Test for being prime with a regular expression in Nim (aka Nimrod)

re_check_prime.nim

# regular expression to check a number for being prime
#
# see: http://www.noulakaz.net/weblog/2007/03/18/a-regular-expression-to-check-for-prime-numbers/

import re, strutils

let rprime = re"^1?$|^(11+?)\1+$"

proc testPrime(n: int): bool =
    not (repeatChar(n, '1') =~ rprime)

for n in 1..10_000:
    echo n, " is", if not testPrime n: " not" else: "", " prime"

It is pretty astonishing how good that works ... and even performs ;-)