#5144: Pattern synonyms -------------------------------------+------------------------------------ Reporter: simonpj | 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: Blocking: | Related Tickets: -------------------------------------+------------------------------------ Comment (by cactus): If your question is whether there's a syntactic way to see if a given pattern synonym import can be used as an expression, then no, not at the moment. So if you do something like {{{ import M(pattern P) x = P }}} then the only error you will get if `P` is not bidirectional is from the type checker: {{{ /tmp/hs/M2.hs:5:5: P used in an expression, but it's a non-bidirectional pattern synonym In the expression: P In an equation for ‛x’: x = P }}} -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/5144#comment:22 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler