elm/exercises/rna-transcription/RNATranscription.example

module RNATranscription (toRNA) where

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