<?php

namespace PhatCats\ObjectTypeclass;

/**

* A fuctor with application. An applicative containing a function can be

* applied to an argument contained in another applicative.

*/

trait ObjectApplicative {

use ObjectFunctor;

/**

* @param A value to be put into a minimal context.

* @return The given value in a context.

*/

abstract public function pure($val);

/**

* Partially applies the function contained in this ObjectApplicative to the value

* contained in the given applicative argument.

*

* @param $applicativeArgument | null: An object whose class implements the

* Functor trait. If null is passed, then the wrapped function

* should be called without arguments.

* @return An ObjectApplicative of the same class as this one containing either

* another partially-applied function or a non-function value.

*/

final public function apply($applicativeArgument = null) {

return is_null($applicativeArgument) ?

$this->applyNoArg() :

$this->applyToArg($applicativeArgument);

}

/**

* Calls the wrapped function with no arguments.

*/

protected abstract function applyNoArg();

/**

* Calls the wrapped function on the value wrapped in the supplied argument.

*/

protected abstract function applyToArg($applicativeArgument);

/**

* The __invoke magic method allows the ObjectApplicative to be called like a

* normal function but whose implementation gives it the ObjectApplicative

* behavior. The implementation of __invoke should handle being called with

* zero or more arguments and "do the right thing."

* @return The value returned by applying the function in a context to one

* or more values in a context. This value is itself put into a

* context: the same context as this one.

*/

public function __invoke() {

$args = func_get_args();

$numArgs = count($args);

if ($numArgs > 0) {

$callback = function ($applicativeFun, $applicativeArg) {

return $applicativeFun->apply($applicativeArg);

};

$result = array_reduce($args, $callback, $this);

} else {

$result = $this->apply();

}

return $result;

}

}