use strict; use warnings;
use Algorithm::Combinatorics qw(permutations);

my $strings = [qw(A
B
C)];

my $iter = permutations($strings, 3);

while (my $c = $iter->next) {
    print "@$c\n";
}
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The problem is that it does not generate things like AAA, BBB, CCC [A, B, C would be the corresponding SMILEs).

I am trying to generate an exhaustive list of SMILES codes, including their repetitions.

permutations are reorderings, i.e. samples without replacement. You seem to want all possible samples with replacement, i.e. variations_with_repetition.