#8581: Add support for explicitly-bidirectional pattern synonyms -------------------------------------+------------------------------------ Reporter: cactus | Owner: cactus Type: feature request | Status: new Priority: normal | Milestone: Component: Compiler | Version: Resolution: | Keywords: Operating System: Unknown/Multiple | Architecture: Unknown/Multiple Type of failure: None/Unknown | Difficulty: Unknown Test Case: | Blocked By: 5144 Blocking: | Related Tickets: -------------------------------------+------------------------------------ Comment (by cactus): I have a working version of this in the `wip/pattern-synonyms` branch. It still needs some finishing (mostly, adding tests). The only difficult part of this work was ensuring that the following works (and is not regarded as a recursive pattern synonym): {{{ pattern P x <- (x:_) where P x = foo [x] foo (P x) = [x, x] }}} -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/8581#comment:4 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler