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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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Provoked by Trac #11948, this patch adds a new warning to GHC
-Wsimplifiable-class-constraints
It warns if you write a class constraint in a type signature that
can be simplified by an existing instance declaration. Almost always
this means you should simplify it right now; type inference is very
fragile without it, as #11948 shows.
I've put the warning as on-by-default, but I suppose that if there are
howls of protest we can move it out (as happened for -Wredundant-constraints.
It actually found an example of an over-complicated context in CmmNode.
Quite a few tests use these weird contexts to trigger something else,
so I had to suppress the warning in those.
The 'haskeline' library has a few occurrences of the warning (which
I think should be fixed), so I switched it off for that library in
warnings.mk.
The warning itself is done in TcValidity.check_class_pred.
HOWEVER, when type inference fails we get a type error; and the error
suppresses the (informative) warning. So as things stand, the warning
only happens when it doesn't cause a problem. Not sure what to do
about this, but this patch takes us forward, I think.
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This re-working of the typechecker algorithm is based on
the paper "Visible type application", by Richard Eisenberg,
Stephanie Weirich, and Hamidhasan Ahmed, to be published at
ESOP'16.
This patch introduces -XTypeApplications, which allows users
to say, for example `id @Int`, which has type `Int -> Int`. See
the changes to the user manual for details.
This patch addresses tickets #10619, #5296, #10589.
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This implements the ideas originally put forward in
"System FC with Explicit Kind Equality" (ICFP'13).
There are several noteworthy changes with this patch:
* We now have casts in types. These change the kind
of a type. See new constructor `CastTy`.
* All types and all constructors can be promoted.
This includes GADT constructors. GADT pattern matches
take place in type family equations. In Core,
types can now be applied to coercions via the
`CoercionTy` constructor.
* Coercions can now be heterogeneous, relating types
of different kinds. A coercion proving `t1 :: k1 ~ t2 :: k2`
proves both that `t1` and `t2` are the same and also that
`k1` and `k2` are the same.
* The `Coercion` type has been significantly enhanced.
The documentation in `docs/core-spec/core-spec.pdf` reflects
the new reality.
* The type of `*` is now `*`. No more `BOX`.
* Users can write explicit kind variables in their code,
anywhere they can write type variables. For backward compatibility,
automatic inference of kind-variable binding is still permitted.
* The new extension `TypeInType` turns on the new user-facing
features.
* Type families and synonyms are now promoted to kinds. This causes
trouble with parsing `*`, leading to the somewhat awkward new
`HsAppsTy` constructor for `HsType`. This is dispatched with in
the renamer, where the kind `*` can be told apart from a
type-level multiplication operator. Without `-XTypeInType` the
old behavior persists. With `-XTypeInType`, you need to import
`Data.Kind` to get `*`, also known as `Type`.
* The kind-checking algorithms in TcHsType have been significantly
rewritten to allow for enhanced kinds.
* The new features are still quite experimental and may be in flux.
* TODO: Several open tickets: #11195, #11196, #11197, #11198, #11203.
* TODO: Update user manual.
Tickets addressed: #9017, #9173, #7961, #10524, #8566, #11142.
Updates Haddock submodule.
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Test Plan: I couldn't add tests because apparently line number
reporting was already working correctly when loading script files. I
don't know how to test by running commands using stdin, is this
supported?
Reviewers: austin, thomie, bgamari
Reviewed By: thomie, bgamari
Subscribers: hvr, thomie
Differential Revision: https://phabricator.haskell.org/D1067
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The idea was promted by Trac #9939, but it was Christmas, so I did
some recreational programming that went much further.
The idea is to warn when a constraint in a user-supplied context is
redundant. Everything is described in detail in
Note [Tracking redundant constraints]
in TcSimplify.
Main changes:
* The new ic_status field in an implication, of type ImplicStatus.
It replaces ic_insol, and includes information about redundant
constraints.
* New function TcSimplify.setImplicationStatus sets the ic_status.
* TcSigInfo has sig_report_redundant field to say whenther a
redundant constraint should be reported; and similarly
the FunSigCtxt constructor of UserTypeCtxt
* EvBinds has a field eb_is_given, to record whether it is a given
or wanted binding. Some consequential chagnes to creating an evidence
binding (so that we record whether it is given or wanted).
* AbsBinds field abs_ev_binds is now a *list* of TcEvBiinds;
see Note [Typechecking plan for instance declarations] in
TcInstDcls
* Some significant changes to the type checking of instance
declarations; Note [Typechecking plan for instance declarations]
in TcInstDcls.
* I found that TcErrors.relevantBindings was failing to zonk the
origin of the constraint it was looking at, and hence failing to
find some relevant bindings. Easy to fix, and orthogonal to
everything else, but hard to disentangle.
Some minor refactorig:
* TcMType.newSimpleWanteds moves to Inst, renamed as newWanteds
* TcClassDcl and TcInstDcls now have their own code for typechecking
a method body, rather than sharing a single function. The shared
function (ws TcClassDcl.tcInstanceMethodBody) didn't have much code
and the differences were growing confusing.
* Add new function TcRnMonad.pushLevelAndCaptureConstraints, and
use it
* Add new function Bag.catBagMaybes, and use it in TcSimplify
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This matches GCC's choice of Unicode quotation marks (i.e. U+2018 and U+2019)
and therefore looks more familiar on the console. This addresses #2507.
Signed-off-by: Herbert Valerio Riedel <hvr@gnu.org>
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major TcErrors refactoring
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Test cases for GHCi data, type, newtype, class, instance,
deriving, etc declarations.
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