Iterator 0.03

Iterator is a general-purpose iterator class.

SYNOPSIS

use Iterator;

# Making your own iterators from scratch:
$iterator = Iterator->new ( sub { code } );

# Accessing an iterator's values in turn:
$next_value = $iterator->value();

# Is the iterator out of values?
$boolean = $iterator->is_exhausted();
$boolean = $iterator->isnt_exhausted();

# Within {code}, above:
Iterator::is_done(); # to signal end of sequence.

This module is meant to be the definitive implementation of iterators, as popularized by Mark Jason Dominus's lectures and recent book (Higher Order Perl, Morgan Kauffman, 2005).

An "iterator" is an object, represented as a code block that generates the "next value" of a sequence, and generally implemented as a closure. When you need a value to operate on, you pull it from the iterator. If it depends on other iterators, it pulls values from them when it needs to. Iterators can be chained together (see Iterator::Util for functions that help you do just that), queueing up work to be done but not actually doing it until a value is needed at the front end of the chain. At that time, one data value is pulled through the chain.

Contrast this with ordinary array processing, where you load or compute all of the input values at once, then loop over them in memory. It's analogous to the difference between looping over a file one line at a time, and reading the entire file into an array of lines before operating on it.

Iterator.pm provides a class that simplifies creation and use of these iterator objects. Other Iterator:: modules (see "SEE ALSO") provide many general-purpose and special-purpose iterator functions.

Some iterators are infinite (that is, they generate infinite sequences), and some are finite. When the end of a finite sequence is reached, the iterator code block should throw an exception of the type Iterator::X::Am_Now_Exhausted; this is usually done via the "is_done" function.. This will signal the Iterator class to mark the object as exhausted. The "is_exhausted" method will then return true, and the "isnt_exhausted" method will return false. Any further calls to the "value" method will throw an exception of the type Iterator::X::Exhausted.

Note that in many, many cases, you will not need to explicitly create an iterator; there are plenty of iterator generation and manipulation functions in the other associated modules. You can just plug them together like building blocks.

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Requirements:

· Perl