Wed Nov 21 06:33:46 PST 2007 [EMAIL PROTECTED]
* MERGE: Zonk quantified tyvars with skolems + Rejig the error messages a
bit; fixes a minor bug
This merges to the 6.8 branch two HEAD patches (names above). The
former "Zonk..." was for some reason partly in the branch already,
which is what led to the complications.
Here are the original patches:
Fri Oct 19 12:56:53 BST 2007 Manuel M T Chakravarty <[EMAIL PROTECTED]>
* Zonk quantified tyvars with skolems
We used to zonk quantified type variables to regular TyVars. However, this
leads to problems. Consider this program from the regression test suite:
eval :: Int -> String -> String -> String
eval 0 root actual = evalRHS 0 root actual
evalRHS :: Int -> a
evalRHS 0 root actual = eval 0 root actual
It leads to the deferral of an equality
(String -> String -> String) ~ a
which is propagated up to the toplevel (see
TcSimplify.tcSimplifyInferCheck).
In the meantime `a' is zonked and quantified to form `evalRHS's signature.
This has the *side effect* of also zonking the `a' in the deferred equality
(which at this point is being handed around wrapped in an implication
constraint).
Finally, the equality (with the zonked `a') will be handed back to the
simplifier by TcRnDriver.tcRnSrcDecls calling TcSimplify.tcSimplifyTop.
If we zonk `a' with a regular type variable, we will have this regular type
variable now floating around in the simplifier, which in many places
assumes to
only see proper TcTyVars.
We can avoid this problem by zonking with a skolem. The skolem is rigid
(which we requirefor a quantified variable), but is still a TcTyVar that the
simplifier knows how to deal with.
Thu Nov 1 17:50:22 GMT 2007 [EMAIL PROTECTED]
* Rejig the error messages a bit; fixes a minor bug
The type checker was only reporting the first message if an equality
failed to match. This patch does a bit of refactoring and fixes the
bug, which was in the bogus use of eqInstMisMatch
in tcSimplify.report_no_instances.b
This is really a bug in 6.8 too, so this would be good to merge across
to the 6.8 branch.
M ./compiler/typecheck/Inst.lhs -5 +3
M ./compiler/typecheck/TcSimplify.lhs -6 +8
M ./compiler/typecheck/TcTyFuns.lhs -38 +43
M ./compiler/typecheck/TcUnify.lhs -8 +7
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