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<h3>
Simon Peyton Jones pushed to branch wip/T17173
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/e1fb31571f4eb16ea6fe2803a088d15bcbc5f0c4">e1fb3157</a></strong>
<div>
<span>by Simon Peyton Jones</span>
<i>at 2020-04-17T16:55:46+01:00</i>
</div>
<pre class="commit-message" style="white-space: pre-wrap; margin: 0;">Do eager instantation in terms

This patch implements eager instantiation, a small but critical change
to the type inference engine, #17173.  The main change is this:

  When inferring types, always return an instantiated type
  (for now, deeply instantiated; in future shallowly instantiated)

There is more discussion in
https://www.tweag.io/posts/2020-04-02-lazy-eager-instantiation.html

There is quite a bit of refactoring in this patch:

* The ir_inst field of GHC.Tc.Utils.TcType.InferResultk
  has entirely gone.  So tcInferInst and tcInferNoInst have collapsed
  into tcInfer.

* Type inference of applications, via tcInferApp and
  tcInferAppHead, are substantially refactored, preparing
  the way for Quick Look impredicativity.

* New pure function GHC.Tc.Gen.Expr.collectHsArgs and applyHsArgs
  are beatifully dual.  We can see the zipper!

* GHC.Tc.Gen.Expr.tcArgs is now much nicer; no longer needs to return
  a wrapper

* In HsExpr, HsTypeApp now contains the the actual type argument,
  and is used in desugaring, rather than putting it in a mysterious
  wrapper.

* I struggled a bit with good error reporting in
  Unify.matchActualFunTysPart. It's a little bit simpler than before,
  but still not great.

Some smaller things

* Rename tcPolyExpr --> tcCheckExpr
         tcMonoExpr --> tcLExpr
* tcPatSig moves from GHC.Tc.Gen.HsType to GHC.Tc.Gen.Pat

Metric Decrease:
    T9961

Reduction of 1.6% in comiler allocation on T9961, I think.
</pre>
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<h4>30 changed files:</h4>
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<a href="#cc97d81e7223ad4a3a5e801156ca632f9fa75654">
compiler/GHC/Hs/Expr.hs
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<a href="#7a1af22e4c32b9aa6ec708d9d3788e1c4db5da9a">
compiler/GHC/Hs/Utils.hs
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<li class="file-stats">
<a href="#6bdd5abc649727f2a802bc96ce5c276de19d3726">
compiler/GHC/HsToCore/Expr.hs
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<a href="#16b273b96a1c03d4261e2ac6de4cc456ba2dd014">
compiler/GHC/Rename/Splice.hs
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<a href="#71fa5eb3ba70e1d3a6181a226c2c227d42f1eb7d">
compiler/GHC/Tc/Gen/Arrow.hs
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<a href="#83f745d921da7adb739e81f83e1c07e723e4a789">
compiler/GHC/Tc/Gen/Bind.hs
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<a href="#902811828741e6bcd64702935bbb54edbbd070ef">
compiler/GHC/Tc/Gen/Expr.hs
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<a href="#8dec347fbe40358b852d7b50ace1e4d62b9b6660">
compiler/GHC/Tc/Gen/Expr.hs-boot
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<a href="#08a3d553a8ca7a753d77697815b63cd85e7dfbd6">
compiler/GHC/Tc/Gen/Foreign.hs
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<a href="#9355bef855426caf5f526925edf351b20f9a86c4">
compiler/GHC/Tc/Gen/HsType.hs
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<a href="#3377164bfe9a1f1a8cfd588703ae1e0ea1e91cf9">
compiler/GHC/Tc/Gen/Match.hs
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<a href="#3ee8be814b6c6727880deab3772e6af922524bf0">
compiler/GHC/Tc/Gen/Pat.hs
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<a href="#04338da99bccd89402218ca19c5724762f0fe641">
compiler/GHC/Tc/Gen/Rule.hs
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<a href="#9ea832ccdb4b5f7508a1efd6caedeafa16b269e7">
compiler/GHC/Tc/Gen/Splice.hs
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<a href="#e65390fa5a32c453a81a1c9a3e1c4464d155ca4a">
compiler/GHC/Tc/Module.hs
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compiler/GHC/Tc/TyCl/PatSyn.hs
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<a href="#93bba9b9e0195db135fec54160523a427ea042fd">
compiler/GHC/Tc/Types/Origin.hs
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<a href="#59d42d45d27a766c3ef299d73c226697153b7f6e">
compiler/GHC/Tc/Utils/Instantiate.hs
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<a href="#c6e4263ee64c68e57b7525127d98243fce38b1ea">
compiler/GHC/Tc/Utils/Monad.hs
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<a href="#94c96afe1bb3b771ffbcfeeca34ce43ebbe76ccb">
compiler/GHC/Tc/Utils/TcMType.hs
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<a href="#5461e7beeb7ae73d7c01f720cbaa3fa2c5333590">
compiler/GHC/Tc/Utils/TcType.hs
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<a href="#74295edeac870ee7f2f3484ebaffab5c948b735a">
compiler/GHC/Tc/Utils/Unify.hs
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<a href="#6a120b0673f8920127d8fffdaa16f01b90cc92d7">
compiler/GHC/Tc/Utils/Zonk.hs
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libraries/base/tests/T9681.stderr
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testsuite/tests/ado/T13242a.stderr
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testsuite/tests/ado/ado002.stderr
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testsuite/tests/annotations/should_fail/annfail08.stderr
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testsuite/tests/driver/T2182.stderr
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testsuite/tests/gadt/gadt13.stderr
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testsuite/tests/ghci/scripts/Defer02.stderr
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<h5>The diff was not included because it is too large.</h5>

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