Description of compat.scm

Purpose:
--------
COMPAT is a compatibility rewrite stage.  It makes unknown calls and
exported procedures (i.e. closures) pass and accept parameters on the
stack, following the current system's standard calling convention.
It also rewrites calls to some pseudo-primitives into calls to
existing primitives and free variables.
(in other words it devides the parameters into ones that are in registers
and ones that have to go on the stack and rewrites them)

In general %fetch-continuation is used for the TOP-LEVEL cont. 

%fetch-stack-closure is used for LAMBDA for a continuation that is for 
variables on stack
for variables on stack in LAMBDA a new env maps them to %stack-closure-ref
and %vector-index.

In CALL when the operator is not a pair or it is a quote
when there are too many operands to put in registers they are
put on the stack. The continuaition is changed into %make-stack-closure
the stack operands are referenced with either LOOKUP or %stack-closure-ref
If the operator is rewriten then the handler replaces the CALL, 
It can also get an out of line handler.

kinds of (rewriten) calls which have extra arguments like arity or cache
(therefore get a handler when CALLed)
%invoke-operator-cache
%invoke-remote-cache
%internal-apply
%invoke-continuation

rewriten operators
%vector-index
%variable-cache-ref {checks that the cont of the call is to a QUOTE or a 
	LOOKUP otherwise error. using %stack-closure-ref} 
	%continue is used to represent the continuation using 
	%invoke-continuation for continuation that are a QUOTE
	uses %variable-read-cache for cell-name
	uses %variable-cell-ref for value-name
	uses %reference-trap? and %hook-variable-cell-ref
%safe-variable-cahce-ref is like %variable-cache-ref except in the end
	it calls %unassigned? instead of %hook-variable-cell-ref and then
	%hook-safe-variable-cell-ref.
%variable-cache-set! the same as above uses %variable-write-cache
	for cell-name.  old-value-name uses %variable-cell-ref
	uses %variable-cell-set! and %hook-variable-cell-set! instead of
	%continuation and %hook...
%primitive-apply uses %primitive-apply/compatible also uses (not introduces)
	 %make-stack-closure and %stack-closure-ref (for a CALL)

%invoke-remote-cache and %primitive-apply/compatible are introduced

Operators removed:
------------------

%*lookup is replaced by a call to the primitive LEXICAL-REFERENCE

%*set! is replaced by a call to the primitive LEXICAL-ASSIGNMENT

%*unassigned? is replaced by a call to the primitive LEXICAL-UNASSIGNED?

%*define is replaced by a call to the primitive LOCAL-ASSIGNMENT

%*define* is replaced by a call to the global procedure DEFINE-MULTIPLE

%*make-enviornment is replaced by a call to the global procedure 
  *MAKE-ENVIRONMENT

%*variable-cache-ref is replaced by a lot of hairy code

%*variable-cache-set! is replaced by a lot of hairy code

%safe-variable-cache-ref is replaced by a lot of hairy code

%copy-program is replaced by a call to a global procedure COPY-PROGRAM

%execute is replaced by a call to a primitive procedure SCODE-EVAL

%primitive-apply is replaced by %PRIMITIVE-APPLY/COMPATIBLE


Operators Introduced:
---------------------

%variable-read-cache as part of rewriting %variable-cache-ref and
	%safe-variable-cache-ref

%variable-write-cache as part of rewriting %variable-cache-set!

%variable-cell-ref as part of rewriting %safe-cache-ref and 
	%safe-variable-cache-ref

%variable-cell-set! as part of rewriting %variable-cache-set!

%hook-variable-cell-ref as part of rewriting %variable-cache-ref

%hook-safe-variable-cell-ref as part of rewriting %safe-variable-cache-ref

%hook-variable-cell-set! as part of rewriting %variable-cache-set!

%reference-trap? as part of rewriting %variable-cache-ref, 
	%safe-variable-cache-ref, and  %variable-cache-set!

%make-stack-closure (also by closeconv.scm) with #F

%primitive-apply/compatible 

Restrictions on Input:
----------------------
Special forms excluded: 
  ACCESS, DEFINE, DELAY, IN-PACKAGE, OR, SET!, THE-ENVIRONMENT
  UNASSIGNED?

Special forms introduced:
-------------------------
  none

Magic Cookies handled specially:
-------------------------------

Guarantees on Output:
---------------------
 none