toplevel-macsyma-eval, continue, and other fun stuff

Greetings all.  I am trying to figure out where the "least dangerous"
place to put a call to a "lasteval" function would be.  As near as I
can tell, the root of the maxima REPL is the function continue defined
in macsys.lisp on line 96.  Within this function, there is this little
tidbit:

   (setq $% (toplevel-macsyma-eval $__))

Clearly, this is referenced throughout Maxima - amusingly enough Maxima
still compiles if I comment out this definiton and replace $% with
(toplevel-macsyma-eval $__) in continue, but there are a large number
of test failures if I do.  So "toplevel-macsyma-eval" isn't really, in
the sense that for a given input this level is reached during the
internal workings of many calculations.  However, the only two places
this appears within the continue function are these two:

172   (set (setq d-tag (makelabel $outchar)) $%)
188   (if (eq (caar r) 'displayinput)
189    (displa `((mlable) ,d-tag ,$%)))

So here is my proposal - keep the definiton of $%, but in the top level
continue loop define something like the following:

   (setq totaleval (lasteval(toplevel-macsyma-eval $__)))

and have the above lines read:

172   (set (setq d-tag (makelabel $outchar)) totaleval)
188   (if (eq (caar r) 'displayinput)
189    (displa `((mlable) ,d-tag ,totaleval)))

lasteval we can then define as a function which applies a user-defined
list of functions to what would have been the $% output.  (That's the
part I don't really know how to do yet, although I imagine it should be
simple enough. Maybe something along the lines of:

(defun lasteval (listoffun arg)
    (cond
       ((null listoffun) (arg))   
       ((lasteval (cdr listoffun)((car listoffun) arg)))))

would work, whatever the legal form of that is. 

CY


		
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