#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 jstolarek):

Does that clarify?

Yes. I don't yet see how to deal with your `E2` example. It looks like we would need to have pattern-exhaustiveness checking for type families. And this would only be possible for closed kinds I think. Well, for open kinds type family would simply be non-injective. I have a few more questions about implementation. These most likely go to Simon. I've been trying to wrap my head around implementation of `doTopReactFunEq` and I have these questions: 1. What does the term "react" mean? As in the name `doTopReact` and the comment below its type signature: "The work item does not react with the inert set..." (TcInteract, L1412). 2. What is "interaction"? As in the module name `TcInteract` or the comment mentioned above: "... so try interaction with top-level instances". 3. What does `EvTerm` data type represent? 4. What are branches in axioms? 5. I don't understand how canonicalization works. Is there an overview somewhere? Other than `Note [Canonicalization]`, which unfortunately is too vague for me :-( -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/6018#comment:86 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler