Examples

It may not be entirely obvious how all of the above fit together. To help make it clear, here’s some examples of pipes and their functions in action.

File Processing Example

The following example will take an input file name $inputFile, load its content into memory, trim whitespace, split it by lines into an array, call a custom pairUp() function on that array, filter the resulting array, and then count the remaining values. All of that in one simple statement.

use function Cline\fp\{pipe, explode, afilter};

$result = pipe($inputFile,
    file_get_contents(...),
    trim(...),
    explode(PHP_EOL),
    pairUp(...),
    afilter(static fn($v): bool => $v[0] > $v[1]),
    count(...),
);

Lazy Generator Example

This example uses a custom function to read lines from a file lazily. That produces a lazy generator, which is then passed to itmap() which will apply parse() to each item in the generator, but is itself a generator so is also lazy. parse() produces a Step object from each line of input. reduce() therefore receives an iterable of Step objects, and applies move() to each one in turn, from a starting point. Each time, move() returns a new Position.

In other words, these few lines of code constitute a complete script parsing engine, albeit a simple one. Because each step is lazy, only one Step is loaded into memory at once.

use function Cline\fp\{pipe, itmap, reduce};

function lines(string $file): iterable
{
    $fp = fopen($file, 'rb');

    while ($line = fgets($fp)) {
        yield trim($line);
    }

    fclose($fp);
}

function parse(string $line): Step
{
    [$cmd, $size] = \explode(' ', $line);
    return new Step(cmd: Command::from($cmd), size: (int)$size);
}

$end = pipe($inputFile,
    lines(...),
    itmap(parse(...)),
    reduce(new Position(0, 0), move(...)),
);

Greedy Array Version

The alternate version below uses the greedy amap() instead. That will produce an already-computed array of Step objects rather than a generator that produces Step objects.

use function Cline\fp\{pipe, amap, reduce};

$end = pipe($inputFile,
    lines(...),
    amap(parse(...)),
    reduce(new Position(0, 0), move(...)),
);