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which (finally) fills out the functionality of polymorphic kinds.
It also fixes numerous bugs.
Main changes are:
Renaming stuff
~~~~~~~~~~~~~~
* New type in HsTypes:
data HsBndrSig sig = HsBSig sig [Name]
which is used for type signatures in patterns, and kind signatures
in types. So when you say
f (x :: [a]) = x ++ x
or
data T (f :: k -> *) (x :: *) = MkT (f x)
the signatures in both cases are a HsBndrSig.
* The [Name] in HsBndrSig records the variables bound by the
pattern, that is 'a' in the first example, 'k' in the second,
and nothing in the third. The renamer initialises the field.
* As a result I was able to get rid of
RnHsSyn.extractHsTyNames :: LHsType Name -> NameSet
and its friends altogether. Deleted the entire module!
This led to some knock-on refactoring; in particular the
type renamer now returns the free variables just like the
term renamer.
Kind-checking types: mainly TcHsType
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
A major change is that instead of kind-checking types in two
passes, we now do one. Under the old scheme, the first pass did
kind-checking and (hackily) annotated the HsType with the
inferred kinds; and the second pass desugared the HsType to a
Type. But now that we have kind variables inside types, the
first pass (TcHsType.tc_hs_type) can go straight to Type, and
zonking will squeeze out any kind unification variables later.
This is much nicer, but it was much more fiddly than I had expected.
The nastiest corner is this: it's very important that tc_hs_type
uses lazy constructors to build the returned type. See
Note [Zonking inside the knot] in TcHsType.
Type-checking type and class declarations: mainly TcTyClsDecls
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
I did tons of refactoring in TcTyClsDecls. Simpler and nicer now.
Typechecking bindings: mainly TcBinds
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
I rejigged (yet again) the handling of type signatures in TcBinds.
It's a bit simpler now. The main change is that tcTySigs goes
right through to a TcSigInfo in one step; previously it was split
into two, part here and part later.
Unsafe coercions
~~~~~~~~~~~~~~~~
Usually equality coercions have exactly the same kind on both
sides. But we do allow an *unsafe* coercion between Int# and Bool,
say, used in
case error Bool "flah" of { True -> 3#; False -> 0# }
-->
(error Bool "flah") |> unsafeCoerce Bool Int#
So what is the instantiation of (~#) here?
unsafeCoerce Bool Int# :: (~#) ??? Bool Int#
I'm using OpenKind here for now, but it's un-satisfying that
the lhs and rhs of the ~ don't have precisely the same kind.
More minor
~~~~~~~~~~
* HsDecl.TySynonym has its free variables attached, which makes
the cycle computation in TcTyDecls.mkSynEdges easier.
* Fixed a nasty reversed-comparison bug in FamInstEnv:
@@ -490,7 +490,7 @@ lookup_fam_inst_env' match_fun one_sided ie fam tys
n_tys = length tys
extra_tys = drop arity tys
(match_tys, add_extra_tys)
- | arity > n_tys = (take arity tys, \res_tys -> res_tys ++ extra_tys)
+ | arity < n_tys = (take arity tys, \res_tys -> res_tys ++ extra_tys)
| otherwise = (tys, \res_tys -> res_tys)
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This big patch implements a kind-polymorphic core for GHC. The current
implementation focuses on making sure that all kind-monomorphic programs still
work in the new core; it is not yet guaranteed that kind-polymorphic programs
(using the new -XPolyKinds flag) will work.
For more information, see http://haskell.org/haskellwiki/GHC/Kinds
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We only use it for "compiler" sources, i.e. not for libraries.
Many modules have a -fno-warn-tabs kludge for now.
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Basically as documented in http://hackage.haskell.org/trac/ghc/wiki/KindFact,
this patch adds a new kind Constraint such that:
Show :: * -> Constraint
(?x::Int) :: Constraint
(Int ~ a) :: Constraint
And you can write *any* type with kind Constraint to the left of (=>):
even if that type is a type synonym, type variable, indexed type or so on.
The following (somewhat related) changes are also made:
1. We now box equality evidence. This is required because we want
to give (Int ~ a) the *lifted* kind Constraint
2. For similar reasons, implicit parameters can now only be of
a lifted kind. (?x::Int#) => ty is now ruled out
3. Implicit parameter constraints are now allowed in superclasses
and instance contexts (this just falls out as OK with the new
constraint solver)
Internally the following major changes were made:
1. There is now no PredTy in the Type data type. Instead
GHC checks the kind of a type to figure out if it is a predicate
2. There is now no AClass TyThing: we represent classes as TyThings
just as a ATyCon (classes had TyCons anyway)
3. What used to be (~) is now pretty-printed as (~#). The box
constructor EqBox :: (a ~# b) -> (a ~ b)
4. The type LCoercion is used internally in the constraint solver
and type checker to represent coercions with free variables
of type (a ~ b) rather than (a ~# b)
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The "Unhelpful" cases are now in a separate type. This allows us to
improve various things, e.g.:
* Most of the panic's in SrcLoc are now gone
* The Lexer now works with RealSrcSpans rather than SrcSpans, i.e. it
knows that it has real locations and thus can assume that the line
number etc really exists
* Some of the more suspicious cases are no longer necessary, e.g.
we no longer need this case in advanceSrcLoc:
advanceSrcLoc loc _ = loc -- Better than nothing
More improvements can probably be made, e.g. tick locations can
probably use RealSrcSpans too.
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They belonged to the old generic deriving mechanism, so they can go. Adapted a lot of code as a consequence.
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(See his Haskell Symposium 2010 paper
"A generic deriving mechaism for Haskell")
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The main thing here is to allow us to provide type
signatures for 'deriving' bindings without pain.
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To print HsTypes correctly we should remember whether the Kind on
a HsTyVarBndr came from type inference, or was put there by the
user. See Note [Printing KindedTyVars] in HsTypes. So instead of
changing a UserTyVar to a KindedTyVar during kind checking, we
simply add a PostTcKind to the UserTyVar.
The change was provoked by Trac #3830, although other changes
mean that #3830 gets a diferent and better error message now.
So this patch is simply doing the Right Thing for the future.
This patch also fixes Trac #3845, which was caused by a *type splice*
not remembering the free *term variables* mentioned in it. Result
was that we build a 'let' when it should have been 'letrec'.
Hence a new FreeVars field in HsSpliceTy.
While I was at it, I got rid of HsSpliceTyOut and use a PostTcKind
on HsSpliceTy instead, just like on the UserTyVar.
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a) Added quasi-quote forms for
declarations
types
e.g. f :: [$qq| ... |]
b) Allow Template Haskell pattern quotes (but not splices)
e.g. f x = [p| Int -> $x |]
c) Improve pretty-printing for HsPat to remove superfluous
parens. (This isn't TH related really, but it affects
some of the same code.)
A consequence of (a) is that when gathering and grouping declarations
in RnSource.findSplice, we must expand quasiquotes as we do so.
Otherwise it's all fairly straightforward. I did a little bit of
refactoring in TcSplice.
User-manual changes still to come.
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This patch implements three significant improvements to Template Haskell.
Declaration-level splices with no "$"
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
This change simply allows you to omit the "$(...)" wrapper for
declaration-level TH splices. An expression all by itself is
not legal, so we now treat it as a TH splice. Thus you can now
say
data T = T1 | T2
deriveMyStuff ''T
where deriveMyStuff :: Name -> Q [Dec]
This makes a much nicer interface for clients of libraries that use
TH: no scary $(deriveMyStuff ''T).
Nested top-level splices
~~~~~~~~~~~~~~~~~~~~~~~~
Previously TH would reject this, saying that splices cannot be nested:
f x = $(g $(h 'x))
But there is no reason for this not to work. First $(h 'x) is run,
yielding code <blah> that is spliced instead of the $(h 'x). Then (g
<blah>) is typechecked and run, yielding code that replaces the
$(g ...) splice.
So this simply lifts the restriction.
Fix Trac #3467: non-top-level type splices
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
It appears that when I added the ability to splice types in TH
programs, I failed to pay attention to non-top-level splices -- that
is, splices inside quotatation brackets.
This patch fixes the problem. I had to modify HsType, so there's a
knock-on change to Haddock.
Its seems that a lot of lines of code has changed, but almost all the
new lines are comments!
General tidying up
~~~~~~~~~~~~~~~~~~
As a result of thinking all this out I re-jigged the data type ThStage,
which had far too many values before. And I wrote a nice state transition
diagram to make it all precise;
see Note [Template Haskell state diagram] in TcSplice
Lots more refactoring in TcSplice, resulting in significantly less code.
(A few more lines, but actually less code -- the rest is comments.)
I think the result is significantly cleaner.
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The main purpose of this patch is to fix Trac #3306, by fleshing out the
syntax for GADT-style record declraations so that you have a context in
the type. The new form is
data T a where
MkT :: forall a. Eq a => { x,y :: !a } -> T a
See discussion on the Trac ticket.
The old form is still allowed, but give a deprecation warning.
When we remove the old form we'll also get rid of the one reduce/reduce
error in the grammar. Hurrah!
While I was at it, I failed as usual to resist the temptation to do lots of
refactoring. The parsing of data/type declarations is now much simpler and
more uniform. Less code, less chance of errors, and more functionality.
Took longer than I planned, though.
ConDecl has record syntax, but it was not being used consistently, so I
pushed that through the compiler.
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Older GHCs can't parse OPTIONS_GHC.
This also changes the URL referenced for the -w options from
WorkingConventions#Warnings to CodingStyle#Warnings for the compiler
modules.
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1. Record disambiguation (-fdisambiguate-record-fields)
In record construction and pattern matching (although not
in record updates) it is clear which field name is intended
even if there are several in scope. This extension uses
the constructor to disambiguate. Thus
C { x=3 }
uses the 'x' field from constructor C (assuming there is one)
even if there are many x's in scope.
2. Record punning (-frecord-puns)
In a record construction or pattern match or update you can
omit the "=" part, thus
C { x, y }
This is just syntactic sugar for
C { x=x, y=y }
3. Dot-dot notation for records (-frecord-dot-dot)
In record construction or pattern match (but not update)
you can use ".." to mean "all the remaining fields". So
C { x=v, .. }
means to fill in the remaining fields to give
C { x=v, y=y }
(assuming C has fields x and y). This might reasonably
considered very dodgy stuff. For pattern-matching it brings
into scope a bunch of things that are not explictly mentioned;
and in record construction it just picks whatver 'y' is in
scope for the 'y' field. Still, Lennart Augustsson really
wants it, and it's a feature that is extremely easy to explain.
Implementation
~~~~~~~~~~~~~~
I thought of using the "parent" field in the GlobalRdrEnv, but
that's really used for import/export and just isn't right for this.
For example, for import/export a field is a subordinate of the *type
constructor* whereas here we need to know what fields belong to a
particular *data* constructor.
The main thing is that we need to map a data constructor to its
fields, and we need to do so in the renamer. For imported modules
it's easy: just look in the imported TypeEnv. For the module being
compiled, we make a new field tcg_field_env in the TcGblEnv.
The important functions are
RnEnv.lookupRecordBndr
RnEnv.lookupConstructorFields
There is still a significant infelicity in the way the renamer
works on patterns, which I'll tackle next.
I also did quite a bit of refactoring in the representation of
record fields (mainly in HsPat).***END OF DESCRIPTION***
Place the long patch description above the ***END OF DESCRIPTION*** marker.
The first line of this file will be the patch name.
This patch contains the following changes:
M ./compiler/deSugar/Check.lhs -3 +5
M ./compiler/deSugar/Coverage.lhs -6 +7
M ./compiler/deSugar/DsExpr.lhs -6 +13
M ./compiler/deSugar/DsMeta.hs -8 +8
M ./compiler/deSugar/DsUtils.lhs -1 +1
M ./compiler/deSugar/MatchCon.lhs -2 +2
M ./compiler/hsSyn/Convert.lhs -3 +3
M ./compiler/hsSyn/HsDecls.lhs -9 +25
M ./compiler/hsSyn/HsExpr.lhs -13 +3
M ./compiler/hsSyn/HsPat.lhs -25 +63
M ./compiler/hsSyn/HsUtils.lhs -3 +3
M ./compiler/main/DynFlags.hs +6
M ./compiler/parser/Parser.y.pp -13 +17
M ./compiler/parser/RdrHsSyn.lhs -16 +18
M ./compiler/rename/RnBinds.lhs -2 +2
M ./compiler/rename/RnEnv.lhs -22 +82
M ./compiler/rename/RnExpr.lhs -34 +12
M ./compiler/rename/RnHsSyn.lhs -3 +2
M ./compiler/rename/RnSource.lhs -50 +78
M ./compiler/rename/RnTypes.lhs -50 +84
M ./compiler/typecheck/TcExpr.lhs -18 +18
M ./compiler/typecheck/TcHsSyn.lhs -20 +21
M ./compiler/typecheck/TcPat.lhs -8 +6
M ./compiler/typecheck/TcRnMonad.lhs -6 +15
M ./compiler/typecheck/TcRnTypes.lhs -2 +11
M ./compiler/typecheck/TcTyClsDecls.lhs -3 +4
M ./docs/users_guide/flags.xml +7
M ./docs/users_guide/glasgow_exts.xml +42
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- With -findexed-types, equational constraints can appear in contexts
wherever class predicates are allowed.
- The two argument types need to be boxed and rank 0.
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Most of the other users of the fptools build system have migrated to
Cabal, and with the move to darcs we can now flatten the source tree
without losing history, so here goes.
The main change is that the ghc/ subdir is gone, and most of what it
contained is now at the top level. The build system now makes no
pretense at being multi-project, it is just the GHC build system.
No doubt this will break many things, and there will be a period of
instability while we fix the dependencies. A straightforward build
should work, but I haven't yet fixed binary/source distributions.
Changes to the Building Guide will follow, too.
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