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Replace a zipEqual with a zip in tcPat when checking a record pat.
The former version caused a panic with DEBUG on if a record pattern
was used with a non-record constructor.

This commit completely re-does the kind-inference mechanism.
Previously it was inter-wound with type inference, but that was
always hard to understand, and it finally broke when we started
checking for ambiguity when type-checking a type signature (details
irrelevant).

So now kind inference is more clearly separated, so that it never
takes place at the same time as type inference.  The biggest change
is in TcTyClsDecls, which does the kind inference for a group of
type and class declarations.  It now contains comments to explain
how it all works.

There are also comments in TypeRep which describes the slightly
tricky way in which we deal with the fact that kind 'type' (written
'*') actually has 'boxed type' and 'unboxed type' as sub-kinds.
The whole thing is a bit of a hack, because we don't really have 
sub-kinding, but it's less of a hack than before.

A lot of general tidying up happened at the same time.
In particular, I removed some dead code here and there

remove unused imports

~~~~~~~~~~~~
		Apr/May 2000
		~~~~~~~~~~~~

This is a pretty big commit!  It adds stuff I've been working on
over the last month or so.  DO NOT MERGE IT WITH 4.07!

Interface file formats have changed a little; you'll need
to make clean before remaking.

						Simon PJ

Recompilation checking
~~~~~~~~~~~~~~~~~~~~~~
Substantial improvement in recompilation checking.  The version management
is now entirely internal to GHC.  ghc-iface.lprl is dead!

The trick is to generate the new interface file in two steps:
  - first convert Types etc to HsTypes etc, and thereby
	build a new ParsedIface
  - then compare against the parsed (but not renamed) version of the old
	interface file
Doing this meant adding code to convert *to* HsSyn things, and to
compare HsSyn things for equality.  That is the main tedious bit.

Another improvement is that we now track version info for
fixities and rules, which was missing before.


Interface file reading
~~~~~~~~~~~~~~~~~~~~~~
Make interface files reading more robust.
  * If the old interface file is unreadable, don't fail. [bug fix]

  * If the old interface file mentions interfaces
    that are unreadable, don't fail. [bug fix]

  * When we can't find the interface file,
    print the directories we are looking in.  [feature]


Type signatures
~~~~~~~~~~~~~~~
  * New flag -ddump-types to print type signatures


Type pruning
~~~~~~~~~~~~
When importing
	data T = T1 A | T2 B | T3 C
it seems excessive to import the types A, B, C as well, unless
the constructors T1, T2 etc are used.  A,B,C might be more types,
and importing them may mean reading more interfaces, and so on.
 So the idea is that the renamer will just import the decl
	data T
unless one of the constructors is used.  This turns out to be quite
easy to implement.  The downside is that we must make sure the
constructors are always available if they are really needed, so
I regard this as an experimental feature.


Elimininate ThinAir names
~~~~~~~~~~~~~~~~~~~~~~~~~
Eliminate ThinAir.lhs and all its works.  It was always a hack, and now
the desugarer carries around an environment I think we can nuke ThinAir
altogether.

As part of this, I had to move all the Prelude RdrName defns from PrelInfo
to PrelMods --- so I renamed PrelMods as PrelNames.

I also had to move the builtinRules so that they are injected by the renamer
(rather than appearing out of the blue in SimplCore).  This is if anything simpler.

Miscellaneous
~~~~~~~~~~~~~
* Tidy up the data types involved in Rules

* Eliminate RnEnv.better_provenance; use Name.hasBetterProv instead

* Add Unique.hasKey :: Uniquable a => a -> Unique -> Bool
  It's useful in a lot of places

* Fix a bug in interface file parsing for __U[!]

*** MERGE WITH 4.07 (once I've checked it works) ***

* Fix result type signatures.  Note that a consequential change is that
  an ordinary binding with a variable on the left
	f = e
  is now treated as a FunMonoBind, not a PatMonoBind.  This makes
  a few things a bit simpler (eg rnMethodBinds)

* Fix warnings for unused imports.  This meant moving where provenances
  are improved in RnNames.  Move mkExportAvails from RnEnv to RnNames.

* Print module names right (small change in Module.lhs and Rename.lhs)

* Remove a few unused bindings
  
* Add a little hack to let us print info about join points that turn
  out not to be let-no-escaped.  The idea is to call them "$j" and report
  any such variables that are not let-no-escaped.

* Some small things aiming towards -ddump-types (harmless but incomplete)

GHC has instance amnesia again, so a bunch of funny
`import Ppr{Core,Type} ()? had to be added. Sorry,
but I need a bootstrapping GHC.

Fix a bug in import listing in interface files that meant we lost track of
interface files.  This fixes the problem that led Sven to add lots of
import PprType() decls.  I've removed them all again!

Adding a bunch of `import PprType ()' to make 4.07 compile itself.
Strangely enough, compilation with 4.06 worked without these, so
this is probably only fighting the symptoms of something deeper,
and somebody should have a look at it. But for now, I simply need
a bootstrapping 4.07...

a) Small wibbles to do with inlining and floating

b) Implement Ralf's request, so that one can write

	type F = forall a. a -> a

	f :: Int -> F
	f = ...

   The for-alls inside F are hoisted out to the top of
   the type signature for f.  This applies uniformly to
   all user-written types

This utterly gigantic commit is what I've been up to in background
mode in the last couple of months.  Originally the main goal
was to get rid of Con (staturated constant applications)
in the CoreExpr type, but one thing led to another, and I kept
postponing actually committing.   Sorry.

	Simon, 23 March 2000


I've tested it pretty thoroughly, but doubtless things will break.

Here are the highlights

* Con is gone; the CoreExpr type is simpler
* NoRepLits have gone
* Better usage info in interface files => less recompilation
* Result type signatures work
* CCall primop is tidied up
* Constant folding now done by Rules
* Lots of hackery in the simplifier
* Improvements in CPR and strictness analysis

Many bug fixes including

* Sergey's DoCon compiles OK; no loop in the strictness analyser
* Volker Wysk's programs don't crash the CPR analyser

I have not done much on measuring compilation times and binary sizes;
they could have got worse.  I think performance has got significantly
better, though, in most cases.


Removing the Con form of Core expressions
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The big thing is that

  For every constructor C there are now *two* Ids:

	C is the constructor's *wrapper*. It evaluates and unboxes arguments
	before calling $wC.  It has a perfectly ordinary top-level defn
	in the module defining the data type.

	$wC is the constructor's *worker*.  It is like a primop that simply
	allocates and builds the constructor value.  Its arguments are the
	actual representation arguments of the constructor.
	Its type may be different to C, because:
		- useless dict args are dropped
		- strict args may be flattened

  For every primop P there is *one* Id, its (curried) Id

  Neither contructor worker Id nor the primop Id have a defminition anywhere.
  Instead they are saturated during the core-to-STG pass, and the code generator
  generates code for them directly. The STG language still has saturated
  primops and constructor applications.

* The Const type disappears, along with Const.lhs.  The literal part
  of Const.lhs reappears as Literal.lhs.  Much tidying up in here,
  to bring all the range checking into this one module.

* I got rid of NoRep literals entirely.  They just seem to be too much trouble.

* Because Con's don't exist any more, the funny C { args } syntax
  disappears from inteface files.


Parsing
~~~~~~~
* Result type signatures now work
	f :: Int -> Int = \x -> x
	-- The Int->Int is the type of f

	g x y :: Int = x+y
	-- The Int is the type of the result of (g x y)


Recompilation checking and make
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
* The .hi file for a modules is not touched if it doesn't change.  (It used to
  be touched regardless, forcing a chain of recompilations.)  The penalty for this
  is that we record exported things just as if they were mentioned in the body of
  the module.  And the penalty for that is that we may recompile a module when
  the only things that have changed are the things it is passing on without using.
  But it seems like a good trade.

* -recomp is on by default

Foreign declarations
~~~~~~~~~~~~~~~~~~~~
* If you say
	foreign export zoo :: Int -> IO Int
  then you get a C produre called 'zoo', not 'zzoo' as before.
  I've also added a check that complains if you export (or import) a C
  procedure whose name isn't legal C.


Code generation and labels
~~~~~~~~~~~~~~~~~~~~~~~~~~
* Now that constructor workers and wrappers have distinct names, there's
  no need to have a Foo_static_closure and a Foo_closure for constructor Foo.
  I nuked the entire StaticClosure story.  This has effects in some of
  the RTS headers (i.e. s/static_closure/closure/g)


Rules, constant folding
~~~~~~~~~~~~~~~~~~~~~~~
* Constant folding becomes just another rewrite rule, attached to the Id for the
  PrimOp.   To achieve this, there's a new form of Rule, a BuiltinRule (see CoreSyn.lhs).
  The prelude rules are in prelude/PrelRules.lhs, while simplCore/ConFold.lhs has gone.

* Appending of constant strings now works, using fold/build fusion, plus
  the rewrite rule
	unpack "foo" c (unpack "baz" c n)  =  unpack "foobaz" c n
  Implemented in PrelRules.lhs

* The CCall primop is tidied up quite a bit.  There is now a data type CCall,
  defined in PrimOp, that packages up the info needed for a particular CCall.
  There is a new Id for each new ccall, with an big "occurrence name"
	{__ccall "foo" gc Int# -> Int#}
  In interface files, this is parsed as a single Id, which is what it is, really.

Miscellaneous
~~~~~~~~~~~~~
* There were numerous places where the host compiler's
  minInt/maxInt was being used as the target machine's minInt/maxInt.
  I nuked all of these; everything is localised to inIntRange and inWordRange,
  in Literal.lhs

* Desugaring record updates was broken: it didn't generate correct matches when
  used withe records with fancy unboxing etc.  It now uses matchWrapper.

* Significant tidying up in codeGen/SMRep.lhs

* Add __word, __word64, __int64 terminals to signal the obvious types
  in interface files.  Add the ability to print word values in hex into
  C code.

* PrimOp.lhs is no longer part of a loop.  Remove PrimOp.hi-boot*


Types
~~~~~
* isProductTyCon no longer returns False for recursive products, nor
  for unboxed products; you have to test for these separately.
  There's no reason not to do CPR for recursive product types, for example.
  Ditto splitProductType_maybe.

Simplification
~~~~~~~~~~~~~~~
* New -fno-case-of-case flag for the simplifier.  We use this in the first run
  of the simplifier, where it helps to stop messing up expressions that
  the (subsequent) full laziness pass would otherwise find float out.
  It's much more effective than previous half-baked hacks in inlining.

  Actually, it turned out that there were three places in Simplify.lhs that
  needed to know use this flag.

* Make the float-in pass push duplicatable bindings into the branches of
  a case expression, in the hope that we never have to allocate them.
  (see FloatIn.sepBindsByDropPoint)

* Arrange that top-level bottoming Ids get a NOINLINE pragma
  This reduced gratuitous inlining of error messages.
  But arrange that such things still get w/w'd.

* Arrange that a strict argument position is regarded as an 'interesting'
  context, so that if we see
	foldr k z (g x)
  then we'll be inclined to inline g; this can expose a build.

* There was a missing case in CoreUtils.exprEtaExpandArity that meant
  we were missing some obvious cases for eta expansion
  Also improve the code when handling applications.

* Make record selectors (identifiable by their IdFlavour) into "cheap" operations.
	  [The change is a 2-liner in CoreUtils.exprIsCheap]
  This means that record selection may be inlined into function bodies, which
  greatly improves the arities of overloaded functions.

* Make a cleaner job of inlining "lone variables".  There was some distributed
  cunning, but I've centralised it all now in SimplUtils.analyseCont, which
  analyses the context of a call to decide whether it is "interesting".

* Don't specialise very small functions in Specialise.specDefn
  It's better to inline it.  Rather like the worker/wrapper case.

* Be just a little more aggressive when floating out of let rhss.
  See comments with Simplify.wantToExpose
  A small change with an occasional big effect.

* Make the inline-size computation think that
	case x of I# x -> ...
  is *free*.


CPR analysis
~~~~~~~~~~~~
* Fix what was essentially a bug in CPR analysis.  Consider

	letrec f x = let g y = let ... in f e1
		     in
		     if ... then (a,b) else g x

  g has the CPR property if f does; so when generating the final annotated
  RHS for f, we must use an envt in which f is bound to its final abstract
  value.  This wasn't happening.  Instead, f was given the CPR tag but g
  wasn't; but of course the w/w pass gives rotten results in that case!!
  (Because f's CPR-ness relied on g's.)

  On they way I tidied up the code in CprAnalyse.  It's quite a bit shorter.

  The fact that some data constructors return a constructed product shows
  up in their CPR info (MkId.mkDataConId) not in CprAnalyse.lhs



Strictness analysis and worker/wrapper
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
* BIG THING: pass in the demand to StrictAnal.saExpr.  This affects situations
  like
	f (let x = e1 in (x,x))
  where f turns out to have strictness u(SS), say.  In this case we can
  mark x as demanded, and use a case expression for it.

  The situation before is that we didn't "know" that there is the u(SS)
  demand on the argument, so we simply computed that the body of the let
  expression is lazy in x, and marked x as lazily-demanded.  Then even after
  f was w/w'd we got

	let x = e1 in case (x,x) of (a,b) -> $wf a b

  and hence

	let x = e1 in $wf a b

  I found a much more complicated situation in spectral/sphere/Main.shade,
  which improved quite a bit with this change.

* Moved the StrictnessInfo type from IdInfo to Demand.  It's the logical
  place for it, and helps avoid module loops

* Do worker/wrapper for coerces even if the arity is zero.  Thus:
	stdout = coerce Handle (..blurg..)
  ==>
	wibble = (...blurg...)
	stdout = coerce Handle wibble
  This is good because I found places where we were saying
	case coerce t stdout of { MVar a ->
	...
	case coerce t stdout of { MVar b ->
	...
  and the redundant case wasn't getting eliminated because of the coerce.

First pass at implicit parameters.  Honest, I didn't really go in *intending*
to modify every file in the typechecker... ;-)  The breadth of the change
is partly due to generalizing contexts so that they are not hardwired to
be (Class, [Type]) pairs.  See types/Type.lhs for details (look for PredType).

Fixed a FunDep leak in tcSimplifyToDicts (they weren't being filtered out),
and fixed bug in instance improvement (matching wasn't being done correctly
for polymorphic instances).

Fixes to Simon's lit-lit pattern commit

Deal better with lit-lit pats

Fix Svens missing-record-field typechecker bug

This commit replaces the old yacc parser with a Happy-generated one.
Notes:

	- The generated .hs file is *big*.  Best to use a recent
	  version of Happy, and even better to add the -c flag
	  to use unsafeCoerce# with ghc (versions 4.02+ please).

	- The lexer has grown all sorts of unsightly growths and
	  should be put down as soon as possible.

	- Parse errors may result in strange diagnostics.  I'm looking
	  into this.

	- HsSyn now contains a few extra constructors due to the way
	  patterns are parsed as expressions in the parser.

	- The layout rule is implemented according to the Haskell
	  report.  I found a couple of places in the libraries where
	  we previously weren't adhering to this - in particular the
	  rule about "nested contexts must be more indented than
	  outer contexts".  The rule is necessary to disambiguate
	  in the presence of empty declaration lists.

RULES-NOTES

Finally!  This commits the ongoing saga of Simon's hygiene sweep

FUNCTIONALITY
~~~~~~~~~~~~~
a) The 'unused variable' warnings from the renamer work.  
b) Better error messages here and there, esp type checker
c) Fixities for Haskell 98 (maybe I'd done that before)
d) Lazy reporting of name clashes for Haskell 98 (ditto)

HYGIENE
~~~~~~~
a) type OccName has its own module.  OccNames are represented
   by a single FastString, not three as in the last round.  This
   string is held in Z-encoded form; a decoding function decodes
   for printing in user error messages.  There's a nice tight
   encoding for (,,,,,,,,,,,,,,,,,,,,,,,,,,,,,)

b) type Module is a proper ADT, in module OccName

c) type RdrName is a proper ADT, in its own module

d) type Name has a new, somwhat tidier, representation

e) much grunting in the renamer to get Provenances right.
   This makes error messages look better (no spurious qualifiers)

Another big commit from Simon.  Actually, the last one
didn't all go into the main trunk; because of a CVS glitch it
ended up in the wrong branch.

So this commit includes:

* Scoped type variables
* Warnings for unused variables should work now (they didn't before)
* Simplifier improvements:
	- Much better treatment of strict arguments
	- Better treatment of bottoming Ids
	- No need for w/w split for fns that are merely strict
	- Fewer iterations needed, I hope
* Less gratuitous renaming in interface files and abs C
* OccName is a separate module, and is an abstract data type

I think the whole Prelude and Exts libraries compile correctly.
Something isn't quite right about typechecking existentials though.

Move 4.01 onto the main trunk.

Fix two small renamer bugs, and Christophs duplicated-constraint-in-interface files bug

Simons changes while away at Tic/WG2.8

Reorganisation of Id, IdInfo.  Remove StdIdInfo, PragmaInfo; add basicTypes/MkId.lhs

Several small fixes to multi-param type classes

- remove unused imports
  - remove dead code

The Great Multi-Parameter Type Classes Merge.

Notes from Simon (abridged):

* Multi-parameter type classes are fully implemented.
* Error messages from the type checker should be noticeably improved
* Warnings for unused bindings (-fwarn-unused-names)
* many other minor bug fixes.

Internally there are the following changes

* Removal of Haskell 1.2 compatibility.
* Dramatic clean-up of the PprStyle stuff.
* The type Type has been substantially changed.
* The dictionary for each class is represented by a new
  data type for that purpose, rather than by a tuple.

reflect change to newOverloadedLit

More small changes to 2.04

Import lists tightened up

New PP

Major update to more-or-less 2.02

More polishing by Simon; to get nofib to run!

SLPJ new renamer and lots more

partain 1.3 changes through 960719

simonpj changes through 960715

partain 1.3 changes through 960629

SLPJ 1.3 changes through 96/06/25

SLPJ changes to 960611

SLPJ changes through 960604