note smls <h3>Non-recursive solution</h3> <p>For completeness, here's a solution that does <i>not</i> use a recursive subroutine:</p> <code> sub nested_foreach(&@) { my \$code = shift; my @indices = map { 0 } @_; # First set of indices is all zeroes my @sizes = map { scalar @\$_ } @_; # Cache array sizes (optional) my \$k; do { # Determine the array elements corresponding to the current set # of indices, and pass them to the closure: \$code->( map { \$_[\$_][\$indices[\$_]] } 0..\$#_ ); # Determine the next set of indices: for (\$k = \$#_; \$k >= 0; \$k--) { \$indices[\$k]++; if (\$indices[\$k] < \$sizes[\$k]) { last; } else { \$indices[\$k] = 0; } } # If \$k went out-of-bounds, there are no more valid iterations: } while (\$k >= 0); } my @a = ...; my @b = ...; my @c = ...; nested_foreach { say join ' ', @_ } \@a, \@b, \@c; </code> <p>The "<i>Determine the next set of indices</i>" step may seem a little complicated at first sight, but it becomes more intuitive if you think of the <code>@indices</code> array as an integer number (with each element representing a digit), and imagine that we want to "increment" that "number" by 1. It's not a decimal (i.e. base-10) number, but rather one where each digit can have a different base (i.e. the sizes of the input arrays) - but that doesn't really change anything.</p> <p>Incrementing the "number" by 1 works just like the <b>integer addition</b> <i>(here with an addend of 1)</i> that you were taught back in primary school: Start with the right-most digit; increment it; if it's still within the valid range of digits then you're done; if instead it went above the limit then wrap it around to zero, "carry the one", and repeat the same steps with the next digit to the left.</p> <hr> <p><i>Update:</i></p> <h3>Performance comparison</h3> <p>Interestingly, my iterative solution seems to be significantly <b>slower</b> than [id://1064678|BrowserUK's recursive solution], at least when running on my PC and with various different numbers/sizes of input arrays I tried:</p> <code> sub nested_foreach(&@) { ... # see above } sub nForX(&@) { ... # see BrowserUK's post } # my @size = (500, 900); # my @size = (5, 5, 5, 5, 5, 5, 5, 5); my @size = (100, 4, 75, 23); my @AoA = map { [map { chr(\$_+64) x int(rand(10)) } 1 .. \$_] } @size; cmpthese -10, { iterative => sub { nested_foreach { join("", @_) } @AoA }, recursive => sub { nForX { join("", @_) } scalar @AoA, @AoA }, }; </code> <code> s/iter iterative recursive iterative 1.86 -- -71% recursive 0.532 249% -- </code> 1064607 1064607