gistfile1.php

<?php

class F
{
	protected $f;
	protected $params = array();

	public function __construct(callable $c, array $params = null)
	{
		$this->f = $c;

		if($params !== null)
		{
			$this->params = $params;
		}
		else {
			$ref = self::callableReflection($c);

			foreach($ref->getParameters() as $p) {
				$this->params[] = [
					'optional' => $p->isOptional(),
					'name'     => $p->getName()
				];
			}
		}
	}

	public function __invoke()
	{
		return call_user_func_array($this->f, func_get_args());
	}

	public function getParameters()
	{
		return $this->params;
	}

	public function compose(F $g)
	{
		return new F(function() use($g) {
			return $this(call_user_func_array($g, func_get_args()));
		}, $g->getParameters());
	}

	public static function callableReflection(callable $callable)
	{
		if(is_array($callable) && count($callable) === 2) {
			return new ReflectionMethod(array_shift($callable), array_shift($callable));
		}
		elseif(is_string($callable) && strpos($callable, ':') !== false) {
			return new ReflectionMethod($callable);
		}
		elseif(is_object($callable)) {
			return new ReflectionMethod($callable, '__invoke');
		}
		else {
			return new ReflectionFunction($callable);
		}
	}
}

$f = new F(function($a) {
	return $a.'bar';
});

var_dump($f('foo'));

$g = new F(function($a) {
	return strtoupper($a);
});

var_dump($g('test'));

$h = $f->compose($g);

var_dump($h('foo'));