diff options
Diffstat (limited to 'src/b.php')
| -rw-r--r-- | src/b.php | 286 |
1 files changed, 286 insertions, 0 deletions
diff --git a/src/b.php b/src/b.php new file mode 100644 index 0000000..6746a58 --- /dev/null +++ b/src/b.php @@ -0,0 +1,286 @@ +<?php + +declare(strict_types=1); + +enum Word { + case PhpTag; + case LessThan; + case LeftParen; + case RightParen; + case LeftBrace; + case RightBrace; + case Semicolon; + case Modulo; + case Increment; + case StrictlyEqual; + case Assign; + case Echo_; + case For_; + case If_; + case ElseIf_; + case Else_; +} + +readonly class Variable { + public function __construct( + public string $name, + ) {} +} + +function split_into_words(string $input): array { + $i = 0; + $result = []; + + while ($i < strlen($input)) { + $first = $input[$i]; + if ($first === '<') { + $second = $input[$i + 1]; + if ($second === '=') { + $result[] = Word::LessThan; + $i += 2; + } else { + $result[] = Word::PhpTag; + $i += 5; + } + } else if ($first === '(') { + $result[] = Word::LeftParen; + $i += 1; + } else if ($first === ')') { + $result[] = Word::RightParen; + $i += 1; + } else if ($first === '{') { + $result[] = Word::LeftBrace; + $i += 1; + } else if ($first === '}') { + $result[] = Word::RightBrace; + $i += 1; + } else if ($first === ';') { + $result[] = Word::Semicolon; + $i += 1; + } else if ($first === '%') { + $result[] = Word::Modulo; + $i += 1; + } else if ($first === '+') { + $result[] = Word::Increment; + $i += 2; + } else if ($first === '=') { + $second = $input[$i + 1]; + if ($second === '=') { + $result[] = Word::StrictlyEqual; + $i += 3; + } else { + $result[] = Word::Assign; + $i += 1; + } + } else if (ctype_space($first)) { + $i += 1; + } else if (ctype_digit($first)) { + $j = $i; + while (ctype_digit($input[$j])) { + $j += 1; + } + $result[] = (int) substr($input, $i, $j - $i); + $i = $j; + } else if (ctype_alpha($first)) { + $j = $i; + while (ctype_alpha($input[$j])) { + $j += 1; + } + $result[] = match (substr($input, $i, $j - $i)) { + 'echo' => Word::Echo_, + 'for' => Word::For_, + 'if' => Word::If_, + 'elseif' => Word::ElseIf_, + 'else' => Word::Else_, + }; + $i = $j; + } else if ($first === '$') { + $i += 1; + $j = $i; + while (ctype_alpha($input[$j])) { + $j += 1; + } + $result[] = new Variable(substr($input, $i, $j - $i)); + $i = $j; + } else if ($first === '"') { + $i += 1; + $j = $i; + $s = ''; + while ($input[$j] !== '"') { + if ($input[$j] === '\\') { + $j += 1; + if ($input[$j] === 'n') { + $s .= "\n"; + } else { + $s .= $input[$j]; + } + } else { + $s .= $input[$j]; + } + $j += 1; + } + $result[] = $s; + $i = $j + 1; + } + } + + return $result; +} + +class Php { + private array $words; + private int $position; + private array $variables; + + public function __construct(array $words) { + $this->words = $words; + $this->position = 0; + $this->variables = []; + } + + public function runPhp(): void { + $this->expectWord(Word::PhpTag); + $this->runStatements(); + } + + private function runStatements(bool $doRun = true): void { + while (true) { + $first = $this->words[$this->position] ?? null; + if ($first === Word::For_) { + $this->runForStatement($doRun); + } else if ($first === Word::If_) { + $this->runIfStatement($doRun); + } else if ($first === Word::Echo_) { + $this->runEchoStatement($doRun); + } else { + break; + } + } + } + + private function runForStatement(bool $doRun = true): void { + $this->position += 1; // skip 'for' + $this->expectWord(Word::LeftParen); + $this->calculateExpression($doRun); + $this->expectWord(Word::Semicolon); + $condition_position = $this->position; + while (true) { + $condition_result = $this->calculateExpression($doRun); + $this->expectWord(Word::Semicolon); + $update_position = $this->position; + if (!$condition_result) { + $this->skipExpression(); + $this->expectWord(Word::RightParen); + $this->expectWord(Word::LeftBrace); + $this->skipProgram(); + $this->expectWord(Word::RightBrace); + break; + } + $this->skipExpression(); + $this->expectWord(Word::RightParen); + $this->expectWord(Word::LeftBrace); + $this->runStatements($doRun); + $this->expectWord(Word::RightBrace); + $this->position = $update_position; + $this->calculateExpression($doRun); + $this->position = $condition_position; + } + } + + private function runIfStatement(bool $doRun = true): void { + $this->position += 1; // skip 'if' or 'elseif' + $this->expectWord(Word::LeftParen); + $condition = $this->calculateExpression($doRun); + $this->expectWord(Word::RightParen); + $this->expectWord(Word::LeftBrace); + $this->runStatements($doRun && $condition); + $this->expectWord(Word::RightBrace); + $next_word = $this->words[$this->position] ?? null; + if ($next_word === Word::ElseIf_) { + $this->runIfStatement($doRun && !$condition); + } else if ($next_word === Word::Else_) { + $this->position += 1; // skip 'else' + $this->expectWord(Word::LeftBrace); + $this->runStatements($doRun && !$condition); + $this->expectWord(Word::RightBrace); + } + } + + private function runEchoStatement(bool $doRun = true): void { + $this->position += 1; // skip 'echo' + $value = $this->calculateExpression($doRun); + if ($doRun) { + echo $value; + } + $this->expectWord(Word::Semicolon); + } + + private function calculateExpression(bool $doRun = true): int|string|bool|null { + $left_hand_side = $this->getNextWord(); + while (true) { + $next_word = $this->words[$this->position]; + if ($next_word === Word::Assign) { + $this->position += 1; // skip '=' + $right_hand_side = $this->getNextWord(); + if ($doRun) { + assert($left_hand_side instanceof Variable); + $left_hand_side = $this->variables[$left_hand_side->name] = $right_hand_side; + } + } else if ($next_word === Word::LessThan) { + $this->position += 1; // skip '<=' + $right_hand_side = $this->getNextWord(); + $left_hand_side = $this->convertWordToValue($left_hand_side) <= $this->convertWordToValue($right_hand_side); + } else if ($next_word === Word::StrictlyEqual) { + $this->position += 1; // skip '===' + $right_hand_side = $this->getNextWord(); + $left_hand_side = $this->convertWordToValue($left_hand_side) === $this->convertWordToValue($right_hand_side); + } else if ($next_word === Word::Modulo) { + $this->position += 1; // skip '%' + $right_hand_side = $this->getNextWord(); + $left_hand_side = $this->convertWordToValue($left_hand_side) % $this->convertWordToValue($right_hand_side); + } else if ($next_word === Word::Increment) { + $this->position += 1; // skip '++' + if ($doRun) { + $left_hand_side = $this->variables[$left_hand_side->name] = $this->variables[$left_hand_side->name] + 1; + } + } else { + return $this->convertWordToValue($left_hand_side); + } + } + } + + private function getNextWord(): int|string|Variable { + $word = $this->words[$this->position]; + $this->position += 1; + return $word; + } + + private function convertWordToValue(int|string|bool|Variable $word): int|string|bool|null { + if ($word instanceof Variable) { + return $this->variables[$word->name]; + } else { + return $word; + } + } + + private function skipExpression(): void { + $this->calculateExpression(doRun: false); + } + + private function skipProgram(): void { + $this->runStatements(doRun: false); + } + + private function expectWord(Word $expected_word): void { + if ($this->words[$this->position] !== $expected_word) { + throw new RuntimeException("Expected $expected_word at position $this->position"); + } + $this->position += 1; + } +} + +$input = file_get_contents('./a.php'); +$words = split_into_words($input); + +$php = new Php($words); +$php->runPhp(); |