php高级函数式编程——创建类似于ramdaJS的curry方法

Question

要求：

1. 占位符支持
2. 部分应用函数可以应用于部分应用函数
3. 咖喱
4. 5.6 PHP 支持

这是我的尝试，但它只支持 hhvm 3.7，正如您在 http://3v4l.org/0i5FV 上的示例中看到的那样

<?php 
class Placeholder{}
function curry(callable $func, ... $curriedArgs) {
    return function(...$fulfillment) use ($func, $curriedArgs) {
        $removedPlaceheldArgs = array_map(function($arg) use ($fulfillment) {
            if ($arg instanceof Placeholder)
                return array_shift($fulfillment);
            return $arg;
        }, $curriedArgs);
        return $func(...array_merge($removedPlaceheldArgs, $fulfillment));
    };
};

这是我的用法示例：

$resultset = json_decode('[{
  "id": 1,
  "gender": "Male",
  "name": "Matthew"
}, {
  "id": 2,
  "gender": "Male",
  "name": "Willie"
}, {
  "id": 3,
  "gender": "Female",
  "name": "Ann"
}, {
  "id": 4,
  "gender": "Female",
  "name": "Margaret"
}, {
  "id": 5,
  "gender": "Female",
  "name": "Marie"
}]',TRUE);

$filterGender = function($row,$gender){
    return $row['gender']==$gender;
};

$detectMen = curry($filterGender,(new Placeholder),'Male');
$detectWomen = curry($filterGender,(new Placeholder),'Female');

var_dump($detectMen(['gender'=>'Male'])); //works -- expected result TRUE

$getLadies = curry('array_filter',(new Placeholder),$detectWomen);

var_dump($getLadies($resultset)); //does not work -- expected result Ladies from result set

可以在 PHP 5.6 中实现 $getLadies 结果而不仅仅是 hhvm 吗？

Answer 1

您可以使用来自Non-standard PHP library 的partial application 和curry 函数：

use function nspl\f\rpartial;

$detectMen = rpartial($filterGender, 'Male');
$detectWomen = rpartial($filterGender, 'Female');

var_dump($detectMen(array('gender' => 'Male')));

$getLadies = rpartial('array_filter', $detectWomen);

var_dump($getLadies($resultset));

Answer 2

它并不漂亮，但这应该是对 Ramda 当前curry 函数的近似模拟。

namespace Phamda {
    function _() {
        static $placeholder;
        if ($placeholder === null) {
            $placeholder = new \stdClass;
        }
        return $placeholder;
    }

    function curryN($n, $f) {
        $curryNRec = function($recv) use ($n, $f, &$curryNRec) {
            return function () use ($recv, $n, $f, &$curryNRec) {
                $left = $n;
                $argsIdx = 0;
                $combined = array();
                $combindedIdx = 0;
                $args = func_get_args();
                while ($combindedIdx < count($recv) || $argsIdx < count($args)) {
                    if ($combindedIdx < count($recv)
                        && ($recv[$combindedIdx] !== _() || $argsIdx > count($args))) {
                        $result = $recv[$combindedIdx];
                    } else {
                        $result = $args[$argsIdx];
                        $argsIdx += 1;
                    }
                    $combined[$combindedIdx] = $result;
                    $combindedIdx += 1;
                    if ($result !== _()) {
                        $left -= 1;
                    }
                }
                if ($left <= 0) {
                    return call_user_func_array($f, $combined);
                } else {
                    return $curryNRec($combined);
                }
            };
        };
        return $curryNRec([]);
    }

    function curry($f) {
        $fRefl = new \ReflectionFunction($f);
        return curryN($fRefl->getNumberOfParameters(), $f);
    }
}

并使用您的示例：

use Phamda as P;

$resultset = json_decode('[{
  "id": 1,
  "gender": "Male",
  "name": "Matthew"
}, {
  "id": 2,
  "gender": "Male",
  "name": "Willie"
}, {
  "id": 3,
  "gender": "Female",
  "name": "Ann"
}, {
  "id": 4,
  "gender": "Female",
  "name": "Margaret"
}, {
  "id": 5,
  "gender": "Female",
  "name": "Marie"
}]', true);

$filterGender = P\curry(function($row, $gender){
    return $row['gender'] == $gender;
});

$detectMen = $filterGender(P\_(), 'Male');
$detectWomen = $filterGender(P\_(), 'Female');

var_dump($detectMen(['gender' => 'Male']));
// bool(true)

$filter = P\curry('array_filter');
$getLadies = $filter(P\_(), $detectWomen);

var_dump($getLadies($resultset));
/*
array(3) {
  [2] =>
  array(3) {
    'id' =>
    int(3)
    'gender' =>
    string(6) "Female"
    'name' =>
    string(3) "Ann"
  }
  [3] =>
  array(3) {
    'id' =>
    int(4)
    'gender' =>
    string(6) "Female"
    'name' =>
    string(8) "Margaret"
  }
  [4] =>
  array(3) {
    'id' =>
    int(5)
    'gender' =>
    string(6) "Female"
    'name' =>
    string(5) "Marie"
  }
}
*/