# Roman numerals/Decode

Roman numerals/Decode
You are encouraged to solve this task according to the task description, using any language you may know.

Create a function that takes a Roman numeral as its argument and returns its value as a numeric decimal integer.

You don't need to validate the form of the Roman numeral.

Modern Roman numerals are written by expressing each decimal digit of the number to be encoded separately,
starting with the leftmost decimal digit and skipping any 0s   (zeroes).

1990 is rendered as   MCMXC     (1000 = M,   900 = CM,   90 = XC)     and
2008 is rendered as   MMVIII       (2000 = MM,   8 = VIII).

The Roman numeral for 1666,   MDCLXVI,   uses each letter in descending order.

## 11l

Translation of: Python
```V roman_values = [(‘I’, 1), (‘IV’, 4), (‘V’, 5), (‘IX’, 9), (‘X’, 10),
(‘XL’, 40), (‘L’, 50), (‘XC’, 90), (‘C’, 100),
(‘CD’, 400), (‘D’, 500), (‘CM’, 900), (‘M’, 1000)]

F roman_value(=roman)
V total = 0
L(symbol, value) reversed(:roman_values)
L roman.starts_with(symbol)
total += value
roman = roman[symbol.len..]
R total

L(value) [‘MCMXC’, ‘MMVIII’, ‘MDCLXVI’]
print(value‘ = ’roman_value(value))```
Output:
```MCMXC = 1990
MMVIII = 2008
MDCLXVI = 1666
```

## 360 Assembly

```*        Roman numerals Decode -   17/04/2019
B      72(R15)            skip savearea
DC     17F'0'             savearea
SAVE   (14,12)            save previous context
LA     R6,1               i=1
DO WHILE=(C,R6,LE,=A(NV))   do i=1 to hbound(vals)
LR     R1,R6                i
SLA    R1,3                 ~
LA     R4,VALS-L'VALS(R1)   @vals(i)
MVC    X,0(R4)              x=vals(i)
SR     R9,R9                prev=0
ST     R9,Y                 y=0
LA     R7,L'X               j=1
DO WHILE=(C,R7,GE,=A(1))      do j=length(x) to 1 by -1
LA     R4,X-1                 @x
AR     R4,R7                  +j
MVC    C,0(R4)                c=substr(x,j,1)
IF   CLI,C,NE,C' ' THEN         if c^=' ' then
SR     R1,R1                  r1=0
LA     R2,1                   k=1
DO WHILE=(C,R2,LE,=A(L'ROMAN))   do k=1 to length(roman)
LA     R3,ROMAN-1               @roman
AR     R3,R2                    +k
IF   CLC,0(L'C,R3),EQ,C THEN      if substr(roman,k,1)=c
LR     R1,R2                      index=k
B      REINDEX                    leave k
ENDIF    ,                        endif
LA     R2,1(R2)                 k=k+1
ENDDO    ,                      enddo k
REINDEX  EQU    *                      r1=index(roman,c)
SLA    R1,2                   ~
L      R8,DECIM-4(R1)         n=decim(index(roman,c))
IF    CR,R8,LT,R9 THEN          if n<prev then
LCR    R8,R8                    n=-n
ENDIF    ,                      endif
L      R2,Y                     y
AR     R2,R8                    +n
ST     R2,Y                     y=y+n
LR     R9,R8                    prev=n
ENDIF    ,                      endif
BCTR   R7,0                   j--
ENDDO    ,                    enddo j
MVC    PG(8),X              x
L      R1,Y                 y
XDECO  R1,XDEC              edit y
MVC    PG+12(4),XDEC+8      output y
XPRNT  PG,L'PG              print buffer
LA     R6,1(R6)             i++
ENDDO    ,                  enddo i
L      R13,4(0,R13)       restore previous savearea pointer
RETURN (14,12),RC=0       restore registers from calling sav
NV       EQU    (X-VALS)/L'VALS
ROMAN    DC     CL7'MDCLXVI'
DECIM    DC     F'1000',F'500',F'100',F'50',F'10',F'5',F'1'
VALS     DC     CL8'XIV',CL8'CMI',CL8'MIC',CL8'MCMXC',CL8'MDCLXVI'
DC     CL8'MMVIII',CL8'MMXIX',CL8'MMMCMXCV'
X        DS     CL(L'VALS)
Y        DS     F
C        DS     CL1
PG       DC     CL80'........ -> ....'
XDEC     DS     CL12
REGEQU
Output:
```XIV      ->   14
CMI      ->  901
MIC      -> 1099
MCMXC    -> 1990
MDCLXVI  -> 1666
MMVIII   -> 2008
MMXIX    -> 2019
MMMCMXCV -> 3995
```

## 8080 Assembly

The routine at `roman` takes the address of a zero-terminated string in BC, and returns the value of the Roman number in that string as a 16-bit integer in HL. The Roman numeral must be in uppercase letters.

```		org	100h
jmp	test
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;; Takes a zero-terminated Roman numeral string in BC
;; and returns 16-bit integer in HL.
;; All registers destroyed.
roman:		dcx	b
romanfindend:	inx	b	; load next character
ldax	b
inr	e
ana	a	; are we there yet
jnz	romanfindend
lxi	h,0	; zero HL to hold the total
push	h	; stack holds the previous roman numeral
romanloop:	dcx	b	; get next roman numeral
ldax	b	; (work backwards)
call	romandgt
jc	romandone	; carry set = not Roman anymore
xthl		; load previous roman numeral
call	cmpdehl	; DE < HL?
mov	h,d	; in any case, DE is now the previous
mov	l,e	; Roman numeral
xthl		; bring back the total
mov	a,d	; DE (current) < HL (previous)
cma		; so this Roman digit must be subtracted
mov	d,a	; from the total.
mov	a,e	; so we negate it before adding it
cma		; two's complement: -de = (~de)+1
mov	e,a
inx	d
jmp	romanloop
romandone:	pop	d	; remove temporary variable from stack
ret
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;; 16-bit compare DE with HL, set flags
;; accordingly. A destroyed.
cmpdehl:	mov	a,d
cmp	h
rnz
mov	a,e
cmp	l
ret
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;; Takes a single Roman 'digit' in A,
;; and returns its value in DE (0 if invalid)
;; All other registers preserved.
romandgt:	push	h	; preserve hl for the caller
lxi	h,romantab
mvi	e,7	; e=counter
romandgtl:	cmp	m	; check table entry
jz	romanfound
inx	h	; move to next table entry
inx	h
inx	h
dcr	e	; decrease counter
jnz	romandgtl
pop	h	; we didn't find it
stc		; set carry
ret		; return with DE=0
romanfound:	inx	h	; we did find it
mov	e,m	; load it into DE
inx	h
mov	d,m
pop	h
ana	a	; clear carry
ret
romantab:	db	'I',1,0	; 16-bit little endian values
db	'V',5,0
db	'X',10,0
db	'L',50,0
db	'C',100,0
db	'D',0f4h,1
db	'M',0e8h,3
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;; The following is testing and I/O code.
test:		mvi	c,10	; read string from console
lxi	d,bufdef
call	5
mvi	c,9	; print newline
lxi	d,nl
call	5
lxi	b,buf	; run `roman' on the input string
call	roman	; the result is now in hl
lxi	d,-10000
call	numout	; print 10000s digit
lxi	d,-1000
call	numout	; print 1000s digit
lxi	d,-100
call 	numout	; print 100s digit
lxi	d,-10
call 	numout	; print 10s digit
lxi	d,-1	; ...print 1s digit
numout:		mvi	a,-1
push	h
numloop:	inr	a
pop	b
push	h
jc	numloop
mvi	c,2
mov	e,a
call	5
pop	h
ret
nl:		db	13,10,'\$'
bufdef:		db	16,0
buf:		ds	17```

## Action!

```CARD FUNC DecodeRomanDigit(CHAR c)
IF c='I THEN RETURN (1)
ELSEIF c='V THEN RETURN (5)
ELSEIF c='X THEN RETURN (10)
ELSEIF c='L THEN RETURN (50)
ELSEIF c='C THEN RETURN (100)
ELSEIF c='D THEN RETURN (500)
ELSEIF c='M THEN RETURN (1000)
FI
RETURN (0)

CARD FUNC DecodeRomanNumber(CHAR ARRAY s)
CARD res,curr,prev
BYTE i

res=0 prev=0 i=s(0)
WHILE i>0
DO
curr=DecodeRomanDigit(s(i))
IF curr<prev THEN
res==-curr
ELSE
res==+curr
FI
prev=curr
i==-1
OD
RETURN (res)

PROC Test(CHAR ARRAY s)
CARD n

n=DecodeRomanNumber(s)
PrintF("%S=%U%E",s,n)
RETURN

PROC Main()
Test("MCMXC")
Test("MMVIII")
Test("MDCLXVI")
Test("MMMDCCCLXXXVIII")
Test("MMMCMXCIX")
RETURN```
Output:
```MCMXC=1990
MMVIII=2008
MDCLXVI=1666
MMMDCCCLXXXVIII=3888
MMMCMXCIX=3999
```

```Pragma Ada_2012;
Pragma Assertion_Policy( Check );

With
Unchecked_Conversion,

Procedure Test_Roman_Numerals is

-- We create an enumeration of valid characters, note that they are
-- character-literals, this is so that we can use literal-strings,
-- and that their size is that of Integer.
Type Roman_Digits is ('I', 'V', 'X', 'L', 'C', 'D', 'M' )
with Size => Integer'Size;

-- We use a representation-clause ensure the proper integral-value
-- of each individual character.
For Roman_Digits use
(
'I' => 1,
'V' => 5,
'X' => 10,
'L' => 50,
'C' => 100,
'D' => 500,
'M' => 1000
);

-- To convert a Roman_Digit to an integer, we now only need to
-- read its value as an integer.
Function Convert is new Unchecked_Conversion
(	Source => Roman_Digits,	Target => Integer );

-- Romena_Numeral is a string of Roman_Digit.
Type Roman_Numeral is array (Positive range <>) of Roman_Digits;

-- The Numeral_List type is used herein only for testing
-- and verification-data.
Type Numeral_List is array (Positive range <>) of
not null access Roman_Numeral;

-- The Test_Cases subtype ensures that Test_Data and Validation_Data
-- both contain the same number of elements, and that the indecies
-- are the same; essentially the same as:
--
--    pragma Assert( Test_Data'Length = Validation_Data'Length
--		   AND Test_Data'First = Validation_Data'First);

subtype Test_Cases is Positive range 1..14;

Test_Data : constant Numeral_List(Test_Cases):=
(
New Roman_Numeral'("III"),	-- 3
New Roman_Numeral'("XXX"),	-- 30
New Roman_Numeral'("CCC"),	-- 300
New Roman_Numeral'("MMM"),	-- 3000

New Roman_Numeral'("VII"),	-- 7
New Roman_Numeral'("LXVI"),	-- 66
New Roman_Numeral'("CL"),	-- 150
New Roman_Numeral'("MCC"),	-- 1200

New Roman_Numeral'("IV"),	-- 4
New Roman_Numeral'("IX"),	-- 9
New Roman_Numeral'("XC"),	-- 90

New Roman_Numeral'("ICM"),	-- 901
New Roman_Numeral'("CIM"),	-- 899

New Roman_Numeral'("MDCLXVI")	-- 1666
);

Validation_Data : constant array(Test_Cases) of Natural:=
(	3, 30, 300, 3000,
7, 66, 150, 1200,
4, 9, 90,
901, 899,
1666
);

-- In Roman numerals, the subtractive form [IV = 4] was used
-- very infrequently, the most common form was the addidive
-- form [IV = 6]. (Consider military logistics and squads.)

Function Sum( Number : Roman_Numeral ) return Natural is
begin
Return Result : Natural:= 0 do
For Item of Number loop
Result:= Result + Convert( Item );
end loop;
End Return;
end Sum;

-- EVAL returns Number read in the subtractive form.
Function Eval( Number : Roman_Numeral ) return Natural is
Current : Roman_Digits:= 'I';
begin
Return Result : Natural:= 0 do
For Item of Number loop
if Current < Item then
Result:= Convert(Item) - Result;
Current:= Item;
else
Result:= Result + Convert(Item);
end if;
end loop;
End Return;
end Eval;

-- Display the given Roman_Numeral via Text_IO.
Procedure Put( S: Roman_Numeral ) is
begin
For Ch of S loop
declare
-- The 'Image attribute returns the character inside
-- single-quotes; so we select the character itself.
C : Character renames Roman_Digits'Image(Ch)(2);
begin
end;
end loop;
end;

-- This displays pass/fail dependant on the parameter.
Function PF ( Value : Boolean ) Return String is
begin
Return Result : String(1..4):= ( if Value then"pass"else"fail" );
End PF;

Begin

for Index in Test_Data'Range loop
declare
Item  : Roman_Numeral renames Test_Data(Index).all;
Value : constant Natural := Eval(Item);
begin
Put( Item );

PF( Value = Validation_Data(Index) )& ']');
end;
end loop;

End Test_Roman_Numerals;
```
Output:
```Starting Test:
III	=  3	[pass]
XXX	=  30	[pass]
CCC	=  300	[pass]
MMM	=  3000	[pass]
VII	=  7	[pass]
LXVI	=  66	[pass]
CL	=  150	[pass]
MCC	=  1200	[pass]
IV	=  4	[pass]
IX	=  9	[pass]
XC	=  90	[pass]
ICM	=  901	[pass]
CIM	=  899	[pass]
MDCLXVI	=  1666	[pass]
Testing complete.```

## ALGOL 68

Works with: ALGOL 68G version Any - tested with release 2.2.0

Note: roman to int will handle multiple subtraction, e.g. IIIIX for 6.

```    PROC roman to int = (STRING roman) INT:
BEGIN
PROC roman digit value = (CHAR roman digit) INT:
(roman digit = "M" | 1000 |:
roman digit = "D" |  500 |:
roman digit = "C" |  100 |:
roman digit = "L" |   50 |:
roman digit = "X" |   10 |:
roman digit = "V" |    5 |:
roman digit = "I" |    1);

INT result := 0, previous value := 0, run := 0;

FOR i FROM LWB roman TO UPB roman
DO
INT value = roman digit value(roman[i]);
IF previous value = value THEN
run +:= value
ELSE
IF previous value < value THEN
result -:= run
ELSE
result +:= run
FI;
run := previous value := value
FI
OD;

result +:= run
END;

MODE TEST = STRUCT (STRING input, INT expected output);

[] TEST roman test = (
("MMXI",    2011), ("MIM",     1999),
("MCMLVI",  1956), ("MDCLXVI", 1666),
("XXCIII",    83), ("LXXIIX",    78),
("IIIIX",      6)
);

print(("Test input  Value   Got", newline, "--------------------------", newline));
FOR i FROM LWB roman test TO UPB roman test
DO
INT output = roman to int(input OF roman test[i]);
printf((\$g, n (12 - UPB input OF roman test[i]) x\$, input OF roman test[i]));
printf((\$g(5), 1x, g(5), 1x\$, expected output OF roman test[i], output));
printf((\$b("ok", "not ok"), 1l\$, output = expected output OF roman test[i]))
OD```

## ALGOL W

```begin
% decodes a roman numeral into an integer                                %
% there must be at least one blank after the numeral                     %
% This takes a lenient view on roman numbers so e.g. IIXX is 18 - see    %
% the Discussion                                                         %
integer procedure romanToDecimal ( string(32) value roman ) ;
begin
integer   decimal, rPos, currDigit, nextDigit, seqValue;
string(1) rDigit;

% the roman number is a sequence of sequences of roman digits        %
% if the previous sequence is of higher value digits than the next,  %
%    the higher value is added to the overall value                  %
% if the previous seequence is of lower value, it is subtracted      %
% e.g. MCMLXII                                                       %
%      the sequences are M, C, M, X, II                              %

% get the value of a sequence of roman digits                        %
integer procedure getSequence ;
if rDigit = " " then begin
% end of the number                                          %
0
end
else begin
% have another sequence                                      %
integer sValue;
sValue := 0;
while roman( rPos // 1 ) = rDigit do begin
sValue := sValue + currDigit;
rPos   := rPos + 1;
end while_have_same_digit ;
% remember the next digit                                    %
rDigit     := roman( rPos // 1 );
% result is the sequence value                               %
sValue
end getSequence ;

% convert a roman digit into its decimal equivalent                  %
% an invalid digit will terminate the program, " " is 0              %
integer procedure getValue( string(1) value romanDigit ) ;
if      romanDigit = "m" or romanDigit = "M" then 1000
else if romanDigit = "d" or romanDigit = "D" then  500
else if romanDigit = "c" or romanDigit = "C" then  100
else if romanDigit = "l" or romanDigit = "L" then   50
else if romanDigit = "x" or romanDigit = "X" then   10
else if romanDigit = "v" or romanDigit = "V" then    5
else if romanDigit = "i" or romanDigit = "I" then    1
else if romanDigit = " "                     then    0
else begin
write( s_w := 0, "Invalid roman digit: """, romanDigit, """" );
assert false;
0
end getValue ;

% get the first sequence                                             %
decimal   := 0;
rPos      := 0;
rDigit    := roman( rPos // 1 );
currDigit := getValue( rDigit );
seqValue  := getSequence;

% handle the sequences                                               %
while rDigit not = " " do begin
% have another sequence                                          %
nextDigit := getValue( rDigit );
if currDigit < nextDigit
then % prev digit is lower  % decimal := decimal - seqValue
else % prev digit is higher % decimal := decimal + seqValue
;
currDigit := nextDigit;
seqValue  := getSequence;
end while_have_a_roman_digit ;

% add the final sequence                                             %
decimal + seqValue
end roman ;

% test the romanToDecimal routine                                        %

procedure testRoman ( string(32) value romanNumber ) ;
write( i_w := 5, romanNumber, romanToDecimal( romanNumber ) );

testRoman( "I"        );    testRoman( "II"       );
testRoman( "III"      );    testRoman( "IV"       );
testRoman( "V"        );    testRoman( "VI"       );
testRoman( "VII"      );    testRoman( "VIII"     );
testRoman( "IX"       );    testRoman( "IIXX"     );
testRoman( "XIX"      );    testRoman( "XX"       );
write( "..." );
testRoman( "MCMXC"    );
testRoman( "MMVIII"   );
testRoman( "MDCLXVI"  );

end.```
Output:
```I                                   1
II                                  2
III                                 3
IV                                  4
V                                   5
VI                                  6
VII                                 7
VIII                                8
IX                                  9
IIXX                               18
XIX                                19
XX                                 20
...
MCMXC                            1990
MMVIII                           2008
MDCLXVI                          1666
```

## ANTLR

### Java

```/* Parse Roman Numerals

Nigel Galloway March 16th., 2012
*/
grammar ParseRN ;

options {
language = Java;
}
@members {
int rnValue;
int ONE;
}

parseRN:	({rnValue = 0;} rn NEWLINE {System.out.println(\$rn.text + " = " + rnValue);})*
;

rn	:	(Thousand {rnValue += 1000;})* hundreds? tens? units?;

hundreds:	{ONE = 0;} (h9 | h5) {if (ONE > 3) System.out.println ("Too many hundreds");};
h9	:	Hundred {ONE += 1;} (FiveHund {rnValue += 400;}| Thousand {rnValue += 900;}|{rnValue += 100;} (Hundred {rnValue += 100; ONE += 1;})*);
h5	:	FiveHund {rnValue += 500;} (Hundred {rnValue += 100; ONE += 1;})*;

tens	:	{ONE = 0;} (t9 | t5) {if (ONE > 3) System.out.println ("Too many tens");};
t9	:	Ten {ONE += 1;} (Fifty {rnValue += 40;}| Hundred {rnValue += 90;}|{rnValue += 10;} (Ten {rnValue += 10; ONE += 1;})*);
t5	:	Fifty {rnValue += 50;} (Ten {rnValue += 10; ONE += 1;})*;

units	:	{ONE = 0;} (u9 | u5) {if (ONE > 3) System.out.println ("Too many ones");};
u9	:	One {ONE += 1;} (Five {rnValue += 4;}| Ten {rnValue += 9;}|{rnValue += 1;} (One {rnValue += 1; ONE += 1;})*);
u5	:	Five {rnValue += 5;} (One {rnValue += 1; ONE += 1;})*;

One	:	'I';
Five	:	'V';
Ten	:	'X';
Fifty	:	'L';
Hundred:	'C';
FiveHund:	'D';
Thousand:	'M' ;
NEWLINE:	'\r'? '\n' ;
```

Using this test data:

```MMXI
MCMLVI
XXCIII
MCMXC
MMVIII
MDCLXVI
IIIIX
MIM
MDCLXVI
LXXIIX
M
MCXI
CMXI
MCM
MMIX
MCDXLIV
MMXII
```

Produces:

```MMXI = 2011
MCMLVI = 1956
line 3:2 missing NEWLINE at 'C'
XX = 20
CIII = 103
```

Note that this implementation does not accept XXC as eighty. The error is detected and ANTLR attempts to continue by inserting the expected NEWLINE after XX and treating CIII as a new Number.

```MCMXC = 1990
MMVIII = 2008
MDCLXVI = 1666
Too many ones
line 7:4 extraneous input 'X' expecting NEWLINE
IIII = 4
```

An implementation above thinks IIIIX is 6. It isn't. ANTLR detects the surfiet of 'I' reports the errors and tries to carry on.

```line 8:2 no viable alternative at input 'M'
MIM = 1000
MDCLXVI = 1666
line 10:5 extraneous input 'X' expecting NEWLINE
LXXII = 72
M = 1000
MCXI = 1111
CMXI = 911
MCM = 1900
MMIX = 2009
MCDXLIV = 1444
MMXII = 2012
```

## APL

Works with: Dyalog APL
```fromRoman←{
rmn←(⎕A,⎕A,'*')[(⎕A,⎕UCS 96+⍳26)⍳⍵]     ⍝ make input uppercase
dgt←↑'IVXLCDM' (1 5 10 50 100 500 1000) ⍝ values of roman digits
~rmn∧.∊⊂dgt[1;]:⎕SIGNAL 11              ⍝ domain error if non-roman input
map←dgt[2;dgt[1;]⍳rmn]                  ⍝ map digits to values
+/map×1-2×(2</map),0                    ⍝ subtractive principle
}
```
Output:
```      fromRoman¨ 'MCMXC' 'MMVIII' 'MDCLXVI' 'MMXXI'
1990 2008 1666 2021```

## AppleScript

#### isPrefixOf

Translation of: JavaScript

(Functional ES5 version)

```------------- INTEGER VALUE OF A ROMAN STRING ------------

-- romanValue :: String -> Int
on romanValue(s)
script roman
property mapping : [["M", 1000], ["CM", 900], ["D", 500], ["CD", 400], ¬
["C", 100], ["XC", 90], ["L", 50], ["XL", 40], ["X", 10], ["IX", 9], ¬
["V", 5], ["IV", 4], ["I", 1]]

-- Value of first Roman glyph + value of remaining glyphs
-- toArabic :: [Char] -> Int
on toArabic(xs)
-- transcribe :: (String, Number) -> Maybe (Number, [String])
script transcribe
on |λ|(pair)
set {r, v} to pair
if isPrefixOf(characters of r, xs) then

-- Value of this matching glyph, with any remaining glyphs
{v, drop(length of r, xs)}
else
{}
end if
end |λ|
end script

if 0 < length of xs then
set parsed to concatMap(transcribe, mapping)
(item 1 of parsed) + toArabic(item 2 of parsed)
else
0
end if
end toArabic
end script

toArabic(characters of s) of roman
end romanValue

--------------------------- TEST -------------------------
on run
map(romanValue, {"MCMXC", "MDCLXVI", "MMVIII"})

--> {1990, 1666, 2008}
end run

-------------------- GENERIC FUNCTIONS -------------------

-- concatMap :: (a -> [b]) -> [a] -> [b]
on concatMap(f, xs)
set lng to length of xs
set acc to {}
tell mReturn(f)
repeat with i from 1 to lng
set acc to acc & (|λ|(item i of xs, i, xs))
end repeat
end tell
if {text, string} contains class of xs then
acc as text
else
acc
end if
end concatMap

-- drop :: Int -> [a] -> [a]
-- drop :: Int -> String -> String
on drop(n, xs)
set c to class of xs
if script is not c then
if string is not c then
if n < length of xs then
items (1 + n) thru -1 of xs
else
{}
end if
else
if n < length of xs then
text (1 + n) thru -1 of xs
else
""
end if
end if
else
take(n, xs) -- consumed
return xs
end if
end drop

-- isPrefixOf :: [a] -> [a] -> Bool
-- isPrefixOf :: String -> String -> Bool
on isPrefixOf(xs, ys)
-- isPrefixOf takes two lists or strings and returns
--  true if and only if the first is a prefix of the second.
script go
on |λ|(xs, ys)
set intX to length of xs
if intX < 1 then
true
else if intX > length of ys then
false
else if class of xs is string then
(offset of xs in ys) = 1
else
set {xxt, yyt} to {uncons(xs), uncons(ys)}
((item 1 of xxt) = (item 1 of yyt)) and ¬
|λ|(item 2 of xxt, item 2 of yyt)
end if
end |λ|
end script
go's |λ|(xs, ys)
end isPrefixOf

-- length :: [a] -> Int
on |length|(xs)
set c to class of xs
if list is c or string is c then
length of xs
else
(2 ^ 29 - 1) -- (maxInt - simple proxy for non-finite)
end if
end |length|

-- map :: (a -> b) -> [a] -> [b]
on map(f, xs)
tell mReturn(f)
set lng to length of xs
set lst to {}
repeat with i from 1 to lng
set end of lst to |λ|(item i of xs, i, xs)
end repeat
return lst
end tell
end map

-- Lift 2nd class handler function into 1st class script wrapper
-- mReturn :: Handler -> Script
on mReturn(f)
if class of f is script then
f
else
script
property |λ| : f
end script
end if
end mReturn

-- uncons :: [a] -> Maybe (a, [a])
on uncons(xs)
set lng to |length|(xs)
if 0 = lng then
missing value
else
if (2 ^ 29 - 1) as integer > lng then
if class of xs is string then
set cs to text items of xs
{item 1 of cs, rest of cs}
else
{item 1 of xs, rest of xs}
end if
else
set nxt to take(1, xs)
if {} is nxt then
missing value
else
{item 1 of nxt, xs}
end if
end if
end if
end uncons
```
Output:
```{1990, 1666, 2008}
```

#### Fold right – subtracting or adding

Works with: Yosemite onwards
```use framework "Foundation"

----------- INTEGER VALUE OF ROMAN NUMBER STRING ---------

-- fromRoman :: String -> Int
on fromRoman(s)
script subtractIfLower
on |λ|(l, rn)
set {r, n} to rn
if l ≥ r then -- Digit values that increase (L to R),
{l, n + l} -- (added)
else
{l, n - l} -- Digit values that go down: subtracted.
end if
end |λ|
end script

item 2 of foldr(subtractIfLower, {0, 0}, ¬
map(my charVal, characters of s))
end fromRoman

-- charVal :: Char -> Int
on charVal(C)
set v to lookup(toUpper(C), ¬
{I:1, |V|:5, X:10, |L|:50, C:100, D:500, M:1000})
if missing value is v then
0
else
v
end if
end charVal

--------------------------- TEST -------------------------
on run
map(fromRoman, ¬
{"MDCLXVI", "MCMXC", "MMVIII", "MMXVI", "MMXXI"})

--> {1666, 1990, 2008, 2016, 2021}
end run

-------------------- GENERIC FUNCTIONS -------------------

-- foldr :: (a -> b -> b) -> b -> [a] -> b
on foldr(f, startValue, xs)
tell mReturn(f)
set v to startValue
set lng to length of xs
repeat with I from lng to 1 by -1
set v to |λ|(item I of xs, v)
end repeat
return v
end tell
end foldr

-- lookup :: a -> Dict -> Maybe b
on lookup(k, dct)
-- Just the value of k in the dictionary,
set ca to current application
set v to (ca's NSDictionary's dictionaryWithDictionary:dct)'s ¬
objectForKey:k
if missing value ≠ v then
item 1 of ((ca's NSArray's arrayWithObject:v) as list)
else
missing value
end if
end lookup

-- map :: (a -> b) -> [a] -> [b]
on map(f, xs)
-- The list obtained by applying f
-- to each element of xs.
tell mReturn(f)
set lng to length of xs
set lst to {}
repeat with I from 1 to lng
set end of lst to |λ|(item I of xs, I, xs)
end repeat
return lst
end tell
end map

-- Lift 2nd class handler function into 1st class
-- script wrapper
-- mReturn :: Handler -> Script
on mReturn(f)
if class of f is script then
f
else
script
property |λ| : f
end script
end if
end mReturn

-- toUpper :: String -> String
on toUpper(str)
tell current application
((its (NSString's stringWithString:(str)))'s ¬
uppercaseStringWithLocale:¬
(its NSLocale's currentLocale())) as text
end tell
end toUpper
```
Output:
```{1666, 1990, 2008, 2016, 2021}
```

## BASIC

### Applesoft BASIC

Translation of: BBC BASIC
``` 10  LET R\$ = "MCMXCIX"
20  GOSUB 100 PRINT "ROMAN NUMERALS DECODED"
30  LET R\$ = "MMXII"
40  GOSUB 100
50  LET R\$ = "MDCLXVI"
60  GOSUB 100
70  LET R\$ = "MMMDCCCLXXXVIII"
80  GOSUB 100
90  END
100  PRINT M\$R\$,
110  LET M\$ =  CHR\$ (13)
120  GOSUB 150"ROMAN NUMERALS DECODE given R\$"
130  PRINT N;
140  RETURN
150  IF  NOT C THEN  GOSUB 250INITIALIZE
160  LET J = 0
170  LET N = 0
180  FOR I =  LEN (R\$) TO 1 STEP  - 1
190      LET P = J
200      FOR J = 1 TO C
210          IF  MID\$ (C\$,J,1) <  >  MID\$ (R\$,I,1) THEN  NEXT J
220      IF J <  = C THEN N = N + R(J) * ((J >  = P) * 2 - 1)
230  NEXT I
240  RETURN
260  LET C =  LEN (C\$)
270  DIM R(C)
280  FOR I = 0 TO C
300      NEXT I
310  RETURN
320  DATA "IVXLCDM",0,1,5,10,50,100,500,1000
```

### BASIC256

```function romToDec (roman\$)
num = 0
prenum = 0
for i = length(roman\$) to 1 step -1
x\$ = mid(roman\$, i, 1)
n = 0
if x\$ = "M" then n = 1000
if x\$ = "D" then n = 500
if x\$ = "C" then n = 100
if x\$ = "L" then n = 50
if x\$ = "X" then n = 10
if x\$ = "V" then n = 5
if x\$ = "I" then n = 1

if n < preNum then num -= n else num += n
preNum = n
next i

return num
end function

#Testing
print "MCMXCIX = "; romToDec("MCMXCIX")     #1999
print "MDCLXVI = "; romToDec("MDCLXVI")     #1666
print "XXV     = "; romToDec("XXV")         #25
print "CMLIV   = "; romToDec("CMLIV")       #954
print "MMXI    = "; romToDec("MMXI")        #2011
```

### BBC BASIC

```      PRINT "MCMXCIX", FNromandecode("MCMXCIX")
PRINT "MMXII", FNromandecode("MMXII")
PRINT "MDCLXVI", FNromandecode("MDCLXVI")
PRINT "MMMDCCCLXXXVIII", FNromandecode("MMMDCCCLXXXVIII")
END

DEF FNromandecode(roman\$)
LOCAL i%, j%, p%, n%, r%()
DIM r%(7) : r%() = 0,1,5,10,50,100,500,1000
FOR i% = LEN(roman\$) TO 1 STEP -1
j% = INSTR("IVXLCDM", MID\$(roman\$,i%,1))
IF j%=0 ERROR 100, "Invalid character"
IF j%>=p% n% += r%(j%) ELSE n% -= r%(j%)
p% = j%
NEXT
= n%
```
Output:
```MCMXCIX         1999
MMXII           2012
MDCLXVI         1666
MMMDCCCLXXXVIII           3888```

### Chipmunk Basic

#### Through IF-THEN statements

Works with: Chipmunk Basic version 3.6.4
Works with: Applesoft BASIC
Works with: MSX_BASIC
Works with: QBasic
```100 cls : rem  100 home  for Applesoft BASIC
110 roman\$ = "MCMXCIX" : print roman\$,"=> "; : gosub 170 : print decimal '1999
120 roman\$ = "XXV" : print roman\$,"=> "; : gosub 170 : print decimal     '25
130 roman\$ = "CMLIV" : print roman\$,"=> "; : gosub 170 : print decimal   '954
140 roman\$ = "MMXI" : print roman\$,"=> "; : gosub 170 : print decimal    '2011
150 end
160 rem Decode from roman
170 decimal = 0
180 predecimal = 0
190 for i = len(roman\$) to 1 step -1
200  x\$ = mid\$(roman\$,i,1)
210  if x\$ = "M" then n = 1000 : goto 280
220  if x\$ = "D" then n = 500 : goto 280
230  if x\$ = "C" then n = 100 : goto 280
240  if x\$ = "L" then n = 50 : goto 280
250  if x\$ = "X" then n = 10 : goto 280
260  if x\$ = "V" then n = 5 : goto 280
270  if x\$ = "I" then n = 1
280  if n < predecimal then decimal = decimal-n
285  if n >= predecimal then decimal = decimal+n
290  predecimal = n
300 next i
310 return
```

#### Through SELECT CASE statement

Works with: Chipmunk Basic version 3.6.4
```100 cls
110 roman\$ = "MCMXCIX" : print roman\$,"=> "; : gosub 170 : print decimal '1999
120 roman\$ = "XXV" : print roman\$,"=> "; : gosub 170 : print decimal     '25
130 roman\$ = "CMLIV" : print roman\$,"=> "; : gosub 170 : print decimal   '954
140 roman\$ = "MMXI" : print roman\$,"=> "; : gosub 170 : print decimal    '2011
150 end
160 rem Decode from roman
170 decimal = 0
180 predecimal = 0
190 for i = len(roman\$) to 1 step -1
200  x\$ = mid\$(roman\$,i,1)
210  select case x\$
220   case "M" : n = 1000
230   case "D" : n = 500
240   case "C" : n = 100
250   case "L" : n = 50
260   case "X" : n = 10
270   case "V" : n = 5
280   case "I" : n = 1
290   case else : print "not a roman numeral" : end
300  end select
310  if n < predecimal then decimal = decimal-n else decimal = decimal+n
320  predecimal = n
330 next i
340 return
```

### FreeBASIC

```' FB 1.05.0 Win64

Function romanDecode(roman As Const String) As Integer
If roman = "" Then Return 0  '' zero denotes invalid roman number
Dim roman1(0 To 2) As String = {"MMM", "MM", "M"}
Dim roman2(0 To 8) As String = {"CM", "DCCC", "DCC", "DC", "D", "CD", "CCC", "CC", "C"}
Dim roman3(0 To 8) As String = {"XC", "LXXX", "LXX", "LX", "L", "XL", "XXX", "XX", "X"}
Dim roman4(0 To 8) As String = {"IX", "VIII", "VII", "VI", "V", "IV", "III", "II", "I"}
Dim As Integer i, value = 0, length = 0
Dim r As String = UCase(roman)

For i = 0 To 2
If Left(r, Len(roman1(i))) = roman1(i) Then
value += 1000 * (3 - i)
length = Len(roman1(i))
r = Mid(r, length + 1)
length = 0
Exit For
End If
Next

For i = 0 To 8
If Left(r, Len(roman2(i))) = roman2(i) Then
value += 100 * (9 - i)
length = Len(roman2(i))
r = Mid(r, length + 1)
length = 0
Exit For
End If
Next

For i = 0 To 8
If Left(r, Len(roman3(i))) = roman3(i) Then
value += 10 * (9 - i)
length = Len(roman3(i))
r = Mid(r, length + 1)
length = 0
Exit For
End If
Next

For i = 0 To 8
If Left(r, Len(roman4(i))) = roman4(i) Then
value += 9 - i
length = Len(roman4(i))
Exit For
End If
Next

' Can't be a valid roman number if there are any characters left
If Len(r) > length Then Return 0
Return value
End Function

Dim a(2) As String = {"MCMXC", "MMVIII" , "MDCLXVI"}
For i As Integer = 0 To 2
Print a(i); Tab(8); " =>"; romanDecode(a(i))
Next

Print
Print "Press any key to quit"
Sleep
```
Output:
```MCMXC   => 1990
MMVIII  => 2008
MDCLXVI => 1666```

### FutureBasic

```window 1

local fn RomantoDecimal( roman as CFStringRef ) as long
long i, n, preNum = 0, num = 0

for i = len(roman) - 1 to 0 step -1
n = 0
select ( fn StringCharacterAtIndex( roman, i ) )
case _"M" : n = 1000
case _"D" : n = 500
case _"C" : n = 100
case _"L" : n = 50
case _"X" : n = 10
case _"V" : n = 5
case _"I" : n = 1
end select
if ( n < preNum ) then num = num - n else num = num + n
preNum = n
next

end fn = num

print @"  MCMXC = "; fn RomantoDecimal( @"MCMXC"   )
print @" MMVIII = "; fn RomantoDecimal( @"MMVIII"  )
print @"  MMXVI = "; fn RomantoDecimal( @"MMXVI"   )
print @"MDCLXVI = "; fn RomantoDecimal( @"MDCLXVI" )
print @" MCMXIV = "; fn RomantoDecimal( @"MCMXIV"  )
print @"  DXIII = "; fn RomantoDecimal( @"DXIII"   )
print @"      M = "; fn RomantoDecimal( @"M"       )
print @"  DXIII = "; fn RomantoDecimal( @"DXIII"   )
print @" XXXIII = "; fn RomantoDecimal( @"XXXIII"  )

HandleEvents```
Output:
``` MCMXC = 1990
MMVIII = 2008
MMXVI = 2016
MDCLXVI = 1666
MCMXIV = 1914
DXIII = 513
M = 1000
DXIII = 513
XXXIII = 33```

### Gambas

```'This code will create a GUI Form and Objects and carry out the Roman Numeral convertion as you type
'The input is case insensitive
'A basic check for invalid charaters is made

hTextBox As TextBox                                           'To allow the creation of a TextBox
hValueBox As ValueBox                                         'To allow the creation of a ValueBox

Public Sub Form_Open()                                        'Form opens..

SetUpForm                                                     'Go to the SetUpForm Routine
hTextBox.text = "MCMXC"                                       'Put a Roman numeral in the TextBox

End

Public Sub TextBoxInput_Change()                              'Each time the TextBox text changes..
Dim cRomanN As Collection = ["M": 1000, "D": 500, "C": 100, "L": 50, "X": 10, "V": 5, "I": 1]  'Collection of nemerals e.g 'M' = 1000
Dim cMinus As Collection = ["IV": -2, "IX": -2, "XL": -20, "XC": - 20, "CD": -200, "CM": -200] 'Collection of the 'one less than' numbers e.g. 'IV' = 4
Dim sClean, sTemp As String                                   'Various string variables
Dim siCount As Short                                          'Counter
Dim iTotal As Integer                                         'Stores the total of the calculation

hTextBox.Text = UCase(hTextBox.Text)                          'Make any text in the TextBox upper case

For siCount = 1 To Len(hTextBox.Text)                         'Loop through each character in the TextBox
If InStr("MDCLXVI", Mid(hTextBox.Text, siCount, 1)) Then    'If a Roman numeral exists then..
sClean &= Mid(hTextBox.Text, siCount, 1)                  'Put it in 'sClean' (Stops input of non Roman numerals)
End If
Next

hTextBox.Text = sClean                                        'Put the now clean text in the TextBox

For siCount = 1 To Len(hTextBox.Text)                         'Loop through each character in the TextBox
iTotal += cRomanN[Mid(hTextBox.Text, siCount, 1)]           'Total up all the characters, note 'IX' will = 11 not 9
Next

For Each sTemp In cMinus                                      'Loop through each item in the cMinus Collection
If InStr(sClean, cMinus.Key) > 0 Then iTotal += Val(sTemp)  'If a 'Minus' value is in the string e.g. 'IX' which has been calculated at 11 subtract 2 = 9
Next

hValueBox.text = iTotal                                       'Display the total

End

Public Sub SetUpForm()                                        'Create the Objects for the Form
Dim hLabel1, hLabel2 As Label                                 'For 2 Labels

Me.height = 150                                               'Form Height
Me.Width = 300                                                'Form Width
Me.Text = "Roman Numeral converter"                           'Text in Form header
Me.Arrangement = Arrange.Vertical                             'Form arrangement

hLabel1 = New Label(Me)                                       'Create a Label
hLabel1.Height = 21                                           'Label Height
hLabel1.expand = True                                         'Expand the Label
hLabel1.Text = "Enter a Roman numeral"                        'Put text in the Label

hTextBox = New TextBox(Me) As "TextBoxInput"                  'Set up a TextBox with an Event Label
hTextBox.Height = 21                                          'TextBox height
hTextBox.expand = True                                        'Expand the TextBox

hLabel2 = New Label(Me)                                       'Create a Label
hLabel2.Height = 21                                           'Label Height
hLabel2.expand = True                                         'Expand the Label
hLabel2.Text = "The decimal equivelent is: -"                 'Put text in the Label

hValueBox = New ValueBox(Me)                                  'Create a ValueBox
hValueBox.Height = 21                                         'ValuBox Height
hValueBox.expand = True                                       'Expand the ValueBox

End
```

### GW-BASIC

The Chipmunk Basic through IF-THEN statements solution works without any changes.

### Liberty BASIC

As Fortran & PureBasic.

```  print "MCMXCIX = "; romanDec( "MCMXCIX") '1999
print "MDCLXVI = "; romanDec( "MDCLXVI") '1666
print "XXV     = "; romanDec( "XXV")     '25
print "CMLIV   = "; romanDec( "CMLIV")   '954
print "MMXI    = "; romanDec( "MMXI")    '2011

end

function romanDec( roman\$)
arabic  =0
lastval =0

for i = len( roman\$) to 1 step -1
select case upper\$( mid\$( roman\$, i, 1))
case "M"
n = 1000
case "D"
n = 500
case "C"
n = 100
case "L"
n = 50
case "X"
n = 10
case "V"
n = 5
case "I"
n = 1
case else
n = 0
end select

if n <lastval then
arabic =arabic -n
else
arabic =arabic +n
end if

lastval =n
next

romanDec =arabic
end function```
Output:
```MCMXCIX = 1999
MDCLXVI = 1666
XXV     = 25
CMLIV   = 954
MMXI    = 2011```

### MSX Basic

The Chipmunk Basic through IF-THEN statements solution works without any changes.

### PureBasic

```Procedure romanDec(roman.s)
Protected i, n, lastval, arabic

For i = Len(roman) To 1 Step -1
Select UCase(Mid(roman, i, 1))
Case "M"
n = 1000
Case "D"
n = 500
Case "C"
n = 100
Case "L"
n = 50
Case "X"
n = 10
Case "V"
n = 5
Case "I"
n = 1
Default
n = 0
EndSelect
If (n < lastval)
arabic - n
Else
arabic + n
EndIf
lastval = n
Next

ProcedureReturn arabic
EndProcedure

If OpenConsole()
PrintN(Str(romanDec("MCMXCIX"))) ;1999
PrintN(Str(romanDec("MDCLXVI"))) ;1666
PrintN(Str(romanDec("XXV")))     ;25
PrintN(Str(romanDec("CMLIV")))   ;954
PrintN(Str(romanDec("MMXI")))    ;2011

Print(#CRLF\$ + #CRLF\$ + "Press ENTER to exit"): Input()
CloseConsole()
EndIf
```
Output:
```1999
1666
25
954
2011```

### QBasic

```FUNCTION romToDec (roman\$)
num = 0
prenum = 0
FOR i = LEN(roman\$) TO 1 STEP -1
x\$ = MID\$(roman\$, i, 1)
n = 0
IF x\$ = "M" THEN n = 1000
IF x\$ = "D" THEN n = 500
IF x\$ = "C" THEN n = 100
IF x\$ = "L" THEN n = 50
IF x\$ = "X" THEN n = 10
IF x\$ = "V" THEN n = 5
IF x\$ = "I" THEN n = 1

IF n < preNum THEN num = num - n ELSE num = num + n
preNum = n
NEXT i

romToDec = num
END FUNCTION

!Testing
PRINT "MCMXCIX = "; romToDec("MCMXCIX")     '1999
PRINT "MDCLXVI = "; romToDec("MDCLXVI")     '1666
PRINT "XXV     = "; romToDec("XXV")         '25
PRINT "CMLIV   = "; romToDec("CMLIV")       '954
PRINT "MMXI    = "; romToDec("MMXI")        '2011
```

### QB64

```SCREEN _NEWIMAGE(400, 600, 32)

CLS

Main:
'------------------------------------------------
' CALLS THE romToDec FUNCTION WITH THE ROMAN
' NUMERALS AND RETURNS ITS DECIMAL EQUIVELENT.
'
PRINT "ROMAN NUMERAL TO DECIMAL CONVERSION"
PRINT: PRINT

PRINT "MDCCIV  = "; romToDec("MDCCIV") '1704
PRINT "MCMXC   = "; romToDec("MCMXC") '1990
PRINT "MMVIII  = "; romToDec("MMVIII") '2008
PRINT "MDCLXVI = "; romToDec("MDCLXVI") '1666
PRINT: PRINT
PRINT "Here are other solutions not from the TASK:"
PRINT "MCMXCIX = "; romToDec("MCMXCIX") '1999
PRINT "XXV     = "; romToDec("XXV") '25
PRINT "CMLIV   = "; romToDec("CMLIV") '954
PRINT "MMXI    = "; romToDec("MMXI") '2011
PRINT "MMIIIX  = "; romToDec("MMIIIX") '2011
PRINT: PRINT
PRINT "2011 can be written either as MMXI or MMIIIX"
PRINT "With the IX = 9, MMIIIX is also 2011."
PRINT "2011 IS CORRECT (MM=2000 + II = 2 + IX = 9)"

END

FUNCTION romToDec (roman AS STRING)
'------------------------------------------------------
' FUNCTION THAT CONVERTS ANY ROMAN NUMERAL TO A DECIMAL
'
prenum = 0: num = 0
LN = LEN(roman)
FOR i = LN TO 1 STEP -1
x\$ = MID\$(roman, i, 1)
n = 1000
SELECT CASE x\$
CASE "M": n = n / 1
CASE "D": n = n / 2
CASE "C": n = n / 10
CASE "L": n = n / 20
CASE "X": n = n / 100
CASE "V": n = n / 200
CASE "I": n = n / n
CASE ELSE: n = 0
END SELECT
IF n < prenum THEN num = num - n ELSE num = num + n
prenum = n
NEXT i

romToDec = num

END FUNCTION```

### Run BASIC

```print "MCMXCIX = "; romToDec( "MCMXCIX") '1999
print "MDCLXVI = "; romToDec( "MDCLXVI") '1666
print "XXV     = "; romToDec( "XXV")     '25
print "CMLIV   = "; romToDec( "CMLIV")   '954
print "MMXI    = "; romToDec( "MMXI")    '2011

function romToDec(roman\$)
for i  = len(roman\$) to 1 step -1
x\$    = mid\$(roman\$, i, 1)
n     = 0
if x\$ = "M" then n = 1000
if x\$ = "D" then n = 500
if x\$ = "C" then n = 100
if x\$ = "L" then n = 50
if x\$ = "X" then n = 10
if x\$ = "V" then n = 5
if x\$ = "I" then n = 1

if n < preNum then num = num - n else num = num + n
preNum = n
next

romToDec =num
end function```

### TechBASIC

```Main:
!------------------------------------------------
! CALLS THE romToDec FUNCTION WITH THE ROMAN
! NUMERALS AND RETURNS ITS DECIMAL EQUIVELENT.
!

PRINT "MCMXC   = "; romToDec("MCMXC")   !1990
PRINT "MMVIII  = "; romToDec("MMVIII")  !2008
PRINT "MDCLXVI = "; romToDec("MDCLXVI") !1666
PRINT:PRINT
PRINT "Here are other solutions not from the TASK:"
PRINT "MCMXCIX = "; romToDec("MCMXCIX") !1999
PRINT "XXV     = "; romToDec("XXV")     !25
PRINT "CMLIV   = "; romToDec("CMLIV")   !954
PRINT "MMXI    = "; romToDec("MMXI")    !2011
PRINT:PRINT
PRINT "Without error checking, this also is 2011, but is wrong"
PRINT "MMIIIX  = "; romToDec("MMIIIX")  !INVAID, 2011

STOP

FUNCTION romToDec(roman AS STRING) AS INTEGER
!------------------------------------------------------
! FUNCTION THAT CONVERTS ANY ROMAN NUMERAL TO A DECIMAL
!
prenum=0!num=0
ln=LEN(roman)
FOR i=ln TO 1 STEP -1
x\$=MID(roman,i,1)
n=1000
SELECT CASE x\$
CASE "M":n=n/1
CASE "D":n=n/2
CASE "C":n=n/10
CASE "L":n=n/20
CASE "X":n=n/100
CASE "V":n=n/200
CASE "I":n=n/n
CASE ELSE:n=0
END SELECT
IF n < preNum THEN num=num-n ELSE num=num+n
preNum=n
next i

romToDec=num

END FUNCTION```
Output:
```MCMXC   = 1990
MMVIII  = 2008
MDCLXVI = 1666

Here are other solutions not from the TASK:
MCMXCIX = 1999
XXV     = 25
CMLIV   = 954
MMXI    = 2011

Without error checking, this also is 2011, but is wrong
MMIIIX  = 2011```

### TI-83 BASIC

Using the Rom‣Dec function "real(21," from Omnicalc.

```PROGRAM:ROM2DEC
:Input Str1
:Disp real(21,Str1)```

Using TI-83 BASIC

```PROGRAM:ROM2DEC
:Input "ROMAN:",Str1
:{1000,500,100,50,10,5,1}➞L1
:0➞P
:0➞Y
:For(I,length(Str1),1,-1)
:inString("MDCLXVI",sub(Str1,I,1))➞X
:If X≤0:Then
:Stop
:End
:L1(x)➞N
:If N<P:Then
:Y–N➞Y
:Else
:Y+N➞Y
:End
:N➞P
:End
:Disp Y```

### True BASIC

```FUNCTION romtodec(roman\$)
LET num = 0
LET prenum = 0
FOR i = len(roman\$) to 1 step -1
LET x\$ = (roman\$)[i:i+1-1]
LET n = 0
IF x\$ = "M" then LET n = 1000
IF x\$ = "D" then LET n = 500
IF x\$ = "C" then LET n = 100
IF x\$ = "L" then LET n = 50
IF x\$ = "X" then LET n = 10
IF x\$ = "V" then LET n = 5
IF x\$ = "I" then LET n = 1
IF n < prenum then LET num = num-n else LET num = num+n
LET prenum = n
NEXT i

LET romtodec = num
END FUNCTION

!Testing
PRINT "MCMXCIX = "; romToDec("MCMXCIX")     !1999
PRINT "MDCLXVI = "; romToDec("MDCLXVI")     !1666
PRINT "XXV     = "; romToDec("XXV")         !25
PRINT "CMLIV   = "; romToDec("CMLIV")       !954
PRINT "MMXI    = "; romToDec("MMXI")        !2011
END
```

### XBasic

Works with: Windows XBasic
```PROGRAM  "romandec"
VERSION  "0.0000"

DECLARE FUNCTION Entry ()
DECLARE FUNCTION romToDec (roman\$)

FUNCTION  Entry ()
PRINT "MCMXCIX = "; romToDec("MCMXCIX")
PRINT "MDCLXVI = "; romToDec("MDCLXVI")
PRINT "XXV     = "; romToDec("XXV")
PRINT "CMLIV   = "; romToDec("CMLIV")
PRINT "MMXI    = "; romToDec("MMXI")
END FUNCTION

FUNCTION romToDec (roman\$)
num = 0
prenum = 0
FOR i = LEN(roman\$) TO 1 STEP -1
x\$ = MID\$(roman\$, i, 1)
SELECT CASE x\$
CASE "M" : n = 1000
CASE "D" : n = 500
CASE "C" : n = 100
CASE "L" : n = 50
CASE "X" : n = 10
CASE "V" : n = 5
CASE "I" : n = 1
END SELECT
IF n < prenum THEN num = num-n ELSE num = num+n
prenum = n
NEXT i

RETURN num
END FUNCTION
END PROGRAM
```

### Yabasic

```romans\$ = "MDCLXVI"
decmls\$ = "1000,500,100,50,10,5,1"

sub romanDec(s\$)
local i, n, prev, res, decmls\$(1)

n = token(decmls\$, decmls\$(), ",")

for i = len(s\$) to 1 step -1
n = val(decmls\$(instr(romans\$, mid\$(s\$, i, 1))))
if n < prev n = 0 - n
res = res + n
prev = n
next i
return res
end sub

? romanDec("MCMXCIX")               // 1999
? romanDec("MDCLXVI")               // 1666
? romanDec("XXV")                   // 25
? romanDec("XIX")                   // 19
? romanDec("XI")                    // 11
? romanDec("CMLIV")                 // 954
? romanDec("MMXI")                  // 2011
? romanDec("CD")                    // 400
? romanDec("MCMXC")                 // 1990
? romanDec("MMVIII")                // 2008
? romanDec("MMIX")                  // 2009
? romanDec("MDCLXVI")               // 1666
? romanDec("MMMDCCCLXXXVIII")       // 3888```

## Arturo

```syms: #[ M: 1000, D: 500, C: 100, L: 50, X: 10, V: 5, I: 1 ]

fromRoman: function [roman][
ret: 0
loop 0..(size roman)-2 'ch [
fst: roman\[ch]
snd: roman\[ch+1]
valueA: syms\[fst]
valueB: syms\[snd]

if? valueA < valueB -> ret: ret - valueA
else				-> ret: ret + valueA
]
return ret + syms\[last roman]
]

loop ["MCMXC" "MMVIII" "MDCLXVI"] 'r -> print [r "->" fromRoman r]
```
Output:
```MCMXC -> 1990
MMVIII -> 2008
MDCLXVI -> 1666```

## AutoHotkey

Works with: AutoHotkey_L
```Roman_Decode(str){
res := 0
Loop Parse, str
{
n := {M: 1000, D:500, C:100, L:50, X:10, V:5, I:1}[A_LoopField]
If ( n > OldN ) && OldN
res -= 2*OldN
res += n, oldN := n
}
return res
}

test = MCMXC|MMVIII|MDCLXVI
Loop Parse, test, |
res .= A_LoopField "`t= " Roman_Decode(A_LoopField) "`r`n"
clipboard := res
```
Output:
```MCMXC	= 1990
MMVIII	= 2008
MDCLXVI	= 1666```

## AWK

```# syntax: GAWK -f ROMAN_NUMERALS_DECODE.AWK
BEGIN {
leng = split("MCMXC MMVIII MDCLXVI",arr," ")
for (i=1; i<=leng; i++) {
n = arr[i]
printf("%s = %s\n",n,roman2arabic(n))
}
exit(0)
}
function roman2arabic(r,  a,i,p,q,u,ua,una,unr) {
r = toupper(r)
unr = "MDCLXVI" # each Roman numeral in descending order
una = "1000 500 100 50 10 5 1" # and its Arabic equivalent
split(una,ua," ")
i = split(r,u,"")
a = ua[index(unr,u[i])]
while (--i) {
p = index(unr,u[i])
q = index(unr,u[i+1])
a += ua[p] * ((p>q) ? -1 : 1)
}
return( (a>0) ? a : "" )
}
```
Output:
```MCMXC = 1990
MMVIII = 2008
MDCLXVI = 1666```

## Batch File

Translation of: Fortran
```@echo off
setlocal enabledelayedexpansion

::Testing...
call :toArabic MCMXC
echo MCMXC = !arabic!
call :toArabic MMVIII
echo MMVIII = !arabic!
call :toArabic MDCLXVI
echo MDCLXVI = !arabic!
call :toArabic CDXLIV
echo CDXLIV = !arabic!
call :toArabic XCIX
echo XCIX = !arabic!
pause>nul
exit/b 0

::The "function"...
:toArabic
set roman=%1
set arabic=
set lastval=
%== Alternative for counting the string length ==%
set leng=-1
for /l %%. in (0,1,1000) do set/a leng+=1&if "!roman:~%%.,1!"=="" goto break
:break
set /a last=!leng!-1
for /l %%i in (!last!,-1,0) do (
set n=0
if /i "!roman:~%%i,1!"=="M" set n=1000
if /i "!roman:~%%i,1!"=="D" set n=500
if /i "!roman:~%%i,1!"=="C" set n=100
if /i "!roman:~%%i,1!"=="L" set n=50
if /i "!roman:~%%i,1!"=="X" set n=10
if /i "!roman:~%%i,1!"=="V" set n=5
if /i "!roman:~%%i,1!"=="I" set n=1

if !n! lss !lastval! (
set /a arabic-=n
) else (
set /a arabic+=n
)
set lastval=!n!
)
goto :EOF
```
Output:
```MCMXC = 1990
MMVIII = 2008
MDCLXVI = 1666
CDXLIV = 444
XCIX = 99```

## BCPL

```get "libhdr"

let roman(s) = valof
\$(  let digit(ch) = valof
\$(  let ds = table 'm','d','c','l','x','v','i'
let vs = table 1000,500,100,50,10,5,1
for i=0 to 6
if ds!i=(ch|32) then resultis vs!i
resultis 0
\$)
let acc = 0
for i=1 to s%0
\$(  let d = digit(s%i)
if d=0 then resultis 0
test i<s%0 & d<digit(s%(i+1))
do acc := acc-d
or acc := acc+d
\$)
resultis acc
\$)

let show(s) be writef("%S: %N*N", s, roman(s))

let start() be
\$(  show("MCMXC")
show("MDCLXVI")
show("MMVII")
show("MMXXI")
\$)```
Output:
```MCMXC: 1990
MDCLXVI: 1666
MMVII: 2007
MMXXI: 2021```

## BQN

```⟨ToArabic⇐A⟩ ← {
c ← "IVXLCDM"         # Characters
v ← ⥊ (10⋆↕4) ×⌜ 1‿5  # Their values
A ⇐ +´∘(⊢×¯1⋆<⟜«) v ⊏˜ c ⊐ ⊢
}
```
Example use:
```   ToArabic¨ "MCMXC"‿"MDCLXVI"‿"MMVII"‿"MMXXI"
⟨ 1990 1666 2007 2021 ⟩
```

## Bracmat

Translation of: Icon and Unicon
```  ( unroman
=   nbr,lastVal,val
.     0:?nbr:?lastVal
& @( low\$!arg
:   ?
%@?L
( ?
&     (m.1000)
(d.500)
(c.100)
(l.50)
(x.10)
(v.5)
(i.1)
: ? (!L.?val) ?
&     (!val:~>!lastVal|!val+-2*!lastVal)
+ !nbr
: ?nbr
& !val:?lastVal
& ~
)
)
| !nbr
)
&     (M.1000)
(MCXI.1111)
(CMXI.911)
(MCM.1900)
(MCMXC.1990)
(MMVIII.2008)
(MMIX.2009)
(MCDXLIV.1444)
(MDCLXVI.1666)
(MMXII.2012)
: ?years
& (test=.out\$(!arg unroman\$!arg))
& (   !years
: ? (?L.?D) (?&test\$!L&~)
| done
);```
Output:
```M 1000
MCXI 1111
CMXI 911
MCM 1900
MCMXC 1990
MMVIII 2008
MMIX 2009
MCDXLIV 1444
MDCLXVI 1666
MMXII 2012```

## C

Note: the code deliberately did not distinguish between "I", "J" or "U", "V", doing what Romans did for fun.

```#include <stdio.h>

int digits[26] = { 0, 0, 100, 500, 0, 0, 0, 0, 1, 1, 0, 50, 1000, 0, 0, 0, 0, 0, 0, 0, 5, 5, 0, 10, 0, 0 };

/* assuming ASCII, do upper case and get index in alphabet. could also be
inline int VALUE(char x) { return digits [ (~0x20 & x) - 'A' ]; }
if you think macros are evil */
#define VALUE(x) digits[(~0x20 & (x)) - 'A']

int decode(const char * roman)
{
const char *bigger;
int current;
int arabic = 0;
while (*roman != '\0') {
current = VALUE(*roman);
/*      if (!current) return -1;
note: -1 can be used as error code; Romans didn't even have zero
*/
bigger = roman;

/* look for a larger digit, like IV or XM */
while (VALUE(*bigger) <= current && *++bigger != '\0');

if (*bigger == '\0')
arabic += current;
else {
arabic += VALUE(*bigger);
while (roman < bigger)
arabic -= VALUE(* (roman++) );
}

roman ++;
}
return arabic;
}

int main()
{
const char * romans[] = { "MCmxC", "MMVIII", "MDClXVI", "MCXLUJ" };
int i;

for (i = 0; i < 4; i++)
printf("%s\t%d\n", romans[i], decode(romans[i]));

return 0;
}
```

## C#

```using System;
using System.Collections.Generic;

namespace Roman
{
internal class Program
{
private static void Main(string[] args)
{
// Decode and print the numerals.
Console.WriteLine("{0}: {1}", "MCMXC", Decode("MCMXC"));
Console.WriteLine("{0}: {1}", "MMVIII", Decode("MMVIII"));
Console.WriteLine("{0}: {1}", "MDCLXVI", Decode("MDCLXVI"));
}

// Dictionary to hold our numerals and their values.
private static readonly Dictionary<char, int> RomanDictionary = new Dictionary<char, int>
{
{'I', 1},
{'V', 5},
{'X', 10},
{'L', 50},
{'C', 100},
{'D', 500},
{'M', 1000}
};

private static int Decode(string roman)
{
/* Make the input string upper-case,
* because the dictionary doesn't support lower-case characters. */
roman = roman.ToUpper();

/* total = the current total value that will be returned.
* minus = value to subtract from next numeral. */
int total = 0, minus = 0;

for (int i = 0; i < roman.Length; i++) // Iterate through characters.
{
// Get the value for the current numeral. Takes subtraction into account.
int thisNumeral = RomanDictionary[roman[i]] - minus;

/* Checks if this is the last character in the string, or if the current numeral
* is greater than or equal to the next numeral. If so, we will reset our minus
* variable and add the current numeral to the total value. Otherwise, we will
* subtract the current numeral from the next numeral, and continue. */
if (i >= roman.Length - 1 ||
thisNumeral + minus >= RomanDictionary[roman[i + 1]])
{
total += thisNumeral;
minus = 0;
}
else
{
minus = thisNumeral;
}
}

}
}
}
```
Output:
```MCMXC: 1990
MMVIII: 2008
MDCLXVI: 1666
```

## C++

```#include <exception>
#include <string>
#include <iostream>
using namespace std;

namespace Roman
{
int ToInt(char c)
{
switch (c)
{
case 'I':  return 1;
case 'V':  return 5;
case 'X':  return 10;
case 'L':  return 50;
case 'C':  return 100;
case 'D':  return 500;
case 'M':  return 1000;
}
throw exception("Invalid character");
}

int ToInt(const string& s)
{
int retval = 0, pvs = 0;
for (auto pc = s.rbegin(); pc != s.rend(); ++pc)
{
const int inc = ToInt(*pc);
retval += inc < pvs ? -inc : inc;
pvs = inc;
}
return retval;
}
}

int main(int argc, char* argv[])
{
try
{
cout << "MCMXC = " << Roman::ToInt("MCMXC") << "\n";
cout << "MMVIII = " << Roman::ToInt("MMVIII") << "\n";
cout << "MDCLXVI = " << Roman::ToInt("MDCLXVI") << "\n";
}
catch (exception& e)
{
cerr << e.what();
return -1;
}
return 0;
}
```
Output:
```MCMXC = 1990
MMVIII = 2008
MDCLXVI = 1666```

## Ceylon

```shared void run() {

value numerals = map {
'I' -> 1,
'V' -> 5,
'X' -> 10,
'L' -> 50,
'C' -> 100,
'D' -> 500,
'M' -> 1000
};

function toHindu(String roman) {
variable value total = 0;
for(i->c in roman.indexed) {
assert(exists currentValue = numerals[c]);
/* Look at the next letter to see if we're looking
at a IV or CM or whatever. If so subtract the
current number from the total. */
if(exists next = roman[i + 1],
exists nextValue = numerals[next],
currentValue < nextValue) {
total -= currentValue;
} else {
total += currentValue;
}
}
}

assert(toHindu("I") == 1);
assert(toHindu("II") == 2);
assert(toHindu("IV") == 4);
assert(toHindu("MDCLXVI") == 1666);
assert(toHindu("MCMXC") == 1990);
assert(toHindu("MMVIII") == 2008);
}
```

## Clojure

```;; Incorporated some improvements from the alternative implementation below
(defn ro2ar [r]
(->> (reverse (.toUpperCase r))
(map {\M 1000 \D 500 \C 100 \L 50 \X 10 \V 5 \I 1})
(partition-by identity)
(map (partial apply +))
(reduce #(if (< %1 %2) (+ %1 %2) (- %1 %2)))))

;; alternative
(def numerals { \I 1, \V 5, \X 10, \L 50, \C 100, \D 500, \M 1000})
(defn from-roman [s]
(->> s .toUpperCase
(map numerals)
(reduce (fn [[sum lastv] curr] [(+ sum curr (if (< lastv curr) (* -2 lastv) 0)) curr]) [0,0])
first))
```
Output:
```(map ro2ar ["MDCLXVI" "MMMCMXCIX" "XLVIII" "MMVIII"])
(1666 3999 48 2008)```

## CLU

```roman = cluster is decode
rep = null

digit_value = proc (c: char) returns (int) signals (invalid)
if c < 'a' then c := char\$i2c(char\$c2i(c) + 32) end
if     c = 'm' then return(1000)
elseif c = 'd' then return(500)
elseif c = 'c' then return(100)
elseif c = 'l' then return(50)
elseif c = 'x' then return(10)
elseif c = 'v' then return(5)
elseif c = 'i' then return(1)
else signal invalid
end
end digit_value

decode = proc (s: string) returns (int) signals (invalid)
acc: int := 0
for i: int in int\$from_to(1, string\$size(s)) do
d: int := digit_value(s[i])
if i < string\$size(s) cand d < digit_value(s[i+1]) then
acc := acc - d
else
acc := acc + d
end
end resignal invalid
return(acc)
end decode
end roman

start_up = proc ()
po: stream := stream\$primary_output()
tests: array[string] := array[string]\$
["MCMXC", "mdclxvi", "MmViI", "mmXXi", "INVALID"]

for test: string in array[string]\$elements(tests) do
stream\$puts(po, test || ": ")
stream\$putl(po, int\$unparse(roman\$decode(test))) except when invalid:
stream\$putl(po, "not a valid Roman numeral!")
end
end
end start_up```
Output:
```MCMXC: 1990
mdclxvi: 1666
MmViI: 2007
mmXXi: 2021
INVALID: not a valid Roman numeral!```

## COBOL

```      IDENTIFICATION DIVISION.
PROGRAM-ID.  UNROMAN.
DATA DIVISION.
WORKING-STORAGE SECTION.
01  filler.
03  i              pic 9(02) comp.
03  j              pic 9(02) comp.
03  k              pic 9(02) comp.
03  l              pic 9(02) comp.
01  inp-roman.
03  inp-rom-ch     pic x(01) occurs 20 times.
01  inp-roman-digits.
03  inp-rom-digit  pic 9(01) occurs 20 times.
01  ws-search-idx        pic 9(02) comp.
01  ws-tbl-table-def.
03  filler pic x(05) value '1000M'.
03  filler pic x(05) value '0500D'.
03  filler pic x(05) value '0100C'.
03  filler pic x(05) value '0050L'.
03  filler pic x(05) value '0010X'.
03  filler pic x(05) value '0005V'.
03  filler pic x(05) value '0001I'.
01  filler redefines ws-tbl-table-def.
03  ws-tbl-roman      occurs 07 times indexed by rx.
05  ws-tbl-rom-val  pic 9(04).
05  ws-tbl-rom-ch   pic x(01).
01  ws-number           pic s9(05) value 0.
01  ws-number-pic       pic zzzz9-.

PROCEDURE DIVISION.
accept inp-roman
perform
until inp-roman = ' '
move zeroes to inp-roman-digits
perform
varying i from 1 by +1 until inp-rom-ch (i) = ' '
set rx to 1
search ws-tbl-roman
at end
move 0 to inp-rom-digit (i)
when ws-tbl-rom-ch (rx) = inp-rom-ch (i)
set inp-rom-digit (i) to rx
end-search
end-perform
compute l = i - 1
move 0 to ws-number
perform
varying i from 1 by +1
until i > l or inp-rom-digit (i) = 0
compute j = inp-rom-digit (i)
compute k = inp-rom-digit (i + 1)
if ws-tbl-rom-val (k)
>  ws-tbl-rom-val (j)
compute ws-number
=      ws-number
-      ws-tbl-rom-val (j)
else
compute ws-number
=      ws-number
+      ws-tbl-rom-val (j)
end-if
end-perform
move ws-number to ws-number-pic
display '----------'
display 'roman=' inp-roman
display 'arabic=' ws-number-pic
if i < l or ws-number = 0
display 'invalid/incomplete roman numeral at pos 'i
' found ' inp-rom-ch (i)
end-if
accept inp-roman
end-perform
stop run
.
END PROGRAM UNROMAN.
```
Output:

input was supplied via STDIN

```----------
roman=MCMLXXXVIII

arabic= 1988
----------
roman=MIX

arabic= 1009
----------
roman=MDCCCLXXXVII

arabic= 1887
----------
roman=IX

arabic=    9
----------
roman=MMMDCCCLXXXVIII

arabic= 3888
----------
roman=K

arabic=    0
invalid/incomplete roman numeral at pos 01 found K
----------
roman=MIXT

arabic= 1009
invalid/incomplete roman numeral at pos 04 found T
----------
roman=MCMB

arabic= 1900
invalid/incomplete roman numeral at pos 04 found B
```

## CoffeeScript

```roman_to_demical = (s) ->
# s is well-formed Roman Numeral >= I
numbers =
M: 1000
D: 500
C: 100
L: 50
X: 10
V: 5
I: 1

result = 0
for c in s
num = numbers[c]
result += num
if old_num < num
# If old_num exists and is less than num, then
# we need to subtract it twice, once because we
# to conform to the Roman convention that XC = 90,
# not 110.
result -= 2 * old_num
old_num = num
result

tests =
IV: 4
XLII: 42
MCMXC: 1990
MMVIII: 2008
MDCLXVI: 1666

for roman, expected of tests
dec = roman_to_demical(roman)
console.log "error" if dec != expected
console.log "#{roman} = #{dec}"
```

## Common Lisp

```(defun mapcn (chars nums string)
(loop as char across string as i = (position char chars) collect (and i (nth i nums))))

(defun parse-roman (R)
(loop with nums = (mapcn "IVXLCDM" '(1 5 10 50 100 500 1000) R)
as (A B) on nums if A sum (if (and B (< A B)) (- A) A)))
```

Description:

```Mapcn is a function to map characters to numbers.  It uses the mapping between its first two arguments, chars and nums,
to map its 3rd argument, string, to a list of numbers.  If a character of string is missing from chars, its number will be
nil.

Parse-roman uses mapcn to map R to a list of numbers, then iterates that list with A and B, adding A to the total whenever
it's not less than B, and subtracting it when it is.  If A is nil, it's skipped.  Such as when the character is not Roman.
If B is nil, A is added and not subtracted.  Such as at the end of the list, or when a non-Roman character, such as a space,
is embedded in the Roman.```

Test code:

```(dolist (r '("MCMXC" "MDCLXVI" "MMVIII"))
(format t "~a:~10t~d~%" r (parse-roman r)))
```
Output:
```MCMXC:    1990
MDCLXVI:  1666
MMVIII:   2008```

## Cowgol

```include "cowgol.coh";
include "argv.coh";

# Decode the Roman numeral in the given string.
# Returns 0 if the string does not contain a valid Roman numeral.
sub romanToDecimal(str: [uint8]): (rslt: uint16) is
# Look up a Roman digit
sub digit(char: uint8): (val: uint16) is
# Definition of Roman numerals
record RomanDigit is
char: uint8;
value: uint16;
end record;

var digits: RomanDigit[] := {
{'I',1}, {'V',5}, {'X',10}, {'L',50},
{'C',100}, {'D',500}, {'M',1000}
};

char := char & ~32; # make uppercase

# Look up given digit
var i: @indexof digits := 0;
while i < @sizeof digits loop
val := digits[i].value;
if digits[i].char == char then
return;
end if;
i := i + 1;
end loop;
val := 0;
end sub;

rslt := 0;
while [str] != 0 loop
var cur := digit([str]); # get value of current digit
if cur == 0 then rslt := 0; return; end if; # stop when invalid
str := @next str;
if digit([str]) > cur then
# a digit followed by a larger digit should be subtracted from
# the total
rslt := rslt - cur;
else
rslt := rslt + cur;
end if;
end loop;
end sub;

# Read a Roman numeral from the command line and print its output
ArgvInit();
var argmt := ArgvNext();
if argmt == (0 as [uint8]) then
# No argument
print("No argument\n");
ExitWithError();
end if;

print_i16(romanToDecimal(argmt));
print_nl();```
Output:
```\$ ./romandec.386 MCMXC
1990
\$ ./romandec.386 MDCLXVI
1666
\$ ./romandec.386 MMVII
2007```

## D

```import std.regex, std.algorithm;

int toArabic(in string s) /*pure nothrow*/ {
static immutable weights = [1000, 900, 500, 400, 100,
90, 50, 40, 10, 9, 5, 4, 1];
static immutable symbols = ["M","CM","D","CD","C","XC",
"L","XL","X","IX","V","IV","I"];

int arabic;
foreach (m; s.matchAll("CM|CD|XC|XL|IX|IV|[MDCLXVI]".regex))
arabic += weights[symbols.countUntil(m.hit)];
return arabic;
}

void main() {
assert("MCMXC".toArabic == 1990);
assert("MMVIII".toArabic == 2008);
assert("MDCLXVI".toArabic == 1666);
}
```

Alternative more functional version:

```import std.regex, std.algorithm;

immutable uint[string] w2s;

pure nothrow static this() {
w2s = ["IX":  9, "C":  100, "D":  500, "CM": 900, "I":   1,
"XC": 90, "M": 1000, "L":   50, "CD": 400, "XL": 40,
"V":   5, "X":   10, "IV":   4];
}

uint toArabic(in string s) /*pure nothrow*/ @safe /*@nogc*/ {
return s
.matchAll("CM|CD|XC|XL|IX|IV|[MDCLXVI]".regex)
.map!(m => w2s[m.hit])
.sum;
}

void main() {
assert("MCMXC".toArabic == 1990);
assert("MMVIII".toArabic == 2008);
assert("MDCLXVI".toArabic == 1666);
}
```

## Delphi /Pascal

```program RomanNumeralsDecode;

{\$APPTYPE CONSOLE}

function RomanToInteger(const aRoman: string): Integer;
function DecodeRomanDigit(aChar: Char): Integer;
begin
case aChar of
'M', 'm': Result := 1000;
'D', 'd': Result := 500;
'C', 'c': Result := 100;
'L', 'l': Result := 50;
'X', 'x': Result := 10;
'V', 'v': Result := 5;
'I', 'i': Result := 1
else
Result := 0;
end;
end;

var
i: Integer;
lCurrVal: Integer;
lLastVal: Integer;
begin
Result := 0;

lLastVal := 0;
for i := Length(aRoman) downto 1 do
begin
lCurrVal := DecodeRomanDigit(aRoman[i]);
if lCurrVal < lLastVal then
Result := Result - lCurrVal
else
Result := Result + lCurrVal;
lLastVal := lCurrVal;
end;
end;

begin
Writeln(RomanToInteger('MCMXC'));    // 1990
Writeln(RomanToInteger('MMVIII'));   // 2008
Writeln(RomanToInteger('MDCLXVI'));  // 1666
end.
```

## EasyLang

```func rom2dec rom\$ .
symbols\$[] = [ "M" "D" "C" "L" "X" "V" "I" ]
values[] = [ 1000 500 100 50 10 5 1 ]
val = 0
for dig\$ in strchars rom\$
for i = 1 to len symbols\$[]
if symbols\$[i] = dig\$
v = values[i]
.
.
val += v
if oldv < v
val -= 2 * oldv
.
oldv = v
.
return val
.
print rom2dec "MCMXC"
print rom2dec "MMVIII"
print rom2dec "MDCLXVI"
```

## ECL

The best declarative approach:

```MapChar(STRING1 c) := CASE(c,'M'=>1000,'D'=>500,'C'=>100,'L'=>50,'X'=>10,'V'=>5,'I'=>1,0);

RomanDecode(STRING s) := FUNCTION
dsS := DATASET([{s}],{STRING Inp});
R := { INTEGER2 i; };

R Trans1(dsS le,INTEGER pos) := TRANSFORM
SELF.i := MapChar(le.Inp[pos]) * IF ( MapChar(le.Inp[pos]) < MapChar(le.Inp[pos+1]), -1, 1 );
END;

RETURN SUM(NORMALIZE(dsS,LENGTH(TRIM(s)),Trans1(LEFT,COUNTER)),i);
END;

RomanDecode('MCMLIV');   //1954
RomanDecode('MCMXC');    //1990
RomanDecode('MMVIII');   //2008
RomanDecode('MDCLXVI');  //1666
RomanDecode('MDLXVI');   //1566
```

Here's an alternative that emulates the wat procedural code would approach the problem:

```IMPORT STD;
RomanDecode(STRING s) := FUNCTION
SetWeights := [1000, 900, 500, 400, 100, 90, 50, 40, 10, 9, 5, 4, 1];
SetSymbols := ['M', 'CM', 'D', 'CD', 'C', 'XC', 'L', 'XL', 'X', 'IX', 'V', 'IV', 'I'];
ProcessRec := RECORD
UNSIGNED val;
STRING Roman;
END;
dsSymbols := DATASET(13,TRANSFORM(ProcessRec,SELF.Roman := s, SELF := []));

RECORDOF(dsSymbols) XF(dsSymbols L, dsSymbols R, INTEGER C) := TRANSFORM
ThisRoman := IF(C=1,R.Roman,L.Roman);
IsDone := ThisRoman = '';
Repeatable := C IN [1,5,9,13];
SymSize := IF(C % 2 = 0, 2, 1);
IsNext := STD.Str.StartsWith(ThisRoman,SetSymbols[C]);
SymLen := IF(IsNext,
IF(NOT Repeatable,
SymSize,
MAP(NOT IsDone AND ThisRoman[1] = ThisRoman[2] AND ThisRoman[1] = ThisRoman[3] => 3,
NOT IsDone AND ThisRoman[1] = ThisRoman[2] => 2,
NOT IsDone  => 1,
0)),
0);

SymbolWeight(STRING s) := IF(NOT Repeatable,
SetWeights[C],
CHOOSE(LENGTH(s),SetWeights[C],SetWeights[C]*2,SetWeights[C]*3,0));

SELF.Roman := IF(IsDone,ThisRoman,ThisRoman[SymLen+1..]);
SELF.val   := IF(IsDone,L.val,L.Val + IF(IsNext,SymbolWeight(ThisRoman[1..SymLen]),0));
END;
i := ITERATE(dsSymbols,XF(LEFT,RIGHT,COUNTER));
RETURN i[13].val;
END;

RomanDecode('MCMLIV');   //1954
RomanDecode('MCMXC');    //1990
RomanDecode('MMVIII');   //2008
RomanDecode('MDCLXVI');  //1666
RomanDecode('MDLXVI');   //1566
```

## Ed

```H
g/[^MDCLXVI]/s///g
# simplify the quirky parts
g/CM/s//CCCCCCCCC/
g/D/s//CCCCC/
g/CD/s//CCCC/
g/XC/s//XXXXXXXXX/
g/L/s//XXXXX/
g/XL/s//XXXX/
g/IX/s//IIIIIIIII/
g/V/s//IIIII/
g/IV/s//IIII/
# convert simplified numerals to integers
g/MMMMMMMMM/s//9/
g/MMMMMMMM/s//8/
g/MMMMMMM/s//7/
g/MMMMMM/s//6/
g/MMMMM/s//5/
g/MMMM/s//4/
g/MMM/s//3/
g/MM/s//2/
g/M/s//1/
v/^[0-9].*\$/s/.*/0&/
g/CCCCCCCCC/s//9/
g/CCCCCCCC/s//8/
g/CCCCCCC/s//7/
g/CCCCCC/s//6/
g/CCCCC/s//5/
g/CCCC/s//4/
g/CCC/s//3/
g/CC/s//2/
g/C/s//1/
v/^[0-9]{2}.*\$/s/^([0-9])(.*)\$/\10\2/
g/XXXXXXXXX/s//9/
g/XXXXXXXX/s//8/
g/XXXXXXX/s//7/
g/XXXXXX/s//6/
g/XXXXX/s//5/
g/XXXX/s//4/
g/XXX/s//3/
g/XX/s//2/
g/X/s//1/
v/^[0-9]{3}.*\$/s/^([0-9]{2})(.*)\$/\10\2/
g/IIIIIIIII/s//9/
g/IIIIIIII/s//8/
g/IIIIIII/s//7/
g/IIIIII/s//6/
g/IIIII/s//5/
g/IIII/s//4/
g/III/s//3/
g/II/s//2/
g/I/s//1/
v/^[0-9]{4}.*\$/s/^([0-9]{3})(.*)\$/\10\2/
g/^0+([0-9])/s//\1/
,p
Q```

## Eiffel

This solution is case insensitive. It performs no input validation other than checking that all Roman digits in the input string are one of M, D, C, L, X, V, and I.

```class
APPLICATION

create
make

feature {NONE} -- Initialization

make
local
numbers: ARRAY [STRING]
do
numbers := <<"MCMXC", "MMVIII", "MDCLXVI",
-- 1990     2008      1666
"MMMCLIX", "MCMLXXVII", "MMX">>
-- 3159       1977         2010
across numbers as n loop
print (n.item +
" in Roman numerals is " +
roman_to_decimal (n.item).out +
" in decimal Arabic numerals.")
print ("%N")
end
end

feature -- Roman numerals

roman_to_decimal (a_str: STRING): INTEGER
-- Decimal representation of Roman numeral `a_str'
require
is_roman (a_str)
local
l_pos: INTEGER
cur: INTEGER -- Value of the digit read in the current iteration
prev: INTEGER -- Value of the digit read in the previous iteration
do
from
l_pos := 0
Result := 0
prev := 1 + max_digit_value
until
l_pos = a_str.count
loop
l_pos := l_pos + 1
cur := roman_digit_to_decimal (a_str.at (l_pos))
if cur <= prev then
Result := Result + cur
else
-- Subtract previous digit from increasing digit
Result := Result - prev + (cur - prev)
end
prev := cur
end
ensure
Result >= 0
end

is_roman (a_string: STRING): BOOLEAN
-- Is `a_string' a valid sequence of Roman digits?
do
Result := across a_string as c all is_roman_digit (c.item) end
end

feature {NONE} -- Implementation

max_digit_value: INTEGER = 1000

is_roman_digit (a_char: CHARACTER): BOOLEAN
-- Is `a_char' a valid Roman digit?
local
l_char: CHARACTER
do
l_char := a_char.as_upper
inspect l_char
when 'I', 'V', 'X', 'L', 'C', 'D', 'M' then
Result := True
else
Result := False
end
end

roman_digit_to_decimal (a_char: CHARACTER): INTEGER
-- Decimal representation of Roman digit `a_char'
require
is_roman_digit (a_char)
local
l_char: CHARACTER
do
l_char := a_char.as_upper
inspect l_char
when 'I' then
Result := 1
when 'V' then
Result := 5
when 'X' then
Result := 10
when 'L' then
Result := 50
when 'C' then
Result := 100
when 'D' then
Result := 500
when 'M' then
Result := 1000
end
ensure
Result > 0
end

end
```

## Elena

ELENA 6.x :

```import extensions;
import system'collections;
import system'routines;
import system'culture;

static RomanDictionary = Dictionary.new()
.setAt("I".toChar(), 1)
.setAt("V".toChar(), 5)
.setAt("X".toChar(), 10)
.setAt("L".toChar(), 50)
.setAt("C".toChar(), 100)
.setAt("D".toChar(), 500)
.setAt("M".toChar(), 1000);

extension op : String
{
toRomanInt()
{
var minus := 0;
var s := self.toUpper();
var total := 0;

for(int i := 0; i < s.Length; i += 1)
{
var thisNumeral := RomanDictionary[s[i]] - minus;
if (i >= s.Length - 1 || thisNumeral + minus >= RomanDictionary[s[i + 1]])
{
total += thisNumeral;
minus := 0
}
else
{
minus := thisNumeral
}
};

^ total
}
}

public program()
{
console.printLine("MCMXC:  ", "MCMXC".toRomanInt());
console.printLine("MMVIII: ", "MMVIII".toRomanInt());
console.printLine("MDCLXVI:", "MDCLXVI".toRomanInt())
}```
Output:
```MCMXC:  1990
MMVIII: 2008
MDCLXVI:1666
```

## Elixir

Translation of: Erlang
```defmodule Roman_numeral do
def decode([]), do: 0
def decode([x]), do: to_value(x)
def decode([h1, h2 | rest]) do
case {to_value(h1), to_value(h2)} do
{v1, v2} when v1 < v2 -> v2 - v1 + decode(rest)
{v1, _} -> v1 + decode([h2 | rest])
end
end

defp to_value(?M), do: 1000
defp to_value(?D), do:  500
defp to_value(?C), do:  100
defp to_value(?L), do:   50
defp to_value(?X), do:   10
defp to_value(?V), do:    5
defp to_value(?I), do:    1
end

Enum.each(['MCMXC', 'MMVIII', 'MDCLXVI', 'IIIID'], fn clist ->
IO.puts "#{clist}\t: #{Roman_numeral.decode(clist)}"
end)
```
Output:
```MCMXC   : 1990
MMVIII  : 2008
MDCLXVI : 1666
```

## Emacs Lisp

```(defun ro2ar (RN)
"Translate a roman number RN into arabic number.
Its argument RN is wether a symbol, wether a list.
Returns the arabic number. (ro2ar 'C) gives 100,
(ro2ar '(X X I V)) gives 24"
(cond
((eq RN 'M) 1000)
((eq RN 'D) 500)
((eq RN 'C) 100)
((eq RN 'L) 50)
((eq RN 'X) 10)
((eq RN 'V) 5)
((eq RN 'I) 1)
((null (cdr RN)) (ro2ar (car RN))) ;; stop recursion
((< (ro2ar (car RN)) (ro2ar (car (cdr RN)))) (- (ro2ar (cdr RN)) (ro2ar (car RN)))) ;; "IV" -> 5-1=4
(t (+ (ro2ar (car RN)) (ro2ar (cdr RN)))))) ;; "VI" -> 5+1=6
```
Output:
```(ro2ar '(M D C L X V I)) ;=> 1666
```

## Erlang

Putting the character X into a list, [X], creates a string with a single character.

```-module( roman_numerals ).

-export( [decode_from_string/1]).

to_value(\$M) -> 1000;
to_value(\$D) ->  500;
to_value(\$C) ->  100;
to_value(\$L) ->   50;
to_value(\$X) ->   10;
to_value(\$V) ->    5;
to_value(\$I) ->    1.

decode_from_string([]) -> 0;
decode_from_string([H1]) -> to_value(H1);
decode_from_string([H1, H2 |Rest]) ->
case {to_value(H1), to_value(H2)} of
{V1, V2} when V1 < V2 -> V2 - V1 + decode_from_string(Rest);
{V1, V1} -> V1 + V1 + decode_from_string(Rest);
{V1, _} -> V1 + decode_from_string([H2|Rest])
end.
```
Output:
```10> roman_numerals:decode_from_string("MCMXC").
1990
11> roman_numerals:decode_from_string("MMVIII").
2008
12> roman_numerals:decode_from_string("MDCLXVI").
1666
```

## ERRE

```PROGRAM ROMAN2ARAB

DIM R%[7]

PROCEDURE TOARAB(ROMAN\$->ANS%)
LOCAL I%,J%,P%,N%
FOR I%=LEN(ROMAN\$) TO 1 STEP -1 DO
J%=INSTR("IVXLCDM",MID\$(ROMAN\$,I%,1))
IF J%=0 THEN
ANS%=-9999  ! illegal character
EXIT PROCEDURE
END IF
IF J%>=P% THEN
N%+=R%[J%]
ELSE
N%-=R%[J%]
END IF
P%=J%
END FOR
ANS%=N%
END PROCEDURE

BEGIN
R%[]=(0,1,5,10,50,100,500,1000)
TOARAB("MCMXCIX"->ANS%)         PRINT(ANS%)
TOARAB("MMXII"->ANS%)           PRINT(ANS%)
TOARAB("MDCLXVI"->ANS%)         PRINT(ANS%)
TOARAB("MMMDCCCLXXXVIII"->ANS%) PRINT(ANS%)
END PROGRAM```

If the answer is -9999, roman number is illegal.

## Euphoria

Translation of: PureBasic
```constant symbols = "MDCLXVI", weights = {1000,500,100,50,10,5,1}
function romanDec(sequence roman)
integer n, lastval, arabic
lastval = 0
arabic = 0
for i = length(roman) to 1 by -1 do
n = find(roman[i],symbols)
if n then
n = weights[n]
end if
if n < lastval then
arabic -= n
else
arabic += n
end if
lastval = n
end for
return arabic
end function

? romanDec("MCMXCIX")
? romanDec("MDCLXVI")
? romanDec("XXV")
? romanDec("CMLIV")
? romanDec("MMXI")```
Output:
```1999
1666
25
954
2011```

## F#

This implementation uses tail recursion. The accumulator (arabic) and the last roman digit (lastval) are recursively passed as each element of the list is consumed.

```let decimal_of_roman roman =
let rec convert arabic lastval = function
let n = match head with
| 'M' | 'm' -> 1000
| 'D' | 'd' -> 500
| 'C' | 'c' -> 100
| 'L' | 'l' -> 50
| 'X' | 'x' -> 10
| 'V' | 'v' -> 5
| 'I' | 'i' -> 1
| _ -> 0
let op = if n > lastval then (-) else (+)
convert (op arabic lastval) n tail
| _ -> arabic + lastval
convert 0 0 (Seq.toList roman)
;;
```

Here is an alternative implementation that uses Seq(uence).fold. It threads a Tuple of the state (accumulator, last roman digit) through the list of characters.

```let decimal_of_roman roman =
let convert (arabic,lastval) c =
let n = match c with
| 'M' | 'm' -> 1000
| 'D' | 'd' -> 500
| 'C' | 'c' -> 100
| 'L' | 'l' -> 50
| 'X' | 'x' -> 10
| 'V' | 'v' -> 5
| 'I' | 'i' -> 1
| _ -> 0
let op = if n > lastval then (-) else (+)
(op arabic lastval, n)
let (arabic, lastval) = Seq.fold convert (0,0) roman
arabic + lastval
;;
```

Test code:

```let tests = ["MCMXC"; "MMVIII"; "MDCLXVII"; "MMMCLIX"; "MCMLXXVII"; "MMX"]
for test in tests do Printf.printf "%s: %d\n" test (decimal_of_roman test)
;;
```
Output:
```MCMXC: 1990
MMVIII: 2008
MDCLXVII: 1667
MMMCLIX: 3159
MCMLXXVII: 1977
MMX: 2010```

## Factor

A roman numeral library ships with Factor.

```USE: roman
( scratchpad ) "MMMCCCXXXIII" roman> .
3333
```

Implementation for decoding:

```CONSTANT: roman-digits
{ "m" "cm" "d" "cd" "c" "xc" "l" "xl" "x" "ix" "v" "iv" "i" }

CONSTANT: roman-values
{ 1000 900 500 400 100 90 50 40 10 9 5 4 1 }

: roman> ( str -- n )
>lower [ roman-digit>= ] monotonic-split
[ roman-value ] map-sum ;

: roman-digit>= ( ch1 ch2 -- ? ) [ roman-digit-index ] bi@ >= ;

: roman-digit-index ( ch -- n ) 1string roman-digits index ;

: roman-value (seq -- n )
[ [ roman-digit-value ] map ] [ all-eq? ] bi
[ sum ] [ first2 swap - ] if ;

: roman-digit-value ( ch -- n )
roman-digit-index roman-values nth ;
```

## FALSE

```[ 32|   {get value of Roman digit on stack}
\$'m= \$[\% 1000\]? ~[
\$'d= \$[\% 500\]? ~[
\$'c= \$[\% 100\]? ~[
\$'l= \$[\% 50\]? ~[
\$'x= \$[\% 10\]? ~[
\$'v= \$[\% 5\]? ~[
\$'i= \$[\% 1\]? ~[
% 0
]?]?]?]?]?]?]?
]r:

0           {accumulator}
[^r;!\$][    {read another, and as long as it is valid...}
\\$@@\\$@@  {copy previous and current}
\>[\_\]?  {if previous smaller than current, negate previous}
]#
%+.         {add final digit to accumulator and output}
10,         {and a newline}```
Output:
```\$ ./false -q romandec.f <<<MCMXC
1990
\$ ./false -q romandec.f <<<MMVIII
2008
\$ ./false -q romandec.f <<<MDCLXVI
1666
\$ ./false -q romandec.f <<<MMXXI
2021```

## Forth

```create (arabic)
1000 128 * char M + ,
500 128 * char D + ,
100 128 * char C + ,
50 128 * char L + ,
10 128 * char X + ,
5 128 * char V + ,
1 128 * char I + ,
does>
7 cells bounds do
i @ over over 127 and = if nip 7 rshift leave else drop then
1 cells +loop dup
;

: >arabic
0 dup >r >r
begin
over over
while
c@ dup (arabic) rot <>
while
r> over r> over over > if 2* negate + else drop then + swap >r >r 1 /string
repeat then drop 2drop r> r> drop
;

s" MCMLXXXIV" >arabic .
```

```\ decode roman numerals using Forth methodology
\ create words to describe and solve the problem
\ ANS/ISO Forth

\ state holders
VARIABLE OLDNDX
VARIABLE CURNDX
VARIABLE NEGFLAG

DECIMAL
CREATE VALUES ( -- addr) 0 , 1 , 5 , 10 , 50 , 100 , 500 , 1000 ,

: NUMERALS ( -- addr len)  S"  IVXLCDM" ;        \ 1st char is a blank
: INIT     ( -- )         CURNDX OFF  OLDNDX OFF  NEGFLAG OFF ;
: REMEMBER ( ndx -- ndx ) CURNDX @ OLDNDX !  DUP CURNDX !  ;
: ]VALUE@  ( ndx -- n )   REMEMBER VALUES [] @ ;
HEX
: TOUPPER ( char -- char ) 05F AND ;

DECIMAL
: >INDEX   ( char -- ndx) TOUPPER >R  NUMERALS TUCK R> SCAN NIP -
DUP 7 > ABORT" Invalid Roman numeral" ;

: >VALUE   ( char -- n ) >INDEX ]VALUE@ ;
: ?ILLEGAL ( ndx --  )   CURNDX @ OLDNDX @ =  NEGFLAG @ AND ABORT" Illegal format" ;

: ?NEGATE ( n -- +n | -n) \ conditional NEGATE
CURNDX @ OLDNDX @ <
IF   NEGFLAG ON  NEGATE
ELSE ?ILLEGAL  NEGFLAG OFF
THEN ;

: >ARABIC  ( addr len -- n )
INIT
0  -ROT            \ accumulator under the stack string args
SWAP DO            \ index the string from back to front
I C@ >VALUE ?NEGATE +
-1 +LOOP ;
```

Alternative Version Forth Console Test

```\ test code  ok
S" i"         >ARABIC . 1  ok
S" ii"        >ARABIC . 2  ok
S" iv"        >ARABIC . 4  ok
S" mdclxvi"   >ARABIC . 1666  ok
S" mm"        >ARABIC . 2000  ok
S" mmm"       >ARABIC . 3000  ok
S" MCMLIV"    >ARABIC . 1954  ok
S" mcmxlvi"   >ARABIC . 1946  ok
S" mdc"       >ARABIC . 1600  ok
S" mdcl"      >ARABIC . 1650  ok
S" mdclxvi"   >ARABIC . 1666  ok
S" mcmlxxxiv" >ARABIC . 1984  ok
```

## Fortran

Works with: Fortran version 90 and later
```program Roman_decode
implicit none

write(*,*) decode("MCMXC"), decode("MMVIII"), decode("MDCLXVI")

contains

function decode(roman) result(arabic)
character(*), intent(in) :: roman
integer :: i, n, lastval, arabic

arabic = 0
lastval = 0
do i = len(roman), 1, -1
select case(roman(i:i))
case ('M','m')
n = 1000
case ('D','d')
n = 500
case ('C','c')
n = 100
case ('L','l')
n = 50
case ('X','x')
n = 10
case ('V','v')
n = 5
case ('I','i')
n = 1
case default
n = 0
end select
if (n < lastval) then
arabic = arabic - n
else
arabic = arabic + n
end if
lastval = n
end do
end function decode
end program Roman_decode
```
Output:
`        1990        2008        1666`

## Go

For fluff, the unicode overbar is recognized as a factor of 1000, as described in WP.

```package main

import (
"errors"
"fmt"
)

var m = map[rune]int{
'I': 1,
'V': 5,
'X': 10,
'L': 50,
'C': 100,
'D': 500,
'M': 1000,
}

func parseRoman(s string) (r int, err error) {
if s == "" {
return 0, errors.New("Empty string")
}
is := []rune(s) // easier to convert string up front
var c0 rune     // c0: roman character last read
var cv0 int     // cv0: value of cv

// the key to the algorithm is to process digits from right to left
for i := len(is) - 1; i >= 0; i-- {
c := is[i]
k := c == '\u0305' // unicode overbar combining character
if k {
if i == 0 {
return 0, errors.New(
"Overbar combining character invalid at position 0")
}
i--
c = is[i]
}
cv := m[c]
if cv == 0 {
if c == 0x0305 {
return 0, fmt.Errorf(
"Overbar combining character invalid at position %d", i)
} else {
return 0, fmt.Errorf(
"Character unrecognized as Roman digit: %c", c)
}
}
if k {
c = -c // convention indicating overbar
cv *= 1000
}

// handle cases of new, same, subtractive, changed, in that order.
switch {
default: // case 4: digit change
fallthrough
case c0 == 0: // case 1: no previous digit
c0 = c
cv0 = cv
case c == c0: // case 2: same digit
case cv*5 == cv0 || cv*10 == cv0: // case 3: subtractive
// handle next digit as new.
// a subtractive digit doesn't count as a previous digit.
c0 = 0
r -= cv  // subtract...
}
r += cv // add, in all cases except subtractive
}
return r, nil
}

func main() {
// parse three numbers mentioned in task description
for _, r := range []string{"MCMXC", "MMVIII", "MDCLXVI"} {
v, err := parseRoman(r)
if err != nil {
fmt.Println(err)
} else {
fmt.Println(r, "==", v)
}
}
}
```
Output:
```MCMXC == 1990
MMVIII == 2008
MDCLXVI == 1666
```

Simpler:

```package main

import (
"fmt"
)

var m = map[rune]int{
'I': 1,
'V': 5,
'X': 10,
'L': 50,
'C': 100,
'D': 500,
'M': 1000,
}

func from_roman(roman string) (arabic int) {
last_digit := 1000
for _, r := range roman {
digit := m[r]
if last_digit < digit {
arabic -= 2 * last_digit
}
last_digit = digit
arabic += digit
}

return arabic
}

func main() {
// parse three numbers mentioned in task description
for _, roman_digit := range []string{"MCMXC", "MMVIII", "MDCLXVI"} {
fmt.Printf("%-10s == %d\n", roman_digit, from_roman(roman_digit))
}
}
```

## Golo

```#!/usr/bin/env golosh
----
This module converts a Roman numeral into a decimal number.
----
module Romannumeralsdecode

augment java.lang.Character {

function decode = |this| -> match {
when this == 'I' then 1
when this == 'V' then 5
when this == 'X' then 10
when this == 'L' then 50
when this == 'C' then 100
when this == 'D' then 500
when this == 'M' then 1000
otherwise 0
}
}

augment java.lang.String {

function decode = |this| {
var accumulator = 0
foreach i in [0..this: length()] {
let currentChar = this: charAt(i)
let nextChar = match {
when i + 1 < this: length() then this: charAt(i + 1)
otherwise null
}
if (currentChar: decode() < (nextChar?: decode() orIfNull 0)) {
# if this is something like IV or IX or whatever
accumulator = accumulator - currentChar: decode()
} else {
accumulator = accumulator + currentChar: decode()
}
}
return accumulator
}
}

function main = |args| {
println("MCMXC = " + "MCMXC": decode())
println("MMVIII = " + "MMVIII": decode())
println("MDCLXVI = " + "MDCLXVI": decode())
}
```

## Groovy

Solution:

```enum RomanDigits {
I(1), V(5), X(10), L(50), C(100), D(500), M(1000);

private magnitude;
private RomanDigits(magnitude) { this.magnitude = magnitude }

String toString() { super.toString() + "=\${magnitude}" }

static BigInteger parse(String numeral) {
assert numeral != null && !numeral.empty
def digits = (numeral as List).collect {
RomanDigits.valueOf(it)
}
def L = digits.size()
(0..<L).inject(0g) { total, i ->
def sign = (i == L - 1 || digits[i] >= digits[i+1]) ? 1 : -1
total + sign * digits[i].magnitude
}
}
}
```

Test:

```println """
Digit Values = \${RomanDigits.values()}
M       => \${RomanDigits.parse('M')}
MCXI    => \${RomanDigits.parse('MCXI')}
CMXI    => \${RomanDigits.parse('CMXI')}
MCM     => \${RomanDigits.parse('MCM')}
MCMXC   => \${RomanDigits.parse('MCMXC')}
MMVIII  => \${RomanDigits.parse('MMVIII')}
MMIX    => \${RomanDigits.parse('MMIX')}
MCDXLIV => \${RomanDigits.parse('MCDXLIV')}
MDCLXVI => \${RomanDigits.parse('MDCLXVI')}
"""
```
Output:
```Digit Values = [I=1, V=5, X=10, L=50, C=100, D=500, M=1000]
M       => 1000
MCXI    => 1111
CMXI    => 911
MCM     => 1900
MCMXC   => 1990
MMVIII  => 2008
MMIX    => 2009
MCDXLIV => 1444
MDCLXVI => 1666```

#### Simple declarative idiom

Compiles with GHC.

```module Main where

------------------------
--  DECODER FUNCTION  --
------------------------

decodeDigit :: Char -> Int
decodeDigit 'I' = 1
decodeDigit 'V' = 5
decodeDigit 'X' = 10
decodeDigit 'L' = 50
decodeDigit 'C' = 100
decodeDigit 'D' = 500
decodeDigit 'M' = 1000
decodeDigit _ = error "invalid digit"

--  We process a Roman numeral from right to left, digit by digit, adding the value.
--  If a digit is lower than the previous then its value is negative.
--  The first digit is always positive.

decode roman = decodeRoman startValue startValue rest
where
(first:rest) = reverse roman
startValue = decodeDigit first

decodeRoman :: Int -> Int -> [Char] -> Int
decodeRoman lastSum _ [] = lastSum
decodeRoman lastSum lastValue (digit:rest) = decodeRoman updatedSum digitValue rest
where
digitValue = decodeDigit digit
updatedSum = (if digitValue < lastValue then (-) else (+)) lastSum digitValue

------------------
--  TEST SUITE  --
------------------

main = do
test "MCMXC" 1990
test "MMVIII" 2008
test "MDCLXVI" 1666

test roman expected = putStrLn (roman ++ " = " ++ (show (arabic)) ++ remark)
where
arabic = decode roman
remark = " (" ++ (if arabic == expected then "PASS" else ("FAIL, expected " ++ (show expected))) ++ ")"
```
Output:
```MCMXC = 1990 (PASS)
MMVIII = 2008 (PASS)
MDCLXVI = 1666 (PASS)
```

#### Same logic as above but in a functional idiom

```module Main where

------------------------
--  DECODER FUNCTION  --
------------------------

decodeDigit :: Char -> Int
decodeDigit 'I' = 1
decodeDigit 'V' = 5
decodeDigit 'X' = 10
decodeDigit 'L' = 50
decodeDigit 'C' = 100
decodeDigit 'D' = 500
decodeDigit 'M' = 1000
decodeDigit _ = error "invalid digit"

--  We process a Roman numeral from right to left, digit by digit, adding the value.
--  If a digit is lower than the previous then its value is negative.
--  The first digit is always positive.

decode roman = fst (foldl addValue (0, 0) (reverse roman))
where
addValue (lastSum, lastValue) digit = (updatedSum, value)
where
value = decodeDigit digit;
updatedSum = (if value < lastValue then (-) else (+)) lastSum value

------------------
--  TEST SUITE  --
------------------

main = do
test "MCMXC" 1990
test "MMVIII" 2008
test "MDCLXVI" 1666

test roman expected = putStrLn (roman ++ " = " ++ (show (arabic)) ++ remark)
where
arabic = decode roman
remark = " (" ++ (if arabic == expected then "PASS" else ("FAIL, expected " ++ (show expected))) ++ ")"
```

#### List comprehension

```import Data.List (isPrefixOf)

mapping = [("M",1000),("CM",900),("D",500),("CD",400),("C",100),("XC",90),
("L",50),("XL",40),("X",10),("IX",9),("V",5),("IV",4),("I",1)]

toArabic :: String -> Int
toArabic "" = 0
toArabic str = num + toArabic xs
where (num, xs):_ = [ (num, drop (length n) str) | (n,num) <- mapping, isPrefixOf n str ]
```

Usage:

```ghci> toArabic "MCMXC"
1990
ghci> toArabic "MMVIII"
2008
ghci> toArabic "MDCLXVI"
1666```

#### mapAccum

Or, expressing romanValue in terms of mapAccumL (avoiding recursive descent, and visiting each k v pair just once)

```import Data.Bifunctor (bimap)
import Data.List (isPrefixOf, mapAccumL)

romanValue :: String -> Int
romanValue =
let tr s (k, v) =
until
(not . isPrefixOf k . fst)
(bimap ((drop . length) k) (v +))
(s, 0)
in sum
. snd
. flip
(mapAccumL tr)
[ ("M", 1000),
("CM", 900),
("D", 500),
("CD", 400),
("C", 100),
("XC", 90),
("L", 50),
("XL", 40),
("X", 10),
("IX", 9),
("V", 5),
("IV", 4),
("I", 1)
]

main :: IO ()
main =
mapM_
(print . romanValue)
[ "MDCLXVI",
"MCMXC",
"MMVIII",
"MMXVI",
"MMXVII"
]
```

Or, in a mapAccumR version:

```import Data.List (mapAccumR)
import qualified Data.Map.Strict as M
import Data.Maybe (maybe)

fromRoman :: String -> Maybe Int
fromRoman cs =
let go l r
| l > r = (- r, l)
| otherwise = (r, l)
in traverse (`M.lookup` mapRoman) cs
>>= ( Just . sum . ((:) <\$> fst <*> snd)
. mapAccumR go 0
)

mapRoman :: M.Map Char Int
mapRoman =
M.fromList \$
zip
"MDCLXVI "
[ 1000,
500,
100,
50,
10,
5,
1,
0
]

--------------------------- TEST -------------------------
main :: IO ()
main =
putStrLn \$
fTable
"Decoding Roman numbers:\n"
show
(maybe "Unrecognised character" show)
fromRoman
[ "MDCLXVI",
"MCMXC",
"MMVIII",
"MMXVI",
"MMXVIII",
"MMXBIII"
]

------------------------ FORMATTING ----------------------
fTable ::
String ->
(a -> String) ->
(b -> String) ->
(a -> b) ->
[a] ->
String
fTable s xShow fxShow f xs =
unlines \$
s :
fmap
( ((<>) . rjust w ' ' . xShow)
<*> ((" -> " <>) . fxShow . f)
)
xs
where
rjust n c = drop . length <*> (replicate n c <>)
w = maximum (length . xShow <\$> xs)
```
Output:
```Decoding Roman numbers:

"MDCLXVI" -> 1666
"MCMXC" -> 1990
"MMVIII" -> 2008
"MMXVI" -> 2016
"MMXVIII" -> 2018
"MMXBIII" -> Unrecognised character```

#### Fold

An alternative solution using a fold. (This turns out to be the fastest of the four approaches here)

Translation of: F#
```import qualified Data.Map.Strict as M

fromRoman :: String -> Int
fromRoman xs = partialSum + lastDigit
where
(partialSum, lastDigit) = foldl accumulate (0, 0) (evalRomanDigit <\$> xs)
accumulate (partial, lastDigit) newDigit
| newDigit <= lastDigit = (partial + lastDigit, newDigit)
| otherwise = (partial - lastDigit, newDigit)

mapRoman :: M.Map Char Int
mapRoman =
M.fromList
[ ('I', 1)
, ('V', 5)
, ('X', 10)
, ('L', 50)
, ('C', 100)
, ('D', 500)
, ('M', 1000)
]

evalRomanDigit :: Char -> Int
evalRomanDigit c =
let mInt = M.lookup c mapRoman
in case mInt of
Just x -> x
_ -> error \$ c : " is not a roman digit"

main :: IO ()
main = print \$ fromRoman <\$> ["MDCLXVI", "MCMXC", "MMVIII", "MMXVI", "MMXVII"]
```

Where the left fold above could also be rewritten | as a right fold.

```import qualified Data.Map.Strict as M
import Data.Maybe (maybe)

------------------ ROMAN NUMERALS DECODED ----------------

mapRoman :: M.Map Char Int
mapRoman =
M.fromList \$
zip "IVXLCDM" \$
scanl (*) 1 (cycle [5, 2])

fromRoman :: String -> Maybe Int
fromRoman cs =
let op l r
| l >= r = (+)
| otherwise = (-)
in snd
. foldr
(\l (r, n) -> (l, op l r n l))
(0, 0)
<\$> traverse (`M.lookup` mapRoman) cs

--------------------------- TEST -------------------------
main :: IO ()
main =
putStrLn \$
fTable
"Roman numeral decoding as a right fold:\n"
show
(maybe "(Unrecognised character seen)" show)
fromRoman
[ "MDCLXVI",
"MCMXC",
"MMVIII",
"MMXVI",
"MMXVII",
"QQXVII"
]

------------------------ FORMATTING ----------------------

fTable ::
String ->
(a -> String) ->
(b -> String) ->
(a -> b) ->
[a] ->
String
fTable s xShow fxShow f xs =
unlines \$
s :
fmap
( ((<>) . rjust w ' ' . xShow)
<*> ((" -> " <>) . fxShow . f)
)
xs
where
rjust n c = drop . length <*> (replicate n c <>)
w = maximum (length . xShow <\$> xs)
```
Output:
```Roman numeral decoding as a right fold:

"MDCLXVI" -> 1666
"MCMXC" -> 1990
"MMVIII" -> 2008
"MMXVI" -> 2016
"MMXVII" -> 2017
"QQXVII" -> (Unrecognised character seen)```

#### sum . catMaybes

Summing a list of Map.lookup results on indexed [Char, Char] pairs.

(Probably more trouble than it's worth in practice, but at least an illustration of some Data.Maybe and Data.Map functions)

```import qualified Data.Map.Strict as M (Map, fromList, lookup)
import Data.Maybe (isNothing, isJust, fromJust, catMaybes)
import Data.List (mapAccumL)

mapRoman :: M.Map String Int
mapRoman =
M.fromList
[ ("M", 1000)
, ("CM", 900)
, ("D", 500)
, ("CD", 400)
, ("C", 100)
, ("XC", 90)
, ("L", 50)
, ("XL", 40)
, ("X", 10)
, ("IX", 9)
, ("V", 5)
, ("IV", 4)
, ("I", 1)
]

fromRoman :: String -> Int
fromRoman s =
let value k = M.lookup k mapRoman
in sum . catMaybes . snd \$
mapAccumL
(\mi (l, r, i) ->
let mValue = value [l, r] -- mapRoman lookup of [left, right] Chars
(lastPair, pairValue)
| isJust mValue = (Just i, mValue) -- Pair match: index updated
| isNothing mi || i - fromJust mi > 1 = (mi, value [l])
| otherwise = (mi, Nothing) -- Left Char was counted in pair
in (lastPair, pairValue))
Nothing -- Accumulator – maybe Index to last matched Char pair
(zip3 s (tail s ++ " ") [0 ..]) -- Indexed character pairs

main :: IO ()
main = print \$ fromRoman <\$> ["MDCLXVI", "MCMXC", "MMVIII", "MMXVI", "MMXVII"]
```
Output:
`[1666,1990,2008,2016,2017]`

## Hoon

Library file (e.g. `/lib/rhonda.hoon`):

```|%
++  parse
|=  t=tape  ^-  @ud
=.  t  (cass t)
=|  result=@ud
|-
?~  t  result
?~  t.t  (add result (from-numeral i.t))
=+  [a=(from-numeral i.t) b=(from-numeral i.t.t)]
?:  (gte a b)  \$(result (add result a), t t.t)
\$(result (sub (add result b) a), t t.t.t)
++  yield
|=  n=@ud  ^-  tape
=|  result=tape
=/  values  to-numeral
|-
?~  values  result
?:  (gte n -.i.values)
\$(result (weld result +.i.values), n (sub n -.i.values))
\$(values t.values)
++  from-numeral
|=  c=@t  ^-  @ud
?:  =(c 'i')  1
?:  =(c 'v')  5
?:  =(c 'x')  10
?:  =(c 'l')  50
?:  =(c 'c')  100
?:  =(c 'd')  500
?:  =(c 'm')  1.000
!!
++  to-numeral
^-  (list [@ud tape])
:*
[1.000 "m"]
[900 "cm"]
[500 "d"]
[400 "cd"]
[100 "c"]
[90 "xc"]
[50 "l"]
[40 "xl"]
[10 "x"]
[9 "ix"]
[5 "v"]
[4 "iv"]
[1 "i"]
~
==
--```

Script file ("generator") (e.g. `/gen/roman.hoon`):

```/+  *roman
:-  %say
|=  [* [x=\$%([%from-roman tape] [%to-roman @ud]) ~] ~]
:-  %noun
^-  tape
?-  -.x
%from-roman  "{<(parse +.x)>}"
%to-roman  (yield +.x)
==```

## Icon and Unicon

```link numbers

procedure main()
every R := "MCMXC"|"MDCLXVI"|"MMVIII" do
write(R, " = ",unroman(R))
end
```

The code for this procedure is copied below:

```procedure unroman(s)		#: convert Roman numeral to integer
local nbr,lastVal,val

nbr := lastVal := 0
s ? {
while val := case map(move(1)) of {
"m": 1000
"d": 500
"c": 100
"l": 50
"x": 10
"v": 5
"i": 1
} do {
nbr +:= if val <= lastVal then val else val - 2 * lastVal
lastVal := val
}
}
return nbr
end
```
Output:
```MCMXC = 1990
MDCLXVI = 1666
MMVIII = 2008```

## Insitux

Translation of: Clojure
```(var numerals {"M" 1000 "D" 500 "C" 100 "L" 50 "X" 10 "V" 5 "I" 1})

; Approach A
(function ro->ar r
(-> (reverse (upper-case r))
(map numerals)
(split-with val)
(map (.. +0))
(reduce @(((< % %1) + -)))))

; Approach B
(function ro->ar r
(-> (upper-case r)
(map numerals)
@(reduce (fn [sum lastv] curr [(+ sum curr ((< lastv curr) (* -2 lastv) 0)) curr]) [0 0])
0))

(map ro->ar ["MDCLXVI" "MMMCMXCIX" "XLVIII" "MMVIII"])```
Output:
```[1666 3999 48 2008]
```

## J

```rom2d=: [: (+/ .*  _1^ 0,~ 2</\ ]) 1 5 10 50 100 500 1000 {~ 'IVXLCDM'&i.
```

Example use:

```   rom2d 'MCMXC'
1990
rom2d 'MDCLXVI'
1666
rom2d 'MMVIII'
2008
```

## Java

Works with: Java version 1.5+
```public class Roman {
private static int decodeSingle(char letter) {
switch(letter) {
case 'M': return 1000;
case 'D': return 500;
case 'C': return 100;
case 'L': return 50;
case 'X': return 10;
case 'V': return 5;
case 'I': return 1;
default: return 0;
}
}
public static int decode(String roman) {
int result = 0;
String uRoman = roman.toUpperCase(); //case-insensitive
for(int i = 0;i < uRoman.length() - 1;i++) {//loop over all but the last character
//if this character has a lower value than the next character
if (decodeSingle(uRoman.charAt(i)) < decodeSingle(uRoman.charAt(i+1))) {
//subtract it
result -= decodeSingle(uRoman.charAt(i));
} else {
result += decodeSingle(uRoman.charAt(i));
}
}
//decode the last character, which is always added
result += decodeSingle(uRoman.charAt(uRoman.length()-1));
return result;
}

public static void main(String[] args) {
System.out.println(decode("MCMXC")); //1990
System.out.println(decode("MMVIII")); //2008
System.out.println(decode("MDCLXVI")); //1666
}
}
```
Output:
```1990
2008
1666```
Works with: Java version 1.8+
```import java.util.Set;
import java.util.EnumSet;
import java.util.Collections;
import java.util.stream.Collectors;
import java.util.stream.LongStream;

public interface RomanNumerals {
public enum Numeral {
M(1000), CM(900), D(500), CD(400), C(100), XC(90), L(50), XL(40), X(10), IX(9), V(5), IV(4), I(1);

public final long weight;

private static final Set<Numeral> SET = Collections.unmodifiableSet(EnumSet.allOf(Numeral.class));

private Numeral(long weight) {
this.weight = weight;
}

public static Numeral getLargest(long weight) {
return SET.stream()
.filter(numeral -> weight >= numeral.weight)
.findFirst()
.orElse(I)
;
}
};

public static String encode(long n) {
return LongStream.iterate(n, l -> l - Numeral.getLargest(l).weight)
.limit(Numeral.values().length)
.filter(l -> l > 0)
.mapToObj(Numeral::getLargest)
.map(String::valueOf)
.collect(Collectors.joining())
;
}

public static long decode(String roman) {
long result =  new StringBuilder(roman.toUpperCase()).reverse().chars()
.mapToObj(c -> Character.toString((char) c))
.map(numeral -> Enum.valueOf(Numeral.class, numeral))
.mapToLong(numeral -> numeral.weight)
.reduce(0, (a, b) -> a + (a <= b ? b : -b))
;
if (roman.charAt(0) == roman.charAt(1)) {
result += 2 * Enum.valueOf(Numeral.class, roman.substring(0, 1)).weight;
}
return result;
}

public static void test(long n) {
System.out.println(n + " = " + encode(n));
System.out.println(encode(n) + " = " + decode(encode(n)));
}

public static void main(String[] args) {
LongStream.of(1999, 25, 944).forEach(RomanNumerals::test);
}
}
```
Output:
```1999 = MCMXCIX
MCMXCIX = 1999
25 = XXV
XXV = 25
944 = CMXLIV
CMXLIV = 944```

## JavaScript

### ES5

#### Imperative

Works with: Rhino
Works with: SpiderMonkey
```var Roman = {
Values: [['CM', 900],  ['CD', 400], ['XC',  90], ['XL',  40], ['IV', 4],
['IX',   9], ['V',   5], ['X',   10], ['L',  50],
['C',  100], ['M', 1000], ['I',    1], ['D',  500]],
UnmappedStr : 'Q',
parse: function(str) {
var result = 0
for (var i=0; i<Roman.Values.length; ++i) {
var pair = Roman.Values[i]
var key = pair[0]
var value = pair[1]
var regex = RegExp(key)
while (str.match(regex)) {
result += value
str = str.replace(regex, Roman.UnmappedStr)
}
}
return result
}
}

var test_data = ['MCMXC', 'MDCLXVI', 'MMVIII']
for (var i=0; i<test_data.length; ++i) {
var test_datum = test_data[i]
print(test_datum + ": " + Roman.parse(test_datum))
}
```
Output:
```MCMXC: 1990
MDCLXVI: 1666
MMVIII: 2008
```

#### Functional

(isPrefixOf example)

```(function (lstTest) {

var mapping = [["M", 1000], ["CM", 900], ["D", 500], ["CD", 400], ["C", 100], [
"XC", 90], ["L", 50], ["XL", 40], ["X", 10], ["IX", 9], ["V", 5], ["IV",
4], ["I", 1]];

// s -> n
function romanValue(s) {
// recursion over list of characters
// [c] -> n
function toArabic(lst) {
return lst.length ? function (xs) {
var lstParse = chain(mapping, function (lstPair) {
return isPrefixOf(
lstPair[0], xs
) ? [lstPair[1], drop(lstPair[0].length, xs)] : []
});
return lstParse[0] + toArabic(lstParse[1]);
}(lst) : 0
}
}

// Monadic bind (chain) for lists
function chain(xs, f) {
return [].concat.apply([], xs.map(f));
}

// [a] -> [a] -> Bool
function isPrefixOf(lstFirst, lstSecond) {
return lstFirst.length ? (
lstSecond.length ?
lstFirst[0] === lstSecond[0] && isPrefixOf(
lstFirst.slice(1), lstSecond.slice(1)
) : false
) : true;
}

// Int -> [a] -> [a]
function drop(n, lst) {
return n <= 0 ? lst : (
lst.length ? drop(n - 1, lst.slice(1)) : []
);
}

return lstTest.map(romanValue);

})(['MCMXC', 'MDCLXVI', 'MMVIII']);
```
Output:
```[1990, 1666, 2008]
```

or, more natively:

```(function (lstTest) {

function romanValue(s) {
return s.length ? function () {
var parse = [].concat.apply([], glyphs.map(function (g) {
return 0 === s.indexOf(g) ? [trans[g], s.substr(g.length)] : [];
}));
return parse[0] + romanValue(parse[1]);
}() : 0;
}

var trans = {
M: 1E3,
CM: 900,
D: 500,
CD: 400,
C: 100,
XC: 90,
L: 50,
XL: 40,
X: 10,
IX: 9,
V: 5,
IV: 4,
I: 1
},
glyphs = Object.keys(trans);

return lstTest.map(romanValue);

})(["MCMXC", "MDCLXVI", "MMVIII", "MMMM"]);
```
Output:
```[1990, 1666, 2008]
```

### ES6

#### Recursion

```(() => {
// romanValue :: String -> Int
const romanValue = s =>
s.length ? (() => {
const parse = [].concat(
...glyphs.map(g => 0 === s.indexOf(g) ? (
[dctTrans[g], s.substr(g.length)]
) : [])
);
return parse[0] + romanValue(parse[1]);
})() : 0;

// dctTrans :: {romanKey: Integer}
const dctTrans = {
M: 1E3,
CM: 900,
D: 500,
CD: 400,
C: 100,
XC: 90,
L: 50,
XL: 40,
X: 10,
IX: 9,
V: 5,
IV: 4,
I: 1
};

// glyphs :: [romanKey]
const glyphs = Object.keys(dctTrans);

// TEST -------------------------------------------------------------------
return ["MCMXC", "MDCLXVI", "MMVIII", "MMMM"].map(romanValue);
})();
```
Output:
```[1990,1666,2008,4000]
```

#### Folding from the right

(fold and foldr examples)

```(() => {
"use strict";

// ------------- ROMAN NUMERALS DECODED --------------

// Folding from right to left,
// lower leftward characters are subtracted,

// fromRoman :: String -> Int
const fromRoman = s =>
[...s]
.map(glyphValue)
.reduceRight(
([r, n], l) => [
l,
l >= r
? n + l
: n - l
],
[0, 0]
)[1];

// glyphValue :: Char -> Maybe Int
const glyphValue = k => ({
I: 1,
V: 5,
X: 10,
L: 50,
C: 100,
D: 500,
M: 1000
}) [k] || 0;

// ---------------------- TEST -----------------------
return [
"MDCLXVI", "MCMXC", "MMVIII", "MMXVI", "MMXVII"
]
.map(fromRoman)
.join("\n");
})();
```
Output:
```1666
1990
2008
2016
2017```

#### Declarative

```(() => {
function toNumeric(value) {
return value
.replace(/IV/, 'I'.repeat(4))
.replace(/V/g, 'I'.repeat(5))
.replace(/IX/, 'I'.repeat(9))
.replace(/XC/, 'I'.repeat(90))
.replace(/XL/, 'I'.repeat(40))
.replace(/X/g, 'I'.repeat(10))
.replace(/L/, 'I'.repeat(50))
.replace(/CD/, 'I'.repeat(400))
.replace(/CM/, 'I'.repeat(900))
.replace(/C/g, 'I'.repeat(100))
.replace(/D/g, 'I'.repeat(500))
.replace(/M/g, 'I'.repeat(1000))
.length;
}

const numerics = ["MMXVI", "MCMXC", "MMVIII", "MM", "MDCLXVI"]
.map(toNumeric);

console.log(numerics);
})();
```
Output:
```[2016, 1990, 2008, 2000, 1666]
```

## jq

Works with: jq version 1.4

This version requires the Roman numerals to be presented in upper case.

```def fromRoman:
if length == 0 then n
elif startswith("M")  then .[1:] | addRoman(1000 + n)
elif startswith("CM") then .[2:] | addRoman(900 + n)
elif startswith("D")  then .[1:] | addRoman(500 + n)
elif startswith("CD") then .[2:] | addRoman(400 + n)
elif startswith("C")  then .[1:] | addRoman(100 + n)
elif startswith("XC") then .[2:] | addRoman(90 + n)
elif startswith("L")  then .[1:] | addRoman(50 + n)
elif startswith("XL") then .[2:] | addRoman(40 + n)
elif startswith("X")  then .[1:] | addRoman(10 + n)
elif startswith("IX") then .[2:] | addRoman(9 + n)
elif startswith("V")  then .[1:] | addRoman(5 + n)
elif startswith("IV") then .[2:] | addRoman(4 + n)
elif startswith("I")  then .[1:] | addRoman(1 + n)
else
error("invalid Roman numeral: " + tostring)
end;

Example:

`[ "MCMXC", "MMVIII", "MDCLXVI" ] | map("\(.) => \(fromRoman)") | .[]`
Output:
```\$ jq -n -f -r fromRoman.jq
MCMXC => 1990
MMVIII => 2008
MDCLXVI => 1666
```

## Jsish

Duplicate of the Jsish module used in Roman_numerals/Encode#Jsish.

Output:
```prompt\$ jsish -e 'require("Roman"); puts(Roman.fromRoman("MDCLXVI"));'
1666```

## Julia

Works with: Julia version 0.6

The Function:

```function parseroman(rnum::AbstractString)
romandigits = Dict('I' => 1, 'V' => 5, 'X' => 10, 'L' => 50,
'C' => 100, 'D' => 500, 'M' => 1000)
mval = accm = 0
for d in reverse(uppercase(rnum))
val = try
romandigits[d]
catch
throw(DomainError())
end
if val > mval maxval = val end
if val < mval
accm -= val
else
accm += val
end
end
return accm
end
```

This function is rather permissive. There are no limitations on the numbers of Roman numerals nor on their order. Because of this and because any out of order numerals subtract from the total represented, it is possible to represent zero and negative integers. Also mixed case representations are allowed. The function does throw an error if the string contains any invalid characters.

Test the code:

```using Printf

test = ["I", "III", "IX", "IVI", "IIM",
"CMMDXL", "icv", "cDxLiV", "MCMLD", "ccccccd",
"iiiiiv", "MMXV", "MCMLXXXIV", "ivxmm", "SPQR"]
for rnum in test
@printf("%15s → %s\n", rnum, try parseroman(rnum) catch "not valid" end)
end
```
Output:
```              I → 1
III → 3
IX → 11
IVI → 7
IIM → 1002
CMMDXL → 2660
icv → 106
cDxLiV → 666
MCMLD → 2650
ccccccd → 1100
iiiiiv → 10
MMXV → 2015
MCMLXXXIV → 2186
ivxmm → 2016
SPQR → not valid```

## K

Translation of: J
```  romd: {v:1 5 10 50 100 500 1000@"IVXLCDM"?/:x; +/v*_-1^(>':v),0}
```

Example:

```  romd'("MCMXC";"MMVIII";"MDCLXVI")
1990 2008 1666
```

## Kotlin

As specified in the task description, there is no attempt to validate the form of the Roman number in the following program - invalid characters and ordering are simply ignored:

```// version 1.0.6

fun romanDecode(roman: String): Int {
if (roman.isEmpty()) return 0
var n = 0
var last = 'O'
for (c in roman) {
when (c) {
'I' -> n += 1
'V' -> if (last == 'I') n += 3   else n += 5
'X' -> if (last == 'I') n += 8   else n += 10
'L' -> if (last == 'X') n += 30  else n += 50
'C' -> if (last == 'X') n += 80  else n += 100
'D' -> if (last == 'C') n += 300 else n += 500
'M' -> if (last == 'C') n += 800 else n += 1000
}
last = c
}
return n
}

fun main(args: Array<String>) {
val romans = arrayOf("I", "III", "IV", "VIII", "XLIX", "CCII", "CDXXXIII", "MCMXC", "MMVIII", "MDCLXVI")
for (roman in romans) println("\${roman.padEnd(10)} = \${romanDecode(roman)}")
}
```
Output:
```I          = 1
III        = 3
IV         = 4
VIII       = 8
XLIX       = 49
CCII       = 202
CDXXXIII   = 433
MCMXC      = 1990
MMVIII     = 2008
MDCLXVI    = 1666
```

## Lasso

```define br => '\r'
//decode roman
define decodeRoman(roman::string)::integer => {
local(ref = array('M'=1000, 'CM'=900, 'D'=500, 'CD'=400, 'C'=100, 'XC'=90, 'L'=50, 'XL'=40, 'X'=10, 'IX'=9, 'V'=5, 'IV'=4, 'I'=1))
local(out = integer)
while(#roman->size) => {
// need to use neset while instead of query expr to utilize loop_abort
while(loop_count <= #ref->size) => {
if(#roman->beginswith(#ref->get(loop_count)->first)) => {
#out += #ref->get(loop_count)->second
#roman->remove(1,#ref->get(loop_count)->first->size)
loop_abort
}
}
}
return #out
}

'MCMXC as integer is '+decodeRoman('MCMXC')
br
'MMVIII as integer is '+decodeRoman('MMVIII')
br
'MDCLXVI as integer is '+decodeRoman('MDCLXVI')
```

## LiveScript

```require! 'prelude-ls': {fold, sum}

# String → Number
decimal_of_roman = do
# [Number, Number] → String → [Number, Number]
_convert = ([acc, last_value], ch) ->
current_value = { M:1000 D:500 C:100 L:50 X:10 V:5 I:1 }[ch] ? 0
op = if last_value < current_value then (-) else (+)
[op(acc, last_value), current_value]
# fold the string and sum the resulting tuple (array)
fold(_convert, [0, 0]) >> sum

{[rom, decimal_of_roman rom] for rom in <[ MCMXC MMVII MDCLXVII MMMCLIX MCMLXXVII MMX ]>}
```

Output:

`{"MCMXC":1990,"MMVII":2007,"MDCLXVII":1667,"MMMCLIX":3159,"MCMLXXVII":1977,"MMX":2010}`

## Logo

```; Roman numeral decoder

; First, some useful substring utilities
to starts_with? :string :prefix
if empty? :prefix [output "true]
if empty? :string [output "false]
if not equal? first :string first :prefix [output "false]
output starts_with? butfirst :string butfirst :prefix
end

to remove_prefix :string :prefix
if or empty? :prefix not starts_with? :string :prefix [output :string]
output remove_prefix butfirst :string butfirst :prefix
end

; Our list of Roman numeral values
make "values [[M 1000] [CM 900] [D  500] [CD 400] [C  100] [XC 90] [L 50]
[XL 40]  [X  10]  [IX 9]   [V  5]   [IV 4]   [I  1]]

; Function to do the work
to from_roman :str
local "n make "n 0
foreach :values [
local "s make "s first ?
local "v make "v last ?
while [starts_with? :str :s] [
make "n sum n :v
make "str remove_prefix :str :s
]
]
output :n
end

foreach [MCMXC MDCLXVI MMVIII] [print (sentence (word ? "|: |) from_roman ?)]
bye```
Output:
```MCMXC:  1990
MDCLXVI:  1666
MMVIII:  2008
```

## Lua

```function ToNumeral( roman )
local Num = { ["M"] = 1000, ["D"] = 500, ["C"] = 100, ["L"] = 50, ["X"] = 10, ["V"] = 5, ["I"] = 1 }
local numeral = 0

local i = 1
local strlen = string.len(roman)
while i < strlen do
local z1, z2 = Num[ string.sub(roman,i,i) ], Num[ string.sub(roman,i+1,i+1) ]
if z1 < z2 then
numeral = numeral + ( z2 - z1 )
i = i + 2
else
numeral = numeral + z1
i = i + 1
end
end

if i <= strlen then numeral = numeral + Num[ string.sub(roman,i,i) ] end

return numeral
end

print( ToNumeral( "MCMXC" ) )
print( ToNumeral( "MMVIII" ) )
print( ToNumeral( "MDCLXVI" ) )
```
```1990
2008
1666```

## M2000 Interpreter

Maximum Roman number is MMMCMXCIX (3999)

```Module RomanNumbers {
flush  ' empty current stack
gosub Initialize
document Doc\$
while not empty
print rom\$;"=";RomanEval\$(rom\$)
Doc\$=rom\$+"="+RomanEval\$(rom\$)+{
}
end while
Clipboard Doc\$
end
Initialize:
function RomanEval\$(rom\$) {
Flush
="invalid"
if filter\$(rom\$,"MDCLXVI")<>"" Then Exit
\\ "Y" is in top of stack
Push "CM", "MD", "Q"
Push "CD", "MD","W"
Push "XC", "DL", "E"
Push "XL", "X","R"
Push "IX","V","T"
Push  "IV","I","Y"
\\ stack flush to doublerom
doublerom=[]
\\  "M" is in top of stack
Data "M", 1000, "Q",900
Data "D", 500,"W", 400
Data "C",100,"E",90
Data "L",50,"R", 40
Data "X", 10, "T", 9
Data "V", 5, "Y", 4, "I",1
\\ stack flush to singlerom
singlerom=[]
acc=0
value=0
count=0
stack doublerom {
if empty then exit
i=instr(rom\$,cc\$)
if i >0 then
tmp\$=mid\$(rom\$,i+2)
L=Len(tmp\$)
if L>0 then if Len(filter\$(tmp\$, exclude\$))<>L then rom\$="A": exit
if Instr(rom\$,mid\$(rom\$,i,1))<i then rom\$="A": exit
insert i,2 rom\$=rep\$  ' replace at pos i with rep\$ and place a space to i+1
end if
loop
}
rom\$=filter\$(rom\$," ") ' remove spaces if exist

stack singlerom {
if empty then exit
count=0
while left\$(rom\$,1)=cc\$
insert 1, 1 rom\$=""
count++
acc+=value
end while
if count>3 then exit
loop
}
if len(rom\$)>0  or count>3 Else
=Str\$(acc,1033)
end if
}
data "MMMCMXCIX", "LXXIIX", "MMXVII", "LXXIX", "CXCIX","MCMXCIX","MMMDCCCLXXXVIII"
data "CMXI","M","MCDXLIV","CCCC","IXV", "XLIXL","LXXIIX","IVM"
data "XXXIX", "XXXX", "XIXX","IVI", "XLIX","XCIX","XCIV","XLVIII"
return
}
RomanNumbers```
Output:
```MMMCMXCIX=3999
LXXIIX=invalid
MMXVII=2017
LXXIX=79
CXCIX=199
MCMXCIX=1999
MMMDCCCLXXXVIII=3888
CMXI=911
M=1000
MCDXLIV=1444
CCCC=invalid
IXV=invalid
XLIXL=invalid
LXXIIX=invalid
IVM=invalid
XXXIX=39
XXXX=invalid
XIXX=invalid
IVI=invalid
XLIX=49
XCIX=99
XCIV=94
XLVIII=48

```

## Maple

```f := n -> convert(n, arabic):
seq(printf("%a\n", f(i)), i in [MCMXC, MMVIII, MDCLXVI]);```
Output:
```1990
2008
1666
```

## Mathematica /Wolfram Language

```FromRomanNumeral["MMCDV"]
```
Output:
`2405`

## MATLAB

```function x = rom2dec(s)
% ROM2DEC converts Roman numbers to decimal

% store Roman digits values: I=1, V=5, X=10, L=50, C=100, D=500, M=1000
digitsValues = [0 0 100 500 0 0 0 0 1 0 0 50 1000 0 0 0 0 0 0 0 0 5 0 10 0 0];
% convert Roman number to array of values
values = digitsValues(s-'A'+1);
% change sign if next value is bigger
x = sum(values .* [sign(diff(-values)+eps),1]);

end
```

Here is a test:

```romanNumbers = {'MMMCMXCIX', 'XLVIII', 'MMVIII'};
for n = 1 : numel(romanNumbers)
fprintf('%10s = %4d\n',romanNumbers{n}, rom2dec(romanNumbers{n}));
end
```
Output:
``` MMMCMXCIX = 3999
XLVIII =   48
MMVIII = 2008
```

## Mercury

```:- module test_roman.

:- interface.

:- import_module io.

:- pred main(io::di, io::uo) is det.

:- implementation.

:- import_module char.
:- import_module exception.
:- import_module int.
:- import_module list.
:- import_module string.

:- type conversion_error --->  not_a_roman_number.

:- func build_int(list(char), int, int) = int.
:- func from_roman(string) = int.
:- pred roman_to_int(char::in, int::out) is semidet.

from_roman(Roman) = Decimal :-
List = reverse(to_char_list(Roman)),
Decimal = build_int(List, 0, 0).

build_int([], LastValue, Accumulator) = LastValue + Accumulator.
build_int([Digit|Rest], LastValue, Accumulator) = Sum :-
( roman_to_int(Digit, Value) ->
( Value < LastValue ->
Sum = build_int(Rest, Value, Accumulator - LastValue)
;   Sum = build_int(Rest, Value, Accumulator + LastValue) )
;   throw(not_a_roman_number) ).

roman_to_int('I', 1).
roman_to_int('V', 5).
roman_to_int('X', 10).
roman_to_int('L', 50).
roman_to_int('C', 100).
roman_to_int('D', 500).
roman_to_int('M', 1000).

main(!IO) :-
command_line_arguments(Args, !IO),
foldl((pred(Arg::in, !.IO::di, !:IO::uo) is det :-
format("%s => %d\n", [s(Arg), i(from_roman(Arg))], !IO)),
Args, !IO).

:- end_module test_roman.```

## Miranda

```main :: [sys_message]
main = [ Stdout (s ++ ": " ++ show (fromroman s) ++ "\n")
| s <- ["MCMXC", "MDCLXVI", "MMVII", "MMXXIII"]
]

fromroman :: [char]->num
fromroman = f
where f []       = 0
f [x]      = r x
f (x:y:xs) = f (y:xs) - r x, if r x < r y
= f (y:xs) + r x, otherwise
r 'M' = 1000
r 'D' = 500
r 'C' = 100
r 'L' = 50
r 'X' = 10
r 'V' = 5
r 'I' = 1```
Output:
```MCMXC: 1990
MDCLXVI: 1666
MMVII: 2007
MMXXIII: 2023```

## Modula-2

```MODULE RomanNumerals;
FROM InOut IMPORT WriteString, WriteCard, WriteLn;
FROM Strings IMPORT Length;

(* Convert given Roman numeral to binary *)
PROCEDURE DecodeRoman(s: ARRAY OF CHAR): CARDINAL;
VAR i, d, len, acc: CARDINAL;

PROCEDURE Digit(d: CHAR): CARDINAL;
BEGIN
CASE CHR( BITSET(ORD(d)) + BITSET{5} ) OF (* lowercase *)
'm': RETURN 1000;
|   'd': RETURN 500;
|   'c': RETURN 100;
|   'l': RETURN 50;
|   'x': RETURN 10;
|   'v': RETURN 5;
|   'i': RETURN 1;
ELSE
RETURN 0;
END;
END Digit;
BEGIN
len := Length(s);
acc := 0;
FOR i := 0 TO len-1 DO
d := Digit(s[i]);
IF d=0 THEN RETURN 0; END;

IF (i # len-1) AND (d < Digit(s[i+1])) THEN
acc := acc - d;
ELSE
acc := acc + d;
END;
END;
RETURN acc;
END DecodeRoman;

PROCEDURE Show(s: ARRAY OF CHAR);
BEGIN
WriteString(s);
WriteString(": ");
WriteCard(DecodeRoman(s), 0);
WriteLn();
END Show;

BEGIN
Show("MCMXC");
Show("MDCLXVI");
Show("mmvii");
Show("mmxxi");
END RomanNumerals.
```
Output:
```MCMXC: 1990
MDCLXVI: 1666
mmvii: 2007
mmxxi: 2021```

## Nanoquery

Translation of: Java
```def decodeSingle(letter)
if letter = "M"
return 1000
else if letter = "D"
return 500
else if letter =  "C"
return 100
else if letter = "L"
return 50
else if letter = "X"
return 10
else if letter = "V"
return 5
else if letter = "I"
return 1
else
return 0
end
end

def decode(roman)
result = 0
uRoman = roman.toUpperCase()

for (i = 0) (i < len(uRoman) - 1) (i += 1)
if decodeSingle(uRoman[i]) < decodeSingle(uRoman[i + 1])
result -= decodeSingle(uRoman[i])
else
result += decodeSingle(uRoman[i])
end
end

result += decodeSingle(uRoman[len(uRoman) - 1])
return result
end

println decode("MCMXC")
println decode("MMVIII")
println decode("MDCLXVI")```
Output:
```1990
2008
1666```

## NetRexx

```/* NetRexx */
options replace format comments java crossref savelog symbols binary

/* 1990  2008   1666    */
years = Rexx('MCMXC MMVIII MDCLXVI')

loop y_ = 1 to years.words
Say years.word(y_).right(10) || ':' decode(years.word(y_))
end y_

return

method decode(arg) public static returns int signals IllegalArgumentException

parse arg.upper roman .
if roman.verify('MDCLXVI') \= 0 then signal IllegalArgumentException

-- always insert the value of the least significant numeral
decnum = rchar(roman.substr(roman.length, 1))
loop d_ = 1 to roman.length - 1
if rchar(roman.substr(d_, 1)) < rchar(roman.substr(d_ + 1, 1)) then do
-- Handle cases where numerals are not in descending order
--   subtract the value of the numeral
decnum = decnum - rchar(roman.substr(d_, 1))
end
else do
-- Normal case
--   add the value of the numeral
decnum = decnum + rchar(roman.substr(d_, 1))
end
end d_

return decnum

method rchar(arg) public static returns int

parse arg.upper ch +1 .
select case ch
when 'M' then digit = 1000
when 'D' then digit =  500
when 'C' then digit =  100
when 'L' then digit =   50
when 'X' then digit =   10
when 'V' then digit =    5
when 'I' then digit =    1
otherwise     digit =    0
end

return digit
```
Output:
```     MCMXC: 1990
MMVIII: 2008
MDCLXVI: 1666
```

## Nim

Translation of: Python
```import tables

let rdecode = {'M': 1000, 'D': 500, 'C': 100, 'L': 50, 'X': 10, 'V': 5, 'I': 1}.toTable

proc decode(roman: string): int =
for i in 0 ..< roman.high:
let (rd, rd1) = (rdecode[roman[i]], rdecode[roman[i+1]])
result += (if rd < rd1: -rd else: rd)
result += rdecode[roman[roman.high]]

for r in ["MCMXC", "MMVIII", "MDCLXVI"]:
echo r, " ", decode(r)
```
Output:
```MCMXC 1990
MMVIII 2008
MDCLXVI 1666```

## OCaml

```let decimal_of_roman roman =
let arabic = ref 0 in
let lastval = ref 0 in
for i = (String.length roman) - 1 downto 0 do
let n =
match roman.[i] with
| 'M' | 'm' -> 1000
| 'D' | 'd' -> 500
| 'C' | 'c' -> 100
| 'L' | 'l' -> 50
| 'X' | 'x' -> 10
| 'V' | 'v' -> 5
| 'I' | 'i' -> 1
| _ -> 0
in
if n < !lastval
then arabic := !arabic - n
else arabic := !arabic + n;
lastval := n
done;
!arabic

let () =
Printf.printf " %d\n" (decimal_of_roman "MCMXC");
Printf.printf " %d\n" (decimal_of_roman "MMVIII");
Printf.printf " %d\n" (decimal_of_roman "MDCLXVI");
;;
```

### Another implementation

Another implementation, a bit more OCaml-esque: no mutable variables, and a recursive function instead of a for loop.

Works with: OCaml version 4.03+
```(* Scan the roman number from right to left. *)
(* When processing a roman digit, if the previously processed roman digit was
* greater than the current one, we must substract the latter from the current
* Example:
* - MCMLXX read from right to left is XXLMCM
*          the sum is 10 + 10 + 50 + 1000 - 100 + 1000 *)
let decimal_of_roman roman =
(* Use 'String.uppercase' for OCaml 4.02 and previous. *)
let rom = String.uppercase_ascii roman in
(* A simple association list. IMHO a Hashtbl is a bit overkill here. *)
let romans = List.combine ['I'; 'V'; 'X'; 'L'; 'C'; 'D'; 'M']
[1; 5; 10; 50; 100; 500; 1000] in
let compare x y =
if x < y then -1 else 1
in
(* Scan the string from right to left using index i, and keeping track of
* the previously processed roman digit in prevdig. *)
let rec doloop i prevdig =
if i < 0 then 0
else
try
let currdig = List.assoc rom.[i] romans in
(currdig * compare currdig prevdig) + doloop (i - 1) currdig
with
(* Ignore any incorrect roman digit and just process the next one. *)
Not_found -> doloop (i - 1) 0
in
doloop (String.length rom - 1) 0

(* Some simple tests. *)
let () =
let testit roman decimal =
let conv = decimal_of_roman roman in
let status = if conv = decimal then "PASS" else "FAIL" in
Printf.sprintf "[%s] %s\tgives %d.\tExpected: %d.\t"
status roman conv decimal
in
print_endline ">>> Usual roman numbers.";
print_endline (testit "MCMXC" 1990);
print_endline (testit "MMVIII" 2008);
print_endline (testit "MDCLXVI" 1666);
print_newline ();

print_endline ">>> Roman numbers with lower case letters are OK.";
print_endline (testit "McmXC" 1990);
print_endline (testit "MMviii" 2008);
print_endline (testit "mdCLXVI" 1666);
print_newline ();

print_endline ">>> Incorrect roman digits are ignored.";
print_endline (testit "McmFFXC" 1990);
print_endline (testit "MMviiiPPPPP" 2008);
print_endline (testit "mdCLXVI_WHAT_NOW" 1666);
print_endline (testit "2 * PI ^ 2" 1);  (* The I in PI... *)
print_endline (testit "E = MC^2" 1100)
```

Output:

```>>> Usual roman numbers.
[PASS] MCMXC	gives 1990.	Expected: 1990.
[PASS] MMVIII	gives 2008.	Expected: 2008.
[PASS] MDCLXVI	gives 1666.	Expected: 1666.

>>> Roman numbers with lower case letters are OK.
[PASS] McmXC	gives 1990.	Expected: 1990.
[PASS] MMviii	gives 2008.	Expected: 2008.
[PASS] mdCLXVI	gives 1666.	Expected: 1666.

>>> Incorrect roman digits are ignored.
[PASS] McmFFXC	gives 1990.	Expected: 1990.
[PASS] MMviiiPPPPP	gives 2008.	Expected: 2008.
[PASS] mdCLXVI_WHAT_NOW	gives 1666.	Expected: 1666.
[PASS] 2 * PI ^ 2	gives 1.	Expected: 1.
[PASS] E = MC^2	gives 1100.	Expected: 1100.
```

## PARI/GP

```fromRoman(s)={
my(v=Vecsmall(s),key=vector(88),cur,t=0,tmp);
key[73]=1;key[86]=5;key[88]=10;key[76]=50;key[67]=100;key[68]=500;key[77]=1000;
cur=key[v[1]];
for(i=2,#v,
tmp=key[v[i]];
if(!cur, cur=tmp; next);
if(tmp>cur,
t+=tmp-cur;
cur=0
,
t+=cur;
cur=tmp
)
);
t+cur
};```

## PascalABC.NET

```function Rim2Arab(S : String) : Integer;
const //римские числа на соответствующие десятичные числа
R : array[1..14] of String[2] = ('M','CM','D','CD','C','XC','L','XL','X','IX','V','IV','I',' ');
A : array[1..14] of Integer = (1000, 900, 500, 400, 100, 90, 50, 40, 10, 9, 5, 4, 1, 0);
begin
var i := 1;
Result := 0;
while S.Length > 0 do
begin
while S.IndexOf(R[i]) = 0 do
begin
S := S.Remove(0, R[i].Length);
Result += A[i]
end;
i += 1;
end;
end;

const
L = 'IVXLCDM';
begin
var S := 'MDCLXVI';//'roman numeral:';
Write(S,': ');
var index := 1;
repeat
if L.IndexOf(S[index]) < 0 then
index += 1
else
begin
var Rim : String := '';
repeat
Rim += S[index];
S := S.Remove(index - 1, 1);
until (S.Length < index) or (L.IndexOf(S[index]) < 0);
S := S.Insert(index - 1, Rim2Arab(Rim).ToString);
end;
until index > S.Length;
WriteLn(S);
end.
```
Output:
```MDCLXVI: 1666
```

### Alternate

Translation of: Kotlin
```function romanDecode(roman: String): Integer;
begin
result := 0;
if roman = '' then exit;
var n := 0;
var last := 'O';
foreach var c in roman do
begin
case c of
'I': n += 1;
'V': if (last = 'I') then n += 3   else n += 5;
'X': if (last = 'I') then n += 8   else n += 10;
'L': if (last = 'X') then n += 30  else n += 50;
'C': if (last = 'X') then n += 80  else n += 100;
'D': if (last = 'C') then n += 300 else n += 500;
'M': if (last = 'C') then n += 800 else n += 1000;
end;
last := c;
end;
result := n;
end;

begin
var romans := |'I', 'III', 'IV', 'VIII', 'XLIX', 'CCII',
'CDXXXIII', 'MCMXC', 'MMVIII', 'MDCLXVI'|;
foreach var roman in romans do
writeln(roman:10, romanDecode(roman):10);
end.
```

## Perl

```use 5.10.0;

{
my @trans = (
[M  => 1000],     [CM => 900],
[D  => 500],      [CD => 400],
[C  => 100],      [XC => 90],
[L  => 50],       [XL => 40],
[X  => 10],       [IX => 9],
[V  => 5],        [IV => 4],
[I  => 1],
);

sub from_roman {
my \$r = shift;
my \$n = 0;
foreach my \$pair (@trans) {
my (\$k, \$v) = @\$pair;
\$n += \$v while \$r =~ s/^\$k//i;
}
return \$n
}
}

say "\$_: ", from_roman(\$_) for qw(MCMXC MDCLXVI MMVIII);
```
Output:
```MCMXC: 1990
MDCLXVI: 1666
MMVIII: 2008```

### Alternate

```#!/usr/bin/perl

use strict;
use warnings;

sub roman2decimal
{
(local \$_, my \$sum, my \$zeros) = (shift, 0, '');
\$zeros .= 0 while
\$sum -= s/I(?=[VX])// - s/V// * 5 - s/I//g . \$zeros,
tr/MDCLX/CLXVI/;
return \$sum;
}

print s/\$/ ": " . roman2decimal(\$_) /er while <DATA>;

__DATA__
MCMXC
MMVIII
MDCLXVI```
Output:
```MCMXC: 1990
MMVIII: 2008
MDCLXVI: 1666
```

### Another Alternate

```#!/usr/bin/perl

use strict;
use warnings;

sub roman2decimal
{
my \$sum = 0;
\$sum += \$^R while \$_[0] =~
/ M  (?{1000})
| D  (?{ 500})
| C  (?{ 100}) (?= [MD] (?{-100}) )?
| L  (?{  50})
| X  (?{  10}) (?= [CL] (?{ -10}) )?
| V  (?{   5})
| I  (?{   1}) (?= [XV] (?{  -1}) )?
/gx;
return \$sum;
}

print s/\$/ ": " . roman2decimal(\$_) /er while <DATA>;

__DATA__
MCMXC
MMVIII
MDCLXVI```
Output:
```MCMXC: 1990
MMVIII: 2008
MDCLXVI: 1666
```

## Phix

```with javascript_semantics
function romanDec(string s)
integer res = 0, prev = 0
for i=length(s) to 1 by -1 do
integer rdx = find(upper(s[i]),"IVXLCDM"),
rn = power(10,floor((rdx-1)/2))
if even(rdx) then rn *= 5 end if
res += iff(rn<prev?-rn:rn)
prev = rn
end for
return {s,res} -- (for output)
end function

?apply({"MCMXC","MMVIII","MDCLXVI"},romanDec)```
Output:
```{{"MCMXC",1990},{"MMVIII",2008},{"MDCLXVI",1666}}
```

### cheating slightly

```with javascript_semantics
requires("1.0.5")
function romanDec(string s)
return {s,scanf(s,"%R")[1][1]}
end function```

same output, if applied the same way as above, error handling omitted

## Phixmonti

```def romanDec   /# s -- n #/
0 >ps 0 >ps
( ( "M" 1000 ) ( "D" 500 ) ( "C" 100 ) ( "L" 50 ) ( "X" 10 ) ( "V" 5 ) ( "I" 1 ) )

swap upper reverse
len while
pop rot rot tochar getd
if
dup ps> < if 0 swap - endif
dup ps> + >ps
>ps
swap
else
"Error: " print ? ""
endif
len
endwhile
drop drop
ps> drop ps>
enddef

/# usage example: "MMXX" romanDec ? (show 2020) #/```

```"MDCLXVI" var romans
( 1000 500 100 50 10 5 1 ) var decmls

def romanDec    /# s -- n #/
0 var prev
0 var res
upper
( len 1 -1 ) for
get
romans swap find nip
dup if
decmls swap get nip
dup prev < if 0 swap - endif
dup res + var res
var prev
else
"Error" ? 0 var res exitfor
endif
endfor
drop
res
enddef```

## PHP

```<?php
/**
*/
\$roman_to_decimal = array(
'I' => 1,
'V' => 5,
'X' => 10,
'L' => 50,
'C' => 100,
'D' => 500,
'M' => 1000,
);

/**
* @param \$number
* @return int
*/
function roman2decimal(\$number)
{
global \$roman_to_decimal;

// breaks the string into an array of chars
\$digits = str_split(\$number);
\$lastIndex = count(\$digits)-1;
\$sum = 0;

foreach(\$digits as \$index => \$digit)
{
if(!isset(\$digits[\$index]))
{
continue;
}

if(isset(\$roman_to_decimal[\$digit]))
{
if(\$index < \$lastIndex)
{
\$left = \$roman_to_decimal[\$digits[\$index]];
\$right = \$roman_to_decimal[\$digits[\$index+1]];
if(\$left < \$right)
{
\$sum += (\$right - \$left);
unset(\$digits[\$index+1],\$left, \$right);
continue;
}
unset(\$left, \$right);
}
}
\$sum += \$roman_to_decimal[\$digit];
}

return \$sum;
}

/*============= OUTPUT =============*/

\$tests = array(
"I" => array(roman2decimal('I'), 1),
"II" => array(roman2decimal('II'), 2),
"III" => array(roman2decimal('III'), 3),
"IV" => array(roman2decimal('IV'), 4),
"V" => array(roman2decimal('V'), 5),
"VI" => array(roman2decimal('VI'), 6),
"VII" => array(roman2decimal('VII'), 7),
"IX" => array(roman2decimal('IX'), 9),
"X" => array(roman2decimal('X'), 10),
"XI" => array(roman2decimal('XI'), 11),
"XIV" => array(roman2decimal('XIV'), 14),
"XV" => array(roman2decimal('XV'), 15),
"XVI" => array(roman2decimal('XVI'), 16),
"XVIV" => array(roman2decimal('XVIV'), 19),
"XIX" => array(roman2decimal('XIX'), 19),
"MDCLXVI" => array(roman2decimal('MDCLXVI'), 1666),
"MCMXC" => array(roman2decimal('MCMXC'), 1990),
"MMVIII" => array(roman2decimal('MMVIII'), 2008),
"MMMCLIX" => array(roman2decimal('MMMCLIX'), 3159),
"MCMLXXVII" => array(roman2decimal('MCMLXXVII'), 1977),
);

foreach(\$tests as \$key => \$value)
{
echo "(\$key == {\$value[0]}) => " . (\$value[0] === \$value[1] ? "true" : "false, should be {\$value[1]}.") . "\n";
}```
Output:
```(I == 1) => true
(II == 2) => true
(III == 3) => true
(IV == 4) => true
(V == 5) => true
(VI == 6) => true
(VII == 7) => true
(IX == 9) => true
(X == 10) => true
(XI == 11) => true
(XIV == 14) => true
(XV == 15) => true
(XVI == 16) => true
(XVIV == 19) => true
(XIX == 19) => true
(MDCLXVI == 1666) => true
(MCMXC == 1990) => true
(MMVIII == 2008) => true
(MMMCLIX == 3159) => true
(MCMLXXVII == 1977) => true
```

## Picat

```go =>
List = ["IV",
"XLII",
"M",
"MCXI",
"CMXI",
"MCM",
"MCMXC",
"MMVIII",
"MMIX",
"MCDXLIV",
"MDCLXVI",
"MMXII"],
foreach(R in List)
printf("%-8s: %w\n", R, roman_decode(R))
end,
nl.

roman_decode(Str) = Res =>
if Str == "" then
Res := ""
else
D = new_map(findall((R=D), roman(R,D))),
Res = 0,
Old = 0,
foreach(S in Str)
N = D.get(S),
% Fix for the Roman convention that XC = 90, not 110.
if Old > 0, N > Old then
Res := Res - 2*Old
end,
Res := Res + N,
Old := N
end
end.

roman('I', 1).
roman('V', 5).
roman('X', 10).
roman('L', 50).
roman('C', 100).
roman('D', 500).
roman('M', 1000).```
Output:
```IV      : 4
XLII    : 42
M       : 1000
MCXI    : 1111
CMXI    : 911
MCM     : 1900
MCMXC   : 1990
MMVIII  : 2008
MMIX    : 2009
MCDXLIV : 1444
MDCLXVI : 1666
MMXII   : 2012```

## PicoLisp

```(de roman2decimal (Rom)
(let L (replace (chop Rom) 'M 1000 'D 500 'C 100 'L 50 'X 10 'V 5 'I 1)
(sum '((A B) (if (>= A B) A (- A))) L (cdr L)) ) )```

Test:

```: (roman2decimal "MCMXC")
-> 1990

: (roman2decimal "MMVIII")
-> 2008

: (roman2decimal "MDCLXVI")
-> 1666```

## PL/I

```test_decode: procedure options (main); /* 28 January 2013 */
declare roman character (20) varying;

do roman = 'i', 'ii', 'iii', 'iv', 'v', 'vi', 'vii', 'viii', 'iix',
'ix', 'x', 'xi', 'xiv', 'MCMLXIV', 'MCMXC', 'MDCLXVI',
'MIM', 'MM', 'MMXIII';
put skip list (roman, decode(roman));
end;

decode: procedure (roman) returns (fixed(15));
declare roman character (*) varying;
declare (current, previous) character (1);
declare n fixed (15);
declare i fixed binary;

previous = ''; n = 0;
do i = length(roman) to 1 by -1;
current = substr(roman, i, 1);
if digit_value(current) < digit_value(previous) then
n = n - digit_value(current);
else if digit_value(current) > digit_value(previous) then
do;
n = n + digit_value(current);
previous = current;
end;
else
n = n + digit_value(current);
end;
return (n);
end decode;

digit_value: procedure (roman_char) returns (fixed);
declare roman_char character(1);
select (roman_char);
when ('M', 'm') return (1000);
when ('D', 'd') return (500);
when ('C', 'c') return (100);
when ('L', 'l') return (50);
when ('X', 'x') return (10);
when ('V', 'v') return (5);
when ('I', 'i') return (1);
otherwise       return (0);
end;
end digit_value;

end test_decode;```
```i                                        1
ii                                       2
iii                                      3
iv                                       4
v                                        5
vi                                       6
vii                                      7
viii                                     8
iix                                      8
ix                                       9
x                                       10
xi                                      11
xiv                                     14
MCMLXIV                               1964
MCMXC                                 1990
MDCLXVI                               1666
MIM                                   1999
MM                                    2000
MMXIII                                2013
```

## PL/M

```100H:
/* CP/M CALLS */
BDOS: PROCEDURE (FN, ARG); DECLARE FN BYTE, ARG ADDRESS; GO TO 5; END BDOS;
EXIT: PROCEDURE; CALL BDOS(0,0); END EXIT;
PRINT: PROCEDURE (S); DECLARE S ADDRESS; CALL BDOS(9,S); END PRINT;

/* CP/M COMMAND LINE ARGUMENT */
DECLARE ARG\$LPTR ADDRESS INITIAL (80H), ARG\$LEN BASED ARG\$LPTR BYTE;
DECLARE ARG\$PTR  ADDRESS INITIAL (81H), ARG     BASED ARG\$PTR BYTE;

/* CONVERT ROMAN NUMERAL TO BINARY */
DECLARE DIGITS (7) BYTE INITIAL ('MDCLXVI');
DECLARE VALUES (7) ADDRESS INITIAL (1000,500,100,50,10,5,1);
DECLARE (RP, V, DVAL) ADDRESS, R BASED RP BYTE;
V = 0;

DECLARE (D, I) BYTE;
DO I = 0 TO LAST(DIGITS);
IF DIGITS(I) = D THEN RETURN VALUES(I);
END;
END GET\$DIGIT;

DO WHILE R <> '\$';
DVAL = GET\$DIGIT(R);
IF DVAL = 0 THEN RETURN 0; /* ERROR */
RP = RP + 1;
IF GET\$DIGIT(R) > DVAL THEN
V = V - DVAL; /* SUBTRACTIVE PRINCIPLE */
ELSE
V = V + DVAL;
END;
RETURN V;

/* PRINT BINARY NUMBER AS DECIMAL */
PRINT\$NUMBER: PROCEDURE (N);
DECLARE S (6) BYTE INITIAL ('.....\$');
DECLARE (N, P) ADDRESS, C BASED P BYTE;
P = .S(5);
DIGIT:
P = P - 1;
C = N MOD 10 + '0';
N = N / 10;
IF N > 0 THEN GO TO DIGIT;
CALL PRINT(P);
END PRINT\$NUMBER;

IF ARG\$LEN = 0 THEN DO;
CALL PRINT(.'NO INPUT\$');
CALL EXIT;
END;

ARG(ARG\$LEN) = '\$';  /* TERMINATE ARGUMENT STRING */
CALL PRINT(.ARG(1)); /* PRINT ROMAN NUMERAL */
CALL PRINT(.': \$');
CALL PRINT\$NUMBER(READ\$ROMAN(.ARG(1))); /* CONVERT AND PRINT VALUE */
CALL EXIT;
EOF```
Output:
```A>ROMAN MCMXC
MCMXC: 1990
A>ROMAN MDCLXVI
MDCLXVI: 1666
A>ROMAN MMVII
MMVII: 2007
A>ROMAN MMXXI
MMXXI: 2021```

## PL/SQL

```/*****************************************************************
* \$Author: Atanas Kebedjiev \$
*****************************************************************
* PL/SQL code can be run as anonymous block.
* To test, execute the whole script or create the functions and then e.g. 'select rdecode('2012') from dual;
* Please note that task definition does not describe fully some current rules, such as
* * subtraction - IX XC CM are the valid subtraction combinations
* * A subtraction character cannot be repeated: 8 is expressed as VIII and not as IIX
* * V L and D cannot be used for subtraction
* * Any numeral cannot be repeated more than 3 times: 1910 should be MCMX and not MDCCCCX
* Code below does not validate the Roman numeral itself and will return a result even for a non-compliant number
* E.g. both MCMXCIX and IMM will return 1999 but the first one is the correct notation
*/

DECLARE

FUNCTION rvalue(c IN CHAR) RETURN NUMBER IS
i INTEGER;
BEGIN
i := 0;
CASE (c)
when 'M' THEN i := 1000;
when 'D' THEN i := 500;
when 'C' THEN i := 100;
when 'L' THEN i := 50;
when 'X' THEN i := 10;
when 'V' THEN i := 5;
when 'I' THEN i := 1;
END CASE;
RETURN i;
END;

FUNCTION decode(rn IN VARCHAR2) RETURN NUMBER IS
i  INTEGER;
l  INTEGER;
cr CHAR;   -- current Roman numeral as substring from r
cv INTEGER; -- value of current Roman numeral

gr CHAR;   -- next Roman numeral
gv NUMBER; --  value of the next numeral;

dv NUMBER; -- decimal value to return
BEGIN
l := length(rn);
i := 1;
dv := 0;
while (i <= l)
LOOP
cr := substr(rn,i,1);
cv := rvalue(cr);

/* Look for a larger numeral in next position, like IV or CM
The number to subtract should be at least 1/10th of the bigger number
CM and XC are valid, but IC and XM are not */
IF (i < l) THEN
gr := substr(rn,i+1,1);
gv := rvalue(gr);
IF (cv < gv ) THEN
dv := dv - cv;
ELSE
dv := dv + cv;
END IF;
ELSE
dv := dv + cv;
END IF;  -- need to add the last value unconditionally

i := i + 1;
END LOOP;

RETURN dv;

END;

BEGIN

DBMS_OUTPUT.PUT_LINE ('MMXII      = ' || rdecode('MMXII'));       -- 2012
DBMS_OUTPUT.PUT_LINE ('MCMLI      = ' || rdecode('MCMLI'));       -- 1951
DBMS_OUTPUT.PUT_LINE ('MCMLXXXVII = ' || rdecode('MCMLXXXVII'));  -- 1987
DBMS_OUTPUT.PUT_LINE ('MDCLXVI    = ' || rdecode('MDCLXVI'));     -- 1666
DBMS_OUTPUT.PUT_LINE ('MCMXCIX    = ' || rdecode('MCMXCIX'));     -- 1999

END;```

## PowerShell

```Filter FromRoman {
\$output = 0

if (\$_ -notmatch '^(M{1,3}|)(CM|CD|D?C{0,3}|)(XC|XL|L?X{0,3}|)(IX|IV|V?I{0,3}|)\$') {
throw 'Incorrect format'
}

\$current = 1000
\$subtractor = 'M'
\$whole = \$False
\$roman = \$_
'C','D','X','L','I','V',' ' `
| %{
if (\$whole = !\$whole) {
\$current /= 10
\$subtractor = \$_ + \$subtractor[0]
\$_ = \$subtractor[1]
}
else {
\$subtractor = \$subtractor[0] + \$_
}

if (\$roman -match \$subtractor) {
\$output += \$current * (4,9)[\$whole]
\$roman = \$roman -replace \$subtractor,''
}
if (\$roman -match (\$_ + '{1,3}')) {
\$output += \$current * (5,10)[\$whole] * \$Matches[0].Length
}
}

\$output
}```
`'XIX','IV','','MMCDLXXIX','MMMI' | FromRoman`
Output:
```19
4
0
2479
3001
```

## Prolog

```decode_digit(i, 1).
decode_digit(v, 5).
decode_digit(x, 10).
decode_digit(l, 50).
decode_digit(c, 100).
decode_digit(d, 500).
decode_digit(m, 1000).

decode_string(Sum, _, [], Sum).

decode_string(LastSum, LastValue, [Digit|Rest], NextSum) :-
decode_digit(Digit, Value),
Value < LastValue,
Sum is LastSum - Value,
decode_string(Sum, Value, Rest, NextSum).

decode_string(LastSum, LastValue, [Digit|Rest], NextSum) :-
decode_digit(Digit, Value),
Value >= LastValue,
Sum is LastSum + Value,
decode_string(Sum, Value, Rest, NextSum).

decode_string(Atom, Value) :-
atom_chars(Atom, String),
reverse(String, [Last|Rest]),
decode_digit(Last, Start),
decode_string(Start, Start, Rest, Value).

test :-
decode_string(mcmxc, 1990),
decode_string(mmviii, 2008),
decode_string(mdclxvi, 1666).```

The program above contains its own test predicate. The respective goal succeeds. Therefore the test passes.

## Python

### Imperative

```_rdecode = dict(zip('MDCLXVI', (1000, 500, 100, 50, 10, 5, 1)))

def decode( roman ):
result = 0
for r, r1 in zip(roman, roman[1:]):
rd, rd1 = _rdecode[r], _rdecode[r1]
result += -rd if rd < rd1 else rd
return result + _rdecode[roman[-1]]

if __name__ == '__main__':
for r in 'MCMXC MMVIII MDCLXVI'.split():
print( r, decode(r) )```
Output:
```MCMXC 1990
MMVIII 2008
MDCLXVI 1666```

Another version, which I believe has clearer logic:

```roman_values = (('I',1), ('IV',4), ('V',5), ('IX',9),('X',10),('XL',40),('L',50),('XC',90),('C',100),
('CD', 400), ('D', 500), ('CM', 900), ('M',1000))

def roman_value(roman):
total=0
for symbol,value in reversed(roman_values):
while roman.startswith(symbol):
total += value
roman = roman[len(symbol):]

if __name__=='__main__':
for value in "MCMXC", "MMVIII", "MDCLXVI":
print('%s = %i' % (value, roman_value(value)))```
Output:
```MCMXC = 1990
MMVIII = 2008
MDCLXVI = 1666
```

### Declarative

Less clear, but a 'one liner':

```numerals = { 'M' : 1000, 'D' : 500, 'C' : 100, 'L' : 50, 'X' : 10, 'V' : 5, 'I' : 1 }
def romannumeral2number(s):
return reduce(lambda x, y: -x + y if x < y else x + y, map(lambda x: numerals.get(x, 0), s.upper()))```

Or, defining intFromRoman as a fold or reduction, and annotating a little more fully:

Works with: Python version 3
```'''Roman numerals decoded'''

from operator import mul
from functools import reduce
from collections import defaultdict
from itertools import accumulate, chain, cycle

# intFromRoman :: String -> Maybe Int
def intFromRoman(s):
'''Just the integer represented by a Roman
numeral string, or Nothing if any
characters are unrecognised.
'''
dct = defaultdict(
lambda: None,
zip(
'IVXLCDM',
accumulate(chain([1], cycle([5, 2])), mul)
)
)

def go(mb, x):
'''Just a letter value added to or
subtracted from a total, or Nothing
if no letter value is defined.
'''
if None in (mb, x):
return None
else:
r, total = mb
return x, total + (-x if x < r else x)

return bindMay(reduce(
go,
[dct[k.upper()] for k in reversed(list(s))],
(0, 0)
))(snd)

# ------------------------- TEST -------------------------
def main():
'''Testing a sample of dates.'''

print(
fTable(__doc__ + ':\n')(str)(
maybe('(Contains unknown character)')(str)
)(
intFromRoman
)([
"MDCLXVI", "MCMXC", "MMVIII",
"MMXVI", "MMXVIII", "MMZZIII"
])
)

# ----------------------- GENERIC ------------------------

# bindMay (>>=) :: Maybe a -> (a -> Maybe b) -> Maybe b
def bindMay(m):
'''Injection operator for the Maybe monad.
If m is Nothing, it is passed straight through.
If m is Just(x), the result is an application
of the (a -> Maybe b) function (mf) to x.'''
return lambda mf: (
m if None is m else mf(m)
)

# maybe :: b -> (a -> b) -> Maybe a -> b
def maybe(v):
'''Either the default value v, if m is Nothing,
or the application of f to x,
where m is Just(x).
'''
return lambda f: lambda m: v if None is m else (
f(m)
)

# snd :: (a, b) -> b
def snd(ab):
'''Second member of a pair.'''
return ab[1]

# ---------------------- FORMATTING ----------------------

# fTable :: String -> (a -> String) ->
# (b -> String) -> (a -> b) -> [a] -> String
def fTable(s):
'''Heading -> x display function ->
fx display function -> f -> xs -> tabular string.
'''
def go(xShow, fxShow, f, xs):
ys = [xShow(x) for x in xs]
w = max(map(len, ys))
return s + '\n' + '\n'.join(map(
lambda x, y: (
f'{y.rjust(w, " ")} -> {fxShow(f(x))}'
),
xs, ys
))
return lambda xShow: lambda fxShow: lambda f: (
lambda xs: go(xShow, fxShow, f, xs)
)

# MAIN ---
if __name__ == '__main__':
main()```
Output:
```Roman numerals decoded:

MDCLXVI -> 1666
MCMXC -> 1990
MMVIII -> 2008
MMXVI -> 2016
MMXVIII -> 2018
MMZZIII -> (Contains unknown character)```

## Quackery

```  [ 2dup <
if
[ dip
[ 2 * - ]
dup ]
nip dup
rot + swap ] is roman    ( t p n --> t p )

[    1 roman ] is I        (   t p --> t p )
[    5 roman ] is V        (   t p --> t p )
[   10 roman ] is X        (   t p --> t p )
[   50 roman ] is L        (   t p --> t p )
[  100 roman ] is C        (   t p --> t p )
[  500 roman ] is D        (   t p --> t p )
[ 1000 roman ] is M        (   t p --> t p )

[ 0 1000 rot
\$ "" swap
witheach
[ space join
join ]
quackery
drop ]       is ->arabic (     \$ --> n   )

\$ "  MCMXC" dup echo\$ say " = " ->arabic echo cr
\$ " MMVIII" dup echo\$ say " = " ->arabic echo cr
\$ "MDCLXVI" dup echo\$ say " = " ->arabic echo cr
cr
\$ "I MIX VIVID MILD MIMIC"
dup echo\$ say " = " ->arabic echo cr```
Output:
```  MCMXC = 1990
MMVIII = 2008
MDCLXVI = 1666

I MIX VIVID MILD MIMIC = 3063```

## R

### version 1

Modelled along the lines of other decode routines on this page, but using a vectorised approach

```romanToArabic <- function(roman) {
romanLookup <- c(I=1L, V=5L, X=10L, L=50L, C=100L, D=500L, M=1000L)
rSplit <- strsplit(toupper(roman), character(0)) # Split input vector into characters
toArabic <- function(item) {
digits <- romanLookup[item]
if (length(digits) > 1L) {
smaller <- (digits[-length(digits)] < digits[-1L])
digits[smaller] <- - digits[smaller]
}
sum(digits)
}
vapply(rSplit, toArabic, integer(1))
}```

Example usage:

`romanToArabic(c("MCMXII", "LXXXVI"))`

### version 2

Using built-in functionality in R

`as.integer(as.roman(c("MCMXII", "LXXXVI"))`

## Racket

```#lang racket
(define (decode/roman number)
(define letter-values
(map cons '(#\M #\D #\C #\L #\X #\V #\I) '(1000 500 100 50 10 5 1)))
(define (get-value letter)
(cdr (assq letter letter-values)))
(define lst (map get-value (string->list number)))
(+ (last lst)
(for/fold ((sum 0))
((i (in-list lst)) (i+1 (in-list (cdr lst))))
(+ sum
(if (> i+1 i)
(- i)
i)))))

(map decode/roman '("MCMXC" "MMVIII" "MDCLXVI"))
;-> '(1990 2008 1666)```

## Raku

(formerly Perl 6) A non-validating version:

```sub rom-to-num(\$r) {
[+] gather \$r.uc ~~ /
^
[
| M  { take 1000 }
| CM { take 900 }
| D  { take 500 }
| CD { take 400 }
| C  { take 100 }
| XC { take 90 }
| L  { take 50 }
| XL { take 40 }
| X  { take 10 }
| IX { take 9 }
| V  { take 5 }
| IV { take 4 }
| I  { take 1 }
]+
\$
/;
}

say "\$_ => &rom-to-num(\$_)" for <MCMXC MDCLXVI MMVIII>;```
Output:
```MCMXC => 1990
MDCLXVI => 1666
MMVIII => 2008```

A validating version. Also handles older forms such as 'IIXX' and "IIII".

```sub rom-to-num(\$r) {
[+] gather \$r.uc ~~ /
^
( (C*)M { take 1000 - 100 * \$0.chars } )*
( (C*)D { take  500 - 100 * \$0.chars } )?
( (X*)C { take  100 -  10 * \$0.chars } )*
( (X*)L { take   50 -  10 * \$0.chars } )?
( (I*)X { take   10 -       \$0.chars } )*
( (I*)V { take    5 -       \$0.chars } )?
(     I { take    1                  } )*
[ \$ || { return NaN } ]
/;
}

say "\$_ => ", rom-to-num(\$_) for <MCMXC mdclxvi MMViii IIXX ILL>;```
Output:
```MCMXC => 1990
mdclxvi => 1666
MMViii => 2008
IIXX => 18
ILL => NaN```

## Red

### version 1

```Red [
Purpose: "Arabic <-> Roman numbers converter"
Date: "07-Oct-2016"
]

table-r2a: reverse [1000 "M" 900 "CM" 500 "D" 400 "CD" 100 "C" 90 "XC" 50 "L" 40 "XL" 10 "X" 9 "IX" 5 "V" 4 "IV" 1 "I"]

roman-to-arabic: func [r [string!] /local a b e] [
a: 0
parse r [any [b: ["I" ["V" | "X" | none] | "X" ["L" | "C" | none] | "C" ["D" | "M" | none] | "V" | "L" | "D" | "M"] e: (a: a + select table-r2a copy/part b e)]]
a
]

; Example usage:
print roman-to-arabic "XXXIII"
print roman-to-arabic "MDCCCLXXXVIII"
print roman-to-arabic "MMXVI"```

## REFAL

```\$ENTRY Go {
= <Prout <RomanDecode 'MCMXC'>>
<Prout <RomanDecode 'MMVIII'>>
<Prout <RomanDecode 'MDCLXVI'>>;
};

RomanDecode {
= 0;
e.D, <Upper e.D>: {
'M'  e.R = <+ 1000 <RomanDecode e.R>>;
'CM' e.R = <+  900 <RomanDecode e.R>>;
'D'  e.R = <+  500 <RomanDecode e.R>>;
'CD' e.R = <+  400 <RomanDecode e.R>>;
'C'  e.R = <+  100 <RomanDecode e.R>>;
'XC' e.R = <+   90 <RomanDecode e.R>>;
'L'  e.R = <+   50 <RomanDecode e.R>>;
'XL' e.R = <+   40 <RomanDecode e.R>>;
'X'  e.R = <+   10 <RomanDecode e.R>>;
'IX' e.R = <+    9 <RomanDecode e.R>>;
'V'  e.R = <+    5 <RomanDecode e.R>>;
'IV' e.R = <+    4 <RomanDecode e.R>>;
'I'  e.R = <+    1 <RomanDecode e.R>>;
};
};```
Output:
```1990
2008
1666```

## REXX

### version 1

Translation of: NetRexx
Works with: Regina
Works with: ooRexx
```/* Rexx */

Do
/* 1990  2008   1666    */
years = 'MCMXC MMVIII MDCLXVI'

Do y_ = 1 to words(years)
Say right(word(years, y_), 10) || ':' decode(word(years, y_))
End y_

Return
End
Exit

decode:
Procedure
Do
Parse upper arg roman .

If verify(roman, 'MDCLXVI') = 0 then Do

/* always insert the value of the least significant numeral */
decnum = rchar(substr(roman, length(roman), 1))
Do d_ = 1 to length(roman) - 1
If rchar(substr(roman, d_, 1)) < rchar(substr(roman, d_ + 1, 1)) then Do
/* Handle cases where numerals are not in descending order */
/*   subtract the value of the numeral */
decnum = decnum - rchar(substr(roman, d_, 1))
End
else Do
/* Normal case */
/*   add the value of the numeral */
decnum = decnum + rchar(substr(roman, d_, 1))
End
End d_
End
else Do
decnum = roman 'contains invalid roman numerals'
End

Return decnum
End
Exit

rchar:
Procedure
Do
Parse upper arg ch +1 .

select
when ch = 'M' then digit = 1000
when ch = 'D' then digit =  500
when ch = 'C' then digit =  100
when ch = 'L' then digit =   50
when ch = 'X' then digit =   10
when ch = 'V' then digit =    5
when ch = 'I' then digit =    1
otherwise          digit =    0
end

Return digit
End
Exit```
Output:
```     MCMXC: 1990
MMVIII: 2008
MDCLXVI: 1666
```

### version 2

This version of the (above) REXX program:

•   removes 3 sets of superfluous   do──end   statements
•   removes dead code (3 REXX statements that can't be executed)
•   replaced   substr(xxx, length(xxx), 1)     with     right(xxx,1)
•   removes a useless   parse   statement
•   compresses 63 lines to 29 lines
•   reordered   if   statements by most likely to occur

This REXX version   won't   handle:

•   Roman numbers like   IIXX
•   the   j   and   u   numerals
•   (deep) parenthesis type Roman numbers
```/*REXX program  converts  Roman numeral number(s)  ───►  Arabic numerals  (or numbers). */
rYear = 'MCMXC'    ;      say right(rYear, 9)":"     rom2dec(rYear)
rYear = 'mmviii'   ;      say right(rYear, 9)":"     rom2dec(rYear)
rYear = 'MDCLXVI'  ;      say right(rYear, 9)":"     rom2dec(rYear)
exit                                             /*stick a fork in it,  we're all done. */
/*──────────────────────────────────────────────────────────────────────────────────────*/
rom2dec: procedure;  arg roman .                 /*obtain the Roman numeral number.     */
if verify(roman, 'MDCLXVI')\==0  then return  "***error***  invalid Roman number:"   roman
do j=1  for length(roman) - 1
x=rChar( substr(roman, j  , 1) )     /*extract the  current  Roman numeral. */
y=rChar( substr(roman, j+1, 1) )     /*extract the     next  Roman numeral. */
if x<y  then # = #-x                 /*Is   x<y ?         Then subtract it. */
else # = #+x                 /*Is   x≥y ?           "    add     "  */
end   /*j*/
return #
/*──────────────────────────────────────────────────────────────────────────────────────*/
rChar: procedure;  arg _                         /*convert Roman number to Arabic digits*/
if _=='I'  then return    1
if _=='V'  then return    5
if _=='X'  then return   10
if _=='L'  then return   50
if _=='C'  then return  100
if _=='D'  then return  500
if _=='M'  then return 1000
return    0               /*indicate an  invalid  Roman numeral. */```

### version 3

This REXX version allows the use of   j   which was being used in the later part of the Holy Roman Empire
(as a trailing   i   in Roman numerals).

Also, this program converts   IIXX   correctly.     (Note:   this Roman numeral was actually chiseled on
some Roman monuments, archways, and tombs/crypts.)

Also supported are larger numbers such as   (M)   which is a Roman numeral(s) within a set of grouping
symbols,   in this case, a set of parenthesis   (brackets and/or braces can also be used).

Deep parentheses are also supported:   (MM)   is two million,   ((MMM))   is three billion.

Normally, the Romans used an overbar (vinculum) for larger numbers (such as   XL   for forty-thousand),
but the use of such a character is very problematic for computers to deal with,   so parenthesis are used

The Romans also had symbols for some fractions which would be a good addition to this task.
Also, lowercase   u   was also used for lowercase   v
Also note that   IIII   is a legal Roman numeral construct;   (as demonstrated by almost any old clock or
"dialed" wristwatch that has Roman numerals).

```/*REXX program  converts  Roman numeral number(s)  ───►  Arabic numerals  (or numbers). */
numeric digits 1000                              /*so we can handle the big numbers.    */
parse arg z                                      /*obtain optional arguments from the CL*/
if z=''  then z= "MCMXC mmviii IIXX LU MDCLXVI MDWLXVI ((mmm)) [[[[[D]]]]]"  /*defaults.*/

do j=1  for words(z);   y=word(z, j)        /*process each of the Roman numbers.   */
say  right(y, 20)':'    rom2dec(y)          /*display original and decimal version.*/
end   /*j*/
exit                                             /*stick a fork in it,  we're all done. */
/*──────────────────────────────────────────────────────────────────────────────────────*/
rom2dec:  procedure;   h='0'x;   #=0;   \$=1;   arg n .         /*"ARG"  uppercases  N.  */
n=translate(n, '()()', "[]{}");  _=verify(n, 'MDCLXVUIJ()')    /*trans grouping symbols.*/
if _\==0  then return '***error*** invalid Roman numeral:'  substr(n,_,1)   /*tell error*/
@.=1; @.m=1000; @.d=500; @.c=100; @.l=50; @.x=10; @.u=5; @.v=5 /*Roman numeral values.  */
/* [↓]  convert number.  */
do k=length(n)  to 1  by -1;  _=substr(n, k, 1)             /*examine a Roman numeral*/
/* [↑]  scale up or down.*/
if _=='(' | _==")"  then  do;  \$=\$*1000; if _=='(' then \$=1 /* (≡scale ↑;  )≡scale ↓ */
iterate                      /*go & process next digit*/
end
_=@._*\$                                                     /*scale it if necessary. */
if _>h  then h=_                                            /*remember Roman numeral.*/
if _<h  then #=#-_                                          /*char>next?  Then sub.  */
else #=#+_                                          /*            else add.  */
end   /*k*/
return #                                                       /*return Arabic number.  */```

output   when using the default inputs:

```               MCMXC: 1990
mmviii: 2008
IIXX: 18
LU: 55
MDCLXVI: 1666
MDWLXVI: ***error*** invalid Roman numeral: W
((mmm)): 3000000000
[[[[[D]]]]]: 500000000000000000
```

## Ring

```symbols = "MDCLXVI"
weights = [1000,500,100,50,10,5,1]

see "MCMXCIX = " + romanDec("MCMXCIX") + nl
see "MDCLXVI =" + romanDec("MDCLXVI") + nl
see "XXV = " + romanDec("XXV") + nl
see "CMLIV = " + romanDec("CMLIV") + nl
see "MMXI = " + romanDec("MMXI") + nl

func romanDec roman
n = 0
lastval = 0
arabic = 0
for i = len(roman) to 1 step -1
n = substr(symbols,roman[i])
if n > 0 n = weights[n] ok
if n < lastval arabic = arabic - n
else arabic = arabic + n ok
lastval = n
next
return arabic```

## RPL

Works with: Halcyon Calc version 4.2.7
RPL code Comment
```≪ DUP SIZE "IVXLCDM" { 1 5 10 50 100 500 1000 }
→ rom siz dig val
≪ 0 1 siz FOR j
rom j DUP SUB
IF dig SWAP POS THEN val LAST GET END
IF DUP2 < THEN SWAP NEG SWAP END
NEXT
0 1 siz START + NEXT +
≫ ≫ 'ROM→' STO
```
```ROM→ ( "ROMAN" -- n )
store input string, length and tables
scan string from highest digit
get jth character
if char in the table then push its value into stack
if > to previous value then change sign of previous value

sum the stack
.
```

## Ruby

```def fromRoman(roman)
r = roman.upcase
n = 0
until r.empty? do
case
when r.start_with?('M')  then v = 1000; len = 1
when r.start_with?('CM') then v = 900;  len = 2
when r.start_with?('D')  then v = 500;  len = 1
when r.start_with?('CD') then v = 400;  len = 2
when r.start_with?('C')  then v = 100;  len = 1
when r.start_with?('XC') then v = 90;   len = 2
when r.start_with?('L')  then v = 50;   len = 1
when r.start_with?('XL') then v = 40;   len = 2
when r.start_with?('X')  then v = 10;   len = 1
when r.start_with?('IX') then v = 9;    len = 2
when r.start_with?('V')  then v = 5;    len = 1
when r.start_with?('IV') then v = 4;    len = 2
when r.start_with?('I')  then v = 1;    len = 1
else
raise ArgumentError.new("invalid roman numerals: " + roman)
end
n += v
r.slice!(0,len)
end
n
end

[ "MCMXC", "MMVIII", "MDCLXVI" ].each {|r| p r => fromRoman(r)}```
Output:
```{"MCMXC"=>1990}
{"MMVIII"=>2008}
{"MDCLXVI"=>1666}
```

or

```SYMBOLS = [ ['M', 1000], ['CM', 900], ['D', 500], ['CD', 400], ['C', 100], ['XC', 90],
['L', 50], ['XL', 40], ['X', 10], ['IX', 9], ['V', 5], ['IV', 4], ['I', 1] ]

def parseRoman(roman)
r = roman.upcase
n = 0
SYMBOLS.each { |sym, val| n += val while r.sub!(/^#{sym}/, "") }
n
end

[ "MCMXC", "MMVIII", "MDCLXVI" ].each {|r| puts "%8s :%5d" % [r, parseRoman(r)]}```
Output:
```   MCMXC : 1990
MMVIII : 2008
MDCLXVI : 1666
```

## Rust

```struct RomanNumeral {
symbol: &'static str,
value: u32
}

const NUMERALS: [RomanNumeral; 13] = [
RomanNumeral {symbol: "M",  value: 1000},
RomanNumeral {symbol: "CM", value: 900},
RomanNumeral {symbol: "D",  value: 500},
RomanNumeral {symbol: "CD", value: 400},
RomanNumeral {symbol: "C",  value: 100},
RomanNumeral {symbol: "XC", value: 90},
RomanNumeral {symbol: "L",  value: 50},
RomanNumeral {symbol: "XL", value: 40},
RomanNumeral {symbol: "X",  value: 10},
RomanNumeral {symbol: "IX", value: 9},
RomanNumeral {symbol: "V",  value: 5},
RomanNumeral {symbol: "IV", value: 4},
RomanNumeral {symbol: "I",  value: 1}
];

fn to_hindu(roman: &str) -> u32 {
match NUMERALS.iter().find(|num| roman.starts_with(num.symbol)) {
Some(num) => num.value + to_hindu(&roman[num.symbol.len()..]),
None => 0, // if string empty, add nothing
}
}

fn main() {
let roms = ["MMXIV", "MCMXCIX", "XXV", "MDCLXVI", "MMMDCCCLXXXVIII"];
for &r in &roms {
// 15 is minimum formatting width of the first argument, there for alignment
println!("{:2\$} = {}", r, to_hindu(r), 15);
}
}```
Output:
```MMXIV           = 2014
MCMXCIX         = 1999
XXV             = 25
MDCLXVI         = 1666
MMMDCCCLXXXVIII = 3888```

## Scala

```def fromRoman( r:String ) : Int = {
val arabicNumerals = List("CM"->900,"M"->1000,"CD"->400,"D"->500,"XC"->90,"C"->100,
"XL"->40,"L"->50,"IX"->9,"X"->10,"IV"->4,"V"->5,"I"->1)

var s = r
arabicNumerals.foldLeft(0){ (n,t) => {
val l = s.length; s = s.replaceAll(t._1,""); val c = (l - s.length)/t._1.length  // Get the frequency
n + (c*t._2)  // Add the arabic numerals up
} }
}

// Here is a another version that does a simple running sum:
def fromRoman2(s: String) : Int = {
val numerals = Map('I' -> 1, 'V' -> 5, 'X' -> 10, 'L' -> 50, 'C' -> 100, 'D' -> 500, 'M' -> 1000)

s.toUpperCase.map(numerals).foldLeft((0,0)) {
case ((sum, last), curr) =>  (sum + curr + (if (last < curr) -2*last else 0), curr) }._1
}
}

// A small test
def test( roman:String ) = println( roman + " => " + fromRoman( roman ) )

test("MCMXC")
test("MMVIII")
test("MDCLXVI")```
Output:
```MCMXC => 1990
MMVIII => 2008
MDCLXVI => 1666```

## Scheme

Works with: Gauche Scheme
```(use gauche.collection) ;; for fold2

(define (char-val char)
(define i (string-scan "IVXLCDM" char))
(* (expt 10 (div i 2)) (expt 5 (mod i 2))))

(define (decode roman)
(fold2
(lambda (n sum prev-val)
(values ((if (< n prev-val) - +) sum n) (max n prev-val)))
0 0
(map char-val (reverse (string->list roman)))))```

Testing:

```(for-each
(^s (format #t "~7d: ~d\n" s (decode s)))
'("MCMLVI" "XXC" "MCMXC" "XXCIII" "IIIIX" "MIM" "LXXIIX"))```
Output:
``` MCMLVI: 1956
XXC: 80
MCMXC: 1990
XXCIII: 83
IIIIX: 6
MIM: 1999
LXXIIX: 78
```

## Seed7

```\$ include "seed7_05.s7i";

const func integer: ROMAN parse (in string: roman) is func
result
var integer: arabic is 0;
local
var integer: index is 0;
var integer: number is 0;
var integer: lastval is 0;
begin
for index range length(roman) downto 1 do
case roman[index] of
when {'M', 'm'}: number := 1000;
when {'D', 'd'}: number :=  500;
when {'C', 'c'}: number :=  100;
when {'L', 'l'}: number :=   50;
when {'X', 'x'}: number :=   10;
when {'V', 'v'}: number :=    5;
when {'I', 'i'}: number :=    1;
otherwise:       raise RANGE_ERROR;
end case;
if number < lastval then
arabic -:= number;
else
arabic +:= number;
end if;
lastval := number;
end for;
end func;

const proc: main is func
begin
writeln(ROMAN parse "MCMXC");
writeln(ROMAN parse "MMVIII");
writeln(ROMAN parse "MDCLXVI");
end func;```

Original source: [1]

Output:
```1990
2008
1666
```

## SenseTalk

```function RomanNumeralsDecode numerals
put {
"M": 1000,
"D": 500,
"C": 100,
"L": 50,
"X": 10,
"V": 5,
"I": 1
} into values

put 0 into total
repeat with each character letter of numerals
if values.(character the counter + 1 of numerals) is less than or equal to values.(letter)
else
subtract values.(letter) from total
end if
end repeat
end RomanNumeralsDecode```
```repeat for each item in [
"MCMXC",
"MMVIII",
"MDCLXVI",
]
put RomanNumeralsDecode(it)
end repeat```
Output:
```1990
2008
1666
```

## Sidef

```func roman2arabic(roman) {

var arabic = 0
var last_digit = 1000

static m = Hash(
I =>    1,
V =>    5,
X =>   10,
L =>   50,
C =>  100,
D =>  500,
M => 1000,
)

roman.uc.chars.map{m{_} \\ 0}.each { |digit|
if (last_digit < digit) {
arabic -= (2 * last_digit)
}
arabic += (last_digit = digit)
}

return arabic
}

%w(MCMXC MMVIII MDCLXVI).each { |roman_digit|
"%-10s == %d\n".printf(roman_digit, roman2arabic(roman_digit))
}```
Output:
```MCMXC      == 1990
MMVIII     == 2008
MDCLXVI    == 1666
```

Simpler solution:

```func roman2arabic(digit) {
digit.uc.trans([
:M:  '1000+',
:CM:  '900+',
:D:   '500+',
:CD:  '400+',
:C:   '100+',
:XC:   '90+',
:L:    '50+',
:XL:   '40+',
:X:    '10+',
:IX:    '9+',
:V:     '5+',
:IV:    '4+',
:I:     '1+',
]).split('+').map{.to_i}.sum;
}

%w(MCMXC MMVIII MDCLXVI).each { |roman_num|
say "#{roman_num}\t-> #{roman2arabic(roman_num)}";
}```
Output:
```MCMXC   -> 1990
MMVIII  -> 2008
MDCLXVI -> 1666
```

## Simula

```BEGIN

INTEGER PROCEDURE FROMROMAN(S); TEXT S;
BEGIN
PROCEDURE P(INTVAL, NUM); INTEGER INTVAL; TEXT NUM;
BEGIN
INTEGER NLEN;
NLEN := NUM.LENGTH;
WHILE INDEX + NLEN - 1 <= SLEN AND THEN
S.SUB(INDEX, NLEN) = NUM DO
BEGIN
RESULT := RESULT + INTVAL;
INDEX := INDEX + NLEN;
END WHILE;
END P;
INTEGER RESULT, INDEX, SLEN;
SLEN := S.LENGTH;
INDEX := 1;
P( 1000, "M"  );
P(  900, "CM" );
P(  500, "D"  );
P(  400, "CD" );
P(  100, "C"  );
P(   90, "XC" );
P(   50, "L"  );
P(   40, "XL" );
P(   10, "X"  );
P(    9, "IX" );
P(    5, "V"  );
P(    4, "IV" );
P(    1, "I"  );
FROMROMAN := RESULT;
END FROMROMAN;

TEXT T;
FOR T :- "MCMXC", "MMVIII", "MDCLXVI" DO
BEGIN
OUTTEXT("ROMAN """);
OUTTEXT(T);
OUTTEXT(""" => ");
OUTINT(FROMROMAN(T), 0);
OUTIMAGE;
END FOR;

END PROGRAM;```
Output:
```ROMAN "MCMXC" => 1990
ROMAN "MMVIII" => 2008
ROMAN "MDCLXVI" => 1666
```

## SNOBOL4

```*        Roman to Arabic
define('arabic(n)s,ch,val,sum,x') :(arabic_end)
arabic  s = 'M1000 D500 C100 L50 X10 V5 I1 '
n = reverse(n)
arab1   n len(1) . ch = :f(arab2)
s ch break(' ') . val
val = lt(val,x) (-1 * val)
sum = sum + val; x = val        :(arab1)
arab2   arabic = sum                    :(return)
arabic_end

*        Test and display
tstr = 'MMX MCMXCIX MCDXCII MLXVI CDLXXVI "
tloop   tstr break(' ') . r span(' ') = :f(out)
astr = astr r '=' arabic(r) ' ' :(tloop)
out     output = astr
end```
Output:
`MMX=2010 MCMXCIX=1999 MCDXCII=1492 MLXVI=1066 CDLXXVI=476`

Here's an alternative version, which is maybe more SNOBOL4-idiomatic and less like one might program it in a more common language:

```*   Roman to Arabic
romans1 = " 0 IX9 IV4 III3 II2 I1 VIII8 VII7 VI6 V5"  :(arabic1_end)
arabic1 ident(romans)                             :s(return)
romans (break("IV") | rem) . b4 rem . rdigit = b4
romans1 " " rdigit any("0123456789") . adigit
romans = replace(romans,"MDCLX","CLXVI")  :(arabic1)
arabic1_end
*   Test and display
tstr = "MMX MCMXCIX MCDXCII MLXVI CDLXXVI "
tloop   tstr break(' ') . r span(' ') =           :f(out)
astr = astr r '=' arabic1(r) ' '          :(tloop)
out     output = astr
end```

The output is the same as in the earlier version.

The following version takes advantage of some of the so-called "SPITBOL extensions", which are to be found in most modern implementations. This allows removing several labels and explicit transfers of control, and moves some of the looping into the pattern matcher. Again, the output is the same.

```*   Roman to Arabic
romans1 = " 0 IX9 IV4 III3 II2 I1 VIII8 VII7 VI6 V5"  :(arabic1_end)
arabic1 ident(romans)                             :s(return)
romans (break("IV") | rem) . b4 rem . rdigit = replace(b4,"MDCLX","CLXVI")
romans1 " " rdigit any("0123456789") . adigit
arabic1_end
*   Test and display
tstr = " MMX MCMXCIX MCDXCII MLXVI CDLXXVI "
tstr span(' ') break(' ') \$ r *?(astr = astr r '=' arabic1(r) ' ') fail
output = astr
end```

## SPL

```r2a(r)=
n = [1,5,10,50,100,500,1000]
a,m = 0
> i, #.size(r)..1, -1
v,c = n[#.pos("IVXLCDM",#.mid(r,i))]
? v<m, v = -v
? c>m, m = c
a += v
<
<= a
.

t = ["MMXI","MIM","MCMLVI","MDCLXVI","XXCIII","LXXIIX","IIIIX"]
> i, 1..#.size(t,1)
#.output(t[i]," = ",r2a(t[i]))
<```
Output:
```MMXI = 2011
MIM = 1999
MCMLVI = 1956
MDCLXVI = 1666
XXCIII = 83
LXXIIX = 78
IIIIX = 6
```

## Swift

```extension Int {
init(romanNumerals: String) {
let values = [
( "M", 1000),
("CM",  900),
( "D",  500),
("CD",  400),
( "C",  100),
("XC",   90),
( "L",   50),
("XL",   40),
( "X",   10),
("IX",    9),
( "V",    5),
("IV",    4),
( "I",    1),
]

self = 0
var raw = romanNumerals
for (digit, value) in values {
while raw.hasPrefix(digit) {
self += value
raw.removeFirst(digit.count)
}
}
}
}```
Output:
`Int(romanNumerals: "MDCLXVI") // 1666`

## Tailspin

```def digits: [(M:1000"1"), (CM:900"1"), (D:500"1"), (CD:400"1"), (C:100"1"), (XC:90"1"), (L:50"1"), (XL:40"1"), (X:10"1"), (IX:9"1"), (V:5"1"), (IV:4"1"), (I:1"1")];
composer decodeRoman
@: 1;
[ <digit>* ] -> \(@: 0"1"; \$... -> @: \$@ + \$; \$@ !\)
rule digit: <value>* (@: \$@ + 1;)
rule value: <='\$digits(\$@)::key;'> -> \$digits(\$@)::value
end decodeRoman

'MCMXC' -> decodeRoman -> !OUT::write
'
' -> !OUT::write
'MMVIII' -> decodeRoman -> !OUT::write
'
' -> !OUT::write
'MDCLXVI' -> decodeRoman -> !OUT::write```
Output:
```1990"1"
2008"1"
1666"1"
```

## Tcl

As long as we assume that we have a valid roman number, this is most easily done by transforming the number into a sum and evaluating the expression:

```proc fromRoman rnum {
set map {M 1000+ CM 900+ D 500+ CD 400+ C 100+ XC 90+ L 50+ XL 40+ X 10+ IX 9+ V 5+ IV 4+ I 1+}
expr [string map \$map \$rnum]0}
}```

Demonstrating:

```foreach r {MCMXC MDCLXVI MMVIII} {
puts "\$r\t-> [fromRoman \$r]"
}```
Output:
```MCMXC	-> 1990
MDCLXVI	-> 1666
MMVIII	-> 2008```

## TMG

Unix TMG dialect. Version without validation:

```loop:   parse(roman)\loop;
roman:  string(!<<MDCLXVI>>) [n=0] num
letter: num/render letter;
num:  <M> [n=+1750]
|  <D> [n=+764]
|  <C> ( <M> [n=+1604]
| <D> [n=+620]
| [n=+144] )
|  <L> [n=+62]
|  <X> ( <C> [n=+132]
| <L> [n=+50]
| [n=+12] )
|  <V> [n=+5]
|  <I> ( <X> [n=+11]
| <V> [n=+4]
| [n++] );
render: decimal(n) = { 1 * };

n:  0;```

Unix TMG dialect. Version with validation:

```loop:   [wsz = &a - &n]
parse(line)\loop
parse(error)\loop;
line:   roman *;
roman:  [n=0] [off=0]
comb((<^>),(<&>),(<M>))
comb((<M>),(<D>),(<C>))
comb((<C>),(<L>),(<X>))
comb((<X>),(<V>),(<I>))
[n>0?] decimal(n) = { 1 * };
comb:   proc(c1,c2,c3)
[v1 = *(wsz*off++ + &a)]
[v2 = *(wsz*off++ + &a)]
[v3 = *(wsz*off   + &a)]
( c3 ( c3 ( c3 [n=+(3*v3)]
| [n=+(2*v3)] )
| c1 [v1>0?] [n=+v1-v3]
| c2 [v2>0?] [n=+v2-v3]
| [n=+v3] )
| c2 [v2>0?] [n=+v2]
( c3 ( c3 ( c3 [n=+(3*v3)]
| [n=+(2*v3)] )
| [n=+v3] )
| () )
| () );
error:  smark ignore(<<>>) string(notnewline) scopy *
= { <error: > 1 * };

notnewline: !<<
>>;

n:  0;
a:  0; 0; 1750; 764; 144; 62; 12; 5; 1;
off:0;
wsz:0;
v1: 0; v2: 0; v3: 0;```

Sample input:

```MMXVI
LV
XII
MCMLIV
IIXX
IM
XXCIII```

Sample output:

```2016
55
12
1954
error: IIXX
error: IM
error: XXCIII```

## TUSCRIPT

```\$\$ MODE TUSCRIPT
LOOP roman_number="MCMXC'MMVIII'MDCLXVI"
arab_number=DECODE (roman_number,ROMAN)
PRINT "Roman number ",roman_number," equals ", arab_number
ENDLOOP```
Output:
```Roman number MCMXC equals 1990
Roman number MMVIII equals 2008
Roman number MDCLXVI equals 1666
```

## UNIX Shell

```#!/bin/bash

roman_to_dec() {
local rnum=\$1
local n=0
local prev=0

for ((i=\${#rnum}-1;i>=0;i--))
do
case "\${rnum:\$i:1}" in
M)  a=1000 ;;
D)  a=500 ;;
C)  a=100 ;;
L)  a=50 ;;
X)  a=10 ;;
V)  a=5 ;;
I)  a=1 ;;
esac

if [[ \$a -lt \$prev ]]
then
let n-=a
else
let n+=a
fi

prev=\$a
done

echo "\$rnum = \$n"
}

roman_to_dec MCMXC
roman_to_dec MMVIII
roman_to_dec MDCLXVI```

## VBA

Convert Romans (i.e : XVI) in integers

```Option Explicit

Sub Main_Romans_Decode()
Dim Arr(), i&

Arr = Array("III", "XXX", "CCC", "MMM", "VII", "LXVI", "CL", "MCC", "IV", "IX", "XC", "ICM", "DCCCXCIX", "CMI", "CIM", "MDCLXVI", "MCMXC", "MMXVII")
For i = 0 To UBound(Arr)
Debug.Print Arr(i) & "   >>> " & lngConvert(CStr(Arr(i)))
Next
End Sub

Function Convert(Letter As String) As Long
Dim Romans(), DecInt(), Pos As Integer

Romans = Array("M", "D", "C", "L", "X", "V", "I")
DecInt = Array(1000, 500, 100, 50, 10, 5, 1)
Pos = -1
On Error Resume Next
Pos = Application.Match(Letter, Romans, 0) - 1
On Error GoTo 0
If Pos <> -1 Then Convert = DecInt(Pos)
End Function

Function lngConvert(strRom As String) 'recursive function
Dim i As Long, iVal As Integer

If Len(strRom) = 1 Then
lngConvert = Convert(strRom)
Else
iVal = Convert(Mid(strRom, 1, 1))
If iVal < Convert(Mid(strRom, 2, 1)) Then iVal = iVal * (-1)
lngConvert = iVal + lngConvert(Mid(strRom, 2, Len(strRom) - 1))
End If
End Function```
Output:
```III   >>> 3
XXX   >>> 30
CCC   >>> 300
MMM   >>> 3000
VII   >>> 7
LXVI   >>> 66
CL   >>> 150
MCC   >>> 1200
IV   >>> 4
IX   >>> 9
XC   >>> 90
ICM   >>> 899
DCCCXCIX   >>> 899
CMI   >>> 901
CIM   >>> 1099
MDCLXVI   >>> 1666
MCMXC   >>> 1990
MMXVII   >>> 2017```

## VBScript

Translation of: 360 Assembly
```' Roman numerals Encode - Visual Basic - 18/04/2019

Function toRoman(ByVal value)
Dim arabic
Dim roman
Dim i, result
arabic = Array(1000, 900, 500, 400, 100, 90, 50, 40, 10, 9, 5, 4, 1)
roman = Array("M", "CM", "D", "CD", "C", "XC", "L", "XL", "X", "IX", "V", "IV", "I")
For i = 0 To 12
Do While value >= arabic(i)
result = result + roman(i)
value = value - arabic(i)
Loop
Next 'i
toRoman = result
End Function 'toRoman

code=MsgBox(n & vbCrlf & toRoman(n),vbOKOnly+vbExclamation,"Roman numerals/Encode")
If code=vbOK Then ok=1```
Output:
```III   >>> 3
XXX   >>> 30
CCC   >>> 300
MMM   >>> 3000
VII   >>> 7
LXVI   >>> 66
CL   >>> 150
MCC   >>> 1200
IV   >>> 4
IX   >>> 9
XC   >>> 90
ICM   >>> 901
DCCCXCIX   >>> 899
CMI   >>> 901
CIM   >>> 1099
MDCLXVI   >>> 1666
MCMXC   >>> 1990
MMXVII   >>> 2017
I   >>> 1
XIV   >>> 14
MMMDCCCLXXXVIII   >>> 3888
MMMCMXCIX   >>> 3999
```

## Vedit macro language

```// Main program for testing the function
//
do {
Get_Input(10, "Enter a roman numeral: ", NOCR+STATLINE)
Call("Roman_to_Arabic")
Reg_Type(10) Message("	= ") Num_Type(#1)
} while(#1)
Return

// Convert Roman numeral into numeric value
//  in:  @10 = Roman numeral
//  out: #1  = numeric value
//
:Roman_to_Arabic:
Buf_Switch(Buf_Free)
Ins_Text("M1000 D500 C100 L50 X10 V5 I1") Ins_Newline
Reg_Ins(10) Ins_Char(' ')
#1 = #2 = 0

Repeat(ALL) {
#3 = #2                                  // #3 = previous character
Goto_Line(2)                             // roman numeral to be converted
if (At_EOL) {
Break                                // all done
}
Reg_Copy_Block(11, CP, CP+1, DELETE)     // next character in roman numeral
if (Search(@11, BEGIN+ADVANCE+NOERR)) {  // find character from the table
#2 = Num_Eval(SUPPRESS)              // corresponding numeric value
if (#2 > #3) {                       // larger than previous digit?
#1 -= #3                         // substract previous digit
} else {
#1 += #3                         // add previous digit
}
}
}
Reg_Empty(11)
Buf_Quit(OK)
Return```
Output:
```iv	=     4
xii	=    12
MDCLXVI	=  1666
MCMXC	=  1990
MMXI	=  2011```

## V (Vlang)

Translation of: Kotlin
```const romans = ["I", "III", "IV", "VIII", "XLIX", "CCII", "CDXXXIII", "MCMXC", "MMVIII", "MDCLXVI"]

fn main() {
for roman in romans {println("\${roman:-10} = \${roman_decode(roman)}")}
}

fn roman_decode(roman string) int {
mut n := 0
mut last := "O"
if roman =="" {return n}
for c in roman {
match c.ascii_str() {
"I" {n++}
"V" {if last == "I" {n += 3}  else {n += 5}}
"X" {if last == "I" {n += 8}   else {n += 10}}
"L" {if last == "X" {n += 30}  else {n += 50}}
"C" {if last == "X" {n += 80}  else {n += 100}}
"D" {if last == "C" {n += 300} else {n += 500}}
"M" {if last == "C" {n += 800} else {n += 1000}}
else {last = c.ascii_str()}
}
}
return n
}```
Output:
```I          = 1
III        = 3
IV         = 4
VIII       = 8
XLIX       = 49
CCII       = 202
CDXXXIII   = 433
MCMXC      = 1990
MMVIII     = 2008
MDCLXVI    = 1666
```

## Wren

Translation of: Kotlin
Library: Wren-fmt
```import "./fmt" for Fmt

var decode = Fn.new { |r|
if (r == "") return 0
var n = 0
var last = "0"
for (c in r) {
var k
if (c == "I") {
k = 1
} else if (c == "V") {
k = (last == "I") ? 3 : 5
} else if (c == "X") {
k = (last == "I") ? 8 : 10
} else if (c == "L") {
k = (last == "X") ? 30 : 50
} else if (c == "C") {
k = (last == "X") ? 80 : 100
} else if (c == "D") {
k = (last == "C") ? 300 : 500
} else if (c == "M") {
k = (last == "C") ? 800 : 1000
}
n = n + k
last = c
}
return n
}

var romans = ["I", "III", "IV", "VIII", "XLIX", "CCII", "CDXXXIII", "MCMXC", "MMVIII", "MDCLXVI"]
for (r in romans) System.print("%(Fmt.s(-10, r)) = %(decode.call(r))")```
Output:
```I          = 1
III        = 3
IV         = 4
VIII       = 8
XLIX       = 49
CCII       = 202
CDXXXIII   = 433
MCMXC      = 1990
MMVIII     = 2008
MDCLXVI    = 1666
```

## XLISP

Uses basic list processing and recursion. Probably not amazingly fast, but quite concise and hopefully clear.

```(defun decode (r)
(define roman '((#\m 1000) (#\d 500) (#\c 100) (#\l 50) (#\x 10) (#\v 5) (#\i 1)))
(defun to-arabic (rn rs a)
(cond
((null rn) a)
((eqv? (car rn) (caar rs)) (to-arabic (cdr rn) roman (if (and (not (eqv? (car rn) (cadr rn))) (< (cadar rs) (to-arabic (cdr rn) roman 0)))
(+ a (cadar rs)) ) ) )
(t (to-arabic rn (cdr rs) a)) ) )
(to-arabic (string->list r) roman 0) )```

Test it in a REPL:

```[1] (mapcar decode '("mcmxc" "mmviii" "mdclxvi"))

(1990 2008 1666)```

## XPL0

```string 0;                       \use zero-terminated strings
code CrLf=9, IntOut=11;

func Roman(Str);                \Convert Roman numeral string to decimal value
char Str;
int  I, Val, Val0, Sum;
[I:= 0;  Sum:= 0;  Val0:= 5000;
loop    [case Str(I) of
^M: Val:= 1000;
^D: Val:= 500;
^C: Val:= 100;
^L: Val:= 50;
^X: Val:= 10;
^V: Val:= 5;
^I: Val:= 1
other return Sum;       \zero string terminator
I:= I+1;
Sum:= Sum + Val;
if Val > Val0 then Sum:= Sum - 2*Val0;
Val0:= Val;
];
];

[IntOut(0, Roman("MCMXC"));    CrLf(0);
IntOut(0, Roman("MMVIII"));   CrLf(0);
IntOut(0, Roman("MDCLXVI"));  CrLf(0);
]```
Output:
```1990
2008
1666
```

## XQuery

```xquery version "3.1";

declare function local:decode-roman-numeral(\$roman-numeral as xs:string) {
\$roman-numeral
=> upper-case()
=> for-each(
function(\$roman-numeral-uppercase) {
analyze-string(\$roman-numeral-uppercase, ".")/fn:match
! map { "M": 1000, "D": 500, "C": 100, "L": 50, "X": 10, "V": 5, "I": 1 }(.)
}
)
=> fold-right([0,0],
function(\$number as xs:integer, \$accumulator as array(*)) {
let \$running-total := \$accumulator?1
let \$previous-number := \$accumulator?2
return
if (\$number lt \$previous-number) then
[ \$running-total - \$number, \$number ]
else
[ \$running-total + \$number, \$number ]
}
)
=> array:get(1)
};

let \$roman-numerals :=
map {
"MCMXCIX": 1999,
"MDCLXVI": 1666,
"XXV": 25,
"XIX": 19,
"XI": 11,
"CMLIV": 954,
"MMXI": 2011,
"CD": 400,
"MCMXC": 1990,
"MMVIII": 2008,
"MMIX": 2009,
"MMMDCCCLXXXVIII": 3888
}
return
map:for-each(
\$roman-numerals,
function(\$roman-numeral, \$expected-value) {
local:decode-roman-numeral(\$roman-numeral) eq \$expected-value
}
)```

## zkl

```var romans = L(
L("M", 1000), L("CM", 900), L("D",  500), L("CD", 400), L("C",  100),
L("XC",  90), L("L",   50), L("XL",  40), L("X",   10), L("IX",   9),
L("V",    5), L("IV",   4), L("I",    1));
fcn toArabic(romanNumber){	// romanNumber needs to be upper case
if (not RegExp("^[CDILMVX]+\$").matches(romanNumber))
throw(Exception.ValueError("Not a Roman number: %s".fmt(romanNumber)));
reg value = 0;
foreach R,N in (romans){
while (0 == romanNumber.find(R)){
value += N;
romanNumber = romanNumber[R.len(),*];
}
}
return(value);
}```
```toArabic("MCMXC")   //-->1990
toArabic("MMVIII")  //-->2008
toArabic("MDCLXVI") //-->1666
```

## Zoea

```program: roman_decimal
input: 'XIII'
output: 13```

## zsh

```#!/bin/zsh
function parseroman () {
local max=0 sum i j
local -A conv
conv=(I 1 V 5 X 10 L 50 C 100 D 500 M 1000)
for j in \${(Oas::)1}; do
i=conv[\$j]
if (( i >= max )); then
(( sum+=i ))
(( max=i ))
else
(( sum-=i ))
fi
done
echo \$sum
}

parseroman MCMXC
parseroman MMVIII
parseroman MDCLXVI```