| Commit message (Collapse) | Author | Age | Files | Lines |
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This patch simplifies GHC to use simple subsumption.
Ticket #17775
Implements GHC proposal #287
https://github.com/ghc-proposals/ghc-proposals/blob/master/
proposals/0287-simplify-subsumption.rst
All the motivation is described there; I will not repeat it here.
The implementation payload:
* tcSubType and friends become noticably simpler, because it no
longer uses eta-expansion when checking subsumption.
* No deeplyInstantiate or deeplySkolemise
That in turn means that some tests fail, by design; they can all
be fixed by eta expansion. There is a list of such changes below.
Implementing the patch led me into a variety of sticky corners, so
the patch includes several othe changes, some quite significant:
* I made String wired-in, so that
"foo" :: String rather than
"foo" :: [Char]
This improves error messages, and fixes #15679
* The pattern match checker relies on knowing about in-scope equality
constraints, andd adds them to the desugarer's environment using
addTyCsDs. But the co_fn in a FunBind was missed, and for some reason
simple-subsumption ends up with dictionaries there. So I added a
call to addTyCsDs. This is really part of #18049.
* I moved the ic_telescope field out of Implication and into
ForAllSkol instead. This is a nice win; just expresses the code
much better.
* There was a bug in GHC.Tc.TyCl.Instance.tcDataFamInstHeader.
We called checkDataKindSig inside tc_kind_sig, /before/
solveEqualities and zonking. Obviously wrong, easily fixed.
* solveLocalEqualitiesX: there was a whole mess in here, around
failing fast enough. I discovered a bad latent bug where we
could successfully kind-check a type signature, and use it,
but have unsolved constraints that could fill in coercion
holes in that signature -- aargh.
It's all explained in Note [Failure in local type signatures]
in GHC.Tc.Solver. Much better now.
* I fixed a serious bug in anonymous type holes. IN
f :: Int -> (forall a. a -> _) -> Int
that "_" should be a unification variable at the /outer/
level; it cannot be instantiated to 'a'. This was plain
wrong. New fields mode_lvl and mode_holes in TcTyMode,
and auxiliary data type GHC.Tc.Gen.HsType.HoleMode.
This fixes #16292, but makes no progress towards the more
ambitious #16082
* I got sucked into an enormous refactoring of the reporting of
equality errors in GHC.Tc.Errors, especially in
mkEqErr1
mkTyVarEqErr
misMatchMsg
misMatchMsgOrCND
In particular, the very tricky mkExpectedActualMsg function
is gone.
It took me a full day. But the result is far easier to understand.
(Still not easy!) This led to various minor improvements in error
output, and an enormous number of test-case error wibbles.
One particular point: for occurs-check errors I now just say
Can't match 'a' against '[a]'
rather than using the intimidating language of "occurs check".
* Pretty-printing AbsBinds
Tests review
* Eta expansions
T11305: one eta expansion
T12082: one eta expansion (undefined)
T13585a: one eta expansion
T3102: one eta expansion
T3692: two eta expansions (tricky)
T2239: two eta expansions
T16473: one eta
determ004: two eta expansions (undefined)
annfail06: two eta (undefined)
T17923: four eta expansions (a strange program indeed!)
tcrun035: one eta expansion
* Ambiguity check at higher rank. Now that we have simple
subsumption, a type like
f :: (forall a. Eq a => Int) -> Int
is no longer ambiguous, because we could write
g :: (forall a. Eq a => Int) -> Int
g = f
and it'd typecheck just fine. But f's type is a bit
suspicious, and we might want to consider making the
ambiguity check do a check on each sub-term. Meanwhile,
these tests are accepted, whereas they were previously
rejected as ambiguous:
T7220a
T15438
T10503
T9222
* Some more interesting error message wibbles
T13381: Fine: one error (Int ~ Exp Int)
rather than two (Int ~ Exp Int, Exp Int ~ Int)
T9834: Small change in error (improvement)
T10619: Improved
T2414: Small change, due to order of unification, fine
T2534: A very simple case in which a change of unification order
means we get tow unsolved constraints instead of one
tc211: bizarre impredicative tests; just accept this for now
Updates Cabal and haddock submodules.
Metric Increase:
T12150
T12234
T5837
haddock.base
Metric Decrease:
haddock.compiler
haddock.Cabal
haddock.base
Merge note: This appears to break the
`UnliftedNewtypesDifficultUnification` test. It has been marked as
broken in the interest of merging.
(cherry picked from commit 66b7b195cb3dce93ed5078b80bf568efae904cc5)
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We now always show "forall {a}. T" for inferred variables,
previously this was controlled by -fprint-explicit-foralls.
This implements part 1 of https://github.com/ghc-proposals/ghc-proposals/pull/179.
Part of GHC ticket #16320.
Furthermore, when printing a levity restriction error, we now display
the HsWrap of the expression. This lets users see the full elaboration with
-fprint-typechecker-elaboration (see also #17670)
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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 patch makes a number of improvements to the output
generated by -ddump-types
* Prints data constructor separately
* Omits empty chunks of output
I was driven initially by the unhelpful existing output for
data constructors, but ended up doing some refactoring.
Lots of error message wibbles, but nothing significant.
Certainly no change in user behaviour.
(NB: It is just possible that I have failed to cleanly
separate this patch from the next one, about
isPredTy and friends.)
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unpackClosure#'s behavior and type has changed. This caused a CPP guard
in the new ghc-heap package to fail when bootstrapping with GHC 8.4.
Test Plan: Validate bootstrapping with GHC 8.4
Reviewers: RyanGlScott
Subscribers: rwbarton, thomie, carter
Differential Revision: https://phabricator.haskell.org/D4716
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This is mostly for congruence with 'subWordC#' and '{add,sub}IntC#'.
I found 'plusWord2#' while implementing this, which both lacks
documentation and has a slightly different specification than
'addWordC#', which means the generic implementation is unnecessarily
complex.
While I was at it, I also added lacking meta-information on PrimOps
and refactored 'subWordC#'s generic implementation to be branchless.
Reviewers: bgamari, simonmar, jrtc27, dfeuer
Reviewed By: bgamari, dfeuer
Subscribers: dfeuer, thomie, carter
Differential Revision: https://phabricator.haskell.org/D4592
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Summary: Bumps several submodules.
Test Plan: ./validate
Reviewers: hvr, bgamari
Reviewed By: bgamari
Subscribers: thomie, carter
GHC Trac Issues: #15018
Differential Revision: https://phabricator.haskell.org/D4609
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This takes care of bumping the `base` and `integer-gmp`
minor version numbers in anticipation of a GHC 8.4.2 release.
While I was in town, I also filled in a `@since TODO` Haddock
annotation for `powModSecInteger` in `integer-gmp` with
`1.0.2.0`, and updated the changelog accordingly.
Test Plan: ./validate
Reviewers: hvr, goldfire, bgamari
Reviewed By: bgamari
Subscribers: thomie, carter
GHC Trac Issues: #15025
Differential Revision: https://phabricator.haskell.org/D4586
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Trac #14394 showed that it's possible to get redundant
constraints in the inferred provided constraints of a pattern
synonym. This patch removes the redundancy with mkMinimalBySCs.
To do this I had to generalise the type of mkMinimalBySCs slightly.
And, to reduce confusing reversal, I made it stable: it now returns
its result in the same order as its input. That led to a raft of
error message wibbles, mostly for the better.
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Summary:
It's simple to treat BodyStmt just like a BindStmt with a wildcard
pattern, which is enough to fix #12143 without going all the way to
using `<*` and `*>` (#10892).
Test Plan:
* new test cases in `ado004.hs`
* validate
Reviewers: niteria, simonpj, bgamari, austin, erikd
Subscribers: rwbarton, thomie
GHC Trac Issues: #12143
Differential Revision: https://phabricator.haskell.org/D4128
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This is prompted by the addition of `compareByteArrays#` in
e3ba26f8b49700b41ff4672f3f7f6a4e453acdcc
NOTE: We may switch to synchronise `ghc-prim` with GHC's version at some point
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Bumps numerous submodules.
Reviewers: austin, hvr
Subscribers: rwbarton, thomie
Differential Revision: https://phabricator.haskell.org/D3974
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(cherry picked from commit 8c5405f63c2de0c445ec171aab63c35786544b9e)
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TcSimplify.decideQuantification was doing the Wrong Thing when
"growing" the type variables to quantify over. We were trying to do
this on a tyvar set where we'd split off the dependent type varaibles;
and we just got it wrong. A kind variable wasn't being generalised
properly, with confusing knock on consequences.
All this led to Trac #13371 and Trac #13393.
This commit tidies it all up:
* The type TcDepVars is renamed as CandidateQTvs;
and splitDepVarsOfType to candidateQTyVarsOfType
* The code in TcSimplify.decideQuantification is simpler.
It no longer does the tricky "grow" stuff over TcDepVars.
Instead it use ordinary VarSets (thereby eliminating the
nasty growThetaTyVarsDSet) and uses that to filter the
result of candidateQTyVarsOfType.
* I documented that candidateQTyVarsOfType returns the type
variables in a good order in which to quantify, and rewrote
it to use an accumulator pattern, so that we would predicatably
get left-to-right ordering.
In doing all this I also made UniqDFM behave a little more nicely:
* When inserting an element that is there already, keep the old tag,
while still overwriting with the new value.
* This means that when doing udfmToList we get back elements in the
order they were originally inserted, rather than in reverse order.
It's not a big deal, but in a subsequent commit I use it to improve
the order of type variables in inferred types.
All this led to a lot of error message wibbles:
- changing the order of quantified variables
- changing the order in which instances are listed in GHCi
- changing the tidying of variables in typechecker erors
There's a submodule update for 'array' because one of its tests
has an error-message change.
I may not have associated all of them with the correct commit.
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Updates a number of submodules.
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This patch does a raft of useful tidy-ups in the type checker.
I've been meaning to do this for some time, and finally made
time to do it en route to ICFP.
1. Modify TcType.ExpType to make a distinct data type,
InferResult for the Infer case, and consequential
refactoring.
2. Define a new function TcUnify.fillInferResult, to fill in
an InferResult. It uses TcMType.promoteTcType to promote
the type to the level of the InferResult.
See TcMType Note [Promoting a type]
This refactoring is in preparation for an improvement
to typechecking pattern bindings, coming next.
I flirted with an elaborate scheme to give better
higher rank inference, but it was just too complicated.
See TcMType Note [Promotion and higher rank types]
3. Add to InferResult a new field ir_inst :: Bool to say
whether or not the type used to fill in the
InferResult should be deeply instantiated. See
TcUnify Note [Deep instantiation of InferResult].
4. Add a TcLevel to SkolemTvs. This will be useful generally
- it's a fast way to see if the type
variable escapes when floating (not used yet)
- it provides a good consistency check when updating a
unification variable (TcMType.writeMetaTyVarRef, the
level_check_ok check)
I originally had another reason (related to the flirting
in (2), but I left it in because it seems like a step in
the right direction.
5. Reduce and simplify the plethora of uExpType,
tcSubType and related functions in TcUnify. It was
such an opaque mess and it's still not great, but it's
better.
6. Simplify the uo_expected field of TypeEqOrigin. Richard
had generatlised it to a ExpType, but it was almost always
a Check type. Now it's back to being a plain TcType which
is much, much easier.
7. Improve error messages by refraining from skolemisation when
it's clear that there's an error: see
TcUnify Note [Don't skolemise unnecessarily]
8. Type.isPiTy and isForAllTy seem to be missing a coreView check,
so I added it
9. Kill off tcs_used_tcvs. Its purpose is to track the
givens used by wanted constraints. For dictionaries etc
we do that via the free vars of the /bindings/ in the
implication constraint ic_binds. But for coercions we
just do update-in-place in the type, rather than
generating a binding. So we need something analogous to
bindings, to track what coercions we have added.
That was the purpose of tcs_used_tcvs. But it only
worked for a /single/ iteration, whereas we may have
multiple iterations of solving an implication. Look
at (the old) 'setImplicationStatus'. If the constraint
is unsolved, it just drops the used_tvs on the floor.
If it becomes solved next time round, we'll pick up
coercions used in that round, but ignore ones used in
the first round.
There was an outright bug. Result = (potentialy) bogus
unused-constraint errors. Constructing a case where this
actually happens seems quite trick so I did not do so.
Solution: expand EvBindsVar to include the (free vars of
the) coercions, so that the coercions are tracked in
essentially the same way as the bindings.
This turned out to be much simpler. Less code, more
correct.
10. Make the ic_binds field in an implication have type
ic_binds :: EvBindsVar
instead of (as previously)
ic_binds :: Maybe EvBindsVar
This is notably simpler, and faster to use -- less
testing of the Maybe. But in the occaional situation
where we don't have anywhere to put the bindings, the
belt-and-braces error check is lost. So I put it back
as an ASSERT in 'setImplicationStatus' (see the use of
'termEvidenceAllowed')
All these changes led to quite bit of error message wibbling
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So that
> :t (id,id,id)
produces
(id,id,id) :: (a3 -> a3, a2 -> a2, a1 -> a1)
instead of
(id,id,id) :: (a2 -> a2, a1 -> a1, a -> a)
Differential Revision: https://phabricator.haskell.org/D2402
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Summary:
There's a precedent for special-casing $, as we already have special
typing rules for it.
Test Plan: validate; new test cases
Reviewers: ezyang, austin, niteria, bgamari, simonpj, erikd
Subscribers: thomie
Differential Revision: https://phabricator.haskell.org/D2345
GHC Trac Issues: #11835
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Summary:
foldUFM introduces unnecessary non-determinism that actually
leads to different generated code as explained in
Note [TrieMap determinism].
As we're switching from UniqFM to UniqDFM here you might be
concerned about performance. There's nothing that ./validate
detects. nofib reports no change in Compile Allocations, but
Compile Time got better on some tests and worse on some,
yielding this summary:
-1 s.d. ----- -3.8%
+1 s.d. ----- +5.4%
Average ----- +0.7%
This is not a fair comparison as the order of Uniques
changes what GHC is actually doing. One benefit from making
this deterministic is also that it will make the
performance results more stable.
Full nofib results: P108
Test Plan: ./validate, nofib
Reviewers: goldfire, simonpj, simonmar, austin, bgamari
Reviewed By: simonpj
Subscribers: thomie
Differential Revision: https://phabricator.haskell.org/D2169
GHC Trac Issues: #4012
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varSetElemsWellScoped introduces unnecessary non-determinism in
inferred type signatures.
Removing this instance required changing the representation of
TcDepVars to use deterministic sets.
This is the last occurence of varSetElemsWellScoped, allowing me to
finally remove it.
Test Plan:
./validate
I will update the expected outputs when commiting, some reordering
of type variables in types is expected.
Reviewers: goldfire, simonpj, austin, bgamari
Reviewed By: simonpj
Subscribers: thomie, simonmar
Differential Revision: https://phabricator.haskell.org/D2135
GHC Trac Issues: #4012
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Summary:
The algorithm for ApplicativeDo rearrangement is based on a heuristic
that runs in O(n^2). This patch adds the optimal algorithm, which is
O(n^3), selected by a flag (-foptimal-applicative-do). It finds better
solutions in a small number of cases (about 2% of the cases where
ApplicativeDo makes a difference), but it can be very slow for large do
expressions. I'm mainly adding it for experimental reasons.
ToDo: user guide docs
Test Plan: validate
Reviewers: simonpj, bgamari, austin, niteria, erikd
Subscribers: thomie
Differential Revision: https://phabricator.haskell.org/D1969
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The idea here is described in [wiki:Typechecker]. Briefly,
this refactor keeps solid track of "synthesis" mode vs
"checking" in GHC's bidirectional type-checking algorithm.
When in synthesis mode, the expected type is just an IORef
to write to.
In addition, this patch does a significant reworking of
RebindableSyntax, allowing much more freedom in the types
of the rebindable operators. For example, we can now have
`negate :: Int -> Bool` and
`(>>=) :: m a -> (forall x. a x -> m b) -> m b`. The magic
is in tcSyntaxOp.
This addresses tickets #11397, #11452, and #11458.
Tests:
typecheck/should_compile/{RebindHR,RebindNegate,T11397,T11458}
th/T11452
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This patch fulfils the request in Trac #11067, #10318, and #10592,
by lifting the conservative restrictions on superclass constraints.
These restrictions are there (and have been since Haskell was born) to
ensure that the transitive superclasses of a class constraint is a finite
set. However (a) this restriction is conservative, and can be annoying
when there really is no recursion, and (b) sometimes genuinely recursive
superclasses are useful (see the tickets).
Dimitrios and I worked out that there is actually a relatively simple way
to do the job. It’s described in some detail in
Note [The superclass story] in TcCanonical
Note [Expanding superclasses] in TcType
In brief, the idea is to expand superclasses only finitely, but to
iterate (using a loop that already existed) if there are more
superclasses to explore.
Other small things
- I improved grouping of error messages a bit in TcErrors
- I re-centred the haddock.compiler test, which was at 9.8%
above the norm, and which this patch pushed slightly over
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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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This also needs to update the primitive/vector submodules in order to
relax upper bounds on ghc-prim.
Like in f8ba4b55cc3a061458f5cfabf17de96128defbbb, a mass-rewrite in testsuite/ via
sed -i s,ghc-prim-0.4.0.0,ghc-prim-0.5.0.0,g $(git grep -Fl 'ghc-prim-0.4.0.0')
was performed.
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This also relaxes a few upper bounds on base in the ghc.git repo;
This required a mass-rewrite in testsuite/
sed -i s,base-4.8.2.0,base-4.9.0.0,g $(git grep -Fl 'base-4.8.2.0')
because it turns out the testsuite is still sensitive to package version
changes.
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Summary:
This is an implementation of the ApplicativeDo proposal. See the Note
[ApplicativeDo] in RnExpr for details on the current implementation,
and the wiki page https://ghc.haskell.org/trac/ghc/wiki/ApplicativeDo
for design notes.
Test Plan: validate
Reviewers: simonpj, goldfire, austin
Subscribers: thomie
Differential Revision: https://phabricator.haskell.org/D729
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