#15583: Treating Constraint as Type when using (type C = Constraint) -------------------------------------+------------------------------------- Reporter: Iceland_jack | Owner: (none) Type: bug | Status: closed Priority: normal | Milestone: 8.6.1 Component: Compiler | Version: 8.5 Resolution: duplicate | Keywords: TypeInType Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: #15412 | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Changes (by RyanGlScott): * status: new => closed * resolution: => duplicate Comment: Yep, this is a duplicate of #15412. Now that that's been fixed, you get the error message you'd expect on the original program: {{{ $ /opt/ghc/8.6.1/bin/ghci Bug.hs GHCi, version 8.6.0.20180823: http://www.haskell.org/ghc/ :? for help Loaded GHCi configuration from /home/rgscott/.ghci [1 of 1] Compiling Main ( Bug.hs, interpreted ) Bug.hs:22:9: error: • Couldn't match expected type ‘a -> a’ with actual type ‘()’ • In the expression: () In an equation for ‘id_’: id_ = () In the instance declaration for ‘Category_ (->)’ • Relevant bindings include id_ :: a -> a (bound at Bug.hs:22:3) | 22 | id_ = () | ^^ }}} -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/15583#comment:2 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler