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<header>Updated: 2017-04-13 18:52:38 CST +08</header>
<main>
<h1 id="php-functional-programming-lambda">PHP Functional Programming Lambda</h1>
<h2 id="recursion">Recursion</h2>
<p>遞迴。例：運算連續整數總合</p>
<ul>
<li>loop</li>
</ul>
<pre><code class="language-php">function head_sum($x) {
for($x; $x > 0; $x--) {
$sum += $x;
}
return $sum;
}
</code></pre>
<ul>
<li>recursion</li>
</ul>
<pre><code class="language-php">function head_sum($x) {
return ($x == 1) ? $x : $x + head_sum($x - 1);
}
head_sum(10)
</code></pre>
<h2 id="anonymous-function">Anonymous function</h2>
<p>匿名函数</p>
<pre><code class="language-php">$value = 5;
$func_name = function($param) use ($value) {
return $param + $value;
};
echo $func_name(3); //8
</code></pre>
<pre><code class="language-php">$plus_one = function($var) {
return $var + 1;
};
$func_name = function($param) use ($plus_one) {
return $param + $plus_one($param);
};
echo $func_name(3); //7
</code></pre>
<h2 id="advanced">Advanced</h2>
<p>判斷隨機數為奇偶數後對陣列裡的值做運算。</p>
<pre><code class="language-php">function get_algorithm($rand_seed_func) {
return (odd_even($rand_seed_func()))
? function($value) {
return $value * $value;
}
: function($value) use ($rand_seed_func) {
return ($value * $value / $rand_seed_func()) + 10;
};
}
function odd_even($value) {
return ($value % 2 === 0);
}
$rand_seed_func = function() {
return rand();
};
$data = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10];
$results = array_map(get_algorithm($rand_seed_func), $data);
</code></pre>
<h2 id="partial-function-application-https-en-wikipedia-org-wiki-partial-application"><a href="https://en.wikipedia.org/wiki/Partial_application">Partial Function Application</a></h2>
<p>從一函數中創造出它的局部函數出來。</p>
<pre><code class="language-php">$first_char = function($string) {
return substr($string, 0, 1);
};
$second_char = function($string) {
return substr($string, 1, 2);
};
array_map($first_char, ['Dino', 'Amy', 'Birdy']);
// ['D', 'A', 'B']
array_map($second_char, ['Dino', 'Amy', 'Birdy']);
// ['i', 'm', 'i']
</code></pre>
<p>動態創建局部函數</p>
<pre><code class="language-php">function partial(/* $func, $args... */)
{
$args = func_get_args();
$func = array_shift($args);
return function() use ($func, $args)
{
return call_user_func_array($func, array_merge($args, func_get_args()));
};
}
function add($a, $b)
{
return $a + $b;
}
$inc = partial('add', 1);
$dec = partial('add', -1);
echo $inc(3); //4
echo $dec(3); //2
</code></pre>
<h2 id="currying-https-en-wikipedia-org-wiki-currying"><a href="https://en.wikipedia.org/wiki/Currying">Currying</a></h2>
<p>將接受多個參數的函數變成一個一個接受單個參數的函數，並返回結果的新函數。使得固定某一值後的函數可再被重覆化利用。</p>
<pre><code class="language-php">$first_char = function($start) {
return function($length) use ($start) {
return function($string) use ($start, $length) {
return substr($string, $start, $length);
};
};
};
$a = $first_char(0);
$b = $a(1);
$b('foo'); //f
$c = $a(2);
$c('foo'); //fo
</code></pre>
<h2 id="memoization">Memoization</h2>
<p>如果你需要返回的函式需要經過繁重的運算或串接，可以使用記憶化將它快取住，下次取用減少資源浪費。</p>
<pre><code class="language-php">function demo() {
static $cache;
if(is_null($cache)) {
$cache = some_expensive_operation();
}
return $cache;
}
</code></pre>
<h2 id="reference">Reference</h2>
<ul>
<li><a href="https://www.simonholywell.com/static/slides/2014-02-12/">Functional Programming in PHP by Simon Holywell</a></li>
<li><a href="http://php.net/manual/en/function.array.php">PHP Manual - Variable functions</a></li>
<li><a href="http://php.net/manual/en/functions.anonymous.php">PHP Manual - Anonymous functions</a></li>
<li><a href="http://eddmann.com/posts/using-partial-application-in-php/">Using Partial Application in PHP • edd mann</a></li>
</ul>
<gcse:searchresults-only></gcse:searchresults-only>
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