#15687: Type synonym unused binds no warning? -------------------------------------+------------------------------------- Reporter: AntC | Owner: (none) Type: feature request | Status: new Priority: normal | Milestone: 8.6.1 Component: Compiler | Version: 8.6.1 (Parser) | Resolution: | Keywords: Operating System: Windows | Architecture: Type of failure: GHC accepts | Unknown/Multiple invalid program | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by goldfire): I'm not sure why you think that `type` should introduce a ''pattern'' synonym (which, indeed, must mention all its variables on the right-hand side). It just introduces a (not necessarily injective) synonym. It's true that `-XTypeSynonymInstances` allows you to use a type synonym in an instance head. This might suggest the pattern-like behavior you seek. But this works via the expansion of the synonym, meaning that a program with both `instance C (Silly Int Bool)` and `instance C (Silly Char Bool)` will be rightly rejected. Note that this behavior is not new. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/15687#comment:1 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler