COMPILATION
===========
For the moment:
% make example

Specfying compile flags:
% OPT="-O0" make example

Supported useful macros (see swan_config.h):
* MODE
% OPT="-O0 -DMODE=0" make example
Verbose debugging mode, no optimization by compiler
% OPT="-O4 -DMODE=1" make example
Very fast mode with *all* debugging turned off and aggressive compiler optimizations

* SUPPORT_GDB
% OPT="-O0 -DSUPPORT_GDB=1" make example
to replicate parts of stack_frames such that gdb finds its way easier.

# * SYNC_THROW -- this has been removed by renaming sync() to ssync().
# Some versions of g++ complain about sync() having different throw() signatures in different places.
# This error messages is sidestepped by:
# % OPT="-O0 -DSYNC_THROW" make example

* DBG_CONTINUATION
% OPT="-O0 -DDBG_CONTINUATION=1" make example
Set to 1 to do additional checking of the continuation. Copies stack stub
to control space and checks on return that it has not been mutated.

* DBG_VERIFY
% OPT="-O0 -DDBG_VERIFY=1" make example
Set to 1 to do additional checking of the sanity of the stack_frame,
in particular the saved BP and SP and the stack_ptr.

* DBG_WF
If set, then sets DBG_CONTINUATION and DBG_VERIFY if they are not already set.

* PENDING_FULL_FRAME
If set, then pending frames are immediately allocated as large (8KB) frames with
the code set up ready for a resume action. If not set, the frame is first allocated
as a more compact pending_frame and is converted to a large frame when it's
execution starts.
It is not (yet) clear what is the best strategy.

For best performance, use
% OPT="-O4 -DSUPPORT_GDB=0 -DDBG_CONTINUATION=0 -DBG_VERIFY=0 -DDBG_WF=0 -DNDEBUG" make example

PROGRAMMING INTERFACE
=====================
By examples.

* Spawn/sync
  chandle<int> k;
  spawn( fib, k, n-1 );
  ...;
  ssync();
  ... = (int)k;

* Call
  int k = call( fib, n - 1 );

* Leaf-call
  leaf_call( printf, "if you need more than %d KB stack space", 4 );