Le 28-08-2013, Thomas Baruchel <baruc...@gmx.com> a écrit :
> The following functions are fully usable; I hope someone will enjoy using
> them.
>
> If you are not interested by the explanations, just jump to the end of the
> message and take my functions for using them.
Despite the very short size of my function, I made a module of it as a
convenience for my own use. I share here my "recursion.py" file in which
I also added some docstrings.
----------------- module "recursion.py" -------------------------------
"""
The recursion module provides convenient functions for handling
recursion with lambda functions.
The famous Y-combinator is provided as a convenience, but the most
distinctive function of the module is the B function for handling
tail-recursion.
Written by Thomas Baruchel
"""
Y = lambda f: (lambda x: x(x))(lambda y: f(lambda *args: y(y)(*args)))
def B(func):
"""
B(lambda) -> lambda
Return a usable function from a lambda expression written with a
tail-recursion style. The new function will be evaluated inside
a loop with no recursive calls, allowing high depths of recursion.
Since the internal loop evaluates the return of the function as long
as it is callable, the function does not work with functions returning
functions (at the end of the recursive calls); there is no restriction
otherwise.
E.g.:
fac = lambda f: lambda a,b: b if a==0 else f(a-1,a*b)
func = B(fac)
func(5,1)
--> 120
or more shortly:
B(lambda f: lambda a,b: b if a==0 else f(a-1,a*b))(5,1)
--> 120
"""
x = (lambda f: (lambda x: x(x))(lambda y:
f(lambda *args: lambda: y(y)(*args))))(func)
def wrapper(*args):
out = x(*args)
while callable(out):
out = out()
return out
return wrapper
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