Roman numerals/Decode

Roman numerals/Decode is a draft programming task. It is not yet considered ready to be promoted as a complete task, for reasons that should be found in its talk page.

Create a function taking a Roman numeral as its argument and returning the value of the numeral.

Modern Roman numerals are written by expressing each decimal digit of the number to be encoded separately, starting with the leftmost digit and skipping any 0s. So 1990 is rendered "MCMXC" (1000 = M, 900 = CM, 90 = XC) and 2008 is rendered "MMVIII" (2000 = MM, 8 = VIII). The Roman numeral for 1666, "MDCLXVI", uses each letter in descending order.

Icon and Unicon

<lang Icon>link numbers

procedure main() every R := "MCMXC"|"MDCLXVI"|"MMVIII" do

  write(R, " = ",unroman(R))

end</lang>

Library: Icon Programming Library

numbers.icn provides unroman

The code for this procedure is copied below:<lang Icon>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</lang>

Output:

MCMXC = 1990
MDCLXVI = 1666
MMVIII = 2008

J

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

Example use:

<lang j> rom2d 'MCMXC' 1990

  rom2d 'MDCLXVI'

1666

  rom2d 'MMVIII'

2008</lang>

Zsh

<lang 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

}</lang>