So it's not clear that a single signature for the two ways of looking at
#8968: Pattern synonyms and GADTs ----------------------------------------------+---------------------------- Reporter: kosmikus | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler (Type checker) | Version: Resolution: | 7.8.1-rc2 Operating System: Unknown/Multiple | Keywords: Type of failure: GHC rejects valid program | Architecture: Test Case: | Unknown/Multiple Blocking: | Difficulty: Unknown | Blocked By: | Related Tickets: ----------------------------------------------+---------------------------- Comment (by kosmikus): the RHS makes sense at all! It look as though we need one for its use as a pattern and one for its use as an expression. Sigh. Yes.
Mind you, the "type as an expression" is easily inferred, as you mention. So perhaps the pattern signature (once we have them) can be taken as applying only to the pattern, not the expression?
I guess it's not clear to me if the other information isn't available as well, if the synonym is used in a function that has a type signature. Is there really a theoretical need to supply a signature for the "pattern type"? See my example in the other comment, I actually wouldn't like to have to pick one. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/8968#comment:10 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler