Iteration primitives using generators
=====================================

This library implements iteration primitives like `map()` and `filter()`
using generators. To a large part this serves as a repository for small
examples of generator usage, but of course the functions are also practically
quite useful.

All functions in this library accept arbitrary iterables, i.e. arrays,
traversables, iterators and aggregates, which makes it quite different from
functions like `array_map()` (which only accept arrays) and the SPL iterators
(which usually only accept iterators, not even aggregates). The operations are
of course lazy.

Install
-------

To install with composer:

```sh
composer require nikic/iter
```

Functionality
-------------

A small usage example for the ``map()`` and ``range()`` functions:

```php
<?php

use iter\func;

require 'path/to/vendor/autoload.php';

$nums = iter\range(1, 10);
$numsTimesTen = iter\map(func\operator('*', 10), $nums);
// => iter(10, 20, 30, 40, 50, 60, 70, 80, 90, 100)
```

You can find documentation and usage examples for the individual functions in
[iter.php](https://github.com/nikic/iter/blob/master/src/iter.php), here I only
list the function signatures as an overview:

    Iterator map(callable $function, iterable $iterable)
    Iterator mapWithKeys(callable $function, iterable $iterable)
    Iterator mapKeys(callable $function, iterable $iterable)
    Iterator flatMap(callable $function, iterable $iterable)
    Iterator reindex(callable $function, iterable $iterable)
    Iterator filter(callable $predicate, iterable $iterable)
    Iterator enumerate(iterable $iterable)
    Iterator toPairs(iterable $iterable)
    Iterator fromPairs(iterable $iterable)
    Iterator reductions(callable $function, iterable $iterable, mixed $startValue = null)
    Iterator zip(iterable... $iterables)
    Iterator zipKeyValue(iterable $keys, iterable $values)
    Iterator chain(iterable... $iterables)
    Iterator product(iterable... $iterables)
    Iterator slice(iterable $iterable, int $start, int $length = INF)
    Iterator take(int $num, iterable $iterable)
    Iterator drop(int $num, iterable $iterable)
    Iterator takeWhile(callable $predicate, iterable $iterable)
    Iterator dropWhile(callable $predicate, iterable $iterable)
    Iterator keys(iterable $iterable)
    Iterator values(iterable $iterable)
    Iterator flatten(iterable $iterable, int $levels = INF)
    Iterator flip(iterable $iterable)
    Iterator chunk(iterable $iterable, int $size, bool $preserveKeys = false)
    Iterator chunkWithKeys(iterable $iterable, int $size)
    Iterator tap(callable $function, iterable $iterable)
    Iterator toIter(iterable $iterable)

    Iterator range(number $start, number $end, number $step = null)
    Iterator repeat(mixed $value, int $num = INF)
    Iterator split(string $separator, string $data)

    mixed    reduce(callable $function, iterable $iterable, mixed $startValue = null)
    bool     any(callable $predicate, iterable $iterable)
    bool     all(callable $predicate, iterable $iterable)
    mixed    search(callable $predicate, iterable $iterable)
    void     apply(callable $function, iterable $iterable)
    string   join(string $separator, iterable $iterable)
    int      count(iterable $iterable)
    bool     isEmpty(iterable $iterable)
    mixed    recurse(callable $function, $iterable)
    array    toArray(iterable $iterable)
    array    toArrayWithKeys(iterable $iterable)
    bool     isIterable($value)

As the functionality is implemented using generators the resulting iterators
are by default not rewindable. This library implements additional functionality
to allow creating rewindable generators.

You can find documentation for this in [iter.rewindable.php](https://github.com/nikic/iter/blob/master/src/iter.rewindable.php),
here is just a small usage example of the two main functions:

```php
<?php

use iter\func;

require 'path/to/vendor/autoload.php';

/* Create a rewindable map function which can be used multiple times */
$rewindableMap = iter\makeRewindable('iter\\map');
$res = $rewindableMap(func\operator('*', 3), [1, 2, 3]);

/* Do a rewindable call to map, just once */
$res = iter\callRewindable('iter\\map', func\operator('*', 3), [1, 2, 3]);
```

The above functions are only useful for your own iterators though; for the
`iter` iterators, rewindable variants are directly provided with an
`iter\rewindable` prefix:

    $res = iter\rewindable\map(func\operator('*', 3), [1, 2, 3]);
    // etc