I unfortunately don’t have the exact code I was working on in front of me, but I was playing around with the -XTypeInType extension to see if I could use it to implement some notion of sub-kinding to start doing “Data Types a la Carte” style things at the type level.
Constrained type families seemed like the most natural way to “promote” those concepts, but maybe there’s a more obvious way I’m missing. I’d be happy to send you a follow up email tomorrow when I’m back at the office if you think this would be a good motivating use case for the feature. V/r, -Evan > On Mar 8, 2016, at 8:21 PM, Richard Eisenberg <[email protected]> wrote: > > > On Mar 8, 2016, at 7:17 PM, Evan Austin <[email protected] > <mailto:[email protected]>> wrote: >> The wiki page for Phase I of Dependent Haskell describes an approach to >> constrained type families: >> https://ghc.haskell.org/trac/ghc/wiki/DependentHaskell/Phase1#Typefamilyequationscanbeconstrained >> >> <https://ghc.haskell.org/trac/ghc/wiki/DependentHaskell/Phase1#Typefamilyequationscanbeconstrained> >> >> Did that land in GHC 8.0 and, if so, is the updated syntax documented >> somewhere? > > No, it didn't make it. The motivating test case seemed contrived and so we > punted on this one. > > Do you have a use case that really needs this feature? That would help to > motivate it for 8.2 or beyond. > > Thanks! > Richard >
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