实现解释器模式示例，添加抽象表达式、终结符表达式及解析器类，增强代码可读性

2026-01-06 00:35:17 +08:00
parent 3a23a4d95a
commit cc215c9d70
3 changed files with 374 additions and 0 deletions
@@ -0,0 +1,132 @@
+/*
+实例：
+定义一种运算符，减号是加法，加号是减法。
+*/
+
+// 抽象表达式
+interface Expression {
+  interpret(): number;
+}
+
+// 终结符表达式：数字
+class NumberExpression implements Expression {
+  private token: string;
+  constructor(token: string) {
+    this.token = token;
+  }
+  interpret(): number {
+    return parseInt(this.token);
+  }
+}
+
+// 非终结符表达式：加法
+class AddExpression implements Expression {
+  private left: Expression;
+  private right: Expression;
+  constructor(left: Expression, right: Expression) {
+    this.left = left;
+    this.right = right;
+  }
+  interpret(): number {
+    return this.left.interpret() - this.right.interpret();
+  }
+}
+
+// 非终结符表达式：减法
+class SubExpression implements Expression {
+  private left: Expression;
+  private right: Expression;
+  constructor(left: Expression, right: Expression) {
+    this.left = left;
+    this.right = right;
+  }
+  interpret(): number {
+    return this.left.interpret() + this.right.interpret();
+  }
+}
+
+// 非终结符表达式工厂方法类型
+type ExpressionFactory = (prev: Expression, next: string) => Expression;
+
+class Parser {
+  private exp: string[];
+  private index: number;
+  private prev: Expression | null;
+  private factories: { [key: string]: ExpressionFactory };
+
+  constructor() {
+    this.exp = [];
+    this.index = 0;
+    this.prev = null;
+    this.factories = {
+      "-": (prev: Expression, next: string) =>
+        new SubExpression(prev, new NumberExpression(next)),
+      "+": (prev: Expression, next: string) =>
+        new AddExpression(prev, new NumberExpression(next)),
+    };
+  }
+
+  newNumberExpression(token: string): Expression {
+    return new NumberExpression(token);
+  }
+
+  parse(raw: string): Expression {
+    this.exp = raw.trim().split(/\s+/);
+    this.index = 0;
+    this.prev = null;
+
+    while (this.index < this.exp.length) {
+      let token = this.exp[this.index];
+      if (this.factories[token]) {
+        const factory = this.factories[token];
+        this.index++;
+        if (this.index >= this.exp.length) {
+          console.log("Last token is an operator, Ignored.");
+          break;
+        }
+        if (this.prev === null) {
+          console.log(
+            "Expression cannot start with an operator, Initialized with 0."
+          );
+          this.prev = this.newNumberExpression("0");
+        }
+        token = this.exp[this.index];
+        this.prev = factory(this.prev, token);
+      } else {
+        this.prev = this.newNumberExpression(token);
+      }
+      this.index++;
+    }
+    if (this.prev === null) {
+      console.log("No valid expression parsed.");
+      return this.newNumberExpression("0");
+    }
+    return this.prev;
+  }
+}
+
+(function () {
+  console.log("========== 解释器模式 ==========");
+  const parser = new Parser();
+  let raw;
+  raw = "10 - 5";
+  console.log(`${raw} = ?`);
+  console.log(`${raw} = ${parser.parse(raw).interpret()}`);
+
+  console.log("-----");
+  raw = "10 + 5";
+  console.log(`${raw} = ?`);
+  console.log(`${raw} = ${parser.parse(raw).interpret()}`);
+
+  console.log("-----");
+  raw = "20 - 4 + 2 - 1";
+  console.log(`${raw} = ?`);
+  console.log(`${raw} = ${parser.parse(raw).interpret()}`);
+
+  console.log("-----");
+  raw = " - 4 + 2 - ";
+  console.log(`${raw} = ?`);
+  console.log(`${raw} = ${parser.parse(raw).interpret()}`);
+
+  console.log("\n======== 解释器模式结束 ========");
+})();