[Haskell-beginners] manipulating Map for music application

[Chaddaï Fouché]

Ooops forgot that Chords are not just lists of Notes :

mapNotesMaybe f compo = mapMaybeWithKey go compo
  where
    go loc chords = mconcat . map (fmap (:[]) . gogo loc) $ chords
    gogo loc chord@(Chord d notes) = fmap (Chord d) . mconcat . map (fmap
(:[]) . f loc chord) $ notes

Le sam. 7 nov. 2015 à 18:41, Chaddaï Fouché <chaddai.fouche at gmail.com> a
écrit :

> This is a bit tricky but mapMaybeWithKey is clearly the tool for the job :
>
> > mapMaybeWithKey :: (k -> a -> Maybe
> <https://hackage.haskell.org/package/base-4.7.0.1/docs/Data-Maybe.html#t:Maybe>
> b) -> Map
> <https://hackage.haskell.org/package/containers-0.5.6.3/docs/Data-Map-Lazy.html#t:Map>
> k a -> Map
> <https://hackage.haskell.org/package/containers-0.5.6.3/docs/Data-Map-Lazy.html#t:Map>
> k b
>
> So :
>
>
> mapNotesMaybe :: (Loc -> Chord -> Note -> Maybe Note) -> Composition ->
> Composition
> mapNotesMaybe f compo = mapMaybeWithKey go compo
>   where
>     go loc chords = mconcat . map (gogo loc) $ chords
>     gogo loc chord = mconcat . map (fmap pure . f loc chord) $ chord
>
> This should work.
>
> --
> Chaddaï
>
>
> Le sam. 7 nov. 2015 à 07:07, Dennis Raddle <dennis.raddle at gmail.com> a
> écrit :
>
>> I have a Haskell program that computes music compositions. A composition
>> consists of sounds that happen at locations. A location is data type Loc.
>> At each location is a list of chords. A chord is data type Chord. Each
>> chord contains some chord-specific data and a list of notes. A note is data
>> type Note.
>>
>> So we have
>>
>> data Note = Note ...
>> data Chord = Chord ChordSpecificData [Note]
>> type Composition = Map Loc [Chord]
>>
>> I would like to write a few different functions that operate over all the
>> notes.
>>
>> The following function breaks out all the notes, tupling them with the
>> associated Locs and Chords:
>> compositionToList :: Composition -> [(Loc,Chord,Note)]
>>
>> The following function transforms Notes, keeping only the Just results.
>> If a Chord gets all its notes eliminated, that Chord is removed. If a Loc
>> has all its Chords removed, that Loc is removed from the Map.
>> mapNotesMaybe :: (Loc -> Chord -> Note -> Maybe Note) -> Composition
>>    -> Composition
>>
>> Any advice for concise code appreciated.
>> Dennis
>>
>>
>> What's a concise way of doing this?
>>
>> Another useful function would be used for mapping
>>
>> Dennis
>>
>> _______________________________________________
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>>
>
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