[Haskell-cafe] fundeps and overlapping/undecidable instances
jeff.polakow at db.com
Fri Dec 7 12:49:46 EST 2007
You should be able to use fundeps to do exactly what you describe below.
Can you make a relatively small self-contained example which exemplifies
the ugliness you see?
haskell-cafe-bounces at haskell.org wrote on 12/07/2007 11:24:35 AM:
> I have some type-level sets using fundeps working whereby equality and
> membership etc are predicate functions. This seems to leads to an
> of ugly code, with `If' class constraints etc getting out of hand -- I
> to treat these as relations instead so providing the definition
> everything that is 'in' and nothing that is 'out'. I've been using
> paper on lightweight static resources  as a template for this. I want
> do something like this (supposing I have an EQ relation, (:::) for
> class Member x y
> instance EQ x y => Member x (y:::ys)
> instance Member x ys => Member x (y:::ys)
> But I can certainly see why this isn't possible (It's the equivalent of
> pattern-matching on the constraints I suppose). Do type families provide
> way to do this kind of thing or do I need a different strategy
> involving GADTs or whatever?
>  http://okmij.org/ftp/Computation/resource-aware-prog/tfp.pdf
> View this message in context: http://www.nabble.com/fundeps-and-
> Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com.
> Haskell-Cafe mailing list
> Haskell-Cafe at haskell.org
This e-mail may contain confidential and/or privileged information. If you
are not the intended recipient (or have received this e-mail in error)
please notify the sender immediately and destroy this e-mail. Any
unauthorized copying, disclosure or distribution of the material in this
e-mail is strictly forbidden.
-------------- next part --------------
An HTML attachment was scrubbed...
More information about the Haskell-Cafe