oops, forgot a reverse

Fix syntax error

Cleanups:

- Move the collect* functions from HsSyn into HsUtils.  Check that we
  have a clean separation of utilties over HsSyn, with the generic
  versions in HsUtils, and the specific versions in RdrHsSyn, RnHsSyn
  and TcHsSyn as appropriate.

- Remove the RdrBinding data type, which was really just a nested list
  with O(1) append, and use OrdList instead.  This makes it much clearer
  that there's nothing strange going on.

- Various other minor cleanups.

Add accurate source location annotations to HsSyn
-------------------------------------------------

Every syntactic entity in HsSyn is now annotated with a SrcSpan, which
details the exact beginning and end points of that entity in the
original source file.  All honest compilers should do this, and it was
about time GHC did the right thing.

The most obvious benefit is that we now have much more accurate error
messages; when running GHC inside emacs for example, the cursor will
jump to the exact location of an error, not just a line somewhere
nearby.  We haven't put a huge amount of effort into making sure all
the error messages are accurate yet, so there could be some tweaking
still needed, although the majority of messages I've seen have been
spot-on.

Error messages now contain a column number in addition to the line
number, eg.

   read001.hs:25:10: Variable not in scope: `+#'

To get the full text span info, use the new option -ferror-spans.  eg.

   read001.hs:25:10-11: Variable not in scope: `+#'

I'm not sure whether we should do this by default.  Emacs won't
understand the new error format, for one thing.

In a more elaborate editor setting (eg. Visual Studio), we can arrange
to actually highlight the subexpression containing an error.  Eventually
this information will be used so we can find elements in the abstract
syntax corresponding to text locations, for performing high-level editor
functions (eg. "tell me the type of this expression I just highlighted").

Performance of the compiler doesn't seem to be adversely affected.
Parsing is still quicker than in 6.0.1, for example.

Implementation:

This was an excrutiatingly painful change to make: both Simon P.J. and
myself have been working on it for the last three weeks or so.  The
basic changes are:

 - a new datatype SrcSpan, which represents a beginning and end position
   in a source file.

 - To reduce the pain as much as possible, we also defined:

      data Located e = L SrcSpan e

 - Every datatype in HsSyn has an equivalent Located version.  eg.

      type LHsExpr id = Located (HsExpr id)

   and pretty much everywhere we used to use HsExpr we now use
   LHsExpr.  Believe me, we thought about this long and hard, and
   all the other options were worse :-)


Additional changes/cleanups we made at the same time:

  - The abstract syntax for bindings is now less arcane.  MonoBinds
    and HsBinds with their built-in list constructors have gone away,
    replaced by HsBindGroup and HsBind (see HsSyn/HsBinds.lhs).

  - The various HsSyn type synonyms have now gone away (eg. RdrNameHsExpr,
    RenamedHsExpr, and TypecheckedHsExpr are now HsExpr RdrName,
    HsExpr Name, and HsExpr Id respectively).

  - Utilities over HsSyn are now collected in a new module HsUtils.
    More stuff still needs to be moved in here.

  - MachChar now has a real Char instead of an Int.  All GHC versions that
    can compile GHC now support 32-bit Chars, so this was a simplification.

Wibbles about argument variance

1. A tiresome change to HsType, to keep a record of whether or not
   the HsForAll was originally explicitly-quantified.  This is
   solely so that the type checker can print out messages that
   show the source code the programmer wrote.  Tiresome but
   easy.

2. Improve reporting of kind errors.

-------------------------
		GHC heart/lung transplant
		-------------------------

This major commit changes the way that GHC deals with importing
types and functions defined in other modules, during renaming and
typechecking.  On the way I've changed or cleaned up numerous other
things, including many that I probably fail to mention here.

Major benefit: GHC should suck in many fewer interface files when
compiling (esp with -O).  (You can see this with -ddump-rn-stats.)

It's also some 1500 lines of code shorter than before.

**	So expect bugs!  I can do a 3-stage bootstrap, and run
**	the test suite, but you may be doing stuff I havn't tested.
** 	Don't update if you are relying on a working HEAD.


In particular, (a) External Core and (b) GHCi are very little tested.

	But please, please DO test this version!


	------------------------
		Big things
	------------------------

Interface files, version control, and importing declarations
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
* There is a totally new data type for stuff that lives in interface files:
	Original names			IfaceType.IfaceExtName
	Types				IfaceType.IfaceType
	Declarations (type,class,id)	IfaceSyn.IfaceDecl
	Unfoldings			IfaceSyn.IfaceExpr
  (Previously we used HsSyn for type/class decls, and UfExpr for unfoldings.)
  The new data types are in iface/IfaceType and iface/IfaceSyn.  They are
  all instances of Binary, so they can be written into interface files.
  Previous engronkulation concering the binary instance of RdrName has
  gone away -- RdrName is not an instance of Binary any more.  Nor does
  Binary.lhs need to know about the ``current module'' which it used to,
  which made it specialised to GHC.

  A good feature of this is that the type checker for source code doesn't
  need to worry about the possibility that we might be typechecking interface
  file stuff.  Nor does it need to do renaming; we can typecheck direct from
  IfaceSyn, saving a whole pass (module TcIface)

* Stuff from interface files is sucked in *lazily*, rather than being eagerly
  sucked in by the renamer. Instead, we use unsafeInterleaveIO to capture
  a thunk for the unfolding of an imported function (say).  If that unfolding
  is every pulled on, TcIface will scramble over the unfolding, which may
  in turn pull in the interface files of things mentioned in the unfolding.

  The External Package State is held in a mutable variable so that it
  can be side-effected by this lazy-sucking-in process (which may happen
  way later, e.g. when the simplifier runs).   In effect, the EPS is a kind
  of lazy memo table, filled in as we suck things in.  Or you could think
  of it as a global symbol table, populated on demand.

* This lazy sucking is very cool, but it can lead to truly awful bugs. The
  intent is that updates to the symbol table happen atomically, but very bad
  things happen if you read the variable for the table, and then force a
  thunk which updates the table.  Updates can get lost that way. I regret
  this subtlety.

  One example of the way it showed up is that the top level of TidyPgm
  (which updates the global name cache) to be much more disciplined about
  those updates, since TidyPgm may itself force thunks which allocate new
  names.

* Version numbering in interface files has changed completely, fixing
  one major bug with ghc --make.  Previously, the version of A.f changed
  only if A.f's type and unfolding was textually different.  That missed
  changes to things that A.f's unfolding mentions; which was fixed by
  eagerly sucking in all of those things, and listing them in the module's
  usage list.  But that didn't work with --make, because they might have
  been already sucked in.

  Now, A.f's version changes if anything reachable from A.f (via interface
  files) changes.  A module with unchanged source code needs recompiling
  only if the versions of any of its free variables changes. [This isn't
  quite right for dictionary functions and rules, which aren't mentioned
  explicitly in the source.  There are extensive comments in module MkIface,
  where all version-handling stuff is done.]

* We don't need equality on HsDecls any more (because they aren't used in
  interface files).  Instead we have a specialised equality for IfaceSyn
  (eqIfDecl etc), which uses IfaceEq instead of Bool as its result type.
  See notes in IfaceSyn.

* The horrid bit of the renamer that tried to predict what instance decls
  would be needed has gone entirely.  Instead, the type checker simply
  sucks in whatever instance decls it needs, when it needs them.  Easy!

  Similarly, no need for 'implicitModuleFVs' and 'implicitTemplateHaskellFVs'
  etc.  Hooray!


Types and type checking
~~~~~~~~~~~~~~~~~~~~~~~
* Kind-checking of types is far far tidier (new module TcHsTypes replaces
  the badly-named TcMonoType).  Strangely, this was one of my
  original goals, because the kind check for types is the Right Place to
  do type splicing, but it just didn't fit there before.

* There's a new representation for newtypes in TypeRep.lhs.  Previously
  they were represented using "SourceTypes" which was a funny compromise.
  Now they have their own constructor in the Type datatype.  SourceType
  has turned back into PredType, which is what it used to be.

* Instance decl overlap checking done lazily.  Consider
	instance C Int b
	instance C a Int
  These were rejected before as overlapping, because when seeking
  (C Int Int) one couldn't tell which to use.  But there's no problem when
  seeking (C Bool Int); it can only be the second.

  So instead of checking for overlap when adding a new instance declaration,
  we check for overlap when looking up an Inst.  If we find more than one
  matching instance, we see if any of the candidates dominates the others
  (in the sense of being a substitution instance of all the others);
  and only if not do we report an error.



	------------------------
	     Medium things
	------------------------

* The TcRn monad is generalised a bit further.  It's now based on utils/IOEnv.lhs,
  the IO monad with an environment.  The desugarer uses the monad too,
  so that anything it needs can get faulted in nicely.

* Reduce the number of wired-in things; in particular Word and Integer
  are no longer wired in.  The latter required HsLit.HsInteger to get a
  Type argument.  The 'derivable type classes' data types (:+:, :*: etc)
  are not wired in any more either (see stuff about derivable type classes
  below).

* The PersistentComilerState is now held in a mutable variable
  in the HscEnv.  Previously (a) it was passed to and then returned by
  many top-level functions, which was painful; (b) it was invariably
  accompanied by the HscEnv.  This change tidies up top-level plumbing
  without changing anything important.

* Derivable type classes are treated much more like 'deriving' clauses.
  Previously, the Ids for the to/from functions lived inside the TyCon,
  but now the TyCon simply records their existence (with a simple boolean).
  Anyone who wants to use them must look them up in the environment.

  This in turn makes it easy to generate the to/from functions (done
  in types/Generics) using HsSyn (like TcGenDeriv for ordinary derivings)
  instead of CoreSyn, which in turn means that (a) we don't have to figure
  out all the type arguments etc; and (b) it'll be type-checked for us.
  Generally, the task of generating the code has become easier, which is
  good for Manuel, who wants to make it more sophisticated.

* A Name now says what its "parent" is. For example, the parent of a data
  constructor is its type constructor; the parent of a class op is its
  class.  This relationship corresponds exactly to the Avail data type;
  there may be other places we can exploit it.  (I made the change so that
  version comparison in interface files would be a bit easier; but in
  fact it tided up other things here and there (see calls to
  Name.nameParent).  For example, the declaration pool, of declararations
  read from interface files, but not yet used, is now keyed only by the 'main'
  name of the declaration, not the subordinate names.

* New types OccEnv and OccSet, with the usual operations.
  OccNames can be efficiently compared, because they have uniques, thanks
  to the hashing implementation of FastStrings.

* The GlobalRdrEnv is now keyed by OccName rather than RdrName.  Not only
  does this halve the size of the env (because we don't need both qualified
  and unqualified versions in the env), but it's also more efficient because
  we can use a UniqFM instead of a FiniteMap.

  Consequential changes to Provenance, which has moved to RdrName.

* External Core remains a bit of a hack, as it was before, done with a mixture
  of HsDecls (so that recursiveness and argument variance is still inferred),
  and IfaceExprs (for value declarations).  It's not thoroughly tested.


	------------------------
	     Minor things
	------------------------

* DataCon fields dcWorkId, dcWrapId combined into a single field
  dcIds, that is explicit about whether the data con is a newtype or not.
  MkId.mkDataConWorkId and mkDataConWrapId are similarly combined into
  MkId.mkDataConIds

* Choosing the boxing strategy is done for *source* type decls only, and
  hence is now in TcTyDecls, not DataCon.

* WiredIn names are distinguished by their n_sort field, not by their location,
  which was rather strange

* Define Maybes.mapCatMaybes :: (a -> Maybe b) -> [a] -> [b]
  and use it here and there

* Much better pretty-printing of interface files (--show-iface)

Many, many other small things.


	------------------------
	     File changes
	------------------------
* New iface/ subdirectory
* Much of RnEnv has moved to iface/IfaceEnv
* MkIface and BinIface have moved from main/ to iface/
* types/Variance has been absorbed into typecheck/TcTyDecls
* RnHiFiles and RnIfaces have vanished entirely.  Their
  work is done by iface/LoadIface
* hsSyn/HsCore has gone, replaced by iface/IfaceSyn
* typecheck/TcIfaceSig has gone, replaced by iface/TcIface
* typecheck/TcMonoType has been renamed to typecheck/TcHsType
* basicTypes/Var.hi-boot and basicTypes/Generics.hi-boot have gone altogether

Replace the handwritten lexer with one generated by Alex.

YOU NOW NEED ALEX (v 2.0 or later) TO COMPILE GHC FROM CVS.

Highlights:

  - Faster than the previous lexer (about 10% of total parse time,
    depending on the token mix).

  - More correct than the previous lexer: a couple of minor wibbles
    in the syntax were fixed.

  - Completely accurate source spans for each token are now collected.
    This information isn't used yet, but it will be used to give much
    more accurate error messages in the future.

  - SrcLoc now contains a column field as well as a line number,
    although this is currently ignored when printing out SrcLocs.

  - StringBuffer is now based on a ByteArray# rather than a Ptr, which
    means that StringBuffers are now garbage collected.  Previously
    StringBuffers were hardly ever released, so a GHCi session would
    leak space as more source files were loaded in.

  - Code size reduction: Lexer.x is about the same size as the old
    Lex.lhs, but StringBuffer.lhs is significantly shorter and
    simpler.  Sadly I wasn't able to get rid of parser/Ctypes.hs
    (yet).

----------------------------------------------
	Add support for Ross Paterson's arrow notation
	----------------------------------------------

Ross Paterson's ICFP'01 paper described syntax to support John Hughes's
"arrows", rather as do-notation supports monads.  Except that do-notation is
relatively modest -- you can write monads by hand without much trouble --
whereas arrow-notation is more-or-less essential for writing arrow programs.
It desugars to a massive pile of tuple construction and selection!

For some time, Ross has had a pre-processor for arrow notation, but the
resulting type error messages (reported in terms of the desugared code)
are impenetrable.  This commit integrates the syntax into GHC.  The
type error messages almost certainly still require tuning, but they should
be better than with the pre-processor.

Main syntactic changes (enabled with -farrows)

   exp ::= ... | proc pat -> cmd

   cmd ::= exp1 -<  exp2   |  exp1 >-  exp2
	|  exp1 -<< exp2   |  exp1 >>- exp2
	| \ pat1 .. patn -> cmd
	| let decls in cmd
	| if exp then cmd1 else cmd2
	| do { cstmt1 .. cstmtn ; cmd }
	| (| exp |) cmd1 .. cmdn
	| cmd1 qop cmd2
	| case exp of { calts }

   cstmt :: = let decls
	 |   pat <- cmd
	 |   rec { cstmt1 .. cstmtn }
	 |   cmd

New keywords and symbols:
	proc rec
	-<   >-   -<<   >>-
	(|  |)

The do-notation in cmds was not described in Ross's ICFP'01 paper; instead
it's in his chapter in The Fun of Programming (Plagrave 2003).

The four arrow-tail forms (-<) etc cover
  (a) which order the pices come in (-<  vs  >-), and
  (b) whether the locally bound variables can be used in the
		arrow part (-<  vs  -<<) .
In previous presentations, the higher-order-ness (b) was inferred,
but it makes a big difference to the typing required so it seems more
consistent to be explicit.

The 'rec' form is also available in do-notation:
  * you can use 'rec' in an ordinary do, with the obvious meaning
  * using 'mdo' just says "infer the minimal recs"


Still to do
~~~~~~~~~~~
Top priority is the user manual.

The implementation still lacks an implementation of
the case form of cmd.


Implementation notes
~~~~~~~~~~~~~~~~~~~~
Cmds are parsed, and indeed renamed, as expressions.  The type checker
distinguishes the two.

Support for interop'ing with .NET via FFI declarations along the
lines of what Hugs98.NET offers, see

 http://haskell.org/pipermail/cvs-hugs/2003-March/001723.html

for FFI decl details.

To enable, configure with --enable-dotnet + have a look
in ghc/rts/dotnet/Makefile for details of what tools are needed to
build the .NET interop layer (tools from VS.NET / Framework SDK.)

The commit doesn't include some library additions + wider-scale
testing is required before this extension can be regarded as available
for general use. 'foreign import dotnet' is currently only supported
by the C backend.

--------------------------
	Minor Template Haskell bug
	--------------------------

This bug meant that spliced-in class declarations yielded a 'op not in scope',
where op was the class operation.  Thanks to Andre Pang for spotting this.

Some consequential tidying up in parsing too.

-------------------------------------
		Main module exports
	-------------------------------------

Make it so that

   	    module Main where ....

exports everything defined in Main, as the report says it should.

----------------------------------
      Fix a long-standing egregious parser bug
	----------------------------------

	*** MERGE TO STABLE ***

	*** NB: the important part of this commit
	***	got committed by accident with an
	***	unrelated message.  This commit
	***	should be from rev 1.50 to 1.52 of RdrHsSyn


GHC has parsed

	data T String = T String

without complaint, ever since day 1!  This led to consequential
incomprehensible messages.  The fix is easy.

Buglet in external-core parsing

-------------------------------------
  Big upheaval to the way that constructors are named
	-------------------------------------

This commit enshrines the new story for constructor names.  We could never
really get External Core to work nicely before, but now it does.

The story is laid out in detail in the Commentary
	ghc/docs/comm/the-beast/data-types.html
so I will not repeat it here.

	[Manuel: the commentary isn't being updated, apparently.]

However, the net effect is that in Core and in External Core, contructors look
like constructors, and the way things are printed is all consistent.

It is a fairly pervasive change (which is why it has been so long postponed),
but I hope the question is now finally closed.

All the libraries compile etc, and I've run many tests, but doubtless there will
be some dark corners.

Check for qualified names in binding positions in the parser instead
of the rename.  In External Core it's OK to have qualified names in
these places.

Fix two separate egregious errors in RdrHsSyn, which I
heavily modified when re-doing the top level plumbing.

One had the effect of throwing away fixity decls if there
was also a class decl

The other threw away all but the first and last equation of
a function definition.

Sorry about having so utterly broken the head, guys.

Fix to mdo, plus SrcLocs on splices and brackets

Missing eqn in getMonoBind

-----------------------------------
	Lots more Template Haskell stuff
	-----------------------------------

At last!  Top-level declaration splices work!
Syntax is

	$(f x)

not "splice (f x)" as in the paper.

Lots jiggling around, particularly with the top-level plumbining.
Note the new data type HsDecls.HsGroup.

--------------------------------------
	Make Template Haskell into the HEAD
	--------------------------------------

This massive commit transfers to the HEAD all the stuff that
Simon and Tim have been doing on Template Haskell.  The
meta-haskell-branch is no more!

WARNING: make sure that you

  * Update your links if you are using link trees.
    Some modules have been added, some have gone away.

  * Do 'make clean' in all library trees.
    The interface file format has changed, and you can
    get strange panics (sadly) if GHC tries to read old interface files:
    e.g.  ghc-5.05: panic! (the `impossible' happened, GHC version 5.05):
	  Binary.get(TyClDecl): ForeignType

  * You need to recompile the rts too; Linker.c has changed


However the libraries are almost unaltered; just a tiny change in
Base, and to the exports in Prelude.


NOTE: so far as TH itself is concerned, expression splices work
fine, but declaration splices are not complete.


		---------------
		The main change
		---------------

The main structural change: renaming and typechecking have to be
interleaved, because we can't rename stuff after a declaration splice
until after we've typechecked the stuff before (and the splice
itself).

* Combine the renamer and typecheker monads into one
	(TcRnMonad, TcRnTypes)
  These two replace TcMonad and RnMonad

* Give them a single 'driver' (TcRnDriver).  This driver
  replaces TcModule.lhs and Rename.lhs

* The haskell-src library package has a module
	Language/Haskell/THSyntax
  which defines the Haskell data type seen by the TH programmer.

* New modules:
	hsSyn/Convert.hs 	converts THSyntax -> HsSyn
	deSugar/DsMeta.hs 	converts HsSyn -> THSyntax

* New module typecheck/TcSplice type-checks Template Haskell splices.

		-------------
		Linking stuff
		-------------

* ByteCodeLink has been split into
	ByteCodeLink	(which links)
	ByteCodeAsm	(which assembles)

* New module ghci/ObjLink is the object-code linker.

* compMan/CmLink is removed entirely (was out of place)
  Ditto CmTypes (which was tiny)

* Linker.c initialises the linker when it is first used (no need to call
  initLinker any more).  Template Haskell makes it harder to know when
  and whether to initialise the linker.


	-------------------------------------
	Gathering the LIE in the type checker
	-------------------------------------

* Instead of explicitly gathering constraints in the LIE
	tcExpr :: RenamedExpr -> TcM (TypecheckedExpr, LIE)
  we now dump the constraints into a mutable varabiable carried
  by the monad, so we get
	tcExpr :: RenamedExpr -> TcM TypecheckedExpr

  Much less clutter in the code, and more efficient too.
  (Originally suggested by Mark Shields.)


		-----------------
		Remove "SysNames"
		-----------------

Because the renamer and the type checker were entirely separate,
we had to carry some rather tiresome implicit binders (or "SysNames")
along inside some of the HsDecl data structures.  They were both
tiresome and fragile.

Now that the typechecker and renamer are more intimately coupled,
we can eliminate SysNames (well, mostly... default methods still
carry something similar).

		-------------
		Clean up HsPat
		-------------

One big clean up is this: instead of having two HsPat types (InPat and
OutPat), they are now combined into one.  This is more consistent with
the way that HsExpr etc is handled; there are some 'Out' constructors
for the type checker output.

So:
	HsPat.InPat	--> HsPat.Pat
	HsPat.OutPat	--> HsPat.Pat
	No 'pat' type parameter in HsExpr, HsBinds, etc

	Constructor patterns are nicer now: they use
		HsPat.HsConDetails
	for the three cases of constructor patterns:
		prefix, infix, and record-bindings

	The *same* data type HsConDetails is used in the type
	declaration of the data type (HsDecls.TyData)

Lots of associated clean-up operations here and there.  Less code.
Everything is wonderful.

Fixed handling of infix operators in types:
- Pretty printing didn't take nested infix operators into account
- Explicit parenthesis were ignored in the fixity parser:
  * I added a constructor `HsParTy' to `HsType' (in the spirit of `HsPar' in
    `HsExpr'), which tracks the use of explicit parenthesis
  * Occurences of `HsParTy' in type-ish things that are not quite types (like
    context predicates) are removed in `ParseUtils'; all other occurences of
    `HsParTy' are removed during type checking (just as it works with `HsPar')

Fix bogon in rebindable syntax implementation

---------------------------------------
	Add rebindable syntax for do-notation
		(this time, on the HEAD)
	---------------------------------------

Make do-notation use rebindable syntax, so that -fno-implicit-prelude
makes do-notation use whatever (>>=), (>>), return, fail are in scope,
rather than the Prelude versions.

On the way, combine HsDo and HsDoOut into one constructor in HsSyn,
and tidy up type checking of HsDo.

----------------------------------
	Do the Right Thing for TyCons where we
	can't see all their constructors.
	----------------------------------

Inside a TyCon, three things can happen

1. GHC knows all the constructors, and has them to hand.
   (Nowadays, there may be zero constructors.)

2. GHC knows all the constructors, but has declined to slurp
   them all in, to avoid sucking in more declarations than
   necessary.  All we remember is the number of constructors,
   so we can get the return convention right.

3. GHC doesn't know anything. This happens *only* for decls
   coming from .hi-boot files, where the programmer declines to
   supply a representation.

Until now, these three cases have been conflated together.  Matters
are worse now that a TyCon really can have zero constructors.  In
fact, by confusing (3) with (1) we can actually generate bogus code.

With this commit, the dataCons field of a TyCon is of type:

data DataConDetails datacon
  = DataCons [datacon]	-- Its data constructors, with fully polymorphic types
			-- A type can have zero constructors

  | Unknown		-- We're importing this data type from an hi-boot file
			-- and we don't know what its constructors are

  | HasCons Int		-- In a quest for compilation speed we have imported
			-- only the number of constructors (to get return
			-- conventions right) but not the constructors themselves

This says exactly what is going on.  There are lots of consequential small
changes.

Don't translate out negative (boxed) literals too early.

----------------------------------
	Implement kinded type declarations
	----------------------------------

This commit allows the programmer to supply kinds in
	* data decls
	* type decls
	* class decls
	* 'forall's in types

e.g. 	data T (x :: *->*) = MkT

        type Composer c = forall (x :: * -> *) (y :: * -> *) (z :: * -> *).
		          (c y z) -> (c x y) -> (c x z);

This is occasionally useful.

It turned out to be convenient to add the form

	(type :: kind)

to the syntax of types too, so you can put kind signatures in types as well.

------------------------------
		Towards kinded data type decls
		------------------------------

Move towards being able to have 'kinded' data type decls.
The burden of this commit, though, is to tidy up the parsing
of data type decls.  Previously we had

	data ctype '=' constrs

where the 'ctype' is a completetely general polymorphic type.
	forall a. (Eq a) => T a

Then a separate function checked that it was of a suitably restricted
form.  The reason for this is the usual thing --- it's hard to tell
when looking at

	data Eq a => T a = ...

whether you are reading the data type or the context when you have
only got as far as 'Eq a'.

However, the 'ctype' trick doesn't work if we want to allow

	data T (a :: * -> *) = ...

So we have to parse the data type decl in a more serious way.
That's what this commit does, and it makes the grammar look much nicer.
The main new producion is tycl_hdr.

*******************************
		       * Merging from ghc-ndp-branch *
		       *******************************

This commit merges the current state of the "parallel array extension" and
includes the following:

* (Almost) completed Milestone 1:
  - The option `-fparr' activates the H98 extension for parallel arrays.
  - These changes have a high likelihood of conflicting (in the CVS sense)
    with other changes to GHC and are the reason for merging now.
  - ToDo: There are still some (less often used) functions not implemented in
	  `PrelPArr' and a mechanism is needed to automatically import
	  `PrelPArr' iff `-fparr' is given.  Documentation that should go into
	  the Commentary is currently in `ghc/compiler/ndpFlatten/TODO'.

* Partial Milestone 2:
  - The option `-fflatten' activates the flattening transformation and `-ndp'
    selects the "ndp" way (where all libraries have to be compiled with
    flattening).  The way option `-ndp' automagically turns on `-fparr' and
    `-fflatten'.
  - Almost all changes are in the new directory `ndpFlatten' and shouldn't
    affect the rest of the compiler.  The only exception are the options and
    the points in `HscMain' where the flattening phase is called when
    `-fflatten' is given.
  - This isn't usable yet, but already implements function lifting,
    vectorisation, and a new analysis that determines which parts of a module
    have to undergo the flattening transformation.  Missing are data structure
    and function specialisation, the unboxed array library (including fusion
    rules), and lots of testing.

I have just run the regression tests on the thing without any problems.  So,
it seems, as if we haven't broken anything crucial.

---------------------------------------------
	More type system extensions (for John Hughes)
	---------------------------------------------

1.  Added a brand-new extension that lets you derive ARBITRARY CLASSES
for newtypes.  Thus

	newtype Age = Age Int deriving( Eq, Ord, Shape, Ix )

The idea is that the dictionary for the user-defined class Shape Age
is *identical* to that for Shape Int, so there is really no deriving
work to do.   This saves you writing the very tiresome instance decl:

	instance Shape Age where
	   shape_op1 (Age x) = shape_op1 x
	   shape_op2 (Age x1) (Age x2) = shape_op2 x1 x2
	   ...etc...

It's more efficient, too, becuase the Shape Age dictionary really
will be identical to the Shape Int dictionary.

There's an exception for Read and Show, because the derived instance
*isn't* the same.

There is a complication where higher order stuff is involved.  Here is
the example John gave:

   class StateMonad s m | m -> s where ...

   newtype Parser tok m a = Parser (State [tok] (Failure m) a)
			  deriving( Monad, StateMonad )

Then we want the derived instance decls to be

   instance Monad (State [tok] (Failure m)) => Monad (Parser tok m)
   instance StateMonad [tok] (State [tok] (Failure m))
	 => StateMonad [tok] (Parser tok m)

John is writing up manual entry for all of this, but this commit
implements it.   I think.


2.  Added -fallow-incoherent-instances, and documented it.  The idea
is that sometimes GHC is over-protective about not committing to a
particular instance, and the programmer may want to say "commit anyway".
Here's the example:

    class Sat a where
      dict :: a

    data EqD a = EqD {eq :: a->a->Bool}

    instance Sat (EqD a) => Eq a where
      (==) = eq dict

    instance Sat (EqD Integer) where
      dict = EqD{eq=(==)}

    instance Eq a => Sat (EqD a) where
      dict = EqD{eq=(==)}

    class Collection c cxt | c -> cxt where
      empty :: Sat (cxt a) => c a
      single :: Sat (cxt a) => a -> c a
      union :: Sat (cxt a) => c a -> c a -> c a
      member :: Sat (cxt a) => a -> c a -> Bool

    instance Collection [] EqD where
      empty = []
      single x = [x]
      union = (++)
      member = elem

It's an updated attempt to model "Restricted Data Types", if you
remember my Haskell workshop paper. In the end, though, GHC rejects
the program (even with fallow-overlapping-instances and
fallow-undecideable-instances), because there's more than one way to
construct the Eq instance needed by elem.

Yet all the ways are equivalent! So GHC is being a bit over-protective
of me, really: I know what I'm doing and I would LIKE it to pick an
arbitrary one. Maybe a flag fallow-incoherent-instances would be a
useful thing to add?

------------------------------------------
	Improved handling of scoped type variables
	------------------------------------------

The main effect of this commit is to allow scoped type variables
in pattern bindings, thus

	(x::a, y::b) = e

This was illegal, but now it's ok.  a and b have the same scope
as x and y.


On the way I beefed up the info inside a type variable
(TcType.TyVarDetails; c.f. IdInfo.GlobalIdDetails) which
helps to improve error messages. Hence the wide ranging changes.
Pity about the extra loop from Var to TcType, but can't be helped.

More instance-gate fiddling.  This must be one of the most
tiremsome bits of the entire compiler, and I appear to be
incapable of modifying it without getting it wrong at least
once.

Still, this commit does tidy things up a bit.

* The type renamers (rnHsType, etc) have moved from RnSource
  into a new module RnTypes.

* This breaks a couple of loops, and lets us nuke RnSource.hi-boot.
  Hurrah!

Simon

--------------------------------------------------
	Be a bit more liberal when slurping instance decls
	--------------------------------------------------

Functional dependencies have (as usual) made things more complicated

Suppose an interface file contains
	interface A where
	  class C a b | a->b where op :: a->b
	  instance C Foo Baz where ...

Now we are compiling
	module B where
	  import A
	  t = op (v::Foo)

Should we slurp the instance decl, even though Baz is nowhere mentioned
in module B?  YES!  Because of the fundep, the (C Foo ?) part is enough to
select this instance decl, and the Baz part follows.

Rather than take fundeps into account "properly", we just slurp
if C is visible and *any one* of the Names in the types
This is a slightly brutal approximation, but most instance decls
are regular H98 ones and it's perfect for them.

Changes:

  HscTypes:
	generalise the types of GatedDecl a bit

  RnHiFiles.loadInstDecl, RnHiFiles.loadRule, RnIfaces.selectGated:
	the meat of the solution

  RdrName, OccName etc:
	some consequential wibbles

------------------------------------
	Tidy up the "syntax rebinding" story
	------------------------------------

I found a bug in the code that dealt with re-binding implicit
numerical syntax:
	literals 	(fromInteger/fromRational)
	negation	(negate)
	n+k patterns	(minus)

This is triggered by the -fno-implicit-prelude flag, and it
used to be handled via the PrelNames.SyntaxMap.

But I found a nicer way to do it that involves much less code,
and doesn't have the bug.  The explanation is with
	RnEnv.lookupSyntaxName

Import wibbles

Wibble for scoped type variables

----------------
	Nuke ClassContext
	----------------

This commit tidies up a long-standing inconsistency in GHC.
The context of a class or instance decl used to be restricted
to predicates of the form
	C t1 .. tn
with
	type ClassContext = [(Class,[Type])]

but everywhere else in the compiler we used

	type ThetaType = [PredType]
where PredType can be any sort of constraint (= predicate).

The inconsistency actually led to a crash, when compiling
	class (?x::Int) => C a where {}

I've tidied all this up by nuking ClassContext altogether, and using
PredType throughout.  Lots of modified files, but all in
more-or-less trivial ways.

I've also added a check that the context of a class or instance
decl doesn't include a non-inheritable predicate like (?x::Int).

Other things

 * rename constructor 'Class' from type TypeRep.Pred to 'ClassP'
   (makes it easier to grep for)

 * rename constructor HsPClass  => HsClassP
		      HsPIParam => HsIParam

A bit more on decoupling the prelude

Add comments and tidy

1. Make the new version machinery work.
   I think it does now!

2. Consequence of (1): Move the generation of
   default method names to one place (namely
   in RdrHsSyn.mkClassOpSigDM

3. Major clean up on HsDecls.TyClDecl
   These big constructors should have been records
   ages ago, and they are now.  At last.