#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: 8.0.2 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: | -------------------------------------+------------------------------------- Changes (by RyanGlScott): * version: 8.0.1 => 8.0.2 Comment: Actually, the `Couldn't match expected type` error was dropped somewhere between 8.0.1 and 8.0.2, since in 8.0.1, you get: {{{ $ /opt/ghc/8.0.1/bin/ghci ../Bug.hs GHCi, version 8.0.1: http://www.haskell.org/ghc/ :? for help Loaded GHCi configuration from /home/rgscott/.ghci [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 }}} But in GHC 8.0.2: {{{ $ /opt/ghc/8.0.2/bin/ghci ../Bug.hs GHCi, version 8.0.2: http://www.haskell.org/ghc/ :? for help Loaded GHCi configuration from /home/rgscott/.ghci [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 }}} -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/14000#comment:3 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler