| Abandoning fundeps would be a sad day for type-level programming. | There are many things other than overlaps that you can do with fundeps | and constraint kinds that you cannot currently do with type families, | such as: | | - Partial application or higher-order programming. | - Short-circuit evaluation, lazy evaluation or type-level case.
Etienne, I think it would be a good service to make Haskell wiki page describing the difference between fundeps and type families, and in particular describing things that can be done with the former but not the latter.
Simon
Thanks for the idea. Here it is. http://hackage.haskell.org/trac/ghc/wiki/TFvsFD I posted my comments on the matter along with many additional comments and examples that I found.
+1 That would be great. I'll link to Etienne's wiki from the Discussion page I've started for NewAxioms http://hackage.haskell.org/trac/ghc/wiki/NewAxioms
In particular, it would be good to tease out where we're getting interference or inter-dependence between different type-level extensions: Overlaps Fundeps UndecidableInstances (that is, breaking the coverage conditions) ScopedTypeVariables
I did not check what extensions were turned on in my examples.
Given that that the Fundeps idea is taken from relational theory, and relations is just another way of representing functions, there ought to be close correspondence to type-level functions.
I put a few examples of the unexpected behaviour of Fundeps on the Wiki page.
To me, NewAxioms is aiming at type-level case, to provide a different style of defining type functions, as well as dis-overlapping overlaps.
I am eager to see that in action. Etienne Laurin