#15144: Type inference regression between GHC 8.0.2 and 8.2.2 -------------------------------------+------------------------------------- Reporter: RyanGlScott | Owner: (none) Type: bug | Status: new Priority: normal | Milestone: 8.6.1 Component: Compiler (Type | Version: 8.2.2 checker) | Resolution: | Keywords: TypeFamilies Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Changes (by RyanGlScott): * keywords: => TypeFamilies Comment: Here's a slightly smaller test case: {{{#!hs {-# LANGUAGE FlexibleContexts #-} {-# LANGUAGE TypeFamilies #-} module Bug where import Data.Coerce import Data.Proxy type family F x f :: Coercible (F a) b => Proxy a -> F a -> b f _ = coerce g p x = f p x }}} {{{ $ /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 Bug ( Bug.hs, interpreted ) Ok, modules loaded: Bug. λ> :t g g :: Coercible b (F a) => Proxy a -> F a -> b }}} {{{ $ /opt/ghc/8.4.2/bin/ghci Bug.hs GHCi, version 8.4.2: http://www.haskell.org/ghc/ :? for help Loaded GHCi configuration from /home/rgscott/.ghci [1 of 1] Compiling Bug ( Bug.hs, interpreted ) Ok, one module loaded. λ> :t g g :: Proxy a -> F a -> F a }}} -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/15144#comment:1 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler