Réf. : [Haskell-beginners] a problem

corentin.dupont at ext.mpsa.com corentin.dupont at ext.mpsa.com
Fri Jun 25 09:27:03 EDT 2010


I would do (no that concise):

toMaybe :: Music_Data_ -> (Maybe Note, Maybe Direction, Maybe Sound)
toMaybe (Music_Data_1 n) = (Just n, Nothing, Nothing)
toMaybe (Music_Data_4 d) = (Nothing, Just d, Nothing)
toMaybe (Music_Data_9 s) = (Nothing, Nothing, Just s)

catMaybes3 (a,b,c) = (catMaybes a, catMaybes b, catMaybes c)

sortOutMusicData :: [Music_Data_] -> ([Note],[Direction],[Sound])
sortOutMusicData = catMaybes3 . unzip3 . map toMaybe


             Michael Mossey                                                
             <mpm at alumni.calt                                              
             ech.edu>                                                 Pour 
             Envoyé par :              beginners at haskell.org               
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             s at haskell.org                                                 
                                       [Haskell-beginners] a problem       
             23/06/2010 10:08                                              

Can I get a suggestion for a concise way to write 'sortOutMusicData' as
described here? This is MusicXML-related.

data Music_Data_ = Music_Data_1 Note
                  | Music_Data_4 Direction
                  | Music_Data_9 Sound

sortOutMusicData :: [Music_Data_] -> ([Note],[Direction],[Sound])

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