#9587: Type checking with type functions introduces many type variables, which remain ambiguous. The code no longer type checks. -------------------------------------+------------------------------------- Reporter: oleg | Owner: Type: bug | Status: new Priority: normal | Milestone: Component: Compiler | Version: 7.8.3 (Type checker) | Keywords: type family, Resolution: | ambiguity check Operating System: | Architecture: Unknown/Multiple Unknown/Multiple | Difficulty: Unknown Type of failure: GHC | Blocked By: rejects valid program | Related Tickets: #9607 Test Case: | Blocking: | Differential Revisions: | -------------------------------------+------------------------------------- Comment (by dfeuer): Replying to [comment:7 oleg]:
I have played with giving type annotations for quite a long time, without success. .... I wonder what wrong could happen if we just assume injectivity in such cases.
If I understand simonpj correctly, he would like to make sure it is possible to give explicit signatures ''first'', even if those would be nasty to write and/or read, and only add inference rules for such afterwards. This sounds reasonable to me, but I'm no expert. Maybe this will finally push him to implement the explicit type applications he's mentioned in the past? -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/9587#comment:8 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler