#6015: "No instance" when using PolyKinds/DataKinds/FunDeps/Undecidable
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Reporter: atnnn | Owner:
Type: feature request | Status: new
Priority: normal | Milestone:
Component: Compiler | Version: 7.4.1
Resolution: | Keywords:
Os: Unknown/Multiple | Architecture: Unknown/Multiple
Failure: GHC rejects valid program | Difficulty: Unknown
Testcase: polykinds/T6015 | Blockedby:
Blocking: | Related:
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Comment(by simonpj@…):
commit 969f8b728be0a2fec8263e8866295776c993394b
{{{
Author: Simon Peyton Jones <[email protected]>
Date: Wed May 16 11:13:52 2012 +0100
Be careful to instantiate kind variables when dealing with functional
dependencies
There were really two bugs
a) When the fundep fires we must apply the matching
substitution to the kinds of the remaining type vars
(This happens in FunDeps.checkClsFD, when we create meta_tvs)
b) When instantiating the un-matched type variables we must
instantiate their kinds properly
(This happens in TcSMonad.instFlexiTcS)
This fixes #6068 and #6015 (second reported bug).
compiler/typecheck/TcInteract.lhs | 6 +--
compiler/typecheck/TcSMonad.lhs | 8 +++-
compiler/types/FunDeps.lhs | 87
++++++++++++++++++++++---------------
3 files changed, 60 insertions(+), 41 deletions(-)
}}}
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Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/6015#comment:9>
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