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| author | Simon Peyton Jones <simonpj@microsoft.com> | 2020-04-08 23:08:12 +0100 |
|---|---|---|
| committer | Marge Bot <ben+marge-bot@smart-cactus.org> | 2020-04-22 23:13:06 -0400 |
| commit | ffde234854f49dba9ec4735aad74b30fd2deee29 (patch) | |
| tree | 80409f70e0de9164441d1cf860b386df4318e5c3 /docs | |
| parent | 34a45ee600d5346f5d1728047fa185698ed7ee84 (diff) | |
| download | haskell-ffde234854f49dba9ec4735aad74b30fd2deee29.tar.gz | |
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.
Diffstat (limited to 'docs')
| -rw-r--r-- | docs/users_guide/8.12.1-notes.rst | 10 |
1 files changed, 10 insertions, 0 deletions
diff --git a/docs/users_guide/8.12.1-notes.rst b/docs/users_guide/8.12.1-notes.rst index 4d151d0ab1..2d142800ca 100644 --- a/docs/users_guide/8.12.1-notes.rst +++ b/docs/users_guide/8.12.1-notes.rst @@ -69,6 +69,16 @@ Language There is a chance we will tweak the lookup scheme in the future, to make this workaround unnecessary. +* GHC now consistently does eager instantiation during type inference. + As a consequence, visible type application (VTA) now only works when + the head of the application is: + * A variable + * An expression with a type signature + For example `(let x = blah in id) @Bool True` no longer typechecks. + You should write `let x = blah in id @Bool True` instead. + + This change prepares the way for Quick Look impredicativity. + Compiler ~~~~~~~~ |