#6020: "Couldn't match kind" with free type variables and PolyKinds
----------------------------------------+-----------------------------------
Reporter: atnnn | Owner:
Type: feature request | Status: new
Priority: normal | Milestone:
Component: Compiler | Version: 7.5
Resolution: | Keywords:
Os: Unknown/Multiple | Architecture: Unknown/Multiple
Failure: GHC rejects valid program | Difficulty: Unknown
Testcase: polykinds/T6020 | Blockedby:
Blocking: | Related:
----------------------------------------+-----------------------------------
Changes (by atnnn):
* status: closed => new
* resolution: fixed =>
Comment:
If I switch to equality constraints and reverse the functional dependency
of Id, I get the same error as above ({{{Couldn't match kind `k0' with
`Bool'}}}):
{{{
{-# LANGUAGE DataKinds, FunctionalDependencies, FlexibleInstances,
UndecidableInstances, PolyKinds, KindSignatures,
ConstraintKinds, FlexibleContexts, GADTs #-}
class Id (a :: k) (b :: k) | b -> a
instance a ~ b => Id a b
class Test (x :: a) (y :: a)
instance (Id x y, Id y z) => Test x z
test :: Test True True => ()
test = ()
main = print test
}}}
If I comment out `main`, it loads fine but GHC now panics when I use
`test`:
{{{
>>> :load "testid.hs"
>>> test
ghc-stage2: panic! (the 'impossible' happened)
(GHC version 7.5.20120425 for x86_64-unknown-linux):
tcTyVarDetails k0{tv alS} [tv]
}}}
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/6020#comment:4>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler
_______________________________________________
Glasgow-haskell-bugs mailing list
Glasgow-haskell-bugs@haskell.org
http://www.haskell.org/mailman/listinfo/glasgow-haskell-bugs
