[Haskell-cafe] help with musical data structures

[Stephen Tetley]

2009/11/15 Henning Thielemann <lemming at henning-thielemann.de>:

> In Haskore there is a type for pitch classes:
>
> http://hackage.haskell.org/packages/archive/haskore/0.1/doc/html/Haskore-Basic-Pitch.html
>  but maybe it is not what you need, since it distinguishes between C sharp
> and D flat and so on.

Hi Henning

The enharmonic doublings and existing Ord instance make Haskore's
PitchClass a tricky proposition for representing the Serialist's view
of pitch classes. An integer (or Z12) represent would be simpler.


To get pitch names I would recover them with a post-processing step,
spelling pitches with respect to a "scale" (here a SpellingMap):

> spell :: SpellingMap -> Pitch -> Pitch

The spell function returns the note in the scale (SpellingMap) if
present, otherwise it returns the original to be printed with an
accidental.

I have my own pitch representation, but a SpellingMap for Haskore would be

> type SpellingMap = Data.Map PitchClass PitchClass

Scales here are functions that generate SpellingMaps rather than
objects themselves.
The modes and major and minor scales have easy generation as they are
someways rotational over the circle of fifths (I've have implemented a
useful algorithm for this but can't readily describe it[1]). Hijaz and
klezmer fans need to construct their spelling maps by hand.

Best wishes

Stephen

[1] Code exists here - vis dependencies and scant documentation that
stop it being useful:
http://code.google.com/p/copperbox/source/browse/trunk/bala/Mullein/src/Mullein/Pitch.hs