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Calling-in section: clarify truth vs. fiction

added design/impl doc describing ConcHask MT extension

- clarified/fixed sched_mutex locking problems when
  calling raiseAsync() from withing the bowels of the Scheduler.
- we now yieldToReturningWorker() as part of the main Scheduler
  loop.
- simplified grabCapability() and waitForWorkCapability() usage.

entry points that scheduled/created an external thread weren't correctly blocking on the TSO condition variable; now fixed.

yieldToReturningWorker(): once yielded to a returning worker,
thread now directly waits for capability to become available
again (via waitForWorkCapability()) -- simplifies Cap. grabbing
'logic' in the Scheduler.

grabReturnCapability(): assume pMutex is held upon entry.

fixed config of PACKAGE_CPP_OPTS in DEBUG mode

debug versions of ACQUIRE_LOCK() and RELEASE_LOCK() macros

GarbageCollect(): thread resurrection now assumes sched_mutex is held

getMBlocks(): if we run into a ENOMEM situation, report blocks requested

quibble

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

Add stuff about non-blocking I/O for Win32

add missing file to source dist

Fix some wibbles with the :m command

Make the earlier context-simplification loop-detection fix work properly

(from Simon P.J) Make generics work with zero-constructor datatypes.

Two new scheduler-API primops:

1) GHC.Conc.forkProcess/forkProcess# :: IO Int
   This is a low-level call to fork() to replace Posix.forkProcess().
   In a Concurrent Haskell setting, only the thread invoking forkProcess()
   is alive in the child process. Other threads will be GC'ed!
      This brings the RTS closer to pthreads, where a call to fork()
   doesn't clone any pthreads, either.
      The result is 0 for the child and the child's pid for the parent.
   The primop will barf() when used on mingw32, sorry.

2) GHC.Conc.labelThread/forkProcess# :: String -> IO ()
   Useful for scheduler debugging: If the RTS is compiled with DEBUGging
   support, this primitive assigns a name to the current thread which
   will be used in debugging output (+RTS -D1). For larger applications,
   simply numbering threads is not sufficient.
     Notice: The Haskell side of this call is always available, but if
   you are not compiling with debugging support, the actual primop will
   turn into a no-op.

Don't claim that i386-unknown-cygwin32 is supported, replace it with
i386-unknown-mingw32.

(the build docs for Win32 are probably also out of date, but I didn't
touch those)

Currently configure falls over if $srcdir/ghc exists and Happy >= 1.9
can't be found.  For a source distribution this is too paranoid,
because we ship the Happy-generated .hs files with the sources.  Now
we ignore a missing Happy if ghc/compiler/parser/Parser.hs exists,
which should be a reasonable heuristic.

If we free a StablePtr which has no StableName attached, then just
add its entry to the free list immediately, rather than waiting for
the garbage collector to free it.

- Revert rev. 1.7, i.e. go back to using malloc/free and a free list
  to manage hash list cells, because the arena method doesn't recycle
  used cells, resulting in memory leaks.

- Add a freeHashList() call which was missing in removeHashTable().

Removed the unnecessary arg from TICK_ENT_{STATIC,DYN}_THK macros in the
"#ifdef TICKY_TICKY" case.  This meant the libraries would not compile with
way=t for SimonPJ even though they did for me...

renameExtCore: bring locally defined names into scope before closing up

Import notNull

Friday afternoon pet peeve removal: define (Util.notNull :: [a] -> Bool) and use it

Catch the use of non-existent output directories &
report this back to the user. By not doing this, we relied
on external tools (such as the linker or assembler) to give
good feedback about this error condition -- this wasn't
the case (cf. GAS on mingw/cygwin.)

To insert more sanity checks of the effective options
(to the batch compiler), use Main.checkOptions

Cleaned up the way the External Core front-end was
integrated with the rest of the compiler;
guided by detailed and helpful feedback from Simon PJ.

Input files ending in ".hcr" are now assumed to contain
external core -- still working on getting the renamer
to slurp in interface files (implicitly) referred to
in the Core source.

More wibbles

More head-healing

Heal the head

This is Haddock, my stab at a Haskell documentation tool.  It's not
quite ready for release yet, but I'm putting it in the repository so
others can take a look.

It uses a locally modified version of the hssource parser, extended
with support for GHC extensions and documentation annotations.

---------------------------------------
	A glorious improvement to CPR analysis
	---------------------------------------

Working on the CPR paper, I finally figured out how to
do a decent job of taking account of strictness analyis when doing
CPR analysis.

There are two places we do that:

1.  Usually, on a letrec for a *thunk* we discard any CPR info from
the RHS.  We can't worker/wrapper a thunk.  BUT, if the let is
	non-recursive
	non-top-level
	used strictly
we don't need to discard the CPR info, because the thunk-splitting
transform (WorkWrap.splitThunk) works.  This idea isn't new in this
commit.


2. Arguments to strict functions.  Consider

  fac n m = if n==0 then m
		    else fac (n-1) (m*n)

Does it have the CPR property?  Apparently not, because it returns the
accumulating parameter, m.  But the strictness analyser will
discover that fac is strict in m, so it will be passed unboxed to
the worker for fac.  More concretely, here is the worker/wrapper
split that will result from strictness analysis alone:

  fac n m = case n of MkInt n' ->
	    case m of MkInt m' ->
	    facw n' m'

  facw n' m' = if n' ==# 0#
	       then I# m'
	       else facw (n' -# 1#) (m' *# n')

Now facw clearly does have the CPR property!  We can take advantage
of this by giving a demanded lambda the CPR property.


To make this work nicely, I've made NewDemandInfo into Maybe Demand
rather than simply Demand, so that we can tell when we are on the
first iteration.  Lots of comments about this in Note [CPR-AND-STRICTNESS].

I don't know how much all this buys us, but it is simple and elegant.

An I/O error while opening/writing the output file is *not* a panic.

Make -fgenerics the default

-----------------------------
	Put existential tyvars second
	[fixes ParsecPerm lint error]
	-----------------------------

In an existential data constr:

	data Eq a => T a = forall b. Ord b => MkT a [b]

the type of MkT is

	MkT :: forall a b . Ord b => a -> [b] -> MkT a

Note that the existential tyvars (b in this case) come *after*
the "ordinary" tyvars.

I had switched this around earlier in the week, but I'm putting
it back (and fixing a bug) because I found it really works better second.

Reason: in a case expression we may find:
	case (e :: T t) of { MkT b (d:Ord b) (x:t) (xs:[b]) -> ... }
It's convenient to apply the rep-type of MkT to 't', to get
	forall b. Ord b => ...
and use that to check the pattern.  Mind you, this is really only
use in CoreLint.

Allow the use of 'let' for implcit bindings.

Support for 'with' is left in place for the time being, but on seeing
a 'with' we emit a non-suppressible warning about 'with' being
deprecated in favour of 'let'.

-----------------------------------------------------
	Fix two nasty, subtle loops in context simplification
	-----------------------------------------------------

The context simplifier in TcSimplify was building a recursive
dictionary, which meant the program looped when run.  The reason
was pretty devious; in fact there are two independent causes.

Cause 1
~~~~~~~
Consider
 	class Eq b => Foo a b
	instance Eq a => Foo [a] a
If we are reducing
	d:Foo [t] t
we'll first deduce that it holds (via the instance decl), thus:
	d:Foo [t] t = $fFooList deq
	deq:Eq t = ...some rhs depending on t...
Now we add d's superclasses.  We must not then overwrite the Eq t
constraint with a superclass selection!!

The only decent way to solve this is to track what dependencies
a binding has; that is what the is_loop parameter to TcSimplify.addSCs
now does.


Cause 2
~~~~~~~
This shows up when simplifying the superclass context of an
instance declaration.  Consider

  class S a

  class S a => C a where { opc :: a -> a }
  class S b => D b where { opd :: b -> b }

  instance C Int where
     opc = opd

  instance D Int where
     opd = opc

From (instance C Int) we get the constraint set {ds1:S Int, dd:D Int}
Simplifying, we may well get:
	$dfCInt = :C ds1 (opd dd)
	dd  = $dfDInt
	ds1 = $p1 dd
Notice that we spot that we can extract ds1 from dd.

Alas!  Alack! We can do the same for (instance D Int):

	$dfDInt = :D ds2 (opc dc)
	dc  = $dfCInt
	ds2 = $p1 dc

And now we've defined the superclass in terms of itself.


Solution: treat the superclass context separately, and simplify it
all the way down to nothing on its own.  Don't toss any 'free' parts
out to be simplified together with other bits of context.

This is done in TcInstDcls.tcSuperClasses, which is well commented.

All this from a bug report from Peter White!

Make this compile with 4.08.

Error message tidy up

oops, accidentally committed some untested (and non-working) cleanups
in the last commit.  This commit fixes it up again.

(fixes the ByteCodeGen panic in GHCi on the HEAD)