[Haskell-cafe] music-related problem

[Henning Thielemann]

On Sun, 4 Jul 2010, Michael Mossey wrote:

> Serguey Zefirov wrote:
>>> The thing that is hard for me to understand is how, in a functional
>>> paradigm, to update the entire Doc by chasing down every tie and making
>>> all necessary updates.
>> 
>> This looks like one of graph algorithms.
>> 
>> Notes are nodes, ties are arcs. Measures, etc are parts of node label.
>> 
>> soundedEnd property can be computed over this.
>> 
>> Actually, it would be wise to parametrize Item with computed
>> attributes so that you can clearly distinguish between documents where
>> soundedEnd is set from documents where it is not.
>
> Ah, this sounds like something I am looking for... parameterizing Item with 
> the computed attributes. But I am not clear about what that would look like. 
> Would Item have kind * -> *? Like
>
> data Item c = Item {pitch::Pitch, end::Loc, computed::c}
>
> ?

I like to support static distinction between raw and processed Measure 
data. It makes your code clearer and safer. You may define

data Item end = Item {pitch::Pitch, end::end}

where 'end = Bool' for raw data, and 'end = Loc' for processed data. (I'm 
not entirely sure, I understood your representation properly, thus the 
particular type examples for 'end' may be inappropriate.)