genexp surprise (wart?)

[Michele Simionato]

Paul Rubin wrote:
> I tried to code the Sieve of Erastosthenes with generators:
>
>     def sieve_all(n = 100):
>         # yield all primes up to n
>         stream = iter(xrange(2, n))
>         while True:
>             p = stream.next()
>             yield p
>             # filter out all multiples of p from stream
>             stream = (q for q in stream if q%p != 0)
>
>     # print primes up to 100
>     print list(sieve_all(100))
>
> but it didn't work.

This is a known issue with the scope rules in loops which has bitten
many (including
myself; there is a long thread involving me and Jacek Generowitz
debating this at
death, you may find it if you google the newsgroup).

I would be curious to know if your code would work the way you expect
in Haskell
(I know it would for 'for' loop, dunno about 'while' loops, I am
completely ignorant
in Haskell).

       Michele Simionato