#8581: Add support for explicitly-bidirectional pattern synonyms -------------------------------------+------------------------------------- Reporter: cactus | Owner: Type: feature request | Status: new Priority: normal | Milestone: 7.12.1 Component: Compiler | Version: Resolution: | Keywords: Operating System: Unknown/Multiple | PatternSynonyms Type of failure: None/Unknown | Architecture: Blocked By: 5144 | Unknown/Multiple Related Tickets: | Test Case: | Blocking: | Differential Revisions: -------------------------------------+------------------------------------- Comment (by dmcclean): Is it true that support for this didn't make it into 7.10? That looks to be the case, although it also looks to be the case that it did sneak in to the documentation: https://downloads.haskell.org/~ghc/7.10.1/docs/html/users_guide/syntax- extns.html#pattern-synonyms But my attempt to use the bidirectional syntax: {{{ {-# LANGUAGE PatternSynonyms #-} data AugmentedRational = Exact' Integer Rational | Approximate (forall a.Floating a => a) pattern Exact z q <- Exact' z q where Exact z q | q == 0 = Exact' 0 0 | otherwise = Exact' z q }}} is rejected with {{{ parse error on input `where' }}} By contrast, the 7.8.4 docs don't list this syntax, see https://downloads.haskell.org/~ghc/7.8.4/docs/html/users_guide/syntax- extns.html#pattern-synonyms. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/8581#comment:22 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler