ローマ数字の計算機のElmコード。Assert関数は自前で用意。モブプログラミングでTDDで書いたもの。アジャイルジャパン2017にて / Roman Numerals Calculator elm code written in a mob programming session in TDD way at Ajile Japan 2017

roman_numerals_calculator.elm

import Html exposing (li, text, ul)
import String exposing (split)

add a b =
  numberToRoman ((romanToNumber a) + (romanToNumber b))
  
romanToNumber roman =
  List.length(split "" roman)
{-  case roman of
  "I" -> 1
  "II" -> 2
  "III" -> 3
  "IV" -> 4
  _ -> -1
-}

numberToRoman number =
  case number of
  1 -> "I"
  2 -> "II"
  3 -> "III"
  4 ->"IV"
  _ -> ""
  
assert a b =
  if a == b then "ok" else "ng"

main =
  ul []
    [ li [] [text (assert (romanToNumber "I") 1)]
    , li [] [text (assert (romanToNumber "II") 2)]
    , li [] [text (assert (romanToNumber "IV") 4)]
    , li [] [text (assert (numberToRoman 1) "I")]
    , li [] [text (assert (add "I" "I") "II")]
    , li [] [text (assert (add "I" "II") "III")] 
    , li [] [text (assert (add "II" "II") "IV")] 
    , li [] [text (assert  )]
    ]