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| author | Simon Peyton Jones <simonpj@microsoft.com> | 2015-04-29 13:43:09 +0100 |
|---|---|---|
| committer | Simon Peyton Jones <simonpj@microsoft.com> | 2015-04-29 15:05:44 +0100 |
| commit | a1275a762ec04c1159ae37199b1c8f998a5c5499 (patch) | |
| tree | 6d01de796910a7857c5f91661a40592f67d62090 /testsuite/tests/typecheck/should_fail/tcfail201.stderr | |
| parent | d9bb0ee78b2104bd5c71508080d068804086ae84 (diff) | |
| download | haskell-a1275a762ec04c1159ae37199b1c8f998a5c5499.tar.gz | |
Improve improvement in the constraint solver
This regrettably-big patch substantially improves the way in which
"improvement" happens in the constraint solver. It was triggered by
trying to crack Trac #10009, but it turned out to solve #10340 as
well.
The big picture, with several of the trickiest examples, is described
in Note [The improvement story] in TcInteract.
The major change is this:
* After solving we explicitly try "improvement", by
- making the unsolved Wanteds into Deriveds
- allowing Deriveds to rewrite Deriveds
This more aggressive rewriting "unlocks" some extra
guess-free unifications.
* The main loop is in TcInteract.solveSimpleWanteds, but I also ended
up refactoring TcSimplify.simpl_loop, and its surrounding code.
Notably, any insolubles from the Givens are pulled out
and treated separately, rather than staying in the inert set
during the solveSimpleWanteds loop.
There are a lot of follow-on changes
* Do not emit generate Derived improvements from Wanteds.
This saves work in the common case where they aren't needed.
* For improvement we should really do type-class reduction on Derived
constraints in doTopReactDict. That entailed changing the GenInst
constructor a bit; a local and minor change
* Some annoying faffing about with dropping derived constraints;
see dropDerivedWC, dropDerivedSimples, dropDerivedInsols,
and their Notes.
* Some substantial refactoring in TcErrors.reportWanteds.
This work wasn't strictly forced, but I got sucked into it.
All the changes are in TcErrors.
* Use TcS.unifyTyVar consistently, rather than setWantedTyBind,
so that unifications are properly tracked.
* Refactoring around solveWantedsTcM, solveWantedsAndDrop.
They previously guaranteed a zonked result, but it's more
straightforward for clients to zonk.
Diffstat (limited to 'testsuite/tests/typecheck/should_fail/tcfail201.stderr')
| -rw-r--r-- | testsuite/tests/typecheck/should_fail/tcfail201.stderr | 4 |
1 files changed, 2 insertions, 2 deletions
diff --git a/testsuite/tests/typecheck/should_fail/tcfail201.stderr b/testsuite/tests/typecheck/should_fail/tcfail201.stderr index a69906452c..f548f0e72c 100644 --- a/testsuite/tests/typecheck/should_fail/tcfail201.stderr +++ b/testsuite/tests/typecheck/should_fail/tcfail201.stderr @@ -1,6 +1,6 @@ -tcfail201.hs:17:58: - Couldn't match expected type ‘a’ with actual type ‘HsDoc id0’ +tcfail201.hs:17:58: error: + Couldn't match expected type ‘a’ with actual type ‘HsDoc t0’ ‘a’ is a rigid type variable bound by the type signature for: gfoldl' :: (forall a1 b. c (a1 -> b) -> a1 -> c b) |