primes.groovy

@Grab("org.functionaljava:functionaljava:3.1")

import fj.F
import fj.data.Stream
import groovy.transform.Memoized

@Memoized
Stream<Integer> primes() {
    Stream.cons(2, { ->
        Stream.range(3).filter { Integer i ->
            primes().takeWhile({ Integer j -> j * j <= i } as F).forall { Integer k -> i % k != 0 }
        }
    })
}

println primes().takeWhile { it <= 20 }