Haskell Quiz/Morse Code/Solution Kristof
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This is a simple solution that uses the list Monad for generating all possibilities.
import Maybe
import Control.Applicative -- for <$>
codes = zip ['A'..'Z']
[ ".-", "-...", "-.-.", "-..", ".", "..-.", "--.", "....",
"..", ".---" , "-.-", ".-..", "--", "-.", "---", ".--.",
"--.-", ".-.", "...", "-" , "..-", "...-", ".--", "-..-",
"-.--", "--.." ]
try_letter str (letter, code) =
let (l,r) = splitAt (length code) str
in if l == code then Just (letter, r) else Nothing
morse "" = return ""
morse str = do (l,r) <- mapMaybe (try_letter str) codes
(l:) <$> morse r
main = mapM_ putStrLn . morse . filter (`elem` ".-") =<< getLine