double x = x + x

from n = n : from (n+1)  

mytake n []     = []
mytake n (x:xs) = if n==0 then [] else x:mytake (n-1) xs

myiterate f a = a : myiterate f (f a)
sieve (p:xs) = filter (\ x -> (x `mod` p) /= 0) xs
primes = map head (myiterate sieve (from 2))