#14164: GHC hangs on type family dependency -------------------------------------+------------------------------------- Reporter: Iceland_jack | Owner: (none) Type: bug | Status: merge Priority: normal | Milestone: Component: Compiler | Version: 8.2.1 Resolution: | Keywords: | InjectiveFamilies Operating System: Unknown/Multiple | Architecture: | Unknown/Multiple Type of failure: None/Unknown | Test Case: indexed- | types/should_compile/T14164 Blocked By: | Blocking: Related Tickets: | Differential Rev(s): Wiki Page: | -------------------------------------+------------------------------------- Comment (by goldfire): I've commented on the [https://phabricator.haskell.org/rGHCd6216443c61cee94d8ffc31ca8510a534d9406b9 commit]. I think the fix is right, but I'm worried about other related scenarios. I suppose I'll repeat my worry here: How do we know when performing a subst over an open type that we're not forgetting to subst in kinds? The in-scope set of a subst is always closed over kinds. But we need the (in-scope set) - (the subst domain), using set subtraction, to ''also'' be closed over kinds. Otherwise, we're substing a kind variable without substing the type variable, leading to problems like the ones here. So I propose adding this to the substitution invariants and checking it appropriately. Thoughts? -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/14164#comment:8 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler