#12203: Allow constructors on LHS of (implicit) bidirectional pattern synonym -------------------------------------+------------------------------------- Reporter: ezyang | Owner: Type: feature request | Status: new Priority: low | Milestone: Component: Compiler (Type | Version: 8.0.1 checker) | Keywords: Resolution: | PatternSynonyms Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by simonpj): Great or not, it's pretty simple. Adding newtype patterns on the left is really quite tricky. It took me 15 mins to grok. As to the parser, it parses patterns as expressions, and then converts them to patterns. Then the patsyn code converst it back (for bidirectional). So maybe we should leave it as an expression! The rule is still simple: to use it as an expression, just use the exression. To use it as a pattern, just treat `unVec e` as the view pattern `(Vec -> e)`. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/12203#comment:8 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler