playing with maybes in elm

maybe-match.elm

-- http://elm-lang.org/try
import Regex (..)
import Maybe (..)
import Graphics.Input as Input
import Graphics.Input.Field as Field
 
maybeMatch : String -> String -> Maybe Match
maybeMatch reg str =
  case find (AtMost 1) (regex reg) str of
    []    -> Nothing
    x::xs -> Just x
    
-- should be a library function
fmap : (a -> b) -> Maybe a -> Maybe b
fmap fn x = case x of
  Nothing -> Nothing
  Just x  -> Just (fn x)
    
-- should be a library function
orElse : Maybe a -> Maybe a -> Maybe a
orElse a b = case a of
  Nothing -> b
  _       -> a

result : String -> String
result str =
  let mbyResult reg res = (\_->res) `fmap` (maybeMatch reg str)
      foo = mbyResult "foo" "foo matched"
      bar = mbyResult "bar" "bar matched"
  in  maybe "nothing matched" id (foo `orElse` bar)
 
content = Input.input Field.noContent
 
main : Signal Element
main = 
   let input = Field.field Field.defaultStyle content.handle id "enter a string"
       output str = str.string |> result |> plainText
       display content = flow down [ input content, output content ]
   in  lift display content.signal