A simple PIC api

[Mark Roos]

>From Jochen

Do I also understand right, that your test for checking if the current 
target is still valid is limited to only the receiver?

Well yes and no.  In my case the test examines all of the arguments on the 
stack and computes
an 'behavior' reference.  This reference is the head of a linked list of 
method dictionaries which
the fallback searches to locate the code for this callsite and that 
behavior.  The yes part is that
in my Smalltalk the behavior is stored in a field of the object on the top 
of the stack.  This happens
to be the receiver.

For the proposed api the test can examine the entire stack and callsite to 
determine the dispatch. 
I do plan to support multi methods which could be an expensive test.  I 
just wanted to do it once 
regardless of the number of guards.

        I also do special 
        things to not add guards if I can, since each guard costs... 
though the 
        information I use there is static so far

I would expect in a perfect world for the guards to be cheap if the jvm 
knew the were part of
a pic.

regards
mark
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