A-M baby

Task/Morse-code/Haskell/morse-code-2.hs

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+module MorseCode (Morse, MSym(..), toMorse) where
+
+import Data.List
+import Data.Maybe
+import qualified Data.Map as M
+
+type Morse = [MSym]
+data MSym = Dot | Dash | SGap | CGap | WGap deriving (Show)
+
+-- Based on the table of International Morse Code letters and numerals at
+-- http://en.wikipedia.org/wiki/Morse_code.
+dict = M.fromList
+       [('a', m ".-"   ), ('b', m "-..." ), ('c', m "-.-." ), ('d', m "-.."  ),
+        ('e', m "."    ), ('f', m "..-." ), ('g', m "--."  ), ('h', m "...." ),
+        ('i', m ".."   ), ('j', m ".---" ), ('k', m "-.-"  ), ('l', m ".-.." ),
+        ('m', m "--"   ), ('n', m "-."   ), ('o', m "---"  ), ('p', m ".--." ),
+        ('q', m "--.-" ), ('r', m ".-."  ), ('s', m "..."  ), ('t', m "-"    ),
+        ('u', m "..-"  ), ('v', m "...-" ), ('w', m ".--"  ), ('x', m "-..-" ),
+        ('y', m "-.--" ), ('z', m "--.." ), ('1', m ".----"), ('2', m "..---"),
+        ('3', m "...--"), ('4', m "....-"), ('5', m "....."), ('6', m "-...."),
+        ('7', m "--..."), ('8', m "---.."), ('9', m "----."), ('0', m "-----")]
+    where m = intersperse SGap . map toSym
+          toSym '.' = Dot
+          toSym '-' = Dash
+
+-- Convert a string to a stream of Morse symbols.  We enhance the usual dots
+-- and dashes with special "gap" symbols, which indicate the border between
+-- symbols, characters and words.  This allows a player to easily adjust its
+-- timing by simply looking at the current symbol, rather than trying to keep
+-- track of state.
+toMorse :: String -> Morse
+toMorse = fromWords . words . weed
+    where fromWords = intercalate [WGap] . map fromWord
+          fromWord  = intercalate [CGap] . map fromChar
+          fromChar  = fromJust . flip M.lookup dict
+          weed      = filter (\c -> c == ' ' || M.member c dict)