Optimize Ben Davies' challenge 133 task 2 solution

&prime-factors is eager to invoke Int.is-prime; cache an infinite
sequence of primes so it gets called once per prime max.

1 files changed, 2 insertions, 1 deletions

diff --git a/challenge-133/ben-davies/raku/ch-2.raku b/challenge-133/ben-davies/raku/ch-2.raku
index ba862a20e4..831d18bda1 100644
--- a/challenge-133/ben-davies/raku/ch-2.raku
+++ b/challenge-133/ben-davies/raku/ch-2.raku
@@ -9,5 +9,6 @@ sub digits(Int:D $x, Int:D $base) {
     $x.polymod($base xx $x.log: $base).reverse
 }
 sub prime-factors(Int:D $x is copy) {
-    gather $x div= take (2..$x).grep(*.is-prime).first($x %% *) while $x > 1
+    state Int:D @primes = (2..*).grep(*.is-prime);
+    gather $x div= take @primes.first($x %% *) while $x > 1
 }