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Haskell Quiz/Morse Code/Solution Dolio - Revision history
2024-03-19T09:57:33Z
Revision history for this page on the wiki
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Dolio: display morse split
2007-04-22T17:36:05Z
<p>display morse split</p>
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<td colspan="2" style="background-color: #fff; color: #202122; text-align: center;">Revision as of 17:36, 22 April 2007</td>
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<td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #ffe49c; vertical-align: top; white-space: pre-wrap;"><div>morseLetter = msum $ zipWith (\c l -> string c >> return l) morse ['a'..'z']</div></td>
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<td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div>morseLetter = msum $ zipWith (\c l -> string c >> return <ins class="diffchange diffchange-inline">(c,</ins>l<ins class="diffchange diffchange-inline">)</ins>) morse ['a'..'z']</div></td>
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<td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #ffe49c; vertical-align: top; white-space: pre-wrap;"><div>main = interact $ unlines<del class="diffchange diffchange-inline"> . concatMap (evalStateT (total $ many morseLetter)) . words</del></div></td>
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<td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div>main = interact $ unlines</div></td>
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Dolio
https://wiki.haskell.org/index.php?title=Haskell_Quiz/Morse_Code/Solution_Dolio&diff=12598&oldid=prev
Dolio: creation
2007-04-22T06:11:56Z
<p>creation</p>
<p><b>New page</b></p><div>[[Category:Haskell Quiz solutions|Morse Code]]<br />
<br />
This solution uses a naive implementation of monadic parser combinators, simply using the state transform of the list monad. For more information on how all this works, a google search for 'monadic parser combinators' should be more than sufficient.<br />
<br />
<haskell><br />
import Data.List<br />
import Control.Monad<br />
import Control.Monad.State<br />
<br />
-- The classic parser monad, with input token type a, and output type b<br />
type Parser a b = StateT [a] [] b<br />
<br />
morse = [ ".-", "-...", "-.-.", "-..", ".", "..-.", "--.", "....", "..", ".---"<br />
, "-.-", ".-..", "--", "-.", "---", ".--.", "--.-", ".-.", "...", "-"<br />
, "..-", "...-", ".--", "-..-", "-.--", "--.." ]<br />
<br />
token :: Parser a a<br />
token = do (a:as) <- get ; put as ; return a<br />
<br />
satisfy :: (a -> Bool) -> Parser a ()<br />
satisfy p = token >>= guard . p<br />
<br />
many :: Parser a a -> Parser a [a]<br />
many p = many1 p `mplus` return []<br />
<br />
many1 :: Parser a a -> Parser a [a]<br />
many1 p = liftM2 (:) p (many p)<br />
<br />
total :: Parser a b -> Parser a b<br />
total p = p >>= \b -> get >>= guard . null >> return b<br />
<br />
string :: String -> Parser Char ()<br />
string [] = return ()<br />
string (x:xs) = satisfy (==x) >> string xs<br />
<br />
morseLetter :: Parser Char Char<br />
morseLetter = msum $ zipWith (\c l -> string c >> return l) morse ['a'..'z']<br />
<br />
main = interact $ unlines . concatMap (evalStateT (total $ many morseLetter)) . words<br />
</haskell></div>
Dolio