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<h3>
Simon Peyton Jones pushed to branch wip/T18126
at <a href="https://gitlab.haskell.org/ghc/ghc">Glasgow Haskell Compiler / GHC</a>
</h3>
<h4>
Commits:
</h4>
<ul>
<li>
<strong><a href="https://gitlab.haskell.org/ghc/ghc/-/commit/df22930c923fdc1046b08cec127b0f53da5af53d">df22930c</a></strong>
<div>
<span>by Simon Peyton Jones</span>
<i>at 2020-08-11T09:18:10+01:00</i>
</div>
<pre class="commit-message" style="white-space: pre-wrap; margin: 0;">Implement Quick Look impredicativity
This patch implements Quick Look impredicativity (#18126), sticking
very closely to the design in
A quick look at impredicativity, Serrano et al, ICFP 2020
The main change is that a big chunk of GHC.Tc.Gen.Expr has been
extracted to two new modules
GHC.Tc.Gen.App
GHC.Tc.Gen.Head
which deal with typechecking n-ary applications, and the head of
such applications, respectively. Both contain a good deal of
documentation.
Three other loosely-related changes are in this patch:
* I implemented (partly by accident) point (2) of the accepted GHC
proposal "Clean up printing of foralls", namely
https://github.com/ghc-proposals/ghc-proposals/blob/
master/proposals/0179-printing-foralls.rst
In particular, see Note [TcRnExprMode] in GHC.Tc.Module
- :type instantiates /inferred/, but not /specified/, quantifiers
- :type +d instantiates /all/ quantifiers
- :type +v is killed off
* HsRecFld (which the renamer introduces for record field selectors),
is now preserved by the typechecker, rather than being rewritten
back to HsVar. This is more uniform, and turned out to be more
convenient in the new scheme of things.
* The GHCi debugger uses a non-standard unification that allows the
unification variables to unify with polytypes. We used to hack
this by using ImpredicativeTypes, but that doesn't work anymore
so I introduces RuntimeUnkTv. See Note [RuntimeUnkTv] in
GHC.Runtime.Heap.Inspect
WARNING: this patch won't validate on its own. It was too
hard to fully disentangle it from the following patch, on
type errors and kind generalisation.
Changes to tests
* Fixes #9730 (test added)
* Fixes #7026 (test added)
* Fixes most of #8808, except function `g2'` which uses a
section (which doesn't play with QL yet -- see #18126)
Test added
* Fixes #1330. NB Church1.hs subsumes Church2.hs, which is now deleted
* Fixes #17332 (test added)
* Fixes #4295
* This patch makes typecheck/should_run/T7861 fail.
But that turns out to be a pre-existing bug: #18467.
So I have just made T7861 into expect_broken(18467)
</pre>
</li>
<li>
<strong><a href="https://gitlab.haskell.org/ghc/ghc/-/commit/0b2e16b2bafa4cb386f61a287bf00a972d4cec51">0b2e16b2</a></strong>
<div>
<span>by Simon Peyton Jones</span>
<i>at 2020-08-11T09:18:10+01:00</i>
</div>
<pre class="commit-message" style="white-space: pre-wrap; margin: 0;">Improve kind generalisation, error messages
This patch does two things:
* It refactors GHC.Tc.Errors a bit. In debugging Quick Look I was
forced to look in detail at error messages, and ended up doing a bit
of refactoring, esp in mkTyVarEqErr'. It's still quite a mess, but
a bit better, I think.
* It makes a significant improvement to the kind checking of type and
class declarations. Specifically, we now ensure that if kind
checking fails with an unsolved constraint, all the skolems are in
scope. That wasn't the case before, which led to some obscure error
messages; and occasional failures with "no skolem info" (eg #16245).
Both of these, and the main Quick Look patch itself, affect a /lot/ of
error messages, as you can see from the number of files changed. I've
checked them all; I think they are as good or better than before.
Smaller things
* I documented the various instances of VarBndr better.
See Note [The VarBndr tyep and its uses] in GHC.Types.Var
* Renamed GHC.Tc.Solver.simpl_top to simplifyTopWanteds
* A bit of refactoring in bindExplicitTKTele, to avoid the
footwork with Either. Simpler now.
* Move promoteTyVar from GHC.Tc.Solver to GHC.Tc.Utils.TcMType
Fixes #16245 (comment 211369), memorialised as
typeecheck/polykinds/T16245a
</pre>
</li>
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<h4>18 changed files:</h4>
<ul>
<li class="file-stats">
<a href="#4aad0050db1a8a20db8bbca149111de99cb299c9">
compiler/GHC/Core/TyCon.hs
</a>
</li>
<li class="file-stats">
<a href="#cc97d81e7223ad4a3a5e801156ca632f9fa75654">
compiler/GHC/Hs/Expr.hs
</a>
</li>
<li class="file-stats">
<a href="#0bae7e7e67b5f9b6ba2a371f8917cf74423a0c6f">
compiler/GHC/Hs/Pat.hs
</a>
</li>
<li class="file-stats">
<a href="#018be522bc4813b147a1525e4f96a7a493207d96">
compiler/GHC/Hs/Type.hs
</a>
</li>
<li class="file-stats">
<a href="#e011edcbdb6414ff00022ab5c1eeee88906a53ab">
compiler/GHC/HsToCore/Coverage.hs
</a>
</li>
<li class="file-stats">
<a href="#6bdd5abc649727f2a802bc96ce5c276de19d3726">
compiler/GHC/HsToCore/Expr.hs
</a>
</li>
<li class="file-stats">
<a href="#446cb12ca6cefaf1c6eb79b7db643632744263c7">
compiler/GHC/Parser/PostProcess.hs
</a>
</li>
<li class="file-stats">
<a href="#cfa41b5649933e5b12f7796e9d49b9dd6a0bc59f">
compiler/GHC/Rename/Pat.hs
</a>
</li>
<li class="file-stats">
<a href="#173c7eb846a4e9b5fee79688a72cbf6a326e4e1e">
compiler/GHC/Runtime/Eval.hs
</a>
</li>
<li class="file-stats">
<a href="#8858278b4cb7284f96b29b5564bcb426de4fae70">
compiler/GHC/Runtime/Heap/Inspect.hs
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</li>
<li class="file-stats">
<a href="#3aa56839e36b2219f9ad54f5646ef3005da9c672">
compiler/GHC/Tc/Deriv/Generate.hs
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</li>
<li class="file-stats">
<a href="#e4b9d5e9d2de37561bfd06a2c97a5c924a1bab76">
compiler/GHC/Tc/Errors.hs
</a>
</li>
<li class="file-stats">
<a href="#897218b3e24728ae9e5b0329b949493f1ede80fb">
compiler/GHC/Tc/Errors/Hole.hs
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</li>
<li class="file-stats">
<a href="#6a1f039ed7725eddef15dd5f4dc318a3434f26c9">
<span class="new-file">
+
compiler/GHC/Tc/Gen/App.hs
</span>
</a>
</li>
<li class="file-stats">
<a href="#71fa5eb3ba70e1d3a6181a226c2c227d42f1eb7d">
compiler/GHC/Tc/Gen/Arrow.hs
</a>
</li>
<li class="file-stats">
<a href="#b18f1cc437ab64ccd37a7cae3b8c3f9071aef45e">
compiler/GHC/Tc/Gen/Default.hs
</a>
</li>
<li class="file-stats">
<a href="#902811828741e6bcd64702935bbb54edbbd070ef">
compiler/GHC/Tc/Gen/Expr.hs
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<li class="file-stats">
<a href="#8dec347fbe40358b852d7b50ace1e4d62b9b6660">
compiler/GHC/Tc/Gen/Expr.hs-boot
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<h5>The diff was not included because it is too large.</h5>
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