rot13.elm

import Graphics.Element (..)
import Graphics.Input.Field as Field
import Signal
import List (head)
import Char (..)
import String (length, slice, toList, indexes, cons, map)
import Text (plainText)

content : Signal.Channel Field.Content
content =
  Signal.channel Field.noContent


main : Signal Element
main =
  Signal.map scene (Signal.subscribe content)


scene : Field.Content -> Element
scene fieldContent =
    flow down
    [ Field.field Field.defaultStyle (Signal.send content) "Type here!" fieldContent
    , plainText (rot13 fieldContent.string)
    ]

rot13 : String -> String
rot13 message =
   message
   |> map (\ch -> 
   if 
     | isLower ch -> rotate 13 ch
     | isUpper ch -> toUpper (rotate 13 (toLower ch))
   
   )
   
rotate : Int -> Char -> Char
rotate i ch =
   charAt <| (charValue ch + i) % (length alphabet)

alphabet = "abcdefghijklmnopqrstuvwxyz"

charAt : Int -> Char
charAt i =
  slice i (i+1) alphabet
  |> toList
  |> head

charValue : Char -> Int
charValue ch =
  head <| indexes (cons ch "") alphabet