#13674: GHC doesn't discharge heterogeneous equality constraint when it ought to -------------------------------------+------------------------------------- Reporter: RyanGlScott | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler (Type | Version: 8.0.1 checker) | Resolution: | Keywords: TypeInType Operating System: Unknown/Multiple | Architecture: Type of failure: GHC rejects | Unknown/Multiple valid program | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by RyanGlScott):
This constraint is an occurs-check failure and is surely going to lead to an error.
Ah, that's a good point. I forgot that `Lcm m m` doesn't reduce as a type family (you're only ever to get out the `lcm` of `m` and `m` at the value level by using `knownNat` with the reflection-style trickery in `magic`, but this doesn't work at the type level). -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/13674#comment:6 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler