#12422: Add decidable equality class -------------------------------------+------------------------------------- Reporter: dfeuer | Owner: Type: feature request | Status: new Priority: normal | Milestone: Component: Core Libraries | Version: 8.0.1 Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by Iceland_jack): Quick thought, is it possible to create a heterogeneous version of `TestEquality` that supports {{{#!hs eqTyCon :: forall (k1 k2 :: *). forall (a :: k1) (b :: k2). TTyCon <k1> a -> TTyCon <k2> b -> Maybe (a :~~: b) }}} Replacing `Maybe (a :~: b)` with `Maybe (a :~~: b)` would still constraint the kinds, would we need {{{#!hs class HTestEquality f1 f2 where htestEquality :: f1 a -> f2 b -> Maybe (a :~~: b) }}} ---- Discussed on `#ghc`, what would break if we made `:~:` heterogeneous? -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/12422#comment:2 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler