Add bind() function

[shadowhand]

Actual changes are in 5d69102

Fixes #5
Refs #4

[jrsinclair]

Would it make more sense to rename bind() to partial(), as you suggest in #5? If we were to implement a function called bind, then I would have assumed its primary function would be to call a method on a given object (as with JavaScript). For example:

<?php
class Identity {

    private $_val;

    public function __construct($val) {
        $this->val = $val;
    }

    public function map($f) {
        return new Identity($f($this->val));
    }

    public function chain($f) {
        return $f($this->val);
    }
}

function bind($method_name, $obj) {
    return function () use ($method_name) {
        $params = func_get_args();
        return call_user_func_array(array($obj, $method_name), $params);
    }
}

$i1        = new Identity(1);
$add1      = function ($x) { return $x + 1; };
$times3    = function ($x) { return new Identity($x * 3); };
$mapOnI1   = bind('map', $i1);
$chainOnI1 = bind('chain', $i1);
$i2        = $mapOn1($add1);     // Identity(2)
$i3        = $chainOn1($times3); // Identity(3)

[i-am-tom]

I'm not sure it makes sense - if you're going to write curried PHP, wouldn't you write them as nested functions anyway? (Genuine question - I haven't touched PHP in about 2 years now)

[jrsinclair]

My point was more about how the function is named. I think it should be called partial() rather than bind(). My reasoning was to prevent confusion for people coming from JavaScript, who might expect a function named bind() to work a bit differently to partial().

Whether or not you need a partial() when you've got curried functions is another question. You certainly don't need it. As @i-am-tom points out, you can just return a nested function. But I can think of some use cases where it might come in handy. It would be a convenience more than anything.