Roman numerals kata in Elm

elm-roman-numerals-kata.elm

import Html exposing (..)

--Helper function from elm-list-extra
find : (a -> Bool) -> List a -> Maybe a
find predicate list =
    case list of
        [] ->
            Nothing

        first::rest ->
            if predicate first then
                Just first
            else
                find predicate rest

conversionTable = 
  [ (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")
  ]


toRomanNumber arabicInput = 
  if arabicInput <= 0 then
    ""
  else
    let
      (arabic, roman) = 
        Maybe.withDefault (0, "") 
          <| find (\(a, r) -> a <= arabicInput) conversionTable
    in
      roman ++ toRomanNumber(arabicInput - arabic)




test input expected =
  div [] [text <| toRomanNumber(input) ++ " = " ++ expected]

main =
  div []
    [ test 0 ""
    , test 1 "I"
    , test 99 "XCIX"
    , test 1000 "M"
    , test 3629 "MMMDCXXIX"
    , test 10000 "MMMMMMMMMM"
    ]