#7176: Failure to let kind variable remain uninstantiated when not needed -------------------------------+-------------------------------------------- Reporter: goldfire | Owner: Type: bug | Status: closed Priority: normal | Milestone: Component: Compiler | Version: 7.6.1-rc1 Resolution: fixed | Keywords: PolyKinds TypeFamilies Os: Unknown/Multiple | Architecture: Unknown/Multiple Failure: None/Unknown | Difficulty: Unknown Testcase: polykinds/T7176 | Blockedby: Blocking: | Related: -------------------------------+-------------------------------------------- Comment(by simonpj@…): commit 1128f1e02ff06fee89b62fb756ac0c28edcf4625 {{{ Author: Simon Peyton Jones Date: Wed Apr 3 14:37:50 2013 +0100 This changes fixes a bad error in canonicalisation, concerning kind equality We care careful not to construct a canonical equality whose LHS and RHS have incompatible kinds. (This is one of the invariants of a canonical equality.) See Note [Equalities with incompatible kinds]. However, what I had not dealt with is when LHS and RHS *look* as if they have different kinds, but after zonking they become the same. Bad! (This led to an ASSERT failure in the test for Trac #7176.) compiler/typecheck/TcCanonical.lhs | 111 +++++++++++++++++++++--------------- 1 files changed, 65 insertions(+), 46 deletions(-) }}} -- Ticket URL: http://hackage.haskell.org/trac/ghc/ticket/7176#comment:4 GHC http://www.haskell.org/ghc/ The Glasgow Haskell Compiler