Plain Simple Stupid Language

stupid.php

<?php if ($_SERVER["REQUEST_METHOD"] == "GET") { ?>
<form action="stupid.php" method="post">
<textarea name="source" cols="80" rows="15">
input n
i = 1;loopi;if i &gt; n fini
j = 1;loopj;if j &gt; n finj
product = i * j
output i * j = product
if j == n last
output /
last
j = j + 1;goto loopj;finj
newline
i = i + 1;goto loopi;fini
</textarea>
Source<br>
<textarea name="input" cols="80" rows="15">
5
</textarea>
Input<br>
<input type="submit">
</form>
<?php exit(); } ?>
<?php
$input = $_POST["input"];
$data = explode(" ", $input);
$datai = 0;
$source = $_POST["source"];
$source = str_replace(";", "\n", $source);
$source = str_replace("\r\n", "\n", $source);
$lines = explode("\n", $source);
$labels = array();
for ($i = 0; $i < count($lines); $i++) {
    $line = $lines[$i];
    $words = explode(" ", $line);
    if (count($words) == 1) {
        $label = $words[0];
        $labels[$label] = $i;
    }
    $lines[$i] = $words;
}
$memory = array();
function get($value) {
    global $memory;
    if (ctype_digit($value)) {
        $value = intval($value);
    }
    if (ctype_alpha($value)) {
        if (array_key_exists($value, $memory)) {
            $value = $memory[$value];
        }
    }
    return $value;
}
$output = array();
$outline = array();
for ($i = 0; $i < count($lines); $i++) {
    $line = $lines[$i];
    if ($line[1] == "=") {
        if (count($line) == 3) {
            $name = $line[0];
            $value = get($line[2]);
        } else {
            $name = $line[0];
            $left = get($line[2]);
            $op = $line[3];
            $right = get($line[4]);
            switch ($op) {
            case "+": $value = $left + $right; break;
            case "-": $value = $left - $right; break;
            case "*": $value = $left * $right; break;
            case "/": $value = intval($left / $right); break;
            case "%": $value = $left % $right; break;
            }
        }
        $memory[$name] = $value;
    }
    $command = $line[0];
    switch ($command) {
    case "input":
        $name = $line[1];
        $memory[$name] = get($data[$datai]);
        $datai++;
        break;
    case "output":
        for ($j = 1; $j < count($line); $j++) {
            $value = get($line[$j]);
            array_push($outline, strval($value));
        }
        break;
    case "newline":
        array_push($output, implode(" ", $outline));
        $outline = array();
        break;
    case "if":
        $left = get($line[1]);
        $op = $line[2];
        $right = get($line[3]);
        switch ($op) {
        case "==": $value = $left == $right; break;
        case "!=": $value = $left != $right; break;
        case "<": $value = $left < $right; break;
        case "<=": $value = $left <= $right; break;
        case ">": $value = $left > $right; break;
        case ">=": $value = $left >= $right; break;
        }
        if ($value) {
            $label = $line[4];
            $i = $labels[$label];
        }
        break;
    case "goto":
        $label = $line[1];
        $i = $labels[$label];
        break;
    }
}
array_push($output, implode(" ", $outline));
echo implode("<br>", $output);
?>