Another approach for a morse code decoder is to use a Dichotomic search.
text = ".--- .... .---- --- --- -.. -..-. --.- .-. .--."
data Tree a = Leaf
| Branch { tag :: a, left :: Tree a, right :: Tree a }
deriving (Read, Show)
dict :: Tree Char
dict = Branch ' '
(Branch 'E'
(Branch 'I'
(Branch 'S'
(Branch 'H'
(Branch '5' Leaf Leaf)
(Branch '4' Leaf Leaf))
(Branch 'V' Leaf (Branch '3' Leaf Leaf)))
(Branch 'U'
(Branch 'F' Leaf Leaf)
(Branch ' ' Leaf (Branch '2' Leaf Leaf))))
(Branch 'A'
(Branch 'R'
(Branch 'L' Leaf Leaf)
(Branch ' ' (Branch '+' Leaf Leaf) Leaf))
(Branch 'W'
(Branch 'P' Leaf Leaf)
(Branch 'J' Leaf (Branch '1' Leaf Leaf)))))
(Branch 'T'
(Branch 'N'
(Branch 'D'
(Branch 'B'
(Branch '6' Leaf Leaf)
(Branch '=' Leaf Leaf))
(Branch 'X' (Branch '/' Leaf Leaf) Leaf))
(Branch 'K'
(Branch 'C' Leaf Leaf)
(Branch 'Y' Leaf Leaf)))
(Branch 'M'
(Branch 'G'
(Branch 'Z' (Branch '7' Leaf Leaf) Leaf)
(Branch 'Q' Leaf Leaf))
(Branch 'O'
(Branch ' ' (Branch '8' Leaf Leaf) Leaf)
(Branch ' '
(Branch '9' Leaf Leaf)
(Branch '0' Leaf Leaf)))))
decodeLetter :: String -> Char
decodeLetter = tag . foldl (flip step) dict
where
step '.' = left
step '-' = right
decode = map decodeLetter . words
main = do
print $ decode text
http://apfelmus.nfshost.com/articles/fun-with-morse-code.html
"JH1OOD/QRP"
Spinor Lab 