#11282: Error warns about non-injectivity of injective type family -------------------------------------+------------------------------------- Reporter: goldfire | Owner: (none) Type: bug | Status: closed Priority: normal | Milestone: Component: Compiler | Version: 7.11 Resolution: duplicate | Keywords: TypeFamilies Operating System: Unknown/Multiple | Architecture: Type of failure: Incorrect | Unknown/Multiple warning at compile-time | Test Case: Blocked By: | Blocking: Related Tickets: #14369 | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Changes (by RyanGlScott): * status: new => closed * resolution: => duplicate * related: => #14369 Comment: Closing as a duplicate of #14369. After commit 8846a7fdcf2060dd37e66b4d1f89bd8fdfad4620 (which fixed #14369), the error message no longer claims that `F` may not be injective: {{{ $ /opt/ghc/8.4.3/bin/ghc Bug.hs -XTypeFamilyDependencies [1 of 1] Compiling Bug ( Bug.hs, Bug.o ) Bug.hs:10:9: error: • Could not deduce: F a ~ F a0 from the context: G a0 bound by the type signature for: meth :: G a0 => F a0 at Bug.hs:10:9-26 The type variable ‘a0’ is ambiguous • In the ambiguity check for ‘meth’ To defer the ambiguity check to use sites, enable AllowAmbiguousTypes In the type signature: meth :: (G a => F a) -> () | 10 | meth :: (G a => F a) -> () | ^^^^^^^^^^^^^^^^^^ }}} -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/11282#comment:6 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler