TypeFamilies vs. FunctionalDependencies & type-level recursion
simonpj at microsoft.com
Tue Aug 2 17:10:09 CEST 2011
| GHC trac ticket on the feature, as you probably saw. After a
| discussion with other people here at
| HacPhi, I've decided that what I'm going to attempt is to add
| type-level Maybes
Hang on! Julien Cretin (from INRIA) is doing an internship here at Cambridge with Dimitrios and me. The primary goal is to support *typed* type-level programming; that is, to add a proper kind system to GHC.
Broadly our approach is like Conor's SHE system, with minor syntactic differences. So type-level Maybes will appear automatically, as a special case, so it's probably a bit of a waste to implement them separately.
There'll also be support for poly-kinded type-level functions, of course.
The stuff will be on a branch in the main ghc repo soon.
Julien: we should start a wiki page (see http://hackage.haskell.org/trac/ghc/wiki/Commentary, and look for the link to "Type level naturals"; one like that). On the wiki you should
* add a link to the latest version of our (evolving) design document.
* specify the branch in the repo that has the stuff
* describe the status
Iavor's stuff is still highly relevant, because it involves a special-purpose constraint solver. But Iavor's stuff is no integrated into HEAD, and we need to talk about how to do that, once you are back from holiday Iavor.
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