elm/exercises/rna-transcription/RNATranscription.example

module RNATranscription exposing (toRNA)

import String


toRNA : String -> Result Char String
toRNA dna =
  dna
    |> String.toList
    |> List.map toRNANucleotide
    |> resultExtraCombine
    |> Result.map (List.map String.fromChar)
    |> Result.map (String.join "")



-- Copied from elm-result-extra


resultExtraCombine : List (Result x a) -> Result x (List a)
resultExtraCombine =
  List.foldr (Result.map2 (::)) (Ok [])


toRNANucleotide : Char -> Result Char Char
toRNANucleotide nuc =
  case nuc of
    'C' ->
      Ok 'G'

    'G' ->
      Ok 'C'

    'A' ->
      Ok 'U'

    'T' ->
      Ok 'A'

    _ ->
      Err nuc