#10873: Bad error message for incorrect pattern synonym signature -------------------------------------+------------------------------------- Reporter: mpickering | Owner: rdragon Type: bug | Status: closed Priority: normal | Milestone: 8.0.1 Component: Compiler (Type | Version: 7.10.2 checker) | Keywords: Resolution: fixed | PatternSynonyms Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Phab:D1866 Wiki Page: | -------------------------------------+------------------------------------- Changes (by bgamari): * status: new => closed * resolution: => fixed Comment: This is greatly improved with the patch in comment:10. The original example now fails with, {{{ Hi.hs:6:22: error: • No instance for (Show a) arising from the "provided" constraints claimed by the signature of ‘Pat’ In other words, a successful match on the pattern Just a does not provide the constraint (Show a) • In the declaration for pattern synonym ‘Pat’ }}} -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/10873#comment:11 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler