[Tutor] Learning Python using other languages --- round two

[Danny Yoo]

[For people who are beginning to learn Python; skip this message.  This is
about something else.  *grin*]


Hi everyone,

A while back, I wrote about thinking about writing a Scheme interpreter in
Python.

    http://aspn.activestate.com/ASPN/Mail/Message/811896


Well, I just couldn't hold back from unleashing this monstrosity.  I bring
to you... Pyscheme!

    http://hkn.eecs.berkeley.edu/~dyoo/python/pyscheme/


I thought it might be interesting for anyone who'd like to see an example
of writing one language in terms of another.  Here's an example of it in
action:


###
dyoo@einfall:~/pyscheme-1.0/pyscheme$ python scheme.py
Welcome to PyScheme!  Type: (QUIT) to quit.


[PyScheme] >>> (define (square x) (* x x))
ok
[PyScheme] >>> (define (cube x) (* (square x) x))
ok
[PyScheme] >>> square
(compound-procedure (x) ((* x x)) <procedure-env>)
[PyScheme] >>> cube
(compound-procedure (x) ((* (square x) x)) <procedure-env>)
[PyScheme] >>> (cube 2)
8
[PyScheme] >>> (cube 2000)
8000000000
[PyScheme] >>> (define (factorial x)
[......1)] >>>    (if (= x 0)
[......2)] >>>        1
[......2)] >>>        (* x (factorial (- x 1)))))
ok
[PyScheme] >>> (factorial 2)
2
[PyScheme] >>> (factorial 3)
6
[PyScheme] >>> (factorial 4)
24
[PyScheme] >>> (quit)
BYE
###


So if you ever wanted to look into the guts of a really ugly program,
Pyscheme is now a candidate.  *grin* I'll have to study Python a little
more, but I'd be really happy if I can get tail recursion to work
properly...  Anyway, this was my side project for the winter, so I wanted
to share it with the people here.