#14253: Pattern match checker mistakenly concludes pattern match on pattern synonym is unreachable -------------------------------------+------------------------------------- Reporter: bgamari | Owner: (none) Type: bug | Status: new Priority: high | Milestone: 8.4.1 Component: Compiler | Version: 8.2.1 Resolution: | Keywords: | PatternSynonyms, | PatternMatchWarnings Operating System: Unknown/Multiple | Architecture: Type of failure: GHC rejects | Unknown/Multiple valid program | Test Case: Blocked By: | Blocking: Related Tickets: #11984, #14098 | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by Ryan Scott <ryan.gl.scott@…>): In [changeset:"0e60cc1825aace414597b644731c30269994f7fb/ghc" 0e60cc1/ghc]: {{{ #!CommitTicketReference repository="ghc" revision="0e60cc1825aace414597b644731c30269994f7fb" Document how GHC disambiguates between multiple COMPLETE sets Summary: Up until now, the knowledge of how GHC chooses which `COMPLETE` set to use in the presence of multiple applicable `COMPLETE` sets for a single data type constructor was only documented in the GHC wiki. But this really should be advertised to anyone who uses `COMPLETE` pragmas heavily, so per SPJ's advice in https://ghc.haskell.org/trac/ghc/ticket/14253#comment:10, this adds this wisdom to the GHC users' guide. Test Plan: Read it Reviewers: austin, bgamari Subscribers: mpickering, rwbarton, thomie GHC Trac Issues: #14253 Differential Revision: https://phabricator.haskell.org/D4005 }}} -- Ticket URL: <http://ghc.haskell.org/trac/ghc/ticket/14253#comment:13> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler