smoutput 'g'
  goto_d.
  smoutput 'h'
)

   H''
a
c
g
e

Java

The closest thing that Java has to a "goto" is labelled loops:

loop1: while (x != 0) {
    loop2: for (int i = 0; i < 10; i++) {
        loop3: do {
            //some calculations...
            if (/*some condition*/) {
                //this continue will skip the rest of the while loop code and start it over at the next iteration
                continue loop1;
            }
            //more calculations skipped by the continue if it is executed
            if (/*another condition*/) {
                //this break will end the for loop and jump to its closing brace
                break loop2;
            }
        } while (y < 10);
        //loop2 calculations skipped if the break is executed
    }
    //loop1 calculations executed after loop2 is done or if the break is executed, skipped if the continue is executed
}

It's frowned upon to use exceptions for non-exceptional paths, so get ready to frown at this fizz-buzz player that makes use of try/catch/finally to jump to the right places for printing:

public class FizzBuzzThrower {
    public static void main( String [] args ) {
        for ( int i = 1; i <= 30; i++ ) {
            try {
                String message = "";
                if ( i % 3 == 0 ) message = "Fizz";
                if ( i % 5 == 0 ) message += "Buzz";
                if ( ! "".equals( message ) ) throw new RuntimeException( message );
                System.out.print( i );
            } catch ( final RuntimeException x ) {
                System.out.print( x.getMessage() );
            } finally {
                System.out.println();
            }
        }
    }
}

jq

Works with: jq version version with "break" statement

jq supports named labels ("label $NAME") and break statements ("break $NAME"). Usage follows the pattern:

label $out | ... break $out ...

When, during program execution, a "break" statement is encountered, the program continues as though the nearest `label $label_name` statement on the left produced `empty`.

The label specified by the "break" statement has to be visible (in the sense of being within scope) at the break statement.

Break statements are used to interrupt a generator. For example, to emit the least positive integer satisfying sin(1/N) == (1/N) using IEEE 64-bit arithmetic:

label $out | 1e7 | while(true; .+1) | if (1/.) | . == sin then (., break $out) else empty end

Here, the "while" filter is an unbounded generator. The answer is 46530688.

The main reason why jq has a "break" statement is so that various control structures, such as the short-circuiting control structures "any" and "all", can be implemented in jq itself.

Indeed, a better way to solve the type of problem mentioned above is by using one of the jq-provided control structures. For example, the above problem can be solved more succinctly and transparently using until/2:

1e7 | until(1/. | . == sin; .+1)

Julia

Julia provides the @goto and @label macros for goto within functions but these cannot be used at the global level or to jump from one function to another. The macros can however be used for a typical use of @goto -- jumping out to a specific level from nested loops within a function.

function example()
    println("Hello ")
    @goto world
    println("Never printed")
    @label world
    println("world")
end

Kotlin

Kotlin does not have a 'goto' statement but does have labelled 'break' and 'continue' statements which enable one to easily break out of a nested loop or continue with a containing loop.

Kotlin also has a labelled 'return' statement to return from a nested function or lambda expression.

For example:

// version 1.0.6

fun main(args: Array<String>) {
    intArrayOf(4, 5, 6).forEach lambda@ {
        if (it == 5) return@lambda
        println(it)
    }
    println()
    loop@ for (i in 0 .. 3) {
        for (j in 0 .. 3) {
            if (i + j == 4) continue@loop
            if (i + j == 5) break@loop
            println(i + j)
        }
    }
}
Output:
4
6

0
1
2
3
1
2
3
2
3
3

Lingo

  • Lingo does not support jumping to markers ("goto").
  • Lingo supports "unwinding the call stack" via the abort command that exits the current call stack:
on foo
  abort()
end
  
on bar ()
  foo()
  put "This will never be printed"
end
  • Rarely used, but Lingo supports saving a continuation via the play ... play done construct:
on testPlayDone ()

  -- Start some asynchronous process (like e.g. a HTTP request).
  -- The result might be saved in some global variable, e.g. in _global.result
  startAsyncProcess()

  -- pauses execution of current function
  play(_movie.frame)

  -- The following will be executed only after 'play done' was called in the asynchronous process code
  put "Done. The asynchronous process returned the result:" && _global.result
end

Logtalk

Jumps are limited to Exceptions.

Lua

Lua 5.2 introduced a goto statement along with labels. It was somewhat controversially implemented instead of a continue keyword, but it is more flexible and supports other types of jumps as well. goto only supports statically-defined labels.

-- Forward jump
goto skip_print
print "won't print"
::skip_print::

-- Backward jump
::loop::
print "infinite loop"
goto loop

-- Labels follow the same scoping rules as local variables, but with no equivalent of upvalues
goto next
do
    ::next:: -- not visible to above goto
    print "won't print"
end
::next:: -- goto actually jumps here

-- goto cannot jump into or out of a function
::outside::
function nope () goto outside end -- error: no visible label 'outside' for <goto> at line 2

goto inside
function nope () ::inside:: end -- error: no visible label 'inside' for <goto> at line 1

-- Convenient for breaking out of nested loops
for i = 1, 10 do
    for j = 1, 10 do
        for k = 1, 10 do
            if i^2 + j^2 == k^2 then
                print(("found: i=%d j=%d k=%d"):format(i, j, k))
                goto exit
            end
        end
    end
end
print "not found"
::exit::

M2000 Interpreter

We can use basic like numbers, and Goto, On Goto, Gosub, On Gosub, and an Exit For to specific label.

We can place statements right in a label if is numeric. If label is not numeric we can place rem only using ' or \

After Else and Then we can place number to jump (same as Goto number). Goto can't take variable. We can use On Goto to use an expression to choose label (we can place numbers or named labels)

Using GOTO and GOSUB

Module Checkit {
      Module Alfa {
            10 Rem this code is like basic
            20 Let K%=1
            30 Let A=2
            40 Print "Begin"
            50 On K% Gosub 110
            60 If A=2 then 520
            70 For I=1 to 10
            80 if i>5 then exit for 120
            90 Gosub 110
            100 Next i 
            110 On A Goto 150,  500
            120 Print "This is the End ?"
            130 Return
            150 Print "from loop pass here", i
            160 Return
            200 Print "ok"
            210 Return
            500 Print "Routine 500"
            510 Goto 200
            520 Let A=1
            530 Gosub 70
            540 Print "Yes"
      }
      Alfa
      \\ this can be done. Code executed like it is from this module
      \\ because 200 is a label inside code of Module Checkit
      \\ and search is not so smart. After first search. position saved in a hash table
      Gosub 200  ' print "ok"
      Gosub 200  ' print "ok"
}
Checkit

Simulate Run Basic Entry

Module LikeRunBasic { 
      for i = 1 to 10
      if i = 5 then goto label5
      next i
      end
       
      label5:
      print i
      while i < 10 {
            if i = 6 then  goto label6
            i = i + 1
      }
      end
       
      label6:
      print i
      if i = 6 then goto finish
      print "Why am I here"
       
      finish:
      print "done"
}
LikeRunBasic

Simulate Go Entry

Module LikeGo {
      \\ simulate Go for
      \\ need to make var Empty, swapping uninitialized array item
      Module EmptyVar (&x) {
            Dim A(1)
            Swap A(0), x
      }
      Function GoFor(&i,  first, comp$, step$) {
            \\ checking for empty we now if i get first value
            if type$(i)="Empty" then {
                  i=first
                  } else {
                  i+=Eval(step$)
            }
            if Eval("i"+comp$) Else Exit
            =true
          }
      def i, j
      EmptyVar &i
      outer:
       {
            if GoFor(&i, 0, "<4", "+1") else exit
            EmptyVar &j
            {
                 if GoFor(&j, 0, "<4", "+1") else exit
                 if i+j== 4 then goto outer
                 if i+j == 5 then goto break_outer
                 print i+j
                 loop
            }
            loop
      } 
      break_outer:
      k = 3
      if k == 3 Then Goto later
      Print k  \\ never executed
      later:
      k++
      Print k
}
LikeGo


\\ or we can use For {} block and put label outer to right place
Module LikeGo {
      For i=0 to 3 {
            For j=0 to 3  {
                  if i+j== 4 then goto outer
                  if i+j == 5 then goto break_outer
                  print i+j
            }
            outer:            
      } 
      break_outer:
      k = 3
      if k == 3 Then Goto later
      Print k  \\ never executed
      later:
      k++
      Print k
}
LikeGo


Module LikeGo_No_Labels {
      For i=0 to 3 {
            For j=0 to 3  {
                  if i+j== 4 then exit ' exit breaks only one block
                  if i+j == 5 then break ' break breaks all blocks, but not the Module's block.
                  print i+j
            }         
      } 
      k = 3
      if k == 3 Else {
            Print k  \\ never executed
      }
      k++
      Print k
}
LikeGo_No_Labels

Mathematica/Wolfram Language

Mathematica and the Wolfram Language supports non-local jumps to a previous Catch[] (via Throw[]).

There is Goto[Label] function in Mathematica. This allows "jumps" to arbitrary locations within (the same or other) functions.

MBS

goto mylabel;

МК-61/52

БП	XX

XX is any address.

MIPS Assembly

j, jr, jal, and jalr are able to take you to anywhere in the CPU's address space.

  •   j 0xNNNNNNNN sets the program counter equal to 0xNNNNNNNN.
  •   jr $NN sets the program counter equal to the value in register $NN.
  •   jal 0xNNNNNNNN sets the program counter equal to 0xNNNNNNNN, and moves the old program counter plus 8 into register $ra.
  •   jalr $NN,0xNNNNNNNN sets the program counter equal to 0xNNNNNNNN and moves the old program counter plus 8 into register $NN.


Most of the time you won't be jumping to a specific address. You can place a label before any instruction, and a jump to that label is the same as a jump to the address of that instruction.

j GoHere             ;the assembler will convert this label to a constant memory address for us. 

nop                  ;     branch delay slot. This instruction would get executed DURING the jump. 
                     ;     But since NOP intentionally does nothing, it's not a problem.

GoHere:      
addiu $t0,1  ;this instruction is the first one executed after jumping.


Branches apply a signed offset to the current program counter. They are limited only by distance; scope does not exist in assembly. Typically you do not have calculate this offset yourself. The assembler will abstract this out of the hardware and let you use a label like you would with a j. The actual offset is calculated during the assembly process, which means you don't have to measure it yourself by counting bytes.

MUMPS

You can go to any point in any routine in the same namespace. In some implementations, you can even go between namespaces. It's not recommended though.

Some interpreters will allow you jump between blocks of the same depth. Others will let you leave, but not enter, a block.

 ;Go to a label within the program file
 Goto Label
 ;Go to a line below a label
 Goto Label+lines
 ;Go to a different file
 Goto ^Routine
 ;Go to a label within a different file
 Goto Label^Routine
 ;and with offset
 Goto Label+2^Routine
 ;
 ;The next two goto commands will both return error M45 in ANSI MUMPS.
NoNo
 For
 . Goto Out
Out Quit
 Goto NoNo+2

Neko

Neko supports colon terminated labels, and a builtin $goto(label). This builtin is special in that the label argument is not dereferenced as a normal Neko expression, but specifically as a label.

$print("start\n")
$goto(skip)
$print("Jumped over")
skip:
$print("end\n")

The NekoVM keeps exception and call stacks in sync when jumping across boundaries to code blocks, but may not include some initiating side effects. For instance, jumping past a try phrase into the middle of the code block (where the try is not evaluated) will not catch the catch of the try catch pair. There are other cases where $goto() can cross semantic boundaries; a practice best avoided.

Nim

Nim has exceptions and labelled breaks:

block outer:
  for i in 0..1000:
    for j in 0..1000:
      if i + j == 3:
        break outer

Oforth

Oforth has no goto and no labels.

Apart from exceptions handling (see exceptions tasks), Oforth has continue (to go to next loop) and break (to leave a loop).

Ol

No jumps in Ol because Ol is purely functional language.

Some portion of code can be restarted (as recursion) and skipped (as continuation).

; recursion:
(let loop ((n 10))
   (unless (= n 0)
      (loop (- n 1))))

; continuation
(call/cc (lambda (break)
   (let loop ((n 10))
      (if (= n 0)
         (break 0))
      (loop (- n 1)))))

(print "ok.")

PARI/GP

GP lacks gotos and continuations, but can break out of arbitrarily many nested loops with break(n) which can be used to simulate goto within a given function. It can also use local values or error to break out of several layers of function calls, if needed.

PARI inherits C's ability to goto or longjmp; the latter is used extensively in the library.

Perl

Perl's goto LABEL and goto EXPR are a little too powerful to be safe. Use only under extreme duress (actually, not even then). goto &SUB is esoteric but much more innocuous and can occasionally be handy.

sub outer {
    print "In outer, calling inner:\n";
    inner();
  OUTER:
    print "at label OUTER\n";
}

sub inner {
    print "In inner\n";

    goto SKIP;      # goto same block level
    print "This should be skipped\n";
  SKIP:
    print "at label SKIP\n";

    goto OUTER;     # goto whatever OUTER label there is on frame stack.
                    # if there isn't any, exception will be raised
    print "Inner should never reach here\n";
}

sub disguise {
    goto &outer;    # a different type of goto, it replaces the stack frame
                    # with the outer() function's and pretend we called
                    # that function to begin with
    print "Can't reach this statement\n";
}

print "Calling outer:\n";
outer();

print "\nCalling disguise:\n";
disguise();

print "\nCalling inner:\n";
inner();                # will die

Phix

In Phix, when absolutely necessary, gotos and labels can be implemented using inline assembly. Using this 'baroque' syntax is viewed as an effective means of dissuading novices from adopting goto as a weapon of choice. Note that pwa/p2js does not support #ilASM{} at all.

#ilASM{ jmp :%somelabel }
    ...
#ilASM{ :%somelabel }

The above shows a global label, which can only be declared in top-level code, not inside a routine, and can be referenced from anywhere.

Local labels are declared with a double colon (::) and referenced with a single colon

#ilASM{ jmp :local
            ...
       ::local }

They can only be referenced at the top level from within the same #ilASM construct, or anywhere within the routine where they are defined. Phix also supports anonymous local labels

#ilASM{ jmp @f
        ...
      @@: 
        ...
        jle @b }

There are also optional (global) labels:

#ilASM{ call :!optlbl
        [32]
          pop eax
        [64]
          pop rax
        []
            ...
       :!optlbl
        [32]
          push dword[esp]
        [64]
          push qword[rsp]
        []
          ret }

These are obviously more useful when the reference and declaration are in separate files: if the file containing the declaration is not included, the reference quietly resolves to 0. The above code shows how to duplicate the return address and discard on return, so that execution carries on at the next instruction if the definition is not present. Optional labels are most heavily used as part of the run-time diagnostics, for example pDiagN.e contains lines such as cmp edx,:!opXore92a which checks to see whether an invalid memory access wants mapping to a "variable has not been assigned a value" error (and retrieve the correct return address for any error that occurs at that specific location); if xor is not used/included, the instruction quietly resolves to cmp edx,0.

Lastly (for completeness) there are init labels, defined using

#ilASM{ :>init }

These are used by the VM (eg builtins\VM\pStack.e declares :>initStack) to specify initialisation code which must be run at startup. They can also be called like a normal global label.

Obviously there are also several hll keywords such as exit and return which can often be used to achieve the same effect in a much more structured fashion.

PicoLisp

PicoLisp supports non-local jumps to a previously setup environment (see exceptions) via 'catch' and 'throw', or to some location in another coroutine with 'yield' (see generator).

'quit' is similar to 'throw', but doesn't require a corresponding 'catch', as it directly jumps to the error handler (where the program may catch that error again).

There is no 'go' or 'goto' function in PicoLisp, but it can be emulated with normal list processing functions. This allows "jumps" to arbitrary locations within (the same or other) functions. The following example implements a "loop":

(de foo (N)
   (prinl "This is 'foo'")
   (printsp N)
   (or (=0 (dec 'N)) (run (cddr foo))) )

Test:

: (foo 7)
This is 'foo'
7 6 5 4 3 2 1 -> 0

PL/I

The goto statement causes control to be transferred to a labeled statement in the current or any outer procedure.

A goto statement cannot transfer control:

  • Into an inactive begin block.
  • From outside into a do group.


In structured programming, the only place where a goto can be is inside on units to handle exceptions without recursion.

on conversion goto restart;

PL/SQL

PL/SQL supports both GOTOs and structured exception handling:

DECLARE
    i number := 5;
    divide_by_zero EXCEPTION;
    PRAGMA exception_init(divide_by_zero, -20000);
BEGIN
    DBMS_OUTPUT.put_line( 'startLoop' );
    <<startLoop>>
        BEGIN    
            if i = 0 then
                raise divide_by_zero;
            end if;
            DBMS_OUTPUT.put_line( 100/i );
            i := i - 1;
            GOTO startLoop;
        EXCEPTION
        WHEN divide_by_zero THEN
            DBMS_OUTPUT.put_line( 'Oops!' );
            GOTO finally;
        END;
    <<endLoop>>
    DBMS_OUTPUT.put_line( 'endLoop' );    

    <<finally>>
    DBMS_OUTPUT.put_line( 'Finally' );
END;
/
Output:
startLoop
20
25
33.33333333333333333333333333333333333333
50
100
Oops!
Finally

PowerShell

A Break statement can include a label. If you use the Break keyword with a label, Windows PowerShell exits the labeled loop instead of exiting the current loop. The syntax for a label is as follows (this example shows a label in a While loop):

:myLabel while (<condition>) { <statement list>}

The label is a colon followed by a name that you assign. The label must be the first token in a statement, and it must be followed by the looping keyword, such as While.


In Windows PowerShell, only loop keywords, such as Foreach, For, and While can have a label.


Break moves execution out of the labeled loop. In embedded loops, this has a different result than the Break keyword has when it is used by itself. This schematic example has a While statement with a For statement:

    :myLabel while (<condition 1>) 
    {
        for ($item in $items) 
        { 
            if (<condition 2>) { break myLabel } 
            $item = $x   # A statement inside the For-loop
        }
    }
    $a = $c  # A statement after the labeled While-loop

If condition 2 evaluates to True, the execution of the script skips down to the statement after the labeled loop. In the example, execution starts again with the statement "$a = $c".

You can nest many labeled loops, as shown in the following schematic example.

:red while (<condition1>)
{
    :yellow while (<condition2>)
    {
        while (<condition3>)
        {
            if ($a) {break}
            if ($b) {break red}
            if ($c) {break yellow}
        }
        # After innermost loop
    }
    # After "yellow" loop
}
# After "red" loop

If the $b variable evaluates to True, execution of the script resumes after the loop that is labeled "red". If the $c variable evaluates to True, execution of the script control resumes after the loop that is labeled "yellow".

If the $a variable evaluates to True, execution resumes after the innermost loop. No label is needed.

Windows PowerShell does not limit how far labels can resume execution. The label can even pass control across script and function call boundaries.

PureBasic

OnErrorGoto(?ErrorHandler)
OpenConsole()
Gosub label4
Goto label3

label1:
Print("eins ")
Return

label2:
Print("zwei ")
Return

label3:
Print("drei ")

label4:
While i<3
  i+1
  Gosub label1 
  Gosub label2
Wend
Print("- ")
i+1
If i<=4 : Return : EndIf
x.i=Val(Input()) : y=1/x
Input()
End

ErrorHandler:
PrintN(ErrorMessage()) : Goto label4
Output:
eins zwei eins zwei eins zwei - drei -

Python

Python has both exceptions and generators but no unstructured goto ability.

The "goto" module was an April Fool's joke, published on 1st April 2004. Yes, it works, but it's a joke nevertheless. Please don't use it in real code! For those who like computer languages with a sense of humour it can be downloded here. It is well documented and comes with many examples. My favorite:

# Example 2: Restarting a loop:
from goto import goto, label
label .start
for i in range(1, 4):
    print i
    if i == 2:
        try:
            output = message
        except NameError:
            print "Oops - forgot to define 'message'!  Start again."
            message = "Hello world"
            goto .start
print output, "\n"

It goes the extra mile and adds a comefrom keyword. This should be used only if you are evil and proud of it. It is reported to have caused maintenance programmers to have so strongly believed themselves insane that it became so. They are now under strong medication in padded cells. Basically whenever the code passes a label it jumps to the comefrom point. For best results I advise writing the comefrom code as far as possible from the label and using no comments near the label.

QBasic

QBasic supports both goto and gosub.

Works with: QBasic version 1.1
Works with: BASIC256
Works with: Yabasic
PRINT "First line."
GOSUB sub1
PRINT "Fifth line."
GOTO Ending

sub1:
PRINT "Second line."
GOSUB sub2
PRINT "Fourth line."
RETURN

Ending:
PRINT "We're just about done..."
GOTO Finished

sub2:
PRINT "Third line."
RETURN

Finished:
PRINT "... with goto and gosub, thankfully."
END
Output:
Igual que la entrada de FutureBasic.

QB64

' Jumps in QB64 are inherited by Qbasic/ QuickBasic/ GWBasic
' here a GOTO demo  of loops FOR-NEXT and WHILE-WEND

Dim S As String, Q As Integer
Randomize Timer
0:
Locate 1, 1: Print "jump demostration"
Print "Press J to jump to FOR NEXT emulator or"
Print "L to jump to WHILE WEND emulator or"
Print "Q for quitting"
Print
S = UCase$(Input$(1))
Cls , Rnd * 7 + 1: Locate 7
Q = 0
If S = "Q" Then End
If S = "J" Then GoTo 1
If S = "L" Then GoTo 2
GoTo 0

1:
If Q = 0 Then Print "FOR NEXT Loop emulation"
Print " Q = "; Q
Q = Q + 1
If Q < 10 Then
    GoTo 1
Else
    Print "For Next emulation terminated":
    GoTo 0
End If

2:
If Q = 0 Then Print " WHILE WEND emulator"
Print " Q = 9 is ";
If Q = 9 Then
    Print "True"
    Print "WHILE WEND emulator terminated"
    GoTo 0
Else
    Print "False"
End If
Q = Q + 1
GoTo 2

Quackery

One way of thinking about Quackery is as an assembly language for a virtual Quack Processor. A Quack Processor is a Stack Processor which does not interact directly with computer memory, but sends requests to a co-processor that specialises in dynamic memory allocation and garbage collection of dynamic arrays. (In practice this is a pretty way of saying "lets Python (the language Quackery is implemented in) do the heavy lifting.").

In Quackery these dynamic arrays, which can be summoned at will, are called nests, and nests contain zero or more numbers (bigints), operators (op-codes), and nests. All nests are editable and executable, and execution consists of traversing a nest from left to right, putting numbers on the stack, performing operators and recursively traversing nests within nests.

This traversal cannot be modified directly, none of the operators can modify the pointer to the current nest or the offset into the nest. (One outcome of having a dynamic memory models is that instead of just using a memory address, you also need a pointer to indicate which nest you are referring to.)

Control flow is achieved by tampering with the call stack that the processor uses to store a nest pointer and offset pair each time it encounters a nest. These are the meta-flow operators, which can be thought of as "granting powers" to their calling nest.

So, for example, the word if conditionally skips over the next item in a nest, iff conditionally skips over the next two items in a nest, and else always skips over the next item in a nest, so you would use if (item) to create an if statement without an else clause, and iff (item) else (item) for one with an else clause.

They are defined, respectively as [ ]if[ ] is if, [ ]iff[ ] is iff, and [ ]else[ ] is else, where the meta-flow words ]if[, ]iff[, and ]else[ work by adding (or not adding) 1 or 2 to the offset on the pointer-offset pair on the top of the call stack.

These, and the rest of the meta-flow operators, are the tools with which the Quackery programmer can build new and novel control flow operators. The meta-flow word-set (used to build Quackery's "mix and match" control-flow word-set) lends itself to single-entry point into a nest, but can be subverted to do all sorts of shenanigans. It includes the word ]bail-by[, which removes a specified number of pointer+offset pairs from the call stack, intended for use by Quackery's exception handling word bail, (see Exceptions#Quackery) but available for mischief. Other control flow high jinks may require some deviousness.

The complete meta-flow word set is ]done[ ]again[ ]if[ ]iff[ ]else[ ]'[ ]this[ ]do[ ]bailby[

Quackery is an assembler insomuch as there is a direct, one to one, left to right correspondence between Quackery source code and the contents of the resultant nest, which is convenient. (There are a few simple-to-understand exceptions, and of course because the assembler is extensible, you can add more of those if you like, but generally it's easy to figure out where a specific item is in the nest.

As an example, this creates the control-flow word jump-into, which will start evaluation of a nest a specified distance in. done causes evaluation of the nest to terminate early (via ]done[, which removes a pointer-offset pair from the call stack) and again causes a jump to the start of the nest. (]again[ sets the number in the pair on the top of the call stack to 0.) So 5 jump-into should start at item number 5 in the nest that follows it, echoing the numbers 2 and 3 to the screen, then branch back to the start end echo the numbers 0 and 1, then terminate.

To achieve this, ]'[ advances the offset on top of the return stack, like ]else[, but also puts a copy of the item skipped over on the stack. (i.e. the nest following jump-into in the example) It puts this, with an offset of 0, onto the call stack (with ]do[. Then it uses ' ]else[ swap of to build a nest of the specified number of instances of ]else[, and puts that on the call stack, so that it will be evaluated after exiting jump-to, and increment the offset of the top of the call stack (i.e. the nest following jump-to) that number of times.

  [ ]'[ ]do[ ' ]else[ swap of ]do[ ] is jump-into ( n --> )

  5 jump-into 
    [ 0 echo 1 echo done 
(     0   1  2   3    4       offsets of each item )
(     5   6  7   8    9         from start of nest )
      2 echo 3 echo again ]
Output:
2301

Racket

Racket, being a descendant of Scheme, supports full continuations.

As a little example:

#lang racket
(define (never-divides-by-zero return)
  (displayln "I'm here")
  (return "Leaving")
  (displayln "Never going to reach this")
  (/ 1 0))

(call/cc never-divides-by-zero)

;    outputs:
;        I'm here
;        "Leaving"    (because that's what the function returns)

Here, return is the program continuation being passed to the function, when it is called, the string "Leaving" i the result of the function and the following code is never executed.

A much more complicated example done here Where we generate elements of a list one at a time:

#lang racket
;; [LISTOF X] -> ( -> X u 'you-fell-off-the-end-off-the-list)
(define (generate-one-element-at-a-time a-list)
  ;; (-> X u 'you-fell-off-the-end-off-the-list)
  ;; this is the actual generator, producing one item from a-list at a time
  (define (generator)
     (call/cc control-state)) 
  ;; [CONTINUATION X] -> EMPTY
  ;; hand the next item from a-list to "return" (or an end-of-list marker)'
  (define (control-state return)
     (for-each 
        (lambda (an-element-from-a-list)
           (set! return ;; fixed
             (call/cc
               (lambda (resume-here)
                 (set! control-state resume-here)
                 (return an-element-from-a-list)))))
        a-list)
     (return 'you-fell-off-the-end-off-the-list))
  ;; time to return the generator
  generator)

Relation

Relation has no jumps.

Retro

Retro allows the user to jump to any address.

:foo #19 &n:inc \ju...... #21 ;

When executed, the stack will contain 20; control does not return to the foo function.

Raku

(formerly Perl 6)

Label-based jumps

    outer-loop: loop {
        inner-loop: loop {
            # NYI # goto inner-loop if rand > 0.5; # Hard goto
            next inner-loop if rand > 0.5; # Next loop iteration
            redo inner-loop if rand > 0.5; # Re-execute block
            last outer-loop if rand > 0.5; # Exit the loop
            ENTER { say "Entered inner loop block" }
            LEAVE { say "Leaving inner loop block" }
        }
        ENTER { say "Entered outer loop block" }
        LEAVE { say "Leaving outer loop block" }
        LAST  { say "Ending outer loop" }
    }

Produces random output, but here's a representative run:

 Entered outer loop block
 Entered inner loop block
 Leaving inner loop block
 Entered inner loop block
 Leaving inner loop block
 Entered inner loop block
 Leaving inner loop block
 Leaving outer loop block
 Ending outer loop

Continuation-based execution

Continuations in Raku are currently limited to use in generators via the gather/take model:

    my @list = lazy gather for ^100 -> $i {
        if $i.is-prime {
            say "Taking prime $i";
            take $i;
        }
    }
    
    say @list[5];

This outputs:

 Taking prime 2
 Taking prime 3
 Taking prime 5
 Taking prime 7
 Taking prime 11
 Taking prime 13
 13

Notice that no further execution of the loop occurs. If we then asked for the element at index 20, we would expect to see 15 more lines of "Taking prime..." followed by the result: 73.

Failures and exceptions

Exceptions are fairly typical in Raku:

    die "This is a generic, untyped exception";

Will walk up the stack until either some `CATCH` block intercepts the specific exception type or we exit the program.

But if a failure should be recoverable (e.g. execution might reasonably continue along another path) a failure is often the right choice. The fail operator is like "return", but the returned value will only be valid in boolean context or for testing definedness. Any other operation will produce the original exception with the original exception's execution context (e.g. traceback) along with the current context.

    sub foo() { fail "oops" }
    my $failure = foo;
    say "Called foo";
    say "foo not true" unless $failure;
    say "foo not defined" unless $failure.defined;
    say "incremented foo" if $failure++; # exception

Produces:

 Called foo
 foo not true
 foo not defined
 oops
   in sub foo at fail.p6 line 1
   in block <unit> at fail.p6 line 2
 Actually thrown at:
   in any  at gen/moar/m-Metamodel.nqp line 3090
   in block <unit> at fail.p6 line 6

However, an exception can `.resume` in order to jump back to the failure point (this is why the stack is not unwound until after exception handling).

  sub foo($i) {
      if $i == 0 {
          die "Are you sure you want /0?";
      }
      say "Dividing by $i";
      1/$i.Num + 0; # Fighting hard to make this fail
  }
  
  for ^10 -> $n {
      say "1/$n  = " ~ foo($n);
  }
  
  CATCH {
      when ~$_ ~~ m:s/Are you sure/ { .resume; #`(yes, I'm sure) }
  }

This code raises an exception on a zero input, but then resumes execution, divides be zero and then raises a divide by zero exception which is not caught:

 Dividing by 0
 Attempt to divide 1 by zero using /
   in sub foo at fail.p6 line 6
   in block <unit> at fail.p6 line 10
 
 Actually thrown at:
   in sub foo at fail.p6 line 6
   in block <unit> at fail.p6 line 10

REXX

REXX signal

Note: some REXXes don't allow jumping into a DO loop, although the language specificiations appear to allow it,
as long as the END or the DO loop isn't executed.
The following used PC/REXX to illustrate this example.

/*REXX pgm demonstrates various jumps (GOTOs).  In REXX, it's a SIGNAL. */
say 'starting...'
signal aJump
say 'this statement is never executed.'

aJump:  say 'and here we are at aJump.'
                                           do j=1  to 10
                                           say  'j=' j
                                           if j==7 then signal bJump
                                           end  /*j*/
bJump:  say 'and here we are at bJump.'

signal cJump
say 'this statement is never executed.'
                                           do k=1 to 10
                                           say 'k=' k
                                   cJump:  say 'and here we are at cJump.'
                                           exit
                                           end  /*k*/
Output:
starting...
and here we are at aJump.
j= 1
j= 2
j= 3
j= 4
j= 5
j= 6
j= 7
and here we are at bJump.
and here we are at cJump.

compared to PL/I goto

After a rather longwinded discussion on the subject I offer here my view: Whereas PL/I disallows the use of GOTO to jump to anywhere

Compiler Messages                                                    
Message       Line.File Message Description                          
IBM1847I S     212.0    GOTO target is inside a (different) DO loop. 

Rexx is very liberal as to the use of Signal.

  As mentioned above some implementations may have restrictions on that.

This Signal jumps into a Do loop inside a Procedure:

i=13                            
signal label                    
say 'This is never executed'    
sub: Procedure Expose i         
  Do i=1 To 10;                 
label:                          
    Say 'label reached, i='i    
    Signal real_start           
    End
  Return                        
 real_start:

Without the 'Signal real_start' which leads us out of the control structure the program would end with a syntax error when encountering the End correponding to the Do.

I recommend to use Signal only for condition handling and 'global' jumps to labels that are not within some structured constructs such as Do...End An example:

/* REXX *************************************************************** 
* 12.12.2012 Walter Pachl                                               
**********************************************************************/ 
Signal On Syntax                                                        
Parse Upper Arg part                                                    
If part<>'' Then                                                        
  Interpret 'Signal' part                                               
  Say 'Executing default part'                                          
  Signal eoj                                                                  
a:Say 'executing part A'                                                
  Signal eoj                                                
b:Say 'executing part B'                                                
  Signal eoj                                                                             
Syntax:                                                                 
  Say 'argument must be a or b or omitted'
  Exit
eoj: say 'here we could print statistics'

This can be useful when the different parts of the program span a few pages. Also a Signal eoj in order to Exit from any point in the program to some final activities can be useful.

Ring

Ring has no labels and goto statements. The exit statements allows leave the current loop and doesn't contain any label where to go.

Robotic

There are multiple ways to use labels and goto statements.

Simple

A simple example of labels and goto:

. "The label 'touch' is used to let the player touch the robot"
. "to execute the following"
end
: "touch"
goto "label_b"

: "label_a"
* "Label A was reached"
end

: "label_b"
* "Label B was reached"
end

It prints "Label B was reached", skipping "label_a" entirely.

Conditional

This will jump to a given label, depending on the condition of "local1":

set "local1" to 2
end
: "touch"
if "local1" = 1 then "label_a"
if "local1" = 2 then "label_b"
end

: "label_a"
* "Label A was reached"
end

: "label_b"
* "Label B was reached"
end

Since "local1" equals 2, it prints "Label B was reached".

Label Zapping

When you goto a label, it chooses the top-most label name in the code. However, with the use of "zap" and "restore", we can use the same label name multiple times in our code:

end
: "touch"
goto "label_a"

: "label_a"
* "Label A was reached"
zap "label_a" 1
end

: "label_a"
* "Alternate Label A was reached"
restore "label_a" 1
end

When the first label is reached, it zaps "label_a" once. This allows us to reach the second label below. Conversely, restoring "label_a" allows us to go back to the first label once more.

Subroutines

With subroutines, we can jump to a given label and come back to where we left off after we called the inital "goto" statement. To use these, the labels and the string supplied in the "goto" statements must have a number sign (#):

. "The 'wait' statements are used to demonstrate what is happening"
set "local1" to 1
end
: "touch"
goto "#label_a"
wait for 50
* "Done with Label A"
wait for 50
goto "#label_b"
wait for 50
* "Skipped finishing Label B and C"
end

: "#label_a"
* "Label A was reached"
goto "#return"

: "#label_b"
* "Label B was reached"
wait for 50
goto "#label_d"

: "#label_c"
* "Label C was reached"
goto "#return"

: "#label_d"
* "Label D was reached"
goto "#top"

The following is printed out in order:

Label A was reached
Done with Label A
Label B was reached
Label D was reached
Skipped finishing Label B and C

Using "#return", we go back up to the last "goto" statement called. However, using "#top" will ignore all the other subroutines called previously and go straight back to the first "goto" statement that started it all (in this case, goto "#label_b").

Ruby

Ruby programs almost never use continuations. MRI copies the call stack when it saves or calls a continuation, so continuations are slow.

The next example abuses a continuation to solve FizzBuzz#Ruby. It is slower and more confusing than an ordinary loop.

Library: continuation
require 'continuation' unless defined? Continuation

if a = callcc { |c| [c, 1] }
  c, i = a
  c[nil] if i > 100

  case 0
  when i % 3
    print "Fizz"
    case 0
    when i % 5
      print "Buzz"
    end
  when i % 5
    print "Buzz"
  else
    print i
  end

  puts
  c[c, i + 1]
end

This code uses the Continuation object c to jump to the top of the loop. For the first iteration, callcc creates c and returns [c, 1]. For later iterations, callcc returns [c, i + 1]. For the last iteration, callcc returns nil to break the loop.

SNOBOL4

Branches are the only kind of control structure in SNOBOL4. They come in three flavours (and one compound one):

  • :(LABEL_UNCONDITIONAL)
  • :S(LABEL_ON_SUCCESS)
  • :F(LABEL_ON_FAILURE)
  • :S(LABEL_ON_SUCCESS)F(LABEL_ON_FAILURE) or :F(LABEL_ON_FAILURE)S(LABEL_ON_SUCCESS)
* Demonstrate an unconditional branch.
      OUTPUT = "Unconditional branch."  :(SKIP1.START)
      OUTPUT = "This will not display."

* Demonstrate a branch on success.
SKIP1.START v = 1
SKIP1.LOOP  gt(v, 5)                 :S(SKIP2.START)
            OUTPUT = "Iteration A" v
            v = v + 1                :(SKIP1.LOOP)

* Demonstrate a branch on failure.
SKIP2.START v = 1
SKIP2.LOOP  le(v, 5)                 :F(SKIP3.START)
            OUTPUT = "Iteration B" v
            v = v + 1                :(SKIP2.LOOP)

* Demonstrate a combined branch.
* Demonstrate also an indirect branch.
SKIP3.START v = 0
            label = "SKIP3.LOOP"
SKIP3.LOOP  v = v + 1
            le(v, 5)                 :S(SKIP3.PRINT)F(EXIT)
SKIP3.PRINT OUTPUT = "Iteration C" v :($label)

EXIT OUTPUT = "Goodbye"

END
Output:
Unconditional branch.
Iteration A1
Iteration A2
Iteration A3
Iteration A4
Iteration A5
Iteration B1
Iteration B2
Iteration B3
Iteration B4
Iteration B5
Iteration C1
Iteration C2
Iteration C3
Iteration C4
Iteration C5
Goodbye

SPL

In SPL jumps can be non-conditional and conditional. This is an example of non-conditional jump to label "myLabel":

myLabel ->
...
:myLabel

This is an example of conditional jump to label "4", which is done if a=0:

4 -> a=0
...
:4

In SPL it is possible not only jump, but also visit a label. "Visiting" a label means that program execution can be returned back to the place from where label was visited. This is an example of visiting label "label 55":

label 55 <->
#.output("1")
:label 55
#.output("2")
<-

and output is:

Output:
2
1
2

SSEM

The SSEM provides two jump instructions: the absolute jump 000 <operand> to CI and the relative jump 100 Add <operand> to CI. The operand in both cases is a memory address, whose contents are to be either loaded into the CI (Current Instruction) register or else added to it. Since CI is incremented after an instruction is executed, not before, the value stored at the operand address must be one less than the value we actually want. For example, this code accomplishes a jump to absolute address 20:

10000000000000000000000000000000   0. 1 to CI
11001000000000000000000000000000   1. 19

and this accomplishes a relative jump forward by five words:

10000000000001000000000000000000  0. Add 1 to CI
00100000000000000000000000000000  1. 4

Tcl

Tcl has both exceptions and (from 8.6 onwards) generators/coroutines but no unstructured goto ability. However, the main case where it might be desired, coding a general state machine, can be handled through metaprogramming (as discussed at some length on the Tcler's Wiki) so the absence is not strongly felt in practice.

TXR

Translation of: Common Lisp

TXR Lisp has a tagbody similar to Common Lisp. Like the Common Lisp one, it establishes an area of the program with forms labeled by symbols or numbers. The forms can branch to these symbols or numbers using go.

When a form initiates a branch, it is gracefully abandoned, which means that unwinding takes place: unwind-protect clean-up forms are called. Once the form is abandoned, control then transfers to the target form.

A go transfer may be used to jump out of a lexical closure, if the tagbody is still active. If a closure is captured in a tagbody which then terminates, and that closure is invoked, and tries to use go to jump to adjacent forms in that terminated tagbody, it is an error. An example of this follows, from an interactive session:

1> (let (fun)
      (tagbody
        again
        (set fun (lambda () (go again))))
      [fun])
** expr-1:4: return*: no block named #:tb-dyn-id-0028 is visible
** during evaluation of form (return* #:tb-id-0024
                                      0)
** ... an expansion of (go again)
** which is located at expr-1:4

The above error messages reveal that TXR Lisp's tagbody is implemented by macros, and relies on a dynamic block return. It is provided mainly for compatibility; Common Lisp users using TXR Lisp may find it handy.

If the tagbody is still active when the lambda tries to perform a go</code, it works:

2> (let (fun)
      (tagbody
        (set fun (lambda () (go out)))
        [fun]
        (put-line "this is skipped")
        out
        (put-line "going out")))
going out
nil


The translated Common Lisp example follows:

(tagbody
  beginning
    (put-line "I am in the beginning")
    (usleep 1000000)
    (go end)
  middle
    (put-line "I am in the middle")
    (usleep 1000000)
    (go beginning)
  end
    (put-line "I am in the end")
    (usleep 1000000)
    (go middle))
Output:
I am in the beginning
I am in the end
I am in the middle
I am in the beginning
I am in the end
I am in the middle
I am in the beginning
...

VBA

Public Sub jump()
    Debug.Print "VBA only allows"
    GoTo 1
    Debug.Print "no global jumps"
1:
    Debug.Print "jumps in procedures with GoTo"
    Debug.Print "However,"
    On 2 GoSub one, two
    Debug.Print "named in the list after 'GoSub'"
    Debug.Print "and execution will continue on the next line"
    On 1 GoTo one, two
    Debug.Print "For On Error, see Exceptions"
one:
    Debug.Print "On <n> GoTo let you jump to the n-th label"
    Debug.Print "and won't let you continue."
    Exit Sub
two:
    Debug.Print "On <n> GoSub let you jump to the n-th label": Return
End Sub
Output:
VBA only allows
jumps in procedures with GoTo
However,
On <n> GoSub let you jump to the n-th label
named in the list after 'GoSub'
and execution will continue on the next line
On <n> GoTo let you jump to the n-th label
and won't let you continue.

VBScript

In VBScript, there is no goto statement. It is a good thing for structured programming.

V (Vlang)

V (Vlang) and 'goto':

1) 'Goto' used only with 'unsafe' statements.

2) 'Goto' only allowed unconditionally jumping to a label within the function it belongs to.

3) Labelled 'break' and 'continue' statements are among the preferred alternatives to 'unsafe goto' usage.

4) Labelled 'break' and 'continue' allow easy breaking out of a nested loop or continuing within a containing loop.

// Unsafe 'goto' pseudo example:

if x {
	// ...
	if y {
		unsafe {
			goto my_label
		}
	}
	// ...
}
my_label:

// Labelled 'break' and 'continue' example:

outer:
for idx := 0; idx < 4; idx++ {
	for jdx := 0; jdx < 4; jdx++ {
		if idx + jdx == 4 {continue outer}
		if idx + jdx == 5 {break outer}
		println(idx + jdx)
	}
}

VTL-2

VTL-2 doesn't do structured programming as such - the only control structure is the goto.
In VTL2, everything is an assignment - including gotos - which are effected by assigning to the system variable #.
The assigned value can be any valid expression - it need not be a constant.
If the expression evaluates to 0, the next statement is executed (or the program stops if there is no next statement).
If the expression evaluates to a line number present in the program, the program continues from that statement.
If the expression does not evaluate to a line number present in the program, the program continues with the next highest line number or stops if there is no line with a number higher that the expression.
The following program demonstrates this - prompiting the user for a label to goto. (In an expression, ? indicates a value should be read from the console, assigning to ? prints the assigned value)

1010 ?="@1010: Where to goto? ";
1020 #=?
1030 ?="@1030"
1040 #=1010
1050 ?="@1050"
1060 #=1010
2000 ?="@2000"
2010 ?="Exiting..."
Output:
@1010: Where to goto? 0
@1030
@1010: Where to goto? 1030
@1030
@1010: Where to goto? 1041
@1050
@1010: Where to goto? 1000+50
@1050
@1010: Where to goto? 9999

Wren

Wren has three jump statements:

  • break breaks out of a for or while loop
  • continue (from v0.4.0) jumps to the next iteration of a for or while loop
  • return returns from a function or method with or without a value.


If called from module level code, return exits the module or, if the script has only a single module, exits the script itself.

Wren also has fibers which are a bit like threads except that they are cooperatively scheduled - they only switch to another fiber when you tell them to. They are also lightweight, requiring just a small amount of memory for their stack which can be expanded if necessary.

A fiber can yield control back to the fiber that called it and be resumed later from where it left off.

The Fiber class also has a try method for catching errors (which won't be described here) and a static abort method which (unless caught) exits the script altogether if an error occurs.

var func = Fn.new {
    for (i in 1..10) {
        if (i == 1) continue // jumps to next iteration when 'i' equals 1
        System.print("i = %(i)")
        if (i > 4) break     // exits the loop when 'i' exceeds 4
    }
    for (j in 1..10) {
        System.print("j = %(j)")
        if (j == 3) return   // returns from the function when 'j' exceeds 3
    }
}

var fiber = Fiber.new {
    System.print("starting")
    Fiber.yield()            // yields control back to the calling fiber
    System.print("resuming") // resumes here when called again
    Fiber.abort("aborting")  // aborts the script
}

func.call()                  // calls the function
fiber.call()                 // calls the fiber
System.print("yielding")
fiber.call()                 // resumes the fiber
return                       // would exit the module (and script) without error but won't be reached
Output:
i = 2
i = 3
i = 4
i = 5
j = 1
j = 2
j = 3
starting
yielding
resuming
aborting
[./jump line 17] in new(_) block argument

XPL0

XPL0 has no goto statement. The closest statements are 'return' 'exit' and 'quit', the latter being used to jump out of a 'loop' from anywhere.

The 'return' command is implied at the end of a procedure, but when explicitly written, it returns to the caller from anywhere (and from a function it returns a value).

Of course there are implied jumps in 'if' statements and in all the looping statements.

An unusual feature is the Restart intrinsic. This is like the 'exit' statement, but it restarts the program. It's sometimes simpler to restart than to unwind nested procedure calls, if for instance an error is detected.

Certain errors, such as divide-by-zero, can cause a program to exit (unless disabled by the Trap intrinsic).

If a 'jump anywhere' must be done, inline assembly code is available.

Yabasic

Yabasic supports both goto and gosub.

Works with: QBasic
Works with: BASIC256
print "First line."
gosub sub1
print "Fifth line."
goto Ending

sub1:
print "Second line."
gosub sub2
print "Fourth line."
return

Ending:
print "We're just about done..."
goto Finished

sub2:
print "Third line."
return

Finished:
print "... with goto and gosub, thankfully."
end
Output:
Igual que la entrada de FutureBasic.

Z80 Assembly

Like the 6502, the Z80 can access the entire address space of the CPU. There are no page faults, segfaults, or W^X protections on the Z80 - anything the program counter "sees" will be executed as code. Writes to read-only memory are silently ignored for the most part, but certain machines such as the Game Boy use runtime writes to ROM as a means of bankswitching, so you'll need to be familiar with your computer's documentation.

Unconditional Jumping to a Fixed Location

JP and CALL are the equivalents of BASIC's GOTO and GOSUB instructions, respectively. Both take a 16-bit memory location as their operand. The only difference between the two is that CALL pushes the program counter onto the stack before jumping. Neither can jump to a variable location in memory; their operand must be embedded directly in the source code.

Program Counter Relative Jumps

JR adds a signed displacement byte to the program counter. This takes one less byte to encode than a JP but cannot jump more than 127 bytes forward or 128 bytes backward. The programmer can either specify a constant value as the operand or a labeled section of code. If a label is used, the assembler will calculate the number of bytes between the JR instruction and that label, and will refuse to assemble the code if the label is too far away.

and &01 ;returns 0 if the accumulator is even and 1 if odd. Also sets the zero flag accordingly.
jr z,SkipOddCode
   ;whatever you want to do when the accumulator is odd goes here, but it must be 127 bytes or fewer.
SkipOddCode:
   ;rest of program


A similar command called DJNZ is often used for looping. It decrements the B register and jumps if and only if B is nonzero. If B is zero, the DJNZ will do nothing and execution will move past it. Like all other jumping commands discussed so far, DJNZ will not alter the processor flags in any way. The same distance restriction of JR also applies to DJNZ. This is the equivalent of the LOOP instruction in x86 Assembly.

ld b,25
loop:
djnz loop  ;loop 25 times.


The block transfer instructions LDIR,LDDR,OTIR,OTDR,CPIR, and CPDR all use a form of program counter relative jumping. They execute their equivalent one-time command and repeatedly jump back to it until their exit conditions are met.

Conditional Jumping

JR,JP,CALL, and RET can be made conditional based on which flags are set. Essentially these are like if statements in a high-level language. If the condition specified by the command is not met, the command will have no effect; otherwise it will result in a jump.

ret po      ;return from subroutine if overflow has not occurred or the bit parity has an odd number of 1s.
call c, foo ;call "foo" if and only if the carry is set.
jp m,&ABCD  ;jump to address &ABCD if the last operation resulted in a negative value.
jr z,25     ;jump 25 bytes forward if the last operation resulted in a zero. (Some assemblers such as VASM make you type "$+25")
            ;(Unlike the others, JR cannot jump based on the sign flag or parity/overflow flag.)

The Game Boy is more limited than the Z80 in this regard, as it has no sign or overflow flags! It can only use the zero and carry flags for jumps.

Jumping to a Variable Location

The incredibly misleading JP (HL) will copy the value in the HL register pair directly to the program counter. You would think based on the parentheses that it looks up the value stored at the memory location in HL, but it doesn't! This is the fastest jump command the Z80 has.

JP (HL) can be used to create a "trampoline," which lets you indirectly call a subroutine, provided that subroutine doesn't take HL as an argument. (Otherwise you'll get some unwanted results.) To do this, you need to know the address of the subroutine you wish to call, load it into HL, then CALL any address that contains either JP (HL) or the byte 0xE9. (JP (HL)'s bytecode is 0xE9). Once you do this, execution will effectively "call" the desired routine. For this to work, the desired routine must end in a RET, and balance the stack properly. That way, when it does RET, it will RET to where you were just after the CALL.

ld hl,foo        ;rather than directly specifying "foo", you would normally retrieve it by indexing a table.
                 ;This was done only to keep the example as simple as possible.
                 ;If you're going to load it as a constant into HL you're better off just CALLing it outright.
            
call Trampoline
;execution will return here, with HL = address of "foo" and A = 0.


;;; somewhere away from the current program counter
Trampoline:
jp (hl)

foo:
ld a,0
ret

NB: If your hardware allows you to define the RST calls to whatever you like, you can speed this up even more by setting one of them to JP (HL), and invoking that RST as your trampoline rather than the call. The only downside is that you can't conditionally execute an RST, but if you were using a trampoline it likely wasn't going to be conditional anyway.


Another (albeit slower) way to jump indirectly is with RET. This command takes the top two bytes off the stack and puts them directly into the program counter. It's intended for use with CALL as a return from subroutine command, but it can also be used to go anywhere by pushing the desired memory address onto the stack and then "returning" to it. This trick is much more useful on other processors that don't have an equivalent to JP (HL), but on the Z80 it's not really that useful.

zkl

No gotos, just exceptions, generators, switch and the run of the mill looping constructs plus break/continue (which are limited to their loop scope). The VM has jmp instructions that the compiler uses to implement looping but those jmps are limited to function scope.

Having to hack up a goto with exceptions, state or duplicate code can be a PITA but luckily those cases seem to be rare and implementing goto could really bugger the VM state.