André Thieme <[EMAIL PROTECTED]> writes:
> def nif(num, pos, zero, neg):
> if num > 0:
> return pos
> else:
> if num == 0:
> return zero
> else:
> return neg
def nif(num, pos, zero, neg):
return (neg, zero, pos)[cmp(num, 0)+1]
> The messages were printed in each case.
> To stop that I need lazy evaluation:
> CL-USER> (mapcar #'(lambda (x)
> (funcall
> (nif x
> #'(lambda () (p))
> #'(lambda () (z))
> #'(lambda () (n)))))
> '(0 2.5 -8))
in Python:
def lazy_nif(num, pos, zero, neg):
return (neg, zero, pos)[cmp(num, 0)+1]() # the () at the end means
funcall
map(lambda x: lazy_nif(x, p, z, n), (0, 2.5, -8))
"nif" is even cleaner in Haskell, if I have this right:
nif x p z n | (x < 0) = n
| (x == 0) = z
| (x > 0) = p
All Haskell evaluation is automatically lazy, so no lambdas etc. needed.
--
http://mail.python.org/mailman/listinfo/python-list
