MorseTree.hs

-----------------------------------------------------------------------------
-- |
-- Module      : MorseTree
-- Copyright   : (c) 2014 Ricky Elrod
-- License     : BSD-style
-- Maintainer  : Ricky Elrod <ricky@elrod.me>
-- Stability   : experimental
-- Portability : Portable
--
-- TODO: Probably should use Data.Tree instead, for better library support.
-- TODO: toMorseChar is partial right now :(
--
-- Represents morse code as a tree structure
-- Idea taken from: http://www.learnmorsecode.com/pix/learn.gif
--
-- >>> map (flip toMorseChar morseTree) [[Dah, Dit, Dit, Dit], [Dit, Dit]
-- ['H', 'I']
-----------------------------------------------------------------------------

data Tree a = Empty | Branch a (Tree a) (Tree a) deriving (Show)
data Elem a = Start | MorseChar a
data Morse = Dit | Dah deriving (Show)

instance Show a => Show (Elem a) where
  show Start         = "<start>"
  show (MorseChar x) = show x

morseTree :: Tree (Elem Char)
morseTree =
  Branch Start
    (Branch (MorseChar 'T')
      (Branch (MorseChar 'M')
        (Branch (MorseChar 'O')
          (Branch (MorseChar '-')
            (Branch (MorseChar '0') Empty Empty)
            (Branch (MorseChar '9') Empty Empty)
          )
          (Branch (MorseChar '.')
            Empty
            (Branch (MorseChar '8') Empty Empty)
          )
        )
        (Branch (MorseChar 'G')
          (Branch (MorseChar 'Q') Empty Empty)
          (Branch (MorseChar 'Z')
            Empty
            (Branch (MorseChar '7') Empty Empty)
          )
        )
      )
      (Branch (MorseChar 'N')
        (Branch (MorseChar 'K')
          (Branch (MorseChar 'Y') Empty Empty)
          (Branch (MorseChar 'C') Empty Empty)
        )
        (Branch (MorseChar 'D')
          (Branch (MorseChar 'X') Empty Empty)
          (Branch (MorseChar 'B')
            Empty
            (Branch (MorseChar '6') Empty Empty)
          )
        )
      )
    )
    (Branch (MorseChar 'E')
      (Branch (MorseChar 'A')
        (Branch (MorseChar 'W')
          (Branch (MorseChar 'J')
            (Branch (MorseChar '1') Empty Empty)
            Empty
          )
          (Branch (MorseChar 'P') Empty Empty)
        )
        (Branch (MorseChar 'R')
          Empty
          (Branch (MorseChar 'L') Empty Empty)
        )
      )
      (Branch (MorseChar 'I')
        (Branch (MorseChar 'U')
          (Branch (MorseChar '_')
            (Branch (MorseChar '2') Empty Empty)
            Empty
          )
          (Branch (MorseChar 'F') Empty Empty)
        )
        (Branch (MorseChar 'S')
          (Branch (MorseChar 'V')
            (Branch (MorseChar '3') Empty Empty)
            Empty
          )
          (Branch (MorseChar 'H')
            (Branch (MorseChar '4') Empty Empty)
            (Branch (MorseChar '5') Empty Empty)
          )
        )
      )
    )

toMorseChar :: [Morse] -> Tree (Elem Char) -> (Elem Char)
toMorseChar (Dit:m) (Branch _ _ r) = toMorseChar m r
toMorseChar (Dah:m) (Branch _ l _) = toMorseChar m l
toMorseChar []      (Branch x _ _) = x