Takes a list or array of array references and returns a function that will return successive permutations of the referenced arrays. Avoids recursion so will work on abitrarily huge sets of data. Runtime scales linearly with the number of sets. Minimal memory usage.
my @aoa = (
    [('a'..'z')],
    [('A'..'Z')],
    [(1..26)],
);


my $iter = make_permutator(@aoa);


while (my @els = $iter->() ){
    print @els,"\n";
}


sub make_permutator{
    my @arefs = @_;
    my @arrayindexes = ();
    foreach (@arefs){
        push @arrayindexes,[$_,0,$#{$_}];
    }
    
    return sub {
            return if $arrayindexes[0]->[1] > $arrayindexes[0]->[2]; 
            my @els =  map { $_->[0]->[ $_->[1]] } @arrayindexes;
            # Check for out of bounds....
            $arrayindexes[$#arrayindexes]->[1]++;
            for (my $i = $#arrayindexes; $i > 0; $i--){
                    if ($arrayindexes[$i]->[1] > $arrayindexes[$i]->[2
+]){
                        $arrayindexes[$i]->[1] = 0;
                        $arrayindexes[$i-1]->[1]++;
                    }else{
                        last;
                    }
            }
            return @els;
            
    };
}

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In reply to Non- recursive permutation of arrays. by shotgunefx

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