Derleyiciler ve Ayrıştırma (Compilers & Parsing) Algoritması

1// Basit Recursive Descent Parser (Expression -> Term [+/- Term]*, Term -> Factor [*// Factor]*)
2class ExpressionParser {
3  private tokens: string[];
4  private index: number = 0;
5
6  constructor(expression: string) {
7    this.tokens = expression.match(/\d+|[+*/()-]/g) ?? [];
8  }
9
10  private peek(): string | null {
11    return this.index < this.tokens.length ? this.tokens[this.index] : null;
12  }
13
14  private consume(expected?: string): string {
15    const t = this.peek();
16    if (expected && t !== expected) {
17      throw new Error(`Beklenen token: ${expected}, Alınan: ${t}`);
18    }
19    this.index++;
20    return t ?? '';
21  }
22
23  parse(): number {
24    const val = this.expression();
25    if (this.index < this.tokens.length) {
26      throw new Error(`Ayrıştırılmamış fazlalık tokenlar: ${this.tokens.slice(this.index).join(' ')}`);
27    }
28    return val;
29  }
30
31  private expression(): number {
32    let val = this.term();
33    while (this.peek() === '+' || this.peek() === '-') {
34      const op = this.consume();
35      const right = this.term();
36      val = op === '+' ? val + right : val - right;
37    }
38    return val;
39  }
40
41  private term(): number {
42    let val = this.factor();
43    while (this.peek() === '*' || this.peek() === '/') {
44      const op = this.consume();
45      const right = this.factor();
46      val = op === '*' ? val * right : val / right;
47    }
48    return val;
49  }
50
51  private factor(): number {
52    const t = this.peek();
53    if (t === '(') {
54      this.consume('(');
55      const val = this.expression();
56      this.consume(')');
57      return val;
58    }
59    if (t && /\d+/.test(t)) {
60      return Number(this.consume());
61    }
62    throw new Error(`Geçersiz token: ${t}`);
63  }
64}