#!/usr/bin/ruby

#
## https://rosettacode.org/wiki/Emirp_primes
#

func forprimes(a, b, callback) {
    for (var p = a.dec.next_prime; p <= b; p.next_prime!) {
        callback(p)
    }
}

func is_emirp(p) {
    var str = Str(p)
    var rev = str.reverse
    (str != rev) && is_prime(Num(rev))
}

func emirp_list(count) {
    var i = 13
    var inc = (100 + 10*count)
    var n = []
    while (n.len < count) {
        forprimes(i, i+inc - 1, {|p|
            is_emirp(p) && (n << p)
        })
        (i, inc) = (i+inc, int(inc * 1.03) + 1000)
    }
    n.splice(count)
    return n
}

var emirps = emirp_list(20)

say ("First 20: ", emirps.join(' '))
say ("Between 7700 and 8000: ", gather {
        forprimes(7700, 8000, {|p| is_emirp(p) && take(p) })
}.join(' '))

assert_eq(emirps, [13, 17, 31, 37, 71, 73, 79, 97, 107, 113, 149, 157, 167, 179, 199, 311, 337, 347, 359, 389])