Comments only

Comments only

-------------------------------------
  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.

---------------------------------------------------
	Important fix to the handling of class methods that
	      mention their own class type variable
	---------------------------------------------------

[NB: I'm not 100% certain that this commit is independent of the
     Template-Haskell-related commit I'm doing at the same time.
     I've tried to separate them but may not have succeeded totally.]

This bug gives utterly bogus (detected by Core Lint) programs.
Isaac Jones discovered it.  Here's an example, now enshrined as tc165.

    class C a where
	f :: (Eq a) => a

    instance C () where
	f = f

The instance decl was translated as

    dfC() = MkC (let f = \dEq -> f in f)

which is utterly wrong.  Reason: the 'f' on the left was being treated
as an available Inst, but it doesn't obey INVARIANT 2 for Insts, which
is that they are applied to all their dictionaries.  (See the data type
decl for Inst.)

Solution: don't include such class methods in the available Insts.

Suppress "No explicit method or default decl given for m"
	if the method name starts with an underscore

	This in response to a suggestion by George Russel

------------------------------------
	(a) Improve reporting of staging errors
	(b) Tidy up the construction of dict funs
			and default methods
	------------------------------------

----------------------------------------
	Class ops that do not introduce for-alls
	----------------------------------------

	MERGE TO STABLE (if poss)

The handling of class ops that do not add an extra for-all
was utterly bogus.  For example:

	class C a where
	    fc :: (?p :: String) => a;

	class D a where
	    fd :: (Ord a) => [a] -> [a]

De-bogus-ing means

a) Being careful when taking apart the class op type in
	MkIface.tcClassOpSig

b) Ditto when making the method Id in an instance binding.
   Hence new function Inst.tcInstClassOp, and its calls
   in TcInstDcls, and TcClassDcls

--------------------------------
   Fix a serious error in the "newtype deriving" feature
	--------------------------------

The "newtype deriving" feature lets you derive arbitrary classes for
a newtype, not just the built-in ones (Read, Show, Ix etc).  It's very
cool, but Hal Duame discovered that it did utterly the Wrong Thing
for superclasses.  E.g.

	newtype Foo = MkFoo Int deriving( Show, Num, Eq )

You'd get a Num instance for Foo that was *identical* to the
Num instance for Int, *including* the Show superclass. So the
superclass in the Num dictionary would show a Foo just like an
Int, which is wrong... it should show as "Foo n".

This commit fixes the problem, by building a new dictionary every time,
but using the methods from the dictionary for the representation type.

I also fixed a bug that prevented it working altogether when the
representation type was not the application of a type constructor.
For example, this now works

	newtype Foo a = MkFoo a deriving( Num, Eq, Show )


I also made it a bit more efficient in the case where the type is
not parameterised.  Then the "dfun" doesn't need to be a function.

--------------------------------
        Implement recursive do-notation
	--------------------------------

This commit adds recursive do-notation, which Hugs has had for some time.

	mdo { x <- foo y ;
	      y <- baz x ;
	      return (y,x) }

turns into

	do { (x,y) <- mfix (\~(x,y) -> do { x <- foo y;
					    y <- baz x }) ;
	     return (y,x) }

This is all based on work by Levent Erkok and John Lanuchbury.

The really tricky bit is in the renamer (RnExpr.rnMDoStmts) where
we break things up into minimal segments.  The rest is easy, including
the type checker.

Levent laid the groundwork, and Simon finished it off. Needless to say,
I couldn't resist tidying up other stuff, so there's no guaranteed I
have not broken something.

--------------------------------------
	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.

--------------------------------------
	Attach inline pragmas to class methods
	--------------------------------------

This fix makes INLINE pragmas on method bindings (in class
or instance decls) work properly.

It seems to have been hanging around in my tree for some time.
To be on the safe side, let's not merge this into 5.04.1, although
it should be fine (an an improvement).

Fix an obscure bug in the creation of default methods for class
ops with higher-rank type.   See the comments with
		TcClassDcl.mkDefMethRhs

Test is should_compile/tc161

		MERGE TO STABLE

FastString cleanup, stage 1.

The FastString type is no longer a mixture of hashed strings and
literal strings, it contains hashed strings only with O(1) comparison
(except for UnicodeStr, but that will also go away in due course).  To
create a literal instance of FastString, use FSLIT("..").

By far the most common use of the old literal version of FastString
was in the pattern

	  ptext SLIT("...")

this combination still works, although it doesn't go via FastString
any more.  The next stage will be to remove the need to use this
special combination at all, using a RULE.

To convert a FastString into an SDoc, now use 'ftext' instead of
'ptext'.

I've also removed all the FAST_STRING related macros from HsVersions.h
except for SLIT and FSLIT, just use the relevant functions from
FastString instead.

-------------------
	Mainly derived Read
	-------------------

This commit is a tangle of several things that somehow got wound up
together, I'm afraid.


The main course
~~~~~~~~~~~~~~~
Replace the derived-Read machinery with Koen's cunning new parser
combinator library.   The result should be
	* much smaller code sizes from derived Read
	* faster execution of derived Read

WARNING: I have not thoroughly tested this stuff; I'd be glad if you did!
	 All the hard work is done, but there may be a few nits.

The Read class gets two new methods, not exposed
in the H98 inteface of course:
  class Read a where
    readsPrec    :: Int -> ReadS a
    readList     :: ReadS [a]
    readPrec     :: ReadPrec a		-- NEW
    readListPrec :: ReadPrec [a]	-- NEW

There are the following new libraries:

  Text.ParserCombinators.ReadP		Koens combinator parser
  Text.ParserCombinators.ReadPrec	Ditto, but with precedences

  Text.Read.Lex				An emasculated lexical analyser
					that provides the functionality
					of H98 'lex'

TcGenDeriv is changed to generate code that uses the new libraries.
The built-in instances of Read (List, Maybe, tuples, etc) use the new
libraries.


Other stuff
~~~~~~~~~~~
1. Some fixes the the plumbing of external-core generation. Sigbjorn
did most of the work earlier, but this commit completes the renaming and
typechecking plumbing.

2. Runtime error-generation functions, such as GHC.Err.recSelErr,
GHC.Err.recUpdErr, etc, now take an Addr#, pointing to a UTF8-encoded
C string, instead of a Haskell string.  This makes the *calls* to these
functions easier to generate, and smaller too, which is a good thing.

In particular, it means that MkId.mkRecordSelectorId doesn't need to
be passed "unpackCStringId", which was GRUESOME; and that in turn means
that tcTypeAndClassDecls doesn't need to be passed unf_env, which is
a very worthwhile cleanup.   Win/win situation.

3.  GHC now faithfully translates do-notation using ">>" for statements
with no binding, just as the report says.  While I was there I tidied
up HsDo to take a list of Ids instead of 3 (but now 4) separate Ids.
Saves a bit of code here and there.  Also introduced Inst.newMethodFromName
to package a common idiom.

------------------------------------
	Change the treatment of the stupid
	   context on data constructors
	-----------------------------------

Data types can have a context:

	data (Eq a, Ord b) => T a b = T1 a b | T2 a

and that makes the constructors have a context too
(notice that T2's context is "thinned"):

	T1 :: (Eq a, Ord b) => a -> b -> T a b
	T2 :: (Eq a) => a -> T a b

Furthermore, this context pops up when pattern matching
(though GHC hasn't implemented this, but it is in H98, and
I've fixed GHC so that it now does):

	f (T2 x) = x
gets inferred type
	f :: Eq a => T a b -> a

I say the context is "stupid" because the dictionaries passed
are immediately discarded -- they do nothing and have no benefit.
It's a flaw in the language.

Up to now I have put this stupid context into the type of
the "wrapper" constructors functions, T1 and T2, but that turned
out to be jolly inconvenient for generics, and record update, and
other functions that build values of type T (because they don't
have suitable dictionaries available).

So now I've taken the stupid context out.  I simply deal with
it separately in the type checker on occurrences of a constructor,
either in an expression or in a pattern.

To this end

* Lots of changes in DataCon, MkId

* New function Inst.tcInstDataCon to instantiate a data constructor



I also took the opportunity to

* Rename
	dataConId --> dataConWorkId
  for consistency.

* Tidied up MkId.rebuildConArgs quite a bit, and renamed it
	mkReboxingAlt

* Add function DataCon.dataConExistentialTyVars, with the obvious meaning

More validity checking, esp for existential ctxt on data cons

--------------------------------------
	Lift the class-method type restriction
	--------------------------------------

Haskell 98 prohibits class method types to mention constraints on the
class type variable, thus:

  class Seq s a where
    fromList :: [a] -> s a
    elem     :: Eq a => a -> s a -> Bool

The type of 'elem' is illegal in Haskell 98, because it contains the
constraint 'Eq a', which constrains only the class type variable (in
this case 'a').

This commit lifts the restriction.  The way we do that is to do a full
context reduction (tcSimplifyCheck) step for each method separately in
TcClassDcl.tcMethodBind, rather than doing a single context reduction
for the whole group of method bindings.

As a result, I had to reorganise the code a bit, and tidy up.

---------------------------------
	Fix a rather obscure bug in tcGen
	---------------------------------

This bug concerns deciding when a type variable "escapes",
and hence we can't generalise it.  Our new subsumption-checking
machinery for higher-ranked types requires a slightly
more general approach than I had before.  The main excitement
is in TcUnify.checkSigTyVars and its friends.

As usual, I moved functions around and cleaned things up a bit;
hence the multi-module commit.

---------
		Main.main
		---------

A bunch of related fixes concerning 'main'

* Arrange that 'main' doesn't need to be defined in module Main;
  it can be imported.

* The typechecker now injects a binding
	Main.$main = PrelTopHandler.runMain main

  So the runtime system now calls Main.$main, not PrelMain.main.
  With z-encoding, this look like
		Main_zdmain_closure

* The function
  	PrelTopHandler.runMain :: IO a -> IO ()
  wraps the programmer's 'main' in an exception-cacthing wrapper.

* PrelMain.hs and Main.hi-boot are both removed from lib/std, along
  with multiple lines of special case handling in lib/std/Makefile.
  This is a worthwhile cleanup.

* Since we now pick up whatever 'main' is in scope, the ranamer gets
  in on the act (RnRnv.checkMain).  There is a little more info to
  get from the renamer to the typechecker, so I've defined a new type
  Rename.RnResult (c.f. TcModule.TcResult)

* With GHCi, it's now a warning, not an error, to omit the binding
  of main (RnEnv.checkMain)

* It would be easy to add a flag "-main-is foo"; the place to use
  that information is in RnEnv.checkMain.


-------

On the way I made a new type,
	type HscTypes.FixityEnv = NameEnv Fixity
and used it in various places I'd tripped over

-----------------------------
	Tidy up the top level of TcModule
	-----------------------------

This commit started life as sorting out the TcInstDcls thing that
we got wrong a few weeks back, but it spiraled out of control.

However, the result is a nice tidy up of TcModule.

typecheckModule/tcModule compiles a module from source code
typecheckIface/tcIface   compiles a module from its interface file
typecheckStmt		 compiles a Stmt
typecheckExpr		 compiles a Expr

tcExtraDecls is used by typecheckStmt/typecheckExpr
	to compile interface-file decls.
	It is just a wrapper for:

tcIfaceImports, which is used by tcExtraDecls and tcIface
	to compile interface file-file decls.

tcImports, is similar to tcIfaceImports, but is used only by tcModule

tcIfaceImports is used when compiling an interface, and can
	therefore be quite a bit simpler

----------------------
	Implement Rank-N types
	----------------------

This commit implements the full glory of Rank-N types, using
the Odersky/Laufer approach described in their paper
	"Putting type annotations to work"

In fact, I've had to adapt their approach to deal with the
full glory of Haskell (including pattern matching, and the
scoped-type-variable extension).  However, the result is:

* There is no restriction to rank-2 types.  You can nest forall's
  as deep as you like in a type.  For example, you can write a type
  like
	p :: ((forall a. Eq a => a->a) -> Int) -> Int
  This is a rank-3 type, illegal in GHC 5.02

* When matching types, GHC uses the cunning Odersky/Laufer coercion
  rules.  For example, suppose we have
	q :: (forall c. Ord c => c->c) -> Int
  Then, is this well typed?
	x :: Int
	x = p q
  Yes, it is, but GHC has to generate the right coercion.  Here's
  what it looks like with all the big lambdas and dictionaries put in:

	x = p (\ f :: (forall a. Eq a => a->a) ->
		 q (/\c \d::Ord c -> f c (eqFromOrd d)))

  where eqFromOrd selects the Eq superclass dictionary from the Ord
  dicationary:		eqFromOrd :: Ord a -> Eq a


* You can use polymorphic types in pattern type signatures.  For
  example:

	f (g :: forall a. a->a) = (g 'c', g True)

  (Previously, pattern type signatures had to be monotypes.)

* The basic rule for using rank-N types is that you must specify
  a type signature for every binder that you want to have a type
  scheme (as opposed to a plain monotype) as its type.

  However, you don't need to give the type signature on the
  binder (as I did above in the defn for f).  You can give it
  in a separate type signature, thus:

	f :: (forall a. a->a) -> (Char,Bool)
	f g = (g 'c', g True)

  GHC will push the external type signature inwards, and use
  that information to decorate the binders as it comes across them.
  I don't have a *precise* specification of this process, but I
  think it is obvious enough in practice.

* In a type synonym you can use rank-N types too.  For example,
  you can write

	type IdFun = forall a. a->a

	f :: IdFun -> (Char,Bool)
	f g = (g 'c', g True)

  As always, type synonyms must always occur saturated; GHC
  expands them before it does anything else.  (Still, GHC goes
  to some trouble to keep them unexpanded in error message.)


The main plan is as before.  The main typechecker for expressions,
tcExpr, takes an "expected type" as its argument.  This greatly
improves error messages.  The new feature is that when this
"expected type" (going down) meets an "actual type" (coming up)
we use the new subsumption function
	TcUnify.tcSub
which checks that the actual type can be coerced into the
expected type (and produces a coercion function to demonstrate).

The main new chunk of code is TcUnify.tcSub.  The unifier itself
is unchanged, but it has moved from TcMType into TcUnify.  Also
checkSigTyVars has moved from TcMonoType into TcUnify.
Result: the new module, TcUnify, contains all stuff relevant
to subsumption and unification.

Unfortunately, there is now an inevitable loop between TcUnify
and TcSimplify, but that's just too bad (a simple TcUnify.hi-boot
file).


All of this doesn't come entirely for free.  Here's the typechecker
line count (INCLUDING comments)
	Before	16,551
	After	17,116

Use (DefMeth Name) rather than (DefMeth Id) in ClassOpItem.  This not
only eliminates a space leak, because Names generally hold on to much
less stuff than Ids, but also turns out to be a minor cleanup.

------------------------------------------
	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.

- Pet peeve removal / code tidyup, replaced various sub-optimal
  uses of 'length' with something a bit better, i.e., replaced
  the following patterns

   *  length as `cmpOp` length bs
   *  length as `cmpOp` val   -- incl. uses where val == 1 and val == 0
   *  {take,drop,splitAt} (length as) bs
   *  length [ () | pat <- as ]

  with uses of misc Util functions.

  I'd be surprised if there's a noticeable reduction in running
  times as a result of these changes, but every little bit helps.

  [ The changes have been tested wrt testsuite/ - I'm seeing a couple
    of unexpected breakages coming from CorePrep, but I'm currently
    assuming that these are due to other recent changes. ]

- compMan/CompManager.lhs: restored 4.08 compilability + some code
  cleanup.

None of these changes are HEADworthy.

Remove unused variable

------------------
		Simon's big commit
		------------------

This commit, which I don't think I can sensibly do piecemeal, consists
of the things I've been doing recently, mainly directed at making
Manuel, George, and Marcin happier with RULES.


Reogranise the simplifier
~~~~~~~~~~~~~~~~~~~~~~~~~
1. The simplifier's environment is now an explicit parameter.  This
makes it a bit easier to figure out where it is going.

2. Constructor arguments can now be arbitrary expressions, except
when the application is the RHS of a let(rec).  This makes it much
easier to match rules like

	RULES
	    "foo"  f (h x, g y) = f' x y

In the simplifier, it's Simplify.mkAtomicArgs that ANF-ises a
constructor application where necessary.  In the occurrence analyser,
there's a new piece of context info (OccEncl) to say whether a
constructor app is in a place where it should be in ANF.  (Unless
it knows this it'll give occurrence info which will inline the
argument back into the constructor app.)

3. I'm experimenting with doing the "float-past big lambda" transformation
in the full laziness pass, rather than mixed in with the simplifier (was
tryRhsTyLam).

4.  Arrange that
	case (coerce (S,T) (x,y)) of ...
will simplify.  Previous it didn't.
A local change to CoreUtils.exprIsConApp_maybe.

5. Do a better job in CoreUtils.exprEtaExpandArity when there's an
error function in one branch.


Phase numbers, RULES, and INLINE pragmas
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1.  Phase numbers decrease from N towards zero (instead of increasing).
This makes it easier to add new earlier phases, which is what users want
to do.

2.  RULES get their own phase number, N, and are disabled in phases before N.

e.g. 	{-# RULES "foo" [2] forall x y.  f (x,y) = f' x y #-}

Note the [2], which says "only active in phase 2 and later".

3.  INLINE and NOINLINE pragmas have a phase number to.  This is now treated
in just the same way as the phase number on RULE; that is, the Id is not inlined
in phases earlier than N.  In phase N and later the Id *may* be inlined, and
here is where INLINE and NOINLINE differ: INLNE makes the RHS look small, so
as soon as it *may* be inlined it probably *will* be inlined.

The syntax of the phase number on an INLINE/NOINLINE pragma has changed to be
like the RULES case (i.e. in square brackets).  This should also make sure
you examine all such phase numbers; many will need to change now the numbering
is reversed.

Inlining Ids is no longer affected at all by whether the Id appears on the
LHS of a rule.  Now it's up to the programmer to put a suitable INLINE/NOINLINE
pragma to stop it being inlined too early.


Implementation notes:

*  A new data type, BasicTypes.Activation says when a rule or inline pragma
is active.   Functions isAlwaysActive, isNeverActive, isActive, do the
obvious thing (all in BasicTypes).

* Slight change in the SimplifierSwitch data type, which led to a lot of
simplifier-specific code moving from CmdLineOpts to SimplMonad; a Good Thing.

* The InlinePragma in the IdInfo of an Id is now simply an Activation saying
when the Id can be inlined.  (It used to be a rather bizarre pair of a
Bool and a (Maybe Phase), so this is much much easier to understand.)

* The simplifier has a "mode" environment switch, replacing the old
black list.  Unfortunately the data type decl has to be in
CmdLineOpts, because it's an argument to the CoreDoSimplify switch

    data SimplifierMode = SimplGently | SimplPhase Int

Here "gently" means "no rules, no inlining".   All the crucial
inlining decisions are now collected together in SimplMonad
(preInlineUnconditionally, postInlineUnconditionally, activeInline,
activeRule).


Specialisation
~~~~~~~~~~~~~~
1.  Only dictionary *functions* are made INLINE, not dictionaries that
have no parameters.  (This inline-dictionary-function thing is Marcin's
idea and I'm still not sure whether it's a good idea.  But it's definitely
a Bad Idea when there are no arguments.)

2.  Be prepared to specialise an INLINE function: an easy fix in
Specialise.lhs

But there is still a problem, which is that the INLINE wins
at the call site, so we don't use the specialised version anyway.
I'm still unsure whether it makes sense to SPECIALISE something
you want to INLINE.





Random smaller things
~~~~~~~~~~~~~~~~~~~~~~

* builtinRules (there was only one, but may be more) in PrelRules are now
  incorporated.   They were being ignored before...

* OrdList.foldOL -->  OrdList.foldrOL, OrdList.foldlOL

* Some tidying up of the tidyOpenTyVar, tidyTyVar functions.  I've
  forgotten exactly what!

----------------------------------------
	Make dict funs and default methods
	into LocalIds only at their binding site
	----------------------------------------
        [part of 3 related commits]

There's a long comment about this with MkId.mkDefaultMethodId,
which I reproduce below.

While I was at it, I renamed setIdNoDiscard to setIdLocalExported.
Which is hardly an improvement, I'm afraid.  This renaming touches
	Var.lhs, Id.lhs, SimplCore.lhs
in a trivial way.

	---------------------

Dict funs and default methods are *not* ImplicitIds.  Their definition
involves user-written code, so we can't figure out their strictness etc
based on fixed info, as we can for constructors and record selectors (say).

We build them as GlobalIds, but when in the module where they are
bound, we turn the Id at the *binding site* into an exported LocalId.
This ensures that they are taken to account by free-variable finding
and dependency analysis (e.g. CoreFVs.exprFreeVars).   The simplifier
will propagate the LocalId to all occurrence sites.

Why shouldn't they be bound as GlobalIds?  Because, in particular, if
they are globals, the specialiser floats dict uses above their defns,
which prevents good simplifications happening.  Also the strictness
analyser treats a occurrence of a GlobalId as imported and assumes it
contains strictness in its IdInfo, which isn't true if the thing is
bound in the same module as the occurrence.

It's OK for dfuns to be LocalIds, because we form the instance-env to
pass on to the next module (md_insts) in CoreTidy, afer tidying
and globalising the top-level Ids.

BUT make sure they are *exported* LocalIds (setIdLocalExported) so
that they aren't discarded by the occurrence analyser.

Improve error message for nullary class

1. Arrange that w/w records unfoldings
   And that the simplifier preserves them

2. Greatly improve structure of checking user types in the typechecker
   Main changes:
	TcMType.checkValidType checks for a valid type
	TcMonoType.tcHsSigType uses checkValidType
	Type and class decls use TcMonoType.tcHsType (which does not
		check for validity) inside the knot in TcTyClsDecls,
		and then runs TcTyDecls.checkValidTyCon
		or TcClassDcl.checkValidClass to check for validity
		once the knot is tied

---------------------------------
	Switch to the new demand analyser
	---------------------------------

This commit makes the new demand analyser the main beast,
with the old strictness analyser as a backup.  When
DEBUG is on, the old strictness analyser is run too, and the
results compared.

WARNING: this isn't thorougly tested yet, so expect glitches.
Delay updating for a few days if the HEAD is mission critical
for you.

But do try it out.  I'm away for 2.5 weeks from Thursday, so
it would be good to shake out any glaring bugs before then.

--------------------------------------------
	Fix another bug in the squash-newtypes story.
	--------------------------------------------

[This one was spotted by Marcin, and is now enshrined in test tc130.]

The desugarer straddles the boundary between the type checker and
Core, so it sometimes needs to look through newtypes/implicit parameters
and sometimes not.  This is really a bit painful, but I can't think of
a better way to do it.

The only simple way to fix things was to pass a bit more type
information in the HsExpr type, from the type checker to the desugarer.
That led to the non-local changes you can see.

On the way I fixed one other thing.  In various HsSyn constructors
there is a Type that is bogus (bottom) before the type checker, and
filled in with a real type by the type checker.  In one place it was
a (Maybe Type) which was Nothing before, and (Just ty) afterwards.
I've defined a type synonym HsTypes.PostTcType for this, and a named
bottom value HsTypes.placeHolderType to use when you want the bottom
value.

----------------
	Squash newtypes
	----------------

This commit squashes newtypes and their coerces, from the typechecker
onwards.  The original idea was that the coerces would not get in the
way of optimising transformations, but despite much effort they continue
to do so.   There's no very good reason to retain newtype information
beyond the typechecker, so now we don't.

Main points:

* The post-typechecker suite of Type-manipulating functions is in
types/Type.lhs, as before.   But now there's a new suite in types/TcType.lhs.
The difference is that in the former, newtype are transparent, while in
the latter they are opaque.  The typechecker should only import TcType,
not Type.

* The operations in TcType are all non-monadic, and most of them start with
"tc" (e.g. tcSplitTyConApp).  All the monadic operations (used exclusively
by the typechecker) are in a new module, typecheck/TcMType.lhs

* I've grouped newtypes with predicate types, thus:
	data Type = TyVarTy Tyvar | ....
		  | SourceTy SourceType

	data SourceType = NType TyCon [Type]
			| ClassP Class [Type]
			| IParam Type

[SourceType was called PredType.]  This is a little wierd in some ways,
because NTypes can't occur in qualified types.   However, the idea is that
a SourceType is a type that is opaque to the type checker, but transparent
to the rest of the compiler, and newtypes fit that as do implicit parameters
and dictionaries.

* Recursive newtypes still retain their coreces, exactly as before. If
they were transparent we'd get a recursive type, and that would make
various bits of the compiler diverge (e.g. things which do type comparison).

* I've removed types/Unify.lhs (non-monadic type unifier and matcher),
merging it into TcType.

Ditto typecheck/TcUnify.lhs (monadic unifier), merging it into TcMType.

-----------------------------
	Get unbox-strict-fields right
	-----------------------------

The problem was that when a library was compiled *without* -funbox-strict-fields,
and the main program was compiled *with* that flag, we were wrongly treating
the fields of imported data types as unboxed.

To fix this I added an extra constructor to StrictnessMark to express whether
the "!" annotation came from an interface file (don't fiddle) or a source
file (decide whether to unbox).

On the way I tided things up:

* StrictnessMark moves to Demand.lhs, and doesn't have the extra DataCon
  fields that kept it in DataCon before.

* HsDecls.BangType has one constructor, not three, with a StrictnessMark field.

* DataCon keeps track of its strictness signature (dcRepStrictness), but not
  its "user strict marks" (which were never used)

* All the functions, like getUniquesDs, that used to take an Int saying how
  many uniques to allocate, now return an infinite list. This saves arguments
  and hassle.  But it involved touching quite a few files.

* rebuildConArgs takes a list of Uniques to use as its unique supply.  This
  means I could combine DsUtils.rebuildConArgs with MkId.rebuildConArgs
  (hooray; the main point of the previous change)


I also tidied up one or two error messages

----------------
	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 major hygiene pass
	--------------------

1. The main change here is to

	Move what was the "IdFlavour" out of IdInfo,
	and into the varDetails field of a Var

   It was a mess before, because the flavour was a permanent attribute
   of an Id, whereas the rest of the IdInfo was ephemeral.  It's
   all much tidier now.

   Main places to look:

	   Var.lhs	Defn of VarDetails
	   IdInfo.lhs	Defn of GlobalIdDetails

   The main remaining infelicity is that SpecPragmaIds are right down
   in Var.lhs, which seems unduly built-in for such an ephemeral thing.
   But that is no worse than before.


2. Tidy up the HscMain story a little.  Move mkModDetails from MkIface
   into CoreTidy (where it belongs more nicely)

   This was partly forced by (1) above, because I didn't want to make
   DictFun Ids into a separate kind of Id (which is how it was before).
   Not having them separate means we have to keep a list of them right
   through, rather than pull them out of the bindings at the end.

3. Add NameEnv as a separate module (to join NameSet).

4. Remove unnecessary {-# SOURCE #-} imports from FieldLabel.

Implement do-style bindings on the GHCi command line.

The syntax for a command-line is exactly that of a do statement, with
the following meanings:

  - `pat <- expr'
    performs expr, and binds each of the variables in pat.

  - `let pat = expr; ...'
    binds each of the variables in pat, doesn't do any evaluation

  - `expr'
    behaves as `it <- expr' if expr is IO-typed, or `let it = expr'
    followed by `print it' otherwise.

Layout wibble

Import wibbles

Check class decls for validity only for source-code, not iface decls

------------------------------------
	   Mainly FunDeps (23 Jan 01)
	------------------------------------

This commit re-engineers the handling of functional dependencies.
A functional dependency is no longer an Inst; instead, the necessary
dependencies are snaffled out of their Class when necessary.

As part of this exercise I found that I had to re-work how to do generalisation
in a binding group.  There is rather exhaustive documentation on the new Plan
at the top of TcSimplify.

	******************
	WARNING: I have compiled all the libraries with this new compiler
		 and all looks well, but I have not run many programs.
		 Things may break.  Let me know if so.
	******************

The main changes are these:

1.  typecheck/TcBinds and TcSimplify have a lot of changes due to the
    new generalisation and context reduction story.  There are extensive
    comments at the start of TcSimplify

2.  typecheck/TcImprove is removed altogether.  Instead, improvement is
    interleaved with context reduction (until a fixpoint is reached).
    All this is done in TcSimplify.

3.  types/FunDeps has new exports
	* 'improve' does improvement, returning a list of equations
	* 'grow' and 'oclose' close a list of type variables wrt a set of
	  PredTypes, but in slightly different ways.  Comments in file.

4.  I improved the way in which we check that main::IO t.  It's tidier now.

In addition

*   typecheck/TcMatches:
	a) Tidy up, introducing a common function tcCheckExistentialPat

	b) Improve the typechecking of parallel list comprehensions,
	   which wasn't quite right before.  (see comments with tcStmts)

	WARNING: (b) is untested!  Jeff, you might want to check.

*   Numerous other incidental changes in the typechecker

*   Manuel found that rules don't fire well when you have partial applications
    from overloading.  For example, we may get

	f a (d::Ord a) = let m_g = g a d
			 in
			 \y :: a -> ...(m_g (h y))...

    The 'method' m_g doesn't get inlined because (g a d) might be a redex.
    Yet a rule that looks like
		g a d (h y) = ...
    won't fire because that doesn't show up.  One way out would be to make
    the rule matcher a bit less paranoid about duplicating work, but instead
    I've added a flag
			-fno-method-sharing
    which controls whether we generate things like m_g in the first place.
    It's not clear that they are a win in the first place.

    The flag is actually consulted in Inst.tcInstId