Simple implementation of tail-call-elimination

[Daniel Faken]

Hello,

  Just thought I'd share this.
  For more info. about tail-call-elimination, continuations, etc. see
the Scheme language or articles about functional programming in
Python.

  Anyone have a suggestion for a better way to do this?
  (more efficient, elegant, etc..)
  This should be easy to implement in C, for speed.

cheers,
Daniel

dfaken at brandeis.edu

---------------
import types

# Tail-Recursion-Elimination tools
#
# Usage: include a keyword parameter with initial value 'TRE' in the
function(s)
#        from which you wish to eliminate tail-recursion - e.g.
'cont=TRE'.
#        Then, where you would normally use "return Fn(a,b,c..)",
instead
#        call the keyword with the function and its arguments as
parameters
#        - e.g. 'cont(Fn,a,b,c,...)'
#        This allows TRE to control the program flow, and eliminate
deep recursion.
#
# Example:
#   def factorial(n,acc=1,cont=TRE):
#	if n <= 1: return acc
#	else:      return cont(factorial,n-1,acc*n)
#
# N.B. this is not yet set up for use with functions
#      which accept keywords or return multiple values

TRE_magic = "TRE magic string"

def TREcont(fn, *rest): return (TRE_magic, fn, rest)

def TRE(fn, *rest):
	x = fn(cont=TREcont, *rest)
	while isinstance(x, types.TupleType) and (x[0] is TRE_magic):
	  x = x[1](*x[2])
	return x