#11367: [Regression] Only one clause allowed in (explicitly bidirectional) pattern synonyms -------------------------------------+------------------------------------- Reporter: Iceland_jack | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 8.1 Resolution: | Keywords: | PatternSynonyms Operating System: Unknown/Multiple | Architecture: Type of failure: GHC rejects | Unknown/Multiple valid program | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by Iceland_jack): Replying to [comment:10 mpickering]:
Could you not view a where clause in a pattern synonym as containing zero bindings (unidirectional) or a single binding (explicitly bidirectional).
Yes you could, without looking I think this would require quite a bit of refactoring because of how everything is dealt with in the parser.
If we take the route of #393 a pattern synonym `where` could always indicate an explicitly bidirectional pattern with a single clause: {{{#!hs pattern A <- 'a' where ---expands-into--> pattern A <- 'a' where A = _ }}} to Simon's point. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/11367#comment:12 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler