[Push] recent updates

[Lee Spector]

Pushers,

I've just updated a couple of Push2 things, mostly in response to 
suggestions from Maarten Keijzer:

- The specification has changed for the result of division or modulus 
by zero: these now act as NOOPs (the thing we usually do for 
"exceptional" conditions in Push) rather than pushing a default value 
(which was a notion inherited from standard GP's protected division).

- Similarly, *.GET instructions act as NOOPs if the provided NAMEs 
don't have bindings.

- The "test1" test suite has been updated (mostly for the above).

- The Lisp source has been updated for the above; the C++ source will 
be updated soon.

- A description of the Push random code generation algorithm has been 
added to the specification 
(http://hampshire.edu/lspector/push2-description.html). This previously 
appeared in the Genetic Programming and Evolvable Machines article on 
Push.

- A brief "Under Discussion" section has also been added to 
http://hampshire.edu/lspector/push2-description.html, mentioning a 
couple of possible future extensions (or at least food for thought).

  -Lee

--
Lee Spector
Dean, Cognitive Science + Associate Professor, Computer Science
Cognitive Science, Hampshire College, Amherst, MA 01002
lspector at hampshire.edu, http://hampshire.edu/lspector/
Phone: 413-559-5352, Fax: 413-559-5438