perl  

Nov 12, 2014 • Michael Chen

To generate a list of numbers, Perl provides the syntax .. (double dots). However, the syntax only provides ascending sequences with 1 increment. What can we do if we need more flexible sequences in Perl?

In the following example, you can see that .. only generate an ascending sequence.

# print out 1 2 3 ... 10
$ perl -le '$, = " "; print (1..10);'

# print out nothing
$ perl -le '$, = " "; print (10..1);'

If you need more flexible iterators or generators, you may check out List::Gen module. This module provides higher order functions, list comprehensions, generators, iterators, and other utility functions.

For example, function range generates a generator that can be used in loop.

use feature qw(say);
use List::Gen qw(range);

# generate 10, 8, 6, 4, 2
my $range = range(10, 1, -2);

for my $i (@{$range}) {
    # do something
}

There are still functions worth exploring. You may check the page of List::Gen to find useful functions.