[grapefruit] Sampling the record of signals
roma at ro-che.info
Fri Apr 24 03:33:49 EDT 2009
Great explanation, thanks!
* Wolfgang Jeltsch <g9ks157k at acme.softbase.org> [2009-04-23 18:18:33+0200]
> Am Mittwoch, 22. April 2009 17:59 schrieb Roman Cheplyaka:
> > Can someone show me how to use map on records?
> > Precisely, I have a record of CSignals and want to sample them (with the
> > same sampler) and to get record of SSignals.
> Hello Roman,
> Data.Record.map uses the same record type for the source and destination
> record. The only thing that can differ is the style.
> If you use signal style records, your source record type will look like this:
> X :& CSignal `Of` val_1 :& … :& CSignal `Of` val_n
> However, your destination record type will look like this:
> X :& SSignal `Of` val_1 :& … :& SSignal `Of` val_n
> So both differ.
> The solution would be to remove the concrete signal type (CSignal or SSignal)
> from the record type and put it into the style instead. This is the same as
> what’s already done with signal, producer and consumer records. Their record
> types only contain sort types of the form signal `Of` val. It’s the concrete
> style that transforms this into signal era val, Consumer signal val or
> Producer signal val.
> So what you should do is using record types like this:
> X :& val_1 :& … :& val_n
> Then define a new “homegenous signal style” like this:
> data HomSignalStyle (signal :: * -> * -> *) era
> instance Style (HomSignalStyle signal era) where
> type K (HomSignalStyle signal era) = PlainKind
> type instance Value (HomSignalStyle signal era) val = signal era val
> Homegenous signal records are now defined to be signal records where not only
> the era but also the signal type (CSignal, SSignal, …) is the same for all
> record fields.
> Now you can implement the sampling of all record fields:
> :: DSignal era ()
> -> TransformerPiece
> (HomSignalStyle CSignal era)
> (HomSignalStyle SSignal era)
> samplingTransformerPiece sampler = TransformerPiece $ (sampler #>)
> sampleRecord :: (Record PlainKind record) =>
> record (HomSignalStyle CSignal era) ->
> record (HomSignalStyle SSignal era)
> sampleRecord = Data.Record.map samplingTransformerPiece
> Warning! All code in this e-mail is untested. :-(
> Please ask if this is not yet clear (which would be understandable :-) ).
> Best wishes,
> Grapefruit mailing list
> Grapefruit at projects.haskell.org
Roman I. Cheplyaka :: http://ro-che.info/
"Don't let school get in the way of your education." - Mark Twain
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