When nesting map{}s inside each other, the inner map{} can not have any idea of what the outer map{}'s value of $_ is, without using a temporary variable, which is terribly inelegant. So I wrote this, which I intend to offer as a sacrifice on the altar of CPAN. Any comments are welcome.
package NestedMap;
require Exporter;
@ISA = qw(Exporter);
@EXPORT = qw(nestedmap);
use strict;
use warnings;
# [POD snipped out]
sub nestedmap(&@) {
my $f = shift;
map {
local @NestedMap::stack = ($_, @NestedMap::stack);
$f->($_);
} @_
}
You might use it thus (from the perldoc):
# show all combinations of (A,B,C) (a,b,c) and (1,2,3)
print join("\n",
nestedmap {
nestedmap {
nestedmap {
join('',@NestedMap::stack[0..2])
} qw(A B C)
} qw(a b c)
} qw(1 2 3)
);
update: thanks to broquaint for pointing out that the example only works in 5.8.0. To get it to co-operate with 5.6.1, change
nestedmap { ... } list
to
nestedmap sub { ... }, list