#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
Keywords: | Os: Unknown/Multiple
Architecture: Unknown/Multiple | Failure: GHC rejects valid program
Difficulty: Unknown | Testcase:
Blockedby: | Blocking:
Related: |
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Comment(by simonpj@…):
commit 6c3045b90fb28861fae826c8bbd53135d3f2a6ce
{{{
Author: Simon Peyton Jones <[email protected]>
Date: Mon May 14 14:05:48 2012 +0100
Fix the the pure unifier so that it unifies kinds
When unifying two type variables we must unify their kinds.
The pure *matcher* was doing so, but the pure *unifier* was not.
This patch fixes Trac #6015, where an instance lookup was failing
when it should have succeeded.
I removed a bunch of code aimed at support sub-kinding. It's
tricky, ad-hoc, and I don't think its necessary any more.
Anything we can do to simplify the sub-kinding story is welcome!
compiler/types/FunDeps.lhs | 4 +++
compiler/types/Unify.lhs | 50
+++++++++++++++----------------------------
2 files changed, 22 insertions(+), 32 deletions(-)
}}}
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Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/6015#comment:4>
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