#12428: Allow pattern synonyms to optionally carry coerceability -------------------------------------+------------------------------------- Reporter: dfeuer | Owner: Type: feature request | Status: new Priority: normal | Milestone: 8.2.1 Component: Compiler | Version: 8.0.1 Resolution: | Keywords: 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): Joachim is right. This has really has nothing to do with pattern synonyms. It would apply just as much if instead of `pattern NewFoo` we offered {{{ getFoo :: Foo a -> a getFoo (Foo (Bar x)) = x }}} Now I suppose you might want to * Export the type `Foo` and function `getFoo`, but not the data constructors `Foo` and `Bar`. * And still get `(Coercible (Foo a) a)` in importing modules, although the relevant data constructors are not in scope. Yes, that's possible. If lots of people want it, I guess we can look for some way to control the export of the `Coercible` instance. But it's rather orthogonal to pattern synonyms. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/12428#comment:6 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler