#7171: erroneous overlapping instances reported with FunDeps
---------------------------------------------+------------------------------
Reporter: jwlato | Owner:
Type: bug | Status: new
Priority: highest | Milestone: 7.6.1
Component: Compiler (Type checker) | Version: 7.6.1-rc1
Resolution: | Keywords: type classes,
fundeps
Os: Unknown/Multiple | Architecture:
Unknown/Multiple
Failure: GHC rejects valid program | Difficulty: Unknown
Testcase: typecheck/should_compile/T7171 | Blockedby:
Blocking: | Related:
---------------------------------------------+------------------------------
Changes (by simonpj):
* milestone: 7.8.1 => 7.6.1
Comment:
I think this is fixed by this HEAD patch, which I have now merged into
7.6:
{{{
commit 702f0db0dd4e85de445e5edb5e6294057ebe6792
Author: Simon Peyton Jones <[email protected]>
Date: Wed Aug 22 18:03:12 2012 +0100
Numerous small changes to the constraint solver
The main thing is that we now keep unsolved Derived constraints in
the
wc_flats of a WantedConstraints, rather than discarding them each
time.
This actually fixes a poential (admittedly obscure) bug, when we
currently
discard a superclass constraint, and may never re-generate it, and
may
thereby miss a functional dependency.
Instead, reportErrors filters out Derived constraints that we
don't want
to report.
The other changes are all small refactorings following our walk-
through.
MERGED from commit 9c0a6bbb0194f65cd62e48936c0c00fc4888eef3 on HEAD
compiler/typecheck/TcErrors.lhs | 53 +++++++++-
compiler/typecheck/TcHsSyn.lhs | 50 ++++------
compiler/typecheck/TcInteract.lhs | 192
+++++++++++++------------------------
compiler/typecheck/TcRnTypes.lhs | 42 ++++----
compiler/typecheck/TcSMonad.lhs | 137 +++++++++++++-------------
compiler/typecheck/TcSimplify.lhs | 86 +----------------
6 files changed, 228 insertions(+), 332 deletions(-)
}}}
Can you try now with the 7.6 branch when the next snapshot appears?
I'll add your example as a regression test (for HEAD).
Simon
--
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/7171#comment:6>
GHC <http://www.haskell.org/ghc/>
The Glasgow Haskell Compiler
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