#14000: Out of scope errors with type families do not mention scope -------------------------------------+------------------------------------- Reporter: EyalLotem | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.0.1 Resolution: | Keywords: TypeFamilies Operating System: Unknown/Multiple | Architecture: Type of failure: Poor/confusing | Unknown/Multiple error message | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by RyanGlScott): Interestingly, I tried a random commit from before GHC 8.0.1 (707b2be97539b83efb91cd9f17f94c91397ad2b4), and I received more information in the error messages: {{{ $ inplace/bin/ghc-stage2 --interactive ../Bug.hs GHCi, version 8.0.0.20160109: http://www.haskell.org/ghc/ :? for help [1 of 1] Compiling Main ( ../Bug.hs, interpreted ) ../Bug.hs:5:1: error: • Couldn't match expected type ‘T a’ with actual type ‘T a0’ NB: ‘T’ is a type function, and may not be injective The type variable ‘a0’ is ambiguous • In the ambiguity check for the inferred type for ‘main’ To defer the ambiguity check to use sites, enable AllowAmbiguousTypes When checking the inferred type main :: forall a. T a ../Bug.hs:5:10: error: Variable not in scope: noSuchThing }}} So at separate commits, GHC (1) started complaining about this `Couldn't match expected type` business (which is questionable), and (2) stopped complaining about `noSuchThing` not being in scope (which is definitely wrong). I've yet to figure out which commits are responsible. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/14000#comment:2 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler