#10125: Improper evaluation of type families -------------------------------------+------------------------------------- Reporter: danilo2 | Owner: Type: bug | Status: closed Priority: high | Milestone: Component: Compiler | Version: 7.8.4 Resolution: invalid | Keywords: Operating System: Unknown/Multiple | Architecture: Type of failure: None/Unknown | Unknown/Multiple Blocked By: | Test Case: Related Tickets: | Blocking: | Differential Revisions: -------------------------------------+------------------------------------- Changes (by simonpj): * status: new => closed * resolution: => invalid Comment: It's a bug in GHC 7.8. The program should be rejected because you have an un-saturated application of `CmpNat` on the last line. I'm afraid that GHC's type inference machinery is only capable of dealing with ''saturated'' applications of type families. Sorry. HEAD and 7.10 reject it with a decent message. I'll close as invalid because GHC doesn't claim to support it. Many people would like to do higher order type-family programming in this way, but it's an open question how to do so with predicable type inference. Simon -- Ticket URL: http://ghc.haskell.org/trac/ghc/ticket/10125#comment:3 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler