#11534: Allow class associated types to reference functional dependencies -------------------------------------+------------------------------------- Reporter: ekmett | Owner: Type: feature request | Status: new Priority: normal | Milestone: Component: Compiler (Type | Version: 7.10.3 checker) | Keywords: TypeFamilies, Resolution: | FunctionalDependencies Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: Other | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by dfeuer): If people want to go forward with desugaring fundeps to type families (sounds great to me), I think it would be lovely to add naming syntax: {{{#!hs class Foo a b c d | (Q, R :: a -> b c), (S :: b d -> a) }}} would desugar to {{{#!hs class (b ~ Q a, c ~ R a, a ~ S b d) => Foo a b c d where type family Q a type family R a type family S b d }}} To work with classes that lack named fundeps, some nasty names could be made available. {{{#!hs class Foo a b c d | a -> b c, b d -> a }}} could desugar to use type families with (exposed, but unlikely) names like `Foo__1_DET_2#`, `Foo__1_DET_3#`, and `Foo__2_4_DET_1#`, naming the positions that determine other positions. It might be good to add dysfunctional "soft dependencies" at the same time, with `~>` syntax and vague semantics to be pinned down later (the idea being that soft dependencies would only guide inference, as best they could, without being relied upon for type checking). -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/11534#comment:27 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler