| Commit message (Collapse) | Author | Age | Files | Lines |
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Previously, `lookupBindGroupOcc`'s error message would recommend all
similar names in scope, regardless of whether they were type
constructors, data constructors, or functions, leading to the
confusion witnessed in #17593. This is easily fixed by only
recommending names in the same namespace, using the
`nameSpacesRelated` function.
Fixes #17593.
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* Add 'dumpAction' hook to DynFlags.
It allows GHC API users to catch dumped intermediate codes and
information. The format of the dump (Core, Stg, raw text, etc.) is now
reported allowing easier automatic handling.
* Add 'traceAction' hook to DynFlags.
Some dumps go through the trace mechanism (for instance unfoldings that
have been considered for inlining). This is problematic because:
1) dumps aren't written into files even with -ddump-to-file on
2) dumps are written on stdout even with GHC API
3) in this specific case, dumping depends on unsafe globally stored
DynFlags which is bad for GHC API users
We introduce 'traceAction' hook which allows GHC API to catch those
traces and to avoid using globally stored DynFlags.
* Avoid dumping empty logs via dumpAction/traceAction (but still write
empty files to keep the existing behavior)
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Metric Decrease:
haddock.compiler
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This is a refactoring with no user-visible changes (except for GHC API
users). Consider the HsExpr constructors that correspond to user-written
pragmas:
HsSCC representing {-# SCC ... #-}
HsCoreAnn representing {-# CORE ... #-}
HsTickPragma representing {-# GENERATED ... #-}
We can factor them out into a separate datatype, HsPragE. It makes the
code a bit tidier, especially in the parser.
Before this patch:
hpc_annot :: { Located ( (([AddAnn],SourceText),(StringLiteral,(Int,Int),(Int,Int))),
((SourceText,SourceText),(SourceText,SourceText))
) }
After this patch:
prag_hpc :: { Located ([AddAnn], HsPragE GhcPs) }
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This patch implements a part of GHC Proposal #229 that covers five
operators:
* the bang operator (!)
* the tilde operator (~)
* the at operator (@)
* the dollar operator ($)
* the double dollar operator ($$)
Based on surrounding whitespace, these operators are disambiguated into
bang patterns, lazy patterns, strictness annotations, type
applications, splices, and typed splices.
This patch doesn't cover the (-) operator or the -Woperator-whitespace
warning, which are left as future work.
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Previously an import cycle between Type and TyCoRep meant that several
functions in TyCoRep ended up SOURCE import coreView. This is quite
unfortunate as coreView is intended to be fused into a larger pattern
match and not incur an extra call.
Fix this with a bit of restructuring:
* Move the functions in `TyCoRep` which depend upon things in `Type`
into `Type`
* Fold contents of `Kind` into `Type` and turn `Kind` into a simple
wrapper re-exporting kind-ish things from `Type`
* Clean up the redundant imports that popped up as a result
Closes #17441.
Metric Decrease:
T4334
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Applicative-do has a bug where it fails to use the monadic fail method
when desugaring patternmatches which can fail. See #15344.
This patch fixes that problem. It required more rewiring than I had expected.
Applicative-do happens mostly in the renamer; that's where decisions about
scheduling are made. This schedule is then carried through the typechecker and
into the desugarer which performs the actual translation. Fixing this bug
required sending information about the fail method from the renamer, through
the type checker and into the desugarer. Previously, the desugarer didn't
have enough information to actually desugar pattern matches correctly.
As a side effect, we also fix #16628, where GHC wouldn't catch missing
MonadFail instances with -XApplicativeDo.
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This introduces three new modules:
- basicTypes/Predicate.hs describes predicates, moving
this logic out of Type. Predicates don't really exist
in Core, and so don't belong in Type.
- typecheck/TcOrigin.hs describes the origin of constraints
and types. It was easy to remove from other modules and
can often be imported instead of other, scarier modules.
- typecheck/Constraint.hs describes constraints as used in
the solver. It is taken from TcRnTypes.
No work other than module splitting is in this patch.
This is the first step toward homogeneous equality, which will
rely more strongly on predicates. And homogeneous equality is the
next step toward a dependently typed core language.
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Previously, all constraints from all top-level groups (as
separated by top-level splices) were lumped together and solved
at the end. This could leak metavariables to TH, though, and
that's bad. This patch solves each group's constraints before
running the next group's splice.
Naturally, we now report fewer errors in some cases.
One nice benefit is that this also fixes #11680, but in a much
simpler way than the original fix for that ticket. Admittedly,
the error messages degrade just a bit from the fix from #11680
(previously, we informed users about variables that will be
brought into scope below a top-level splice, and now we just
report an out-of-scope error), but the amount of complexity
required throughout GHC to get that error was just not worth it.
This patch thus reverts much of
f93c9517a2c6e158e4a5c5bc7a3d3f88cb4ed119.
Fixes #16980
Test cases: th/T16980{,a}
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Currently, newtype constructors are not marked as used when they are
accessed under the hood by uses of `coerce`, as described in #10347.
This fixes #10347 by co-opting the `tcg_keep` field of `TcGblEnv`
to track uses of newtype constructors in the `Coercible` solver.
See `Note [Tracking unused binding and imports]` in `TcRnTypes`.
Since #10347 is fixed, I was able to simplify the code in `TcDeriv`
slightly, as the hack described in
`Note [Newtype deriving and unused constructors]`
is no longer necessary.
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You can always just not use or even build `iserv`. I don't think the
maintenance cost of the CPP is worth...I can't even tell what the
benefit is.
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This patch also changes the way we handle empty lists, simplifying
them somewhat. See Note [Empty lists]. Previously, we had to
special-case empty lists in the type-checker. Now no more!
Finally, this patch improves some documentation around the ir_inst
field used in the type-checker.
This breaks a test case, but I really think the problem is #17251,
not really related to this patch.
Test case: typecheck/should_compile/T13680
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This commit refactors interface file generation to allow information
from the later passed (NCG, STG) to be stored in interface files.
We achieve this by splitting interface file generation into two parts:
* Partial interfaces, built based on the result of the core pipeline
* A fully instantiated interface, which also contains the final
fingerprints and can optionally contain information produced by the backend.
This change is required by !1304 and !1530.
-dynamic-too handling is refactored too: previously when generating code
we'd branch on -dynamic-too *before* code generation, but now we do it
after.
(Original code written by @AndreasK in !1530)
Performance
~~~~~~~~~~~
Before this patch interface files where created and immediately flushed
to disk which made space leaks impossible.
With this change we instead use NFData to force all iface related data
structures to avoid space leaks.
In the process of refactoring it was discovered that the code in the
ToIface Module allocated a lot of thunks which were immediately forced
when writing/forcing the interface file. So we made this module more
strict to avoid creating many of those thunks.
Bottom line is that allocations go down by about ~0.1% compared to
master.
Residency is not meaningfully different after this patch.
Runtime was not benchmarked.
Co-Authored-By: Andreas Klebinger <klebinger.andreas@gmx.at>
Co-Authored-By: Ömer Sinan Ağacan <omer@well-typed.com>
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Implements GHC Proposal #54: .../ghc-proposals/blob/master/proposals/0054-kind-signatures.rst
With this patch, a type constructor can now be given an explicit
standalone kind signature:
{-# LANGUAGE StandaloneKindSignatures #-}
type Functor :: (Type -> Type) -> Constraint
class Functor f where
fmap :: (a -> b) -> f a -> f b
This is a replacement for CUSKs (complete user-specified
kind signatures), which are now scheduled for deprecation.
User-facing changes
-------------------
* A new extension flag has been added, -XStandaloneKindSignatures, which
implies -XNoCUSKs.
* There is a new syntactic construct, a standalone kind signature:
type <name> :: <kind>
Declarations of data types, classes, data families, type families, and
type synonyms may be accompanied by a standalone kind signature.
* A standalone kind signature enables polymorphic recursion in types,
just like a function type signature enables polymorphic recursion in
terms. This obviates the need for CUSKs.
* TemplateHaskell AST has been extended with 'KiSigD' to represent
standalone kind signatures.
* GHCi :info command now prints the kind signature of type constructors:
ghci> :info Functor
type Functor :: (Type -> Type) -> Constraint
...
Limitations
-----------
* 'forall'-bound type variables of a standalone kind signature do not
scope over the declaration body, even if the -XScopedTypeVariables is
enabled. See #16635 and #16734.
* Wildcards are not allowed in standalone kind signatures, as partial
signatures do not allow for polymorphic recursion.
* Associated types may not be given an explicit standalone kind
signature. Instead, they are assumed to have a CUSK if the parent class
has a standalone kind signature and regardless of the -XCUSKs flag.
* Standalone kind signatures do not support multiple names at the moment:
type T1, T2 :: Type -> Type -- rejected
type T1 = Maybe
type T2 = Either String
See #16754.
* Creative use of equality constraints in standalone kind signatures may
lead to GHC panics:
type C :: forall (a :: Type) -> a ~ Int => Constraint
class C a where
f :: C a => a -> Int
See #16758.
Implementation notes
--------------------
* The heart of this patch is the 'kcDeclHeader' function, which is used to
kind-check a declaration header against its standalone kind signature.
It does so in two rounds:
1. check user-written binders
2. instantiate invisible binders a la 'checkExpectedKind'
* 'kcTyClGroup' now partitions declarations into declarations with a
standalone kind signature or a CUSK (kinded_decls) and declarations
without either (kindless_decls):
* 'kinded_decls' are kind-checked with 'checkInitialKinds'
* 'kindless_decls' are kind-checked with 'getInitialKinds'
* DerivInfo has been extended with a new field:
di_scoped_tvs :: ![(Name,TyVar)]
These variables must be added to the context in case the deriving clause
references tcTyConScopedTyVars. See #16731.
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Add GHC.Hs module hierarchy replacing hsSyn.
Metric Increase:
haddock.compiler
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GHC used to reject programs of this form:
```
newtype Age = MkAge Int
deriving Eq via Const Int a
```
That's because an earlier implementation of `DerivingVia` would
generate the following instance:
```
instance Eq Age where
(==) = coerce @(Const Int a -> Const Int a -> Bool)
@(Age -> Age -> Bool)
(==)
```
Note that the `a` in `Const Int a` is not bound anywhere, which
causes all sorts of issues. I figured that no one would ever want to
write code like this anyway, so I simply banned "floating" `via` type
variables like `a`, checking for their presence in the aptly named
`reportFloatingViaTvs` function.
`reportFloatingViaTvs` ended up being implemented in a subtly
incorrect way, as #15831 demonstrates. Following counsel with the
sage of gold fire, I decided to abandon `reportFloatingViaTvs`
entirely and opt for a different approach that would _accept_
the instance above. This is because GHC now generates this instance
instead:
```
instance forall a. Eq Age where
(==) = coerce @(Const Int a -> Const Int a -> Bool)
@(Age -> Age -> Bool)
(==)
```
Notice that we now explicitly quantify the `a` in
`instance forall a. Eq Age`, so everything is peachy scoping-wise.
See `Note [Floating `via` type variables]` in `TcDeriv` for the full
scoop.
A pleasant benefit of this refactoring is that it made it much easier
to catch the problem observed in #16181, so this patch fixes that
issue too.
Fixes #15831. Fixes #16181.
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Before, `type DefUses = [DefUse]`. But lists are a terrible choice of
data structure here, as we frequently append to the right of a
`DefUses`, which yields some displeasing asymptotics. Let's instead
use `OrdList`, which has constant-time appending to the right.
This is one step on the way to #10347.
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9366e019 introduced a check for orphan roles to fix #8485
6ab5da99 changed the lookup code and made the check redundant.
Now it is removed.
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To avoid having to `panic` any time a TTG extension constructor is
consumed, this MR introduces an uninhabited 'NoExtCon' type and uses
that in every extension constructor's type family instance where it
is appropriate. This also introduces a 'noExtCon' function which
eliminates a 'NoExtCon', much like 'Data.Void.absurd' eliminates
a 'Void'.
I also renamed the existing `NoExt` type to `NoExtField` to better
distinguish it from `NoExtCon`. Unsurprisingly, there is a lot of
code churn resulting from this.
Bumps the Haddock submodule. Fixes #15247.
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Partial type sigs had grown hair. tcHsParialSigType was
doing lots of unnecessary work, and tcInstSig was cloning it
unnecessarily -- and the result didn't even work: #16728.
This patch cleans it all up, described by TcHsType
Note [Checking parital type signatures]
I basically just deleted code... but very carefully!
Some refactoring along the way
* Distinguish more explicintly between "anonymous" wildcards "_"
and "named" wildcards "_a". I changed the names of a number
of functions to make this distinction much more apparent.
The patch also revealed that the code in `TcExpr`
that implements the special typing rule for `($)` was wrong.
It called `getRuntimeRep` in a situation where where was no
particular reason to suppose that the thing had kind `TYPE r`.
This caused a crash in typecheck/should_run/T10846.
The fix was easy, and actually simplifies the code in `TcExpr`
quite a bit. Hooray.
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GHC Proposal: 0013-unlifted-newtypes.rst
Discussion: https://github.com/ghc-proposals/ghc-proposals/pull/98
Issues: #15219, #1311, #13595, #15883
Implementation Details:
Note [Implementation of UnliftedNewtypes]
Note [Unifying data family kinds]
Note [Compulsory newtype unfolding]
This patch introduces the -XUnliftedNewtypes extension. When this
extension is enabled, GHC drops the restriction that the field in
a newtype must be of kind (TYPE 'LiftedRep). This allows types
like Int# and ByteArray# to be used in a newtype. Additionally,
coerce is made levity-polymorphic so that it can be used with
newtypes over unlifted types.
The bulk of the changes are in TcTyClsDecls.hs. With -XUnliftedNewtypes,
getInitialKind is more liberal, introducing a unification variable to
return the kind (TYPE r0) rather than just returning (TYPE 'LiftedRep).
When kind-checking a data constructor with kcConDecl, we attempt to
unify the kind of a newtype with the kind of its field's type. When
typechecking a data declaration with tcTyClDecl, we again perform a
unification. See the implementation note for more on this.
Co-authored-by: Richard Eisenberg <rae@richarde.dev>
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As discussed in #16331, the GHCI macro, defined through 'ghci' flags
in ghc.cabal.in, ghc-bin.cabal.in and ghci.cabal.in, is supposed to indicate
whether GHC is built with support for an internal interpreter, that runs in
the same process. It is however overloaded in a few places to mean
"there is an interpreter available", regardless of whether it's an internal
or external interpreter.
For the sake of clarity and with the hope of more easily being able to
build stage 1 GHCs with external interpreter support, this patch splits
the previous GHCI macro into 3 different ones:
- HAVE_INTERNAL_INTERPRETER: GHC is built with an internal interpreter
- HAVE_EXTERNAL_INTERPRETER: GHC is built with support for external interpreters
- HAVE_INTERPRETER: HAVE_INTERNAL_INTERPRETER || HAVE_EXTERNAL_INTERPRETER
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Associated type family default declarations behave strangely in a
couple of ways:
1. If one tries to bind the type variables with an explicit `forall`,
the `forall`'d part will simply be ignored. (#16110)
2. One cannot use visible kind application syntax on the left-hand
sides of associated default equations, unlike every other form
of type family equation. (#16356)
Both of these issues have a common solution. Instead of using
`LHsQTyVars` to represent the left-hand side arguments of an
associated default equation, we instead use `HsTyPats`, which is what
other forms of type family equations use. In particular, here are
some highlights of this patch:
* `FamEqn` is no longer parameterized by a `pats` type variable, as
the `feqn_pats` field is now always `HsTyPats`.
* The new design for `FamEqn` in chronicled in
`Note [Type family instance declarations in HsSyn]`.
* `TyFamDefltEqn` now becomes the same thing as `TyFamInstEqn`. This
means that many of `TyFamDefltEqn`'s code paths can now reuse the
code paths for `TyFamInstEqn`, resulting in substantial
simplifications to various parts of the code dealing with
associated type family defaults.
Fixes #16110 and #16356.
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GHC Proposal #36 describes a transition plan away from CUSKs and to
top-level kind signatures:
1. Introduce a new extension, -XCUSKs, on by default, that detects CUSKs
as they currently exist.
2. We turn off the -XCUSKs extension in a few releases and remove it
sometime thereafter.
This patch implements phase 1 of this plan, introducing a new language
extension to control whether CUSKs are enabled. When top-level kind
signatures are implemented, we can transition to phase 2.
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This patch removes 'EWildPat', 'EAsPat', 'EViewPat', and 'ELazyPat'
from 'HsExpr' by using the ambiguity resolution system introduced
earlier for the command/expression ambiguity.
Problem: there are places in the grammar where we do not know whether we
are parsing an expression or a pattern, for example:
do { Con a b <- x } -- 'Con a b' is a pattern
do { Con a b } -- 'Con a b' is an expression
Until we encounter binding syntax (<-) we don't know whether to parse
'Con a b' as an expression or a pattern.
The old solution was to parse as HsExpr always, and rejig later:
checkPattern :: LHsExpr GhcPs -> P (LPat GhcPs)
This meant polluting 'HsExpr' with pattern-related constructors. In
other words, limitations of the parser were affecting the AST, and all
other code (the renamer, the typechecker) had to deal with these extra
constructors.
We fix this abstraction leak by parsing into an overloaded
representation:
class DisambECP b where ...
newtype ECP = ECP { runECP_PV :: forall b. DisambECP b => PV (Located b) }
See Note [Ambiguous syntactic categories] for details.
Now the intricacies of parsing have no effect on the hsSyn AST when it
comes to the expression/pattern ambiguity.
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When encountering type signatures for unknown names, suggest similar
alternatives.
This fixes issue #16504
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This moves all URL references to Trac Wiki to their corresponding
GitLab counterparts.
This substitution is classified as follows:
1. Automated substitution using sed with Ben's mapping rule [1]
Old: ghc.haskell.org/trac/ghc/wiki/XxxYyy...
New: gitlab.haskell.org/ghc/ghc/wikis/xxx-yyy...
2. Manual substitution for URLs containing `#` index
Old: ghc.haskell.org/trac/ghc/wiki/XxxYyy...#Zzz
New: gitlab.haskell.org/ghc/ghc/wikis/xxx-yyy...#zzz
3. Manual substitution for strings starting with `Commentary`
Old: Commentary/XxxYyy...
New: commentary/xxx-yyy...
See also !539
[1]: https://gitlab.haskell.org/bgamari/gitlab-migration/blob/master/wiki-mapping.json
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As per https://prime.haskell.org/wiki/Libraries/Proposals/MonadFail
Coauthored-by: Ben Gamari <ben@well-typed.com>
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This moves all URL references to Trac tickets to their corresponding
GitLab counterparts.
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Before this patch GHC was trying to be too clever
(Trac #16344); it succeeded in kind-checking this
polymorphic-recursive declaration
data T ka (a::ka) b
= MkT (T Type Int Bool)
(T (Type -> Type) Maybe Bool)
As Note [No polymorphic recursion] discusses, the "solution" was
horribly fragile. So this patch deletes the key lines in
TcHsType, and a wodge of supporting stuff in the renamer.
There were two regressions, both the same: a closed type family
decl like this (T12785b) does not have a CUSK:
type family Payload (n :: Peano) (s :: HTree n x) where
Payload Z (Point a) = a
Payload (S n) (a `Branch` stru) = a
To kind-check the equations we need a dependent kind for
Payload, and we don't get that any more. Solution: make it
a CUSK by giving the result kind -- probably a good thing anyway.
The other case (T12442) was very similar: a close type family
declaration without a CUSK.
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`instance forall c. c` claimed that `c` was out of scope because the
renamer was invoking `lookupGlobalOcc` on `c` (in
`RnNames.getLocalNonValBinders`) without binding `c` first. To avoid
this, this patch changes GHC to invoke `lookupGlobalOcc_maybe` on `c`
instead, and if that returns `Nothing`, then bail out, resulting
in a better error message.
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This patch fixes two rather gnarly test cases:
* Trac #16342 (mutual recursion)
See Note [Tricky scoping in generaliseTcTyCon]
* Trac #16221 (shadowing)
See Note [Unification variables need fresh Names]
The main changes are:
* Substantial reworking of TcTyClsDecls.generaliseTcTyCon
This is the big change, and involves the rather tricky
function TcHsSyn.zonkRecTyVarBndrs.
See Note [Inferring kinds for type declarations] and
Note [Tricky scoping in generaliseTcTyCon] for the details.
* bindExplicitTKBndrs_Tv and bindImplicitTKBndrs_Tv both now
allocate /freshly-named/ unification variables. Indeed, more
generally, unification variables are always fresh; see
Note [Unification variables need fresh Names] in TcMType
* Clarify the role of tcTyConScopedTyVars.
See Note [Scoped tyvars in a TcTyCon] in TyCon
As usual, this dragged in some more refactoring:
* Renamed TcMType.zonkTyCoVarBndr to zonkAndSkolemise
* I renamed checkValidTelescope to checkTyConTelescope;
it's only used on TyCons, and indeed takes a TyCon as argument.
* I folded the slightly-mysterious reportFloatingKvs into
checkTyConTelescope. (Previously all its calls immediately
followed a call to checkTyConTelescope.) It makes much more
sense there.
* I inlined some called-once functions to simplify
checkValidTyFamEqn. It's less spaghetti-like now.
* This patch also fixes Trac #16251. I'm not quite sure why #16251
went wrong in the first place, nor how this patch fixes it, but
hey, it's good, and life is short.
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This implements GHC proposal 35
(https://github.com/ghc-proposals/ghc-proposals/blob/master/proposals/0035-forall-arrow.rst)
by adding the ability to write kinds with
visible dependent quantification (VDQ).
Most of the work for supporting VDQ was actually done _before_ this
patch. That is, GHC has been able to reason about kinds with VDQ for
some time, but it lacked the ability to let programmers directly
write these kinds in the source syntax. This patch is primarly about
exposing this ability, by:
* Changing `HsForAllTy` to add an additional field of type
`ForallVisFlag` to distinguish between invisible `forall`s (i.e,
with dots) and visible `forall`s (i.e., with arrows)
* Changing `Parser.y` accordingly
The rest of the patch mostly concerns adding validity checking to
ensure that VDQ is never used in the type of a term (as permitting
this would require full-spectrum dependent types). This is
accomplished by:
* Adding a `vdqAllowed` predicate to `TcValidity`.
* Introducing `splitLHsSigmaTyInvis`, a variant of `splitLHsSigmaTy`
that only splits invisible `forall`s. This function is used in
certain places (e.g., in instance declarations) to ensure that GHC
doesn't try to split visible `forall`s (e.g., if it tried splitting
`instance forall a -> Show (Blah a)`, then GHC would mistakenly
allow that declaration!)
This also updates Template Haskell by introducing a new `ForallVisT`
constructor to `Type`.
Fixes #16326. Also fixes #15658 by documenting this feature in the
users' guide.
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Implements GHC Proposal #24: .../ghc-proposals/blob/master/proposals/0024-no-kind-vars.rst
Fixes Trac #16334, Trac #16315
With this patch, scoping rules for type and kind variables have been
unified: kind variables no longer receieve special treatment. This
simplifies both the language and the implementation.
User-facing changes
-------------------
* Kind variables are no longer implicitly quantified when an explicit
forall is used:
p :: Proxy (a :: k) -- still accepted
p :: forall k a. Proxy (a :: k) -- still accepted
p :: forall a. Proxy (a :: k) -- no longer accepted
In other words, now we adhere to the "forall-or-nothing" rule more
strictly.
Related function: RnTypes.rnImplicitBndrs
* The -Wimplicit-kind-vars warning has been deprecated.
* Kind variables are no longer implicitly quantified in constructor
declarations:
data T a = T1 (S (a :: k) | forall (b::k). T2 (S b) -- no longer accepted
data T (a :: k) = T1 (S (a :: k) | forall (b::k). T2 (S b) -- still accepted
Related function: RnTypes.extractRdrKindSigVars
* Implicitly quantified kind variables are no longer put in front of
other variables:
f :: Proxy (a :: k) -> Proxy (b :: j)
f :: forall k j (a :: k) (b :: j). Proxy a -> Proxy b -- old order
f :: forall k (a :: k) j (b :: j). Proxy a -> Proxy b -- new order
This is a breaking change for users of TypeApplications. Note that
we still respect the dpendency order: 'k' before 'a', 'j' before 'b'.
See "Ordering of specified variables" in the User's Guide.
Related function: RnTypes.rnImplicitBndrs
* In type synonyms and type family equations, free variables on the RHS
are no longer implicitly quantified unless used in an outermost kind
annotation:
type T = Just (Nothing :: Maybe a) -- no longer accepted
type T = Just Nothing :: Maybe (Maybe a) -- still accepted
The latter form is a workaround due to temporary lack of an explicit
quantification method. Ideally, we would write something along these
lines:
type T @a = Just (Nothing :: Maybe a)
Related function: RnTypes.extractHsTyRdrTyVarsKindVars
* Named wildcards in kinds are fixed (Trac #16334):
x :: (Int :: _t) -- this compiles, infers (_t ~ Type)
Related function: RnTypes.partition_nwcs
Implementation notes
--------------------
* One of the key changes is the removal of FKTV in RnTypes:
- data FreeKiTyVars = FKTV { fktv_kis :: [Located RdrName]
- , fktv_tys :: [Located RdrName] }
+ type FreeKiTyVars = [Located RdrName]
We used to keep track of type and kind variables separately, but
now that they are on equal footing when it comes to scoping, we
can put them in the same list.
* extract_lty and family are no longer parametrized by TypeOrKind,
as we now do not distinguish kind variables from type variables.
* PatSynExPE and the related Note [Pattern synonym existentials do not scope]
have been removed (Trac #16315). With no implicit kind quantification,
we can no longer trigger the error.
* reportFloatingKvs and the related Note [Free-floating kind vars]
have been removed. With no implicit kind quantification,
we can no longer trigger the error.
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This patch removes 'HsArrApp' and 'HsArrForm' from 'HsExpr' by
introducing a new ambiguity resolution system in the parser.
Problem: there are places in the grammar where we do not know whether we
are parsing an expression or a command:
proc x -> do { (stuff) -< x } -- 'stuff' is an expression
proc x -> do { (stuff) } -- 'stuff' is a command
Until we encounter arrow syntax (-<) we don't know whether to parse
'stuff' as an expression or a command.
The old solution was to parse as HsExpr always, and rejig later:
checkCommand :: LHsExpr GhcPs -> P (LHsCmd GhcPs)
This meant polluting 'HsExpr' with command-related constructors. In
other words, limitations of the parser were affecting the AST, and
all other code (the renamer, the typechecker) had to deal with these
extra constructors by panicking.
We fix this abstraction leak by parsing into an intermediate
representation, 'ExpCmd':
data ExpCmdG b where
ExpG :: ExpCmdG HsExpr
CmdG :: ExpCmdG HsCmd
type ExpCmd = forall b. ExpCmdG b -> PV (Located (b GhcPs))
checkExp :: ExpCmd -> PV (LHsExpr GhcPs)
checkCmd :: ExpCmd -> PV (LHsCmd GhcPs)
checkExp f = f ExpG -- interpret as an expression
checkCmd f = f CmdG -- interpret as a command
See Note [Ambiguous syntactic categories] for details.
Now the intricacies of parsing have no effect on the hsSyn AST when it
comes to the expression/command ambiguity.
Future work: apply the same principles to the expression/pattern
ambiguity.
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