#6018: Injective type families -------------------------------------+------------------------------------- Reporter: lunaris | Owner: jstolarek Type: feature | Status: new request | Milestone: 7.10.1 Priority: normal | Version: 7.4.1 Component: Compiler | Keywords: TypeFamilies, Resolution: | Injective Operating System: | Architecture: Unknown/Multiple Unknown/Multiple | Difficulty: Unknown Type of failure: | Blocked By: None/Unknown | Related Tickets: #4259 Test Case: | Blocking: | Differential Revisions: Phab:D202 | -------------------------------------+------------------------------------- Comment (by simonpj): Sure. Take as long as you need. I was offering to do the type inference piece, which seemed to be the bit you are stalled on. So if you do parser, renamer, and typechecking of the `TyCon` declaration, so we have the injectivity info in the `TyCon`, that would do it I think. In practical terms, a branch in a github repo that I can pull and push to would work well. All I plan to do is add a rule along the lines of {{{ [W] F ty1 ~ rhs [W] F ty2 ~ rhs ===> add a new constraint (if F is injective) [D] ty1 ~ ty2 }}} very like functional dependencies for type classes. I'm not sure that there is time to get this implemented, tested etc before the 7.10 freeze, but we'll see. Simon -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/6018#comment:93 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler