#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: | -------------------------------------+------------------------------------- Comment (by jstolarek): Richard, I don't understand your terminology here (though I do understand the `F` example):

The equations defining a head-injective function all have RHSs with different heads. What appears below the heads does not matter.

Could you explain what you mean by `RHSs with different heads` and `below the heads`? Up till now I thought that the term "head" refers to `type family F a` part of the declaration. I also don't understand why `G` is not head-injective, but perhaps this will become clear to me once earlier questions are answered. -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/6018#comment:50 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler