#8961: Require PatternSynonyms language extension to *use* pattern synonyms -------------------------------------+------------------------------------- Reporter: cactus | Owner: cactus Type: bug | Status: closed Priority: normal | Milestone: 7.8.1 Component: Compiler (Type | Version: 7.8.1-rc2 checker) | Keywords: Resolution: fixed | Architecture: Unknown/Multiple Operating System: Unknown/Multiple | Difficulty: Easy (less than 1 Type of failure: None/Unknown | hour) Test Case: | Blocked By: Blocking: | Related Tickets: -------------------------------------+------------------------------------- Comment (by isaacdupree): I'm sceptical of this change. It means a library module can't transparently replace a data type with a pattern synonym in a new version. Modules that depend on the library would break unless they add a flag. Unlike with GADTs, this ability is one of the reasons for pattern synonyms existing. (The consistency and immaturity arguments are tempting, though.) Is there a technical reason along the lines of #2905's `RelaxedPolyRec` that makes pattern-matching pattern synonyms work poorly without a language extension? -Isaac -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/8961#comment:9 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler