-=item cross BLOCK ARRAY ARRAY
-
-Evaluates BLOCK for each combination of elements in ARRAY1 and ARRAY2
-and returns a new list consisting of BLOCK's return values.
-The two elements are set to $a and $b.
-Note that those two are aliases to the original value so changing them
-will modify the input arrays.
-
- # append each to each
- @a = qw/a b c/;
- @b = qw/1 2 3/;
- @x = pairwise { "$a$b" } @a, @b;
- # returns a1, a2, a3, b1, b2, b3, c1, c2, c3
-
-As cross expects an array but returns a list it is not directly chainable
-at the moment. This will be corrected in the future.
-
-=cut
-sub cross(&\@\@) {
- my $op = shift;
- use vars qw/@A @B/;
- local (*A, *B) = @_; # syms for caller's input arrays
-
- # Localise $a, $b
- my ($caller_a, $caller_b) = do {
- my $pkg = caller();
- no strict 'refs';
- \*{$pkg.'::a'}, \*{$pkg.'::b'};
- };
-
- local(*$caller_a, *$caller_b);
-
- # This map expression is also the return value.
- map { my $a_index = $_;
- map { my $b_index = $_;
- # assign to $a, $b as refs to caller's array elements
- (*$caller_a, *$caller_b) = \($A[$a_index], $B[$b_index]);
- $op->(); # perform the transformation
- } 0 .. $#B;
- } 0 .. $#A;