#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 goldfire): Replying to [comment:76 simonpj]:

* My brain is too small to think about verifying injectivity for closed families. Richard?

I've put some comments on the wiki page. But the whole thing makes me a little nervous, as closed type families are really squirrelly. I would want something resembling a proof before feeling truly confident. As a first pass, we could always treat the equations of a closed family as independent (like an open family). I believe that such a treatment would be fully conservative. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/6018#comment:81 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler