class TailCall(Exception):
def __init__(self, f, *args, **kwargs):
self.f = f
self.args = args
self.kwargs = kwargs
def has_tail_calls(f):
def tail_call_wrapper(*args, **kwargs):
current_func = f
while True:
try:
return current_func(*args, **kwargs)
except TailCall, e:
current_func = getattr(e.f, '_tail_callable', e.f)
args = e.args
kwargs = e.kwargs
tail_call_wrapper._tail_callable = f
tail_call_wrapper.__doc__ = f.__doc__
return tail_call_wrapper
@has_tail_calls
def sum_range(n, total=0):
"""Sum the integers from 1 to n.
Obviously the same as n(n+1)/2, but this is a test, not a demo.
>>> sum_range(1)
1
>>> sum_range(100)
5050
>>> sum_range(100000)
5000050000L
"""
if not n:
return total
else:
raise TailCall(sum_range, n - 1, n + total)
@has_tail_calls
def fact2(n, v=1):
"""Factorial.
>>> fact2(1)
1
>>> fact2(2)
2
>>> fact2(3)
6
>>> fact2(4)
24
>>> fact2(20)
2432902008176640000L
"""
if not n:
return v
else:
raise TailCall(fact2, n - 1, v * n)
if __name__ == '__main__':
import doctest
doctest.testmod()
