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----------------------------------
	Fix a predicate-simplification bug
	----------------------------------

Fixes a bug pointed out by Marcin

    data R = R {f :: Int}
    foo:: (?x :: Int) => R -> R
    foo r = r {f = ?x}

    Test.hs:4:
	Could not deduce `?x :: Int' from the context ()
	arising from use of implicit parameter `?x' at Test.hs:4
	In the record update: r {f = ?x}
	In the definition of `foo': r {f = ?x}

The predicate simplifier was declining to 'inherit' an
implicit parameter.  This is right for a let-binding, but
wrong for an expression binding.  For example, a simple
expression type signature:

		(?x + 1) :: Int

This was rejected because the ?x constraint could not be
floated out -- but that's wrong for expressions.

****	MERGE WITH 5.00 BRANCH     ********

	--------------------------------
	Monomorphism restriction for implicit parameters
	--------------------------------

This commit tidies up the way in which monomorphic bindings
are dealt with, incidentally fixing a bug to do with implicit
parameters.

The tradeoffs concerning monomorphism and implicit paramters are
now documented in TcSimplify.lhs, and all the strategic choices
are made there (rather than in TcBinds where they were before).

I've continued with choice (B) -- which Jeff first implemented --
because that's what Hugs does, lacking any other consensus.

------------------------------------------------
	Dramatically improve the error messages arising
	from failed unifications triggered by 'improvement'
	------------------------------------------------

A bit more plumbing in FunDeps, and consequential wibbles elsewhere

Changes this:

    Couldn't match `Int' against `[(String, Int)]'
	Expected type: Int
	Inferred type: [(String, Int)]

to this:

    Foo.hs:8:
	Couldn't match `Int' against `[(String, Int)]'
	    Expected type: Int
	    Inferred type: [(String, Int)]
	When using functional dependencies to combine
	  ?env :: Int, arising from a type signature at Foo.hs:7
	  ?env :: [(String, Int)],
	    arising from use of implicit parameter `?env' at Foo.hs:8
	When generalising the types for ident

****	MERGE WITH 5.00 BRANCH     ********

	--------------------------------
	Fix a bad implicit parameter bug
	--------------------------------

TcSimplify.tcSimplifyIPs was just completely wrong; it wasn't
doing improvement properly nor binding values properly. Sigh.

To make this work nicely I added
	Inst.instName :: Inst -> Name

Add comments

Don't use the same simplify code for both restricted and unrestricted
bindings.  In particular, a restricted binding shouldn't try to capture
implicit params.

Improve error reporting

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

Improve rule matching

When doing constraint simplification on the LHS of a rule,
we *don't* want to do superclass commoning up.  Consider

	fromIntegral :: (Integral a, Num b) => a -> b
	{-# RULES "foo"  fromIntegral = id :: Int -> Int #-}

Here, a=b=Int, and Num Int is a superclass of Integral Int. But we *dont*
want to get

	forall dIntegralInt.
	fromIntegral Int Int dIntegralInt (scsel dIntegralInt) = id Int

because the scsel (super class selection) will mess up matching.
Instead we want

	forall dIntegralInt, dNumInt.
	fromIntegral Int Int dIntegralInt dNumInt = id Int


TcSimplify.tcSimplifyToDicts is the relevant function, but I had
to generalise the main simplification loop a little (adding the
type WantSCs).

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.

Typechecking [TcModule, TcBinds, TcHsSyn, TcInstDcls, TcSimplify]
~~~~~~~~~~~~
* Fix a bug in TcSimplify that broke functional dependencies.
  Interleaving unification and context reduction is trickier 
  than I thought.  Comments in the code amplify.  

* Fix a functional-dependency bug, that meant that this pgm:
	class C a b | a -> b where f :: a -> b
	
	g :: (C a b, Eq b) => a -> Bool
	g x = f x == f x
  gave an ambiguity error report.  I'm afraid I've forgotten
  what the problem was.


* Correct the implementation of the monomorphism restriction,
  in TcBinds.generalise.  This fixes Marcin's bug report:
	test1 :: Eq a => a -> b -> b
	test1 x y = y

	test2 = test1 (3::Int)
  Previously we were erroneously inferring test2 :: () -> ()

* Make the "unf_env" that is looped round in TcModule go round
  in a big loop, not just round tcImports.  This matters when
  we have mutually recursive modules, so that the Ids bound in
  the source code may appear in the imports.  Sigh.  But no big
  deal.

  It does mean that you have to be careful not to call isLocalId,
  isDataConId etc, because they consult the IdInfo of an Id, which 
  in turn may be determined by the loop-tied unf_env.

More on functional dependencies

My last commit allowed this:

	instance C a b => C [a] [b] where ...

if we have

	class C a b | a -> b

This commit completes the change, by making the 
improvement stages improve only the 'shape' of the second
argument of C.  

I also had to change the iteration in TcSimplify -- see
the comments in TcSimplify.inferLoop.

Fix superclass bug in context reduction (gave infinite loops before!)

Fix typos in comments.

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

Remove bogus zonkInst

Compiles now

merge rev. 1.46.2.3 from ghc-4-07-branch (fix line numbers in
defaulting warnings).

1.	Outputable.PprStyle now carries a bit more information
	In particular, the printing style tells whether to print
	a name in unqualified form.  This used to be embedded in
	a Name, but since Names now outlive a single compilation unit,
	that's no longer appropriate.

	So now the print-unqualified predicate is passed in the printing
	style, not embedded in the Name.

   2.	I tidied up HscMain a little.  Many of the showPass messages
	have migraged into the repective pass drivers

Track renaming of typecheck/TcInstUtil to types/InstEnv.

Flags hacking:

   - `dopt_GlasgowExts'  is now written `dopt Opt_GlasgowExts'
   - convert all the warning options into DynFlags

Mostly typechecker stuff.

Simons work, mainly on the type checker

--------------------------------------
	Adding generics		SLPJ Oct 2000
	--------------------------------------

This big commit adds Hinze/PJ-style generic class definitions, based
on work by Andrei Serjantov.  For example:

  class Bin a where
    toBin   :: a -> [Int]
    fromBin :: [Int] -> (a, [Int])

    toBin {| Unit |}    Unit	  = []
    toBin {| a :+: b |} (Inl x)   = 0 : toBin x
    toBin {| a :+: b |} (Inr y)   = 1 : toBin y
    toBin {| a :*: b |} (x :*: y) = toBin x ++ toBin y


    fromBin {| Unit |}    bs      = (Unit, bs)
    fromBin {| a :+: b |} (0:bs)  = (Inl x, bs')    where (x,bs') = fromBin bs
    fromBin {| a :+: b |} (1:bs)  = (Inr y, bs')    where (y,bs') = fromBin bs
    fromBin {| a :*: b |} bs  	  = (x :*: y, bs'') where (x,bs' ) = fromBin bs
							  (y,bs'') = fromBin bs'

Now we can say simply

  instance Bin a => Bin [a]

and the compiler will derive the appropriate code automatically.

		(About 9k lines of diffs.  Ha!)


Generic related things
~~~~~~~~~~~~~~~~~~~~~~

* basicTypes/BasicTypes: The EP type (embedding-projection pairs)

* types/TyCon:
	An extra field in an algebraic tycon (genInfo)

* types/Class, and hsSyn/HsBinds:
	Each class op (or ClassOpSig) carries information about whether
	it  	a) has no default method
		b) has a polymorphic default method
		c) has a generic default method
	There's a new data type for this: Class.DefMeth

* types/Generics:
	A new module containing good chunk of the generic-related code
	It has a .hi-boot file (alas).

* typecheck/TcInstDcls, typecheck/TcClassDcl:
	Most of the rest of the generics-related code

* hsSyn/HsTypes:
	New infix type form to allow types of the form
		data a :+: b = Inl a | Inr b

* parser/Parser.y, Lex.lhs, rename/ParseIface.y:
	Deal with the new syntax

* prelude/TysPrim, TysWiredIn:
	Need to generate generic stuff for the wired-in TyCons

* rename/RnSource RnBinds:
	A rather gruesome hack to deal with scoping of type variables
	from a generic patterns.  Details commented in the ClassDecl
	case of RnSource.rnDecl.

	Of course, there are many minor renamer consequences of the
	other changes above.

* lib/std/PrelBase.lhs
	Data type declarations for Unit, :+:, :*:


Slightly unrelated housekeeping
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
* hsSyn/HsDecls:
	ClassDecls now carry the Names for their implied declarations
	(superclass selectors, tycon, etc) in a list, rather than
	laid out one by one.  This simplifies code between the parser
	and the type checker.

* prelude/PrelNames, TysWiredIn:
	All the RdrNames are now together in PrelNames.

* utils/ListSetOps:
	Add finite mappings based on equality and association lists (Assoc a b)
	Move stuff from List.lhs that is related

--------------------------------------------------
	Tidying up HsLit, and making it possible to define
		your own numeric library

		Simon PJ 22 Sept 00
	--------------------------------------------------

** NOTE: I did these changes on the aeroplane.  They should compile,
	 and the Prelude still compiles OK, but it's entirely 
	 possible that I've broken something

The original reason for this many-file but rather shallow
commit is that it's impossible in Haskell to write your own
numeric library.  Why?  Because when you say '1' you get 
(Prelude.fromInteger 1), regardless of what you hide from the
Prelude, or import from other libraries you have written.  So the
idea is to extend the -fno-implicit-prelude flag so that 
in addition to no importing the Prelude, you can rebind 
	fromInteger	-- Applied to literal constants
	fromRational	-- Ditto
	negate		-- Invoked by the syntax (-x)
	the (-) used when desugaring n+k patterns

After toying with other designs, I eventually settled on a simple,
crude one: rather than adding a new flag, I just extended the
semantics of -fno-implicit-prelude so that uses of fromInteger,
fromRational and negate are all bound to "whatever is in scope" 
rather than "the fixed Prelude functions".  So if you say

	{-# OPTIONS -fno-implicit-prelude #-}
	module M where
 	import MyPrelude( fromInteger )

	x = 3

the literal 3 will use whatever (unqualified) "fromInteger" is in scope,
in this case the one gotten from MyPrelude.


On the way, though, I studied how HsLit worked, and did a substantial tidy
up, deleting quite a lot of code along the way.  In particular.

* HsBasic.lhs is renamed HsLit.lhs.  It defines the HsLit type.

* There are now two HsLit types, both defined in HsLit.
	HsLit for non-overloaded literals (like 'x')
	HsOverLit for overloaded literals (like 1 and 2.3)

* HsOverLit completely replaces Inst.OverloadedLit, which disappears.
  An HsExpr can now be an HsOverLit as well as an HsLit.

* HsOverLit carries the Name of the fromInteger/fromRational operation,
  so that the renamer can help with looking up the unqualified name 
  when -fno-implicit-prelude is on.  Ditto the HsExpr for negation.
  It's all very tidy now.

* RdrHsSyn contains the stuff that handles -fno-implicit-prelude
  (see esp RdrHsSyn.prelQual).  RdrHsSyn also contains all the "smart constructors"
  used by the parser when building HsSyn.  See for example RdrHsSyn.mkNegApp
  (previously the renamer (!) did the business of turning (- 3#) into -3#).

* I tidied up the handling of "special ids" in the parser.  There's much
  less duplication now.

* Move Sven's Horner stuff to the desugarer, where it belongs.  
  There's now a nice function DsUtils.mkIntegerLit which brings together
  related code from no fewer than three separate places into one single
  place.  Nice!

* A nice tidy-up in MatchLit.partitionEqnsByLit became possible.

* Desugaring of HsLits is now much tidier (DsExpr.dsLit)

* Some stuff to do with RdrNames is moved from ParseUtil.lhs to RdrHsSyn.lhs,
  which is where it really belongs.

* I also removed 
	many unnecessary imports from modules 
	quite a bit of dead code
  in divers places

Functional Dependencies were not getting simplified away when the dictionary
that generated them was simplified by instance resolution.  Fixed.

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

This commit moves the instance environment out of the Class data
structure, where it was immutable, to part of the type-checker
environment.  This change is absolutely essential as part of
our move to GHCi, and I think it's also going to be necessary
for Andrei's work on generic functions.

As part of this change, we can remove

  a) types/InstEnv.*	(thereby also removing a hi-boot loop)
  b) a tc-fixpoint-loop in TcModule

Both of these are worthwhile simplifications.

*** NO NEED TO MERGE WITH 4.07 ***
    (but it would do no harm)

* Improve an error message when overlapping instance
  declarations are present.  Carl Witty reported this
  infelicitous message.  The problem arises for this code:

	class Foo a
	class (Foo a) => Bar a
	
	data Dat a = Dat
	
	instance Foo (Dat a)
	instance Foo (Dat Integer)
	
	instance Bar (Dat a)

  The instance decl for Bar should say

	instance Foo (Dat a) => Bar (Dat a) 

  because the overlapping instance decls for Foo can't
  be resolved (or at least might vary depending on how
  a is instantiated).

Cleanup pass on functional dependencies.  Most noticeably, make it so that
signatures involving classes with functional dependencies work.  Also,
Fundeps are now properly handled by the simplifier, resolving problems
where the fundeps were sometimes being discarded too early, and sometimes
hanging around too long.  Took out the early ambiguity testing in the
renamer, because that's too early (you don't know the fundeps yet).  Now,
the ambiguity test happens in the typechecker.
Functional Dependencies should now be up to snuff with Mark's paper,
however, the derived instances and superclass extensions found in hugs
are still not in there.
It would be nice if this were merged into 4.07.  I have diffs against
the 4.07 tree in case it's too thorny working around Simon's big commit.

Wobble.  Fine tuning tcSimplifyAndCheck a bit further (wrt implicit params).
The key is that a method that doesn't constrain a local tyvar, but does has
implicit params, needs to be reduced further.

A clean-up pass on fundeps and implicit params.  Haven't yet incorporated
changes from Hugs/GHC meeting yet, tho.
  - Fixed up several places in Type.lhs where IPNotes were probably being
    incorrectly handled.  Strongly suggests a better solution should be
    implemented for marking implicit params than piggybacking on NoteTys.
  - tcSimplifyAndCheck was handling implicit params incorrectly
    (holding on to them when it should have been booting them out to frees).
  - Improved improvement WRT type signatures (the signature is now taken
    into account when improving).
  - Added improvement when matching against local polymorphic types.

Improve the error messages given when a definition isn't polymorphic enough.
In paticular, for this program:

    let v = runST (newSTRef True)
    in
    runST (readSTRef v)

we get the message

    Inferred type is less polymorphic than expected
	Quantified type variable `s' escapes
	It is reachable from the type variable(s) `a'
	  which are free in the signature
    Signature type:     forall s. ST s a
    Type to generalise: ST s (STRef s Bool)
    When checking an expression type signature
    In the first argument of `runST', namely `(newSTRef True)'
    In the right-hand side of a pattern binding: runST (newSTRef True)

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.

Further refine and fix how `with' partitions the LIE.  Also moved the
partitioning function from Inst to TcSimplify.  Fixed layout bug with
`with'.  Fixed another wibble w/ importing defs w/ implicit params.
Make 4-tuples outputable (a convenience in debugging measure).

Fix signatures w/ implicit parameter types in them (in particular,
correctly handle the case where there are no type variables).  Also
made a few more things Outputable.  Nuke outdated comment in Parser.y.

Misc. fixes to implicit parameters support.

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).