#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 simonpj):
That doesn't happen:
I think you mean more than `:t` reports the wrong result. Consider {{{ f :: Proxy b -> Proxy b -> Int f = error "urk" g :: Proxy a -> Proxy (Test a a) -> Int g x y = f x y }}} This indeed fails with {{{ T15557.hs:25:13: error: • Couldn't match type ‘a’ with ‘Test a a’ }}} I'd need to look back carefully at the paper to see what should happen, but no time for that today. Richard may opine on his return. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/15557#comment:1 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler