From b7388cdc04ee6385fea7cd5e6e2fdc57b1845624 Mon Sep 17 00:00:00 2001
From: nsfisis <nsfisis@gmail.com>
Date: Wed, 30 Oct 2024 19:05:32 +0900
Subject: Add slides

---
 src/.editorconfig |   5 +
 src/a.php         |  13 +++
 src/b.php         | 286 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 304 insertions(+)
 create mode 100644 src/.editorconfig
 create mode 100644 src/a.php
 create mode 100644 src/b.php

(limited to 'src')

diff --git a/src/.editorconfig b/src/.editorconfig
new file mode 100644
index 0000000..819fb4e
--- /dev/null
+++ b/src/.editorconfig
@@ -0,0 +1,5 @@
+root = true
+
+[*.php]
+indent_style = space
+indent_size = 4
diff --git a/src/a.php b/src/a.php
new file mode 100644
index 0000000..1003341
--- /dev/null
+++ b/src/a.php
@@ -0,0 +1,13 @@
+<?php
+for ($i = 1; $i <= 100; $i++) {
+    if ($i % 15 === 0) {
+        echo "FizzBuzz";
+    } elseif ($i % 3 === 0) {
+        echo "Fizz";
+    } elseif ($i % 5 === 0) {
+        echo "Buzz";
+    } else {
+        echo $i;
+    }
+    echo "\n";
+}
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();
-- 
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