> > http://en.literateprograms.org/Sieve_of_Eratosthenes_%28Haskell%29
> I'm not sure that's even valid Haskell though. Looks like two type
> definitions for the same function, and even if you correct that I
> don't think it produces what one might think it does. At least not on
> GHC :-)
The second type definition on the referred page is not needed
(actually you don't need either defn). The function works
but you have to give it [2..], all natural numbers >= 2. The
prime sieve definition I like most is this:
sieve (a:xs) = a:sieve [x | x<- xs, x `mod` a > 0]
primes = sieve [2..]
Now you can just do
100 `take` primes
to get first 100 primes.
A stream such as primes will (and must) return the same Nth
value every time so after computing a value it will be cached
for later. A stream in effect has storage proportional to
the number of cdr (i.e. tail) operations done on it. A
channel on the other hand needs fixed minimum storage to
affect one value transfer and it has no memory of what was
already transferred.
