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Lots of refactoring. In particular I have now combined
TansformStmt and GroupStmt into a single constructor TransStmt.
This gives lots of useful code sharing.
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The previous patch simply gave up for view patterns; this version
instead treats them like n+k patterns and gives signficantly better
results.
Less code, too.
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When matching against a GADT, some of the constructors may be impossible.
For example
data T a where
T1 :: T Int
T2 :: T Bool
T3 :: T a
f :: T Int -> Int
f T1 = 3
f T3 = 4
Here, does not have any missing cases, despite omittting T2, because
T2 :: T Bool.
This patch teaches the overlap checker about GADTs, which happily
turned out to be rather easy even though the overlap checker needs
a serious rewrite.
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The real work of fixing Trac #2246 is to use shortCutLit in
MatchLit.dsOverLit, so that type information discovered late in the
day by the type checker can still be exploited during desugaring.
However, as usual I found myself doing some refactoring along the
way, to tidy up the handling of overloaded literals. The main
change is to split HsOverLit into a record, which in turn uses
a sum type for the three variants. This makes the code significantly
more modular.
data HsOverLit id
= OverLit {
ol_val :: OverLitVal,
ol_rebindable :: Bool, -- True <=> rebindable syntax
-- False <=> standard syntax
ol_witness :: SyntaxExpr id, -- Note [Overloaded literal witnesses]
ol_type :: PostTcType }
data OverLitVal
= HsIntegral !Integer -- Integer-looking literals;
| HsFractional !Rational -- Frac-looking literals
| HsIsString !FastString -- String-looking literals
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This patch implements three new features:
* view patterns (syntax: expression -> pat in a pattern)
* working versions of record wildcards and record puns
See the manual for detailed descriptions.
Other minor observable changes:
* There is a check prohibiting local fixity declarations
when the variable being fixed is not defined in the same let
* The warn-unused-binds option now reports warnings for do and mdo stmts
Implementation notes:
* The pattern renamer is now in its own module, RnPat, and the
implementation is now in a CPS style so that the correct context is
delivered to pattern expressions.
* These features required a fairly major upheaval to the renamer.
Whereas the old version used to collect up all the bindings from a let
(or top-level, or recursive do statement, ...) and put them into scope
before renaming anything, the new version does the collection as it
renames. This allows us to do the right thing with record wildcard
patterns (which need to be expanded to see what names should be
collected), and it allows us to implement the desired semantics for view
patterns in lets. This change had a bunch of domino effects brought on
by fiddling with the top-level renaming.
* Prior to this patch, there was a tricky bug in mkRecordSelId in HEAD,
which did not maintain the invariant necessary for loadDecl. See note
[Tricky iface loop] for details.
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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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This has been a long-standing ToDo.
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The class is named IsString with the single method fromString.
Overloaded strings work the same way as overloaded numeric literals.
In expressions a string literals gets a fromString applied to it.
In a pattern there will be an equality comparison with the fromString:ed literal.
Use -foverloaded-strings to enable this extension.
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This patch is a start on removing import lists and generally tidying
up the top of each module. In addition to removing import lists:
- Change DATA.IOREF -> Data.IORef etc.
- Change List -> Data.List etc.
- Remove $Id$
- Update copyrights
- Re-order imports to put non-GHC imports last
- Remove some unused and duplicate imports
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The newtype-deriving mechanism generates a HsSyn case expression looking
like this
case (d `cast` co) of { ... }
That is, the case expression scrutinises a dictionary. This is
otherwise never seen in HsSyn, and it made the desugarer
(Check.get_unused_cons) crash in tcTyConAppTyCon.
It would really be better to generate Core in TcInstDecls (the newtype
deriving part) but I'm not going to do that today. Instead, I made
Check.get_unused_cons a bit more robust.
Audrey tried to fix this over the weekend, but her fix was, alas, utterly
bogus, which caused mysterious failures later. I completely undid this
change.
Anyway it should work now!
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Wed Jul 19 09:55:27 EDT 2006 kevind@bu.edu
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Broken up massive patch -=chak
Original log message:
This is (sadly) all done in one patch to avoid Darcs bugs.
It's not complete work... more FC stuff to come. A compiler
using just this patch will fail dismally.
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MERGE TO STABLE
Fixes Trac #827
Test is should_compiler/ds058
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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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