madlisp/src/Reader.php

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<?php
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/**
* MadLisp language
* @link http://madlisp.com/
* @copyright Copyright (c) 2020 Pekka Laiho
*/
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namespace MadLisp;
class Reader
{
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public function read(array $tokens)
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{
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if (empty($tokens)) {
return null;
}
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$index = 0;
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return $this->readForm($tokens, $index);
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}
private function readForm(array $tokens, int &$index)
{
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if ($tokens[$index] == "'") {
return $this->readSpecialForm($tokens, $index, 'quote');
} elseif ($tokens[$index] == "`") {
return $this->readSpecialForm($tokens, $index, 'quasiquote');
} elseif ($tokens[$index] == "~") {
return $this->readSpecialForm($tokens, $index, 'unquote');
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} elseif ($tokens[$index] == '(') {
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return $this->readList($tokens, $index);
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} elseif ($tokens[$index] == '[') {
return $this->readVector($tokens, $index);
} elseif ($tokens[$index] == '{') {
return $this->readHash($tokens, $index);
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} else {
return $this->readAtom($tokens, $index);
}
}
private function readSpecialForm(array $tokens, int &$index, string $symbol)
{
$index++;
$contents = [new Symbol($symbol)];
if ($index < count($tokens) && !in_array($tokens[$index], [')', ']', '}'])) {
$contents[] = $this->readForm($tokens, $index);
}
return new MList($contents);
}
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private function readList(array $tokens, int &$index): MList
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{
return new MList($this->readCollection($tokens, $index, ')'));
}
private function readVector(array $tokens, int &$index): Vector
{
return new Vector($this->readCollection($tokens, $index, ']'));
}
private function readHash(array $tokens, int &$index): Hash
{
$contents = $this->readCollection($tokens, $index, '}');
return Util::makeHash($contents);
}
private function readCollection(array $tokens, int &$index, string $endTag): array
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{
$result = [];
// start tag
$index++;
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while ($tokens[$index] != $endTag) {
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$result[] = $this->readForm($tokens, $index);
}
// end tag
$index++;
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return $result;
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}
private function readAtom(array $tokens, int &$index)
{
$a = $tokens[$index++];
if ($a === 'true') {
return true;
} elseif ($a === 'false') {
return false;
} elseif ($a === 'null') {
return null;
} elseif (substr($a, 0, 1) === '"') {
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// string, handle special characters
$a = substr($a, 1, -1);
$a = str_replace("\\\\", chr(0x7f), $a);
$a = str_replace("\\n", "\n", $a);
$a = str_replace("\\r", "\r", $a);
$a = str_replace("\\\"", "\"", $a);
return str_replace(chr(0x7f), "\\", $a);
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} elseif (is_numeric($a)) {
if (filter_var($a, FILTER_VALIDATE_INT) !== false) {
return intval($a);
} else {
return floatval($a);
}
} else {
return new Symbol($a);
}
}
}