How do I read two items at a time in a Perl foreach loop?

Question

What I\'m looking for is something like:

@list = qw(1 2 3 4 5 6);
foreach (@list) {
  #perl magic goes here 
  print \"i: $i, j:$j\\n\";
}

Answer 1

How about a general purpose functional solution.

use Carp; # so mapn can croak about errors

sub mapn (&$@) {
    my ($sub, $n, @ret) = splice @_, 0, 2;
    croak '$_[1] must be >= 1' unless $n >= 1;
    while (@_) {
        local *_ = \$_[0];
        push @ret, $sub->(splice @_, 0, $n)
    }
    @ret
}

sub by ($@) {mapn {[@_]} shift, @_}
sub every ($@); *every = \&by;

The mapn function works just like map, except the first argument after its block is the number of elements to take. It places the first element in $_ and all of the elements in @_ .

print mapn {"@_\n"} 2 => 1 .. 5;
# prints
1 2
3 4
5

The next two identical subs, by and every create useful adverbs for the various looping constructs. They process the list with mapn, and return a list of array refs of the desired size

print "@$_\n" for every 2 => 1..10;

print map {"@$_\n"} grep {$_->[1] > 5} by 2 => 1..10;

I find this to be a cleaner and more intuitive solution than natatime, or other one off solutions like a c style for loop.