#9226: Internal error when using equality constraint in pattern synonyms -------------------------------------+------------------------------------- Reporter: Iceland_jack | Owner: Type: bug | Status: new Priority: lowest | Milestone: Component: Compiler | Version: 7.8.2 Resolution: | Keywords: renamer, pattern Operating System: Linux | synonyms, GADTs Type of failure: GHC rejects | Architecture: x86 valid program | Difficulty: Unknown Test Case: | Blocked By: Blocking: | Related Tickets: -------------------------------------+------------------------------------- Changes (by simonpj): * cc: cactus (added) Comment: You are absolutely right; there is a gaping hole in the pattern-synonym implementation. Gergo, the issue is this. When typechecking anything to do with GADTs, we need a type signature. The [wiki:PatternSynonyms wiki page] describes signatures for pattern synonyms, but they are not implemented. the `HsBinds.Sig` type has `PatSynSig`, but the parser does not recognise them, nor does the typechechecker do anything with them. Notably, in `tcPatSynDecl` we'll need to implement different code to ''check'' that the synonym has a specified type than to ''infer'' the type it has. While fixing this, I found another crash. This {{{ pattern PUnit1 = (RUnit, ()) :: (Rep a, a) }}} crashes with {{{ T9226.hs:15:38: GHC internal error: ‘a’ is not in scope during type checking, but it passed the renamer }}} Would you like to look at this Gergo? I'm happy to help. Meanwhile, iceland_jack, I think you're stalled till we do this. Thanks for reporting it. Simon -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/9226#comment:1 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler