#14386: GHC doesn't allow Coercion between partly-saturated type constructors -------------------------------------+------------------------------------- Reporter: Iceland_jack | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.3 Resolution: | Keywords: roles 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 nomeata):
With quantified constraints, could we write?
I don’t think so. It would require a rule “eta-expansion rule” {{{ ∀a. T1 a ~R T2 b −−−−−−−−−−−−−− T1 ~R T2 }}} which does not exist. But others will have to tell you if that can exist or if it would break things. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/14386#comment:5 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler