An implementation for currying in PHP
Currying a function means the ability to pass a subset of arguments to a function, and receive back another function that accept the rest of the arguments. As soon as the last one is passed it gets back the final result.
Like this:
use Cypress\Curry as C;
$adder = function ($a, $b, $c, $d) {
return $a + $b + $c + $d;
};
$firstTwo = C\curry($adder, 1, 2);
echo $firstTwo(3, 4); // output 10
$firstThree = $firstTwo(3);
echo $firstThree(14); // output 20Currying is a powerful (yet simple) concept, very popular in other, more purely functional languages. In haskell for example, currying is the default behavior for every function.
In PHP we still need to rely on a wrapper to simulate the behavior
composer require cypresslab/php-curryIn your PHP scripts (with composer autoloader in place) just import the namespace and use it!
use Cypress\Curry as C;
$chunker = C\curry('array_chunk', ['a', 'b']);
var_dump($chunker(1)); // output [['a'], ['b']]
var_dump($chunker(2)); // output [['a', 'b']]It's possible to curry a function from left (default) or from right.
$divider = function ($a, $b) {
return $a / $b;
};
$divide10By = C\curry($divider, 10);
$divideBy10 = C\curry_right($divider, 10);
echo $divide10By(10); // output 1
echo $divideBy10(100); // output 10You can also curry a function and passing the parameters as an array, just use the *_args version of the function
use Cypress\Curry as C;
$divider = function ($a, $b) {
return $a / $b;
};
$division = C\curry_args($adder, [100, 10]);
echo $division(); // output 10
$division2 = C\curry_right_args($adder, [100, 10]);
echo $division2(); // output 0.1Optional parameters and currying do not play very nicely togheter. This library exclude optional parameters by default.
$haystack = "haystack";
$searches = ['h', 'a', 'z'];
$strpos = C\curry('strpos', $haystack); // You can pass function as string too!
var_dump(array_map($strpos, $searches)); // output [0, 1, false]But strpos has an optional $offset parameter that by default has not been considered.
If you want to take it into account you should fix the curry to a given length
$haystack = "haystack";
$searches = ['h', 'a', 'z'];
$strpos = C\curry_fixed(3, 'strpos', $haystack);
$finders = array_map($strpos, $searches);
var_dump(array_map(function ($finder) {
return $finder(2);
}, $finders)); // output [false, 5, false]curry_right have its fixed version named curry_right_fixed