pyvm -- faster python

[Rocco Moretti]

Paul Rubin wrote:

> Despite the shrieks of the "Python is not Lisp!" crowd, Python
> semantics and Lisp semantics aren't THAT different, and yet compiled
> Lisp implementations com completely beat the pants off of interpreted
> Python in terms of performance.  

I know little about Lisp compilation, so I could be mistaken, but I was 
under the impression that one of the differences between Python & Lisp 
is directly relevant to compilation issues.

Python, as a procedural language, makes extensive use of globals & 
mutable variables. Not only can the contents of a variable change, but 
that change can non-explicitly affect a function in a "remote" part of 
the program, hence the requirement for the Global Interpreter Lock. 
Tracking how changes propagate in Python is non-trivial, as evidenced by 
the difficulty of replacing the GIL with a less "obtrusive" alternative.

IIUC, in Lisp, as a functional language, "all politics is local." 
Global-like variables are much rarer, and mutability is severely 
limited. In this case it is much easier to track how a piece of code 
alters the program's state - the propagation of those changes are 
handled explicitly, and once you have a reference to a piece of data, 
you don't have to worry about some other function changing the value on 
you. As such, it's a lot easier to write an optimizing compiler - you 
can place much greater limits on what is known at compile time.

It's been quite a while since I've looked at Lisp/functional languages, 
though, so I could be misunderstanding what I remember.