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Thu Dec 31 11:04:51 CET 2009

VM refactoring again

The first things to eliminate are the continuation transformers.  Eval
and apply could be made to modify the continuation directly.

Benchmark: boot.scm compilation in debug mode on zni.
tom@zni:~/libprim/sc$ rm -f boot-expanded.scm ; time make boot-expanded.scm
./sc --boot /home/tom/libprim/sc/boot.scm --eval '(script)' /home/tom/libprim/sc/expand.scm /home/tom/libprim/sc/boot.scm boot-expanded.scm

real	0m9.082s
user	0m9.077s
sys	0m0.008s

How to do this?  Restructure the main loop: use the state vector only
as a mark point to recover from GC restarts.

So, first objective: eliminate the state object.  (current redex +
continuation).

( This keeps eluding me: the current structure is really too
high-level to allow simple imperative optimizations...)

Plan: 

* flatten the state object into an expression + continuation object in
  the global state vector.
 

The problem this leads to is that _sc_step_value returns a state
object, which is a code + kontinuation (c . k) pair.  Essentially,
this needs to be transformed into a loop, updating a central machine.

It doesn't look like it is useful to start modifying the current
implementation in-place.  It needs to be completely rewritten.  I'm
going to revert the code back.




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