#15557: Reduce type families in equations' RHS when testing equation compatibility -------------------------------------+------------------------------------- Reporter: mniip | Owner: (none) Type: feature request | Status: new Priority: normal | Milestone: 8.6.1 Component: Compiler (Type | Version: 8.4.3 checker) | Resolution: | Keywords: TypeFamilies Operating System: Unknown/Multiple | Architecture: Type of failure: GHC rejects | Unknown/Multiple valid program | Test Case: Blocked By: | Blocking: Related Tickets: #8423 #15546 | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by mniip): Correction: an `apart` constraint might sometimes not get discharged if the same tyvar occurs multiple times, e.g: {{{ type family Eq a b where Eq a a = True Eq a b = False }}} {{{ TF a a ~ True apart(<c, c>, <a, b>) => TF a b ~ False }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/15557#comment:4> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler