[Haskell-beginners] manipulating Map for music application

[Dennis Raddle]

Thanks! I'm a Haskell beginner and will relish the opportunity to learn
more by studying your code.

On Sat, Nov 7, 2015 at 9:47 AM, Chaddaï Fouché <chaddai.fouche at gmail.com>
wrote:

> 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
>>>
>>> _______________________________________________
>>> Beginners mailing list
>>> Beginners at haskell.org
>>> http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners
>>>
>>
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