Op 2005-01-18, Diez B. Roggisch schreef <[EMAIL PROTECTED]>: >> Something else I was thinking about. I think it would be nice if the >> python compilor could figure out whether a genexp in a list or tuple >> expression always generates the same list or tuple and then instead >> of generating code would generate the list or tuple in place. > > This won't ever happen in python - at least not in python otherwise similar > to the one we know... > > The thing you're after is known as "common subexpression elemination" and > can only be done in purely functional languages. While that certainly is an > interesting property of a language, it e.g. forbids functions like > time.time() - a too huge paradigm shift for python. >
I don't see how generating byte code for a = 9; when seeing the expression a = 3 + 6, would be a problem for non-functional languages. I agree that things like [time.time() for i in xrange(10)] shouldn't be pregenerated and that the problem is more complicated as I thought. But during compilation the compilor could do an anlysis of the code do determine whether there are side effects or not. If the compilor then would store a code in the byte code for functions that are guaranteed side-effect free and only pregenerated objects generated by expressions with no side-effect, some common subexpression elimination could be done even in a non-functional language. -- Antoon Pardon -- http://mail.python.org/mailman/listinfo/python-list
