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| author | Simon Peyton Jones <simonpj@microsoft.com> | 2018-05-18 08:43:11 +0100 |
|---|---|---|
| committer | Simon Peyton Jones <simonpj@microsoft.com> | 2018-05-18 17:16:17 +0100 |
| commit | 2bbdd00c6d70bdc31ff78e2a42b26159c8717856 (patch) | |
| tree | 60701b6613e1822f3007d87e8d4f0bbc707ea4bf /testsuite/tests/ado | |
| parent | efe405447b9fa88cebce718a6329091755deb9ad (diff) | |
| download | haskell-2bbdd00c6d70bdc31ff78e2a42b26159c8717856.tar.gz | |
Orient TyVar/TyVar equalities with deepest on the left
Trac #15009 showed that, for Given TyVar/TyVar equalities, we really
want to orient them with the deepest-bound skolem on the left. As it
happens, we also want to do the same for Wanteds, but for a different
reason (more likely to be touchable). Either way, deepest wins:
see TcUnify Note [Deeper level on the left].
This observation led me to some significant changes:
* A SkolemTv already had a TcLevel, but the level wasn't really being
used. Now it is!
* I updated added invariant (SkolInf) to TcType
Note [TcLevel and untouchable type variables], documenting that
the level number of all the ic_skols should be the same as the
ic_tclvl of the implication
* FlatSkolTvs and FlatMetaTvs previously had a dummy level-number of
zero, which messed the scheme up. Now they get a level number the
same way as all other TcTyVars, instead of being a special case.
* To make sure that FlatSkolTvs and FlatMetaTvs are untouchable (which
was previously done via their magic zero level) isTouchableMetaTyVar
just tests for those two cases.
* TcUnify.swapOverTyVars is the crucial orientation function; see the
new Note [TyVar/TyVar orientation]. I completely rewrote this function,
and it's now much much easier to understand.
I ended up doing some related refactoring, of course
* I noticed that tcImplicitTKBndrsX and tcExplicitTKBndrsX were doing
a lot of useless work in the case where there are no skolems; I
added a fast-patch
* Elminate the un-used tcExplicitTKBndrsSig; and thereby get rid of
the higher-order parameter to tcExpliciTKBndrsX.
* Replace TcHsType.emitTvImplication with TcUnify.checkTvConstraints,
by analogy with TcUnify.checkConstraints.
* Inline TcUnify.buildImplication into its only call-site in
TcUnify.checkConstraints
* TcS.buildImplication becomes TcS.CheckConstraintsTcS, with a
simpler API
* Now that we have NoEvBindsVar we have no need of termEvidenceAllowed;
nuke the latter, adding Note [No evidence bindings] to TcEvidence.
Diffstat (limited to 'testsuite/tests/ado')
| -rw-r--r-- | testsuite/tests/ado/T13242a.stderr | 5 |
1 files changed, 2 insertions, 3 deletions
diff --git a/testsuite/tests/ado/T13242a.stderr b/testsuite/tests/ado/T13242a.stderr index c3dbbba970..e03f471e8b 100644 --- a/testsuite/tests/ado/T13242a.stderr +++ b/testsuite/tests/ado/T13242a.stderr @@ -1,8 +1,7 @@ T13242a.hs:10:5: error: • Couldn't match expected type ‘a0’ with actual type ‘a’ - because type variable ‘a’ would escape its scope - This (rigid, skolem) type variable is bound by + ‘a’ is a rigid type variable bound by a pattern with constructor: A :: forall a. Eq a => a -> T, in a pattern binding in 'do' block @@ -28,7 +27,7 @@ T13242a.hs:13:11: error: These potential instances exist: instance Eq Ordering -- Defined in ‘GHC.Classes’ instance Eq Integer - -- Defined in ‘integer-gmp-1.0.1.0:GHC.Integer.Type’ + -- Defined in ‘integer-gmp-1.0.2.0:GHC.Integer.Type’ instance Eq a => Eq (Maybe a) -- Defined in ‘GHC.Base’ ...plus 22 others ...plus six instances involving out-of-scope types |