Michele Simionato wrote:
On Sep 3, 6:41 pm, Ethan Furman <et...@stoneleaf.us> wrote:
The original thread by Bearophile:
http://mail.python.org/pipermail/python-list/2009-May/711848.html
I have read the thread. What Bearophile wants can be implemented with
a bytecode hack, no
need for the decorator module. Let me call 'recur' the self-function,
like in Clojure.
You can define a decorator that makes "self-conscious" a recursive
function as follows:
# requires byteplay by Noam Raphael
# see http://byteplay.googlecode.com/svn/trunk/byteplay.py
from byteplay import Code, LOAD_GLOBAL, STORE_FAST, LOAD_FAST
def enable_recur(f):
print f.func_code.co_names
if 'recur' not in f.func_code.co_names:
return f # do nothing on non-recursive functions
c = Code.from_code(f.func_code)
c.code[1:1] = [(LOAD_GLOBAL, f.__name__), (STORE_FAST, 'recur')]
for i, (opcode, value) in enumerate(c.code[2:]):
if opcode == LOAD_GLOBAL and value == 'recur':
c.code[i+2] = (LOAD_FAST, 'recur')
f.func_code = c.to_code()
return f
## example of use
@enable_recur
def f(x):
if x == 1:
return 1
else:
return x*recur(x-1)
print f(4) # =>24
Please accept this without explanation since it would take me a lot of
time
to explain how it works. Just accept that bytecode hacks are
incredible
(and nonportable too) ;-)
Michele Simionato
No worries -- not sure I would understand the explanation at this point,
anyway!
Just to verify, using the decorator module is portable, yes?
~Ethan~
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