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<!DOCTYPE HTML/><html lang="en-US"><head><meta charset="UTF-8"/><meta http-equiv="X-UA-Compatible" content="IE=edge"/><meta name="viewport" content="width=device-width, initial-scale=1"/><title>Reinventing the Wheel: PHP Generators</title><meta name="generator" content="Custom"/><meta property="og:title" content="Reinventing the Wheel: PHP Generators"/><meta property="og:locale" content="en_US"/><meta name="description" content="Attempt of a lunatic to recreate functionalities that a language already has using the same language, and failing."/><meta property="og:description" content="Attempt of a lunatic to recreate functionalities that a language already has using the same language, and failing."/><meta name="keywords" content="php, generators"/><link rel="canonical" href="https://mliezun.github.io/2020/01/24/php-generator.html"/><meta property="og:url" content="https://mliezun.github.io/2020/01/24/php-generator.html"/><meta property="og:site_name" content="mliezun.github.io"/><meta property="og:image" content="https://mliezun.github.io/assets/images/nyc.jpg"/><link rel="icon" type="image/x-icon" href="/assets/images/favicon.ico"/><meta property="og:type" content="article"/><meta name="twitter:card" content="summary"/><meta property="twitter:title" content="Reinventing the Wheel: PHP Generators"/><meta name="twitter:creator" content="@migueliezun"/><meta name="twitter:image" content="https://mliezun.github.io/assets/images/nyc.jpg"/>
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</div><h2>Reinventing the Wheel: PHP Generators
</h2><div>

</div><h3>First thing first. How a generator works?
</h3><div>

</div><h4>Starting back at C
</h4><div>
Let's create a function that each time we call it we get the next number of the fibonacci sequence.

<pre class="triple-quote c">
int fibonacci()
{
static int a = 0;
static int b = 1;
int aux = b;
b = a + b;
a = aux;
return a;
}
</pre>

If we call fibonacci(), the first time we'll get 1, the second time 1, the third 2, the fourth 3, and so on...

This happens because we declared variables <span class="single-quote">a, b</span> to be static. This means that they mantain the value after the function returns. Normally, what happens (if we don't declare a variable as static) is that the variables inside the function don't mantain the values of the last execution.


</div><h4>First generator for PHP
</h4><div>
The equivalent function in PHP is pretty similar to C's approach.

<pre class="triple-quote php">


function fibonacci()
{
static $a = 0;
static $b = 1;
$aux = $b;
$b = $a + $b;
$a = $aux;
return $a;
}

$out = [];

for ($i = 1; $i <= 10; $i++) {
$out[] = fibonacci();
}

echo implode(', ', $out) . "\n";

/*
Output: 1, 1, 2, 3, 5, 8, 13, 21, 34, 55
*/
</pre>

Let's compare this to the <span class="single-quote">real</span> PHP version using <span class="single-quote">yield</span>.

<pre class="triple-quote php">


function fibonacci($N)
{
$a = 0;
$b = 1;
for ($i = 0; $i < $N; $i++) {
$aux = $b;
$b = $a + $b;
$a = $aux;
yield $a;
}
}

$out = [];

foreach (fibonacci(10) as $fib) {
$out[] = $fib;
}

echo implode(', ', $out) . "\n";

/*
Output: 1, 1, 2, 3, 5, 8, 13, 21, 34, 55
*/
</pre>


</div><h4>Creating a custom version of PHP <span class="single-quote">yield</span>
</h4><div>
This is my own version using the library parallel and channels (probably uses yield internally).

<pre class="triple-quote php">


class MyGenerator implements Iterator
{
private $chan;
private $current;
private $iteratorFn;
private $runtime;
private $key = -1;
private $valid = true;

public function __construct($iteratorFn)
{
$this->iteratorFn = $iteratorFn;
$this->runtime = new \parallel\Runtime();
$channel = new \parallel\Channel();

$this->runtime->run(function() use ($iteratorFn, $channel) {
$iteratorFn(function ($val) use ($channel) {
$channel->send($val);
});
$channel->close();
});

$this->chan = $channel;
$this->next();
}

public function current()
{
return $this->current;
}

public function next()
{
try {
++$this->key;
$val = $this->chan->recv();
$this->current = $val;
} catch (\parallel\Channel\Error\Closed $e) {
$this->valid = false;
}
return $this->current;
}

public function key() {return $this->key;}
public function valid() {return $this->valid;}
public function rewind() {}
}


function fibonacci($N)
{
return new MyGenerator(function ($yield) use ($N) {
$a = 0;
$b = 1;
for ($i = 0; $i < $N; $i++) {
$aux = $b;
$b = $a + $b;
$a = $aux;
$yield($a);
}
});
}

$out = [];

foreach (fibonacci(10) as $fib) {
$out[] = $fib;
}

echo implode(', ', $out) . "\n";
</pre>


</div><h4>Performance comparison: PHP vs Custom
</h4><div>

</div><h5>Tested code
</h5><div>
<pre class="triple-quote php">
for ($i = 0; $i < 1000; ++$i) {
foreach (fibonacci(100) as $fib) {
$out[] = $fib;
}
}
</pre>


</div><h5><span class="single-quote">yield</span> version
</h5><div>
<pre class="triple-quote ">
real 0m0,083s
user 0m0,059s
sys 0m0,023s
</pre>


</div><h5><span class="single-quote">MyGenerator</span> version
</h5><div>
<pre class="triple-quote ">
real 0m2,138s
user 0m1,426s
sys 0m1,363s
</pre>

So, it's aproximately 26 times slower :-)

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44 changes: 44 additions & 0 deletions docs/2020/02/12/crafting-interpreters.html
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<!DOCTYPE HTML/><html lang="en-US"><head><meta charset="UTF-8"/><meta http-equiv="X-UA-Compatible" content="IE=edge"/><meta name="viewport" content="width=device-width, initial-scale=1"/><title>Crafting interpreters</title><meta name="generator" content="Custom"/><meta property="og:title" content="Crafting interpreters"/><meta property="og:locale" content="en_US"/><meta name="description" content="Lox language interpreter based on the book craftinginterpreters.com by Bob Nystrom."/><meta property="og:description" content="Lox language interpreter based on the book craftinginterpreters.com by Bob Nystrom."/><meta name="keywords" content="interpreter,parser,lexer"/><link rel="canonical" href="https://mliezun.github.io/2020/02/12/crafting-interpreters.html"/><meta property="og:url" content="https://mliezun.github.io/2020/02/12/crafting-interpreters.html"/><meta property="og:site_name" content="mliezun.github.io"/><meta property="og:image" content="https://mliezun.github.io/assets/images/nyc.jpg"/><link rel="icon" type="image/x-icon" href="/assets/images/favicon.ico"/><meta property="og:type" content="article"/><meta name="twitter:card" content="summary"/><meta property="twitter:title" content="Crafting interpreters"/><meta name="twitter:creator" content="@migueliezun"/><meta name="twitter:image" content="https://mliezun.github.io/assets/images/nyc.jpg"/>
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</div><h2>Crafting interpreters
</h2><div>
I've just finished the section 2 of the book _Crafting Interpreters_, and I wanted to upload it to github right away.

Take a look at the <a href="https://github.com/mliezun/jlox">source code</a>.

Beside the lox specification I've added:

<li>The keyword <span class="single-quote">until</span> that is a variation of <span class="single-quote">while</span> loops (as in ruby). also</li>
<li><span class="single-quote">print</span> is a function instead of a statement.</li>
<li><span class="single-quote">eval</span> function that let's you eval source code in runtime.</li>
<li>Class methods.</li>

I'll implement another language interpreter, this time using <span class="single-quote">golang</span> and with a syntax similar to ruby.

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