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Add record syntax for GADTs
	~~~~~~~~~~~~~~~~~~~~~~~~~~~

Atrijus Tang wanted to add record syntax for GADTs and existential
types, so he and I worked on it a bit at ICFP.  This commit is the
result.  Now you can say

 data T a where
  T1 { x :: a }           	 :: T [a]
  T2 { x :: a, y :: Int } 	 :: T [a]
  forall b. Show b =>
 	T3 { naughty :: b, ok :: Int } :: T Int
  T4 :: Eq a => a -> b -> T (a,b)

Here the constructors are declared using record syntax.

Still to come after this commit:
  - User manual documentation
  - More regression tests
  - Some missing cases in the parser (e.g. T3 won't parse)
Autrijus is going to do these.


Here's a quick summary of the rules.  (Atrijus is going to write
proper documentation shortly.)

Defnition: a 'vanilla' constructor has a type of the form
	forall a1..an. t1 -> ... -> tm -> T a1 ... an
No existentials, no context, nothing.  A constructor declared with
Haskell-98 syntax is vanilla by construction.  A constructor declared
with GADT-style syntax is vanilla iff its type looks like the above.
(In the latter case, the order of the type variables does not matter.)

* You can mix record syntax and non-record syntax in a single decl

* All constructors that share a common field 'x' must have the
  same result type (T [a] in the example).

* You can use field names without restriction in record construction
  and record pattern matching.

* Record *update* only works for data types that only have 'vanilla'
  constructors.

* Consider the field 'naughty', which uses a type variable that does
  not appear in the result type ('b' in the example).  You can use the
  field 'naughty' in pattern matching and construction, but NO
  SELECTOR function is generated for 'naughty'.  [An attempt to use
  'naughty' as a selector function will elicit a helpful error
  message.]

* Data types declared in GADT syntax cannot have a context. So this
is illegal:
	data (Monad m) => T a where
		  ....

* Constructors in GADT syntax can have a context (t.g. T3, T4 above)
  and that context is stored in the constructor and made available
  when the constructor is pattern-matched on.  WARNING: not competely
  implemented yet, but that's the plan.



Implementation notes
~~~~~~~~~~~~~~~~~~~~
- Data constructors (even vanilla ones) no longer share the type
  variables of their parent type constructor.

- HsDecls.ConDecl has changed quite a bit

- TyCons don't record the field labels and type any more (doesn't
  make sense for existential fields)

- GlobalIdDetails records which selectors are 'naughty', and hence
  don't have real code.

add protos for HeapStackCheck.cmm:stg_block_blackhole_* entry points

- we should be acquiring the sm_lock around allocGroup()
- sanity check threads as they are pulled off the blackhole_queue

MERGE TO STABLE

Fix a bug in TcUnify.unifyTyConApp that made a GADT program fail.
The trouble happens if the type that we are expecting to be
a TyConApp is of form (m a b), where 'm' is refined to a type
constructor.  Then we want to get nice rigid results, and we weren't.

Small refactoring

DEBUG_FILL_SLOP: don't do anything on SMP, zeroing slop words isn't safe

checkHeap: just return on SMP, we can't do heap sanity checking
because we can't zero slop words safely.

Fix assertion failure in memInventory() with SMP

When blocking on a BLACKHOLE, we must wait until we have finished
manipulating the current thread's stack before we release sched_mutex,
otherwise another thread can pick up the thread from the
blackhole_queue and start running it.

Mac OS X/Darwin PowerPC: Fix a problem introduced by the recent Darwin/x86
commit.

Make the code that allocates jump islands for PowerPC aware of how we shift
.o files in memory to compensate for Mach-O's lax alignment rules.

Small fixes to the Win32 build log

Fix bug in previous commit (fixes recent seg faults in nightly stage2)

identify "mode" as a class of flags, in addition to "static" and "dyanmic"

flag reference update: a bunch of static flags are now dynamic

Fix a bug I just found: hiding a package if later versions are exposed
wasn't actually checking the exposed flag.

comment typo

From: Autrijus Tang <autrijus@autrijus.org>

remove old comment

From: Autrijus Tang <autrijus@autrijus.org>

add dataConFieldType

From: Autrijus Tang <autrijus@autrijus.org>

refactoring (use record fields instead of selector functions)

From: Autrijus Tang <autrijus@autrijus.org>

add splitHsFunType

From: Autrijus Tang <autrijus@autrijus.org>

small refactoring

From: Autrijus Tang <autrijus@autrijus.org>

DEBUG_FILL_SLOP(): fill slop for AP_STACK closures too

Mention that assertions are turned off by -O

remove duplicate mention of -fignore-asserts

Synched all FPTOOLS_CHECK_HTYPE definitions with the latest changes in
libraries/OpenAL/aclocal.m4. Although it is not strictly necessary, keeping
things identical is good for consistency. At some point in time we should
really find a way to eliminate all this redundancy... *sigh*

x86 & PIC: make floating point constants on x86 PIC-aware

Darwin/x86: Try again to get stack alignment right.

PowerPC: track changes in the rest of the register allocator

in --make mode, don't re-link when the executable is up to date.

distill a bit of wisdom from the mailing list

Document the -x flag

move RTLD_* tests down to unix package

Update the license: we now use a BSD license, although the release
will be binary-only.

Make outOfLineFloatOp PIC/dynamic-linking-aware on i386

Fix last commit: it's opt_Static in the HEAD branch, not a local variable
"static".

Fixed a few underquoted definitions.

PIC version for genSwitch on i386

A hack to make -dynamic work again:
when a library listed in extraLibraries ends with "_cbits", append "_dyn"
when -dynamic is passed, i.e. extraLibraries = ["foo", "HSbase_cbits"]
loads -lfoo and -lHSbase_cbits in the static case, but -lfoo and
-lHSbase_cbits_dyn in the -dynamic case.

It's an ugly hack, but it affects only the case when -dynamic is passed,
which would not work otherwise right now, so let's

MERGE TO STABLE

Update for Sparc/Solaris from Christian Meader.  This might fix GHCi
on Sparc.

- Mention bundled documentation
- Add some more copyrights
- Add authors