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<h3>
 Marge Bot pushed to branch master
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/ffde234854f49dba9ec4735aad74b30fd2deee29">ffde2348</a></strong>
<div>
<span>by Simon Peyton Jones</span>
<i>at 2020-04-22T23:13:06-04:00</i>
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<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.
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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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<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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compiler/GHC/Tc/Gen/Expr.hs-boot
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compiler/GHC/Tc/Gen/Foreign.hs
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compiler/GHC/Tc/Gen/HsType.hs
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compiler/GHC/Tc/Gen/Match.hs
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compiler/GHC/Tc/Gen/Pat.hs
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compiler/GHC/Tc/Gen/Rule.hs
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compiler/GHC/Tc/Utils/Instantiate.hs
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compiler/GHC/Tc/Utils/Monad.hs
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compiler/GHC/Tc/Utils/TcMType.hs
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compiler/GHC/Tc/Utils/TcType.hs
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compiler/GHC/Tc/Utils/Unify.hs
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compiler/GHC/Tc/Utils/Zonk.hs
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<h5>The diff was not included because it is too large.</h5>

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