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| author | Richard Eisenberg <rae@richarde.dev> | 2020-04-29 17:14:53 +0100 |
|---|---|---|
| committer | Marge Bot <ben+marge-bot@smart-cactus.org> | 2020-05-06 04:39:32 -0400 |
| commit | 7ab6ab093c86227b6d33a5185ebbd11928ac9754 (patch) | |
| tree | 9012ba8808f2e7d5271d2d8a225c2223f4ba6aa2 /testsuite/tests/th | |
| parent | 40c71c2cf38b4e134d81b7184a4d5e02949ae70c (diff) | |
| download | haskell-7ab6ab093c86227b6d33a5185ebbd11928ac9754.tar.gz | |
Refactor hole constraints.
Previously, holes (both expression holes / out of scope variables and
partial-type-signature wildcards) were emitted as *constraints* via
the CHoleCan constructor. While this worked fine for error reporting,
there was a fair amount of faff in keeping these constraints in line.
In particular, and unlike other constraints, we could never change
a CHoleCan to become CNonCanonical. In addition:
* the "predicate" of a CHoleCan constraint was really the type
of the hole, which is not a predicate at all
* type-level holes (partial type signature wildcards) carried
evidence, which was never used
* tcNormalise (used in the pattern-match checker) had to create
a hole constraint just to extract it again; it was quite messy
The new approach is to record holes directly in WantedConstraints.
It flows much more nicely now.
Along the way, I did some cleaning up of commentary in
GHC.Tc.Errors.Hole, which I had a hard time understanding.
This was instigated by a future patch that will refactor
the way predicates are handled. The fact that CHoleCan's
"predicate" wasn't really a predicate is incompatible with
that future patch.
No test case, because this is meant to be purely internal.
It turns out that this change improves the performance of
the pattern-match checker, likely because fewer constraints
are sloshing about in tcNormalise. I have not investigated
deeply, but an improvement is not a surprise here:
-------------------------
Metric Decrease:
PmSeriesG
-------------------------
Diffstat (limited to 'testsuite/tests/th')
| -rw-r--r-- | testsuite/tests/th/T12411.stderr | 4 |
1 files changed, 2 insertions, 2 deletions
diff --git a/testsuite/tests/th/T12411.stderr b/testsuite/tests/th/T12411.stderr index 65f77d0723..13b778f8a1 100644 --- a/testsuite/tests/th/T12411.stderr +++ b/testsuite/tests/th/T12411.stderr @@ -2,7 +2,7 @@ T12411.hs:4:6: error: Variable not in scope: (@) - :: (a0 -> f0 a0) -> t0 -> Language.Haskell.TH.Lib.Internal.DecsQ + :: (a1 -> f0 a1) -> t0 -> Language.Haskell.TH.Lib.Internal.DecsQ T12411.hs:4:7: error: - Data constructor not in scope: Q :: [a1] -> t0 + Data constructor not in scope: Q :: [a0] -> t0 |