I have an issue related to the question about Forth and can't solve it

Programming JavaScript
1

In question Forth, only two test cases fail with my code, and I can’t solve them.

2

Here is my code.

export class Forth {
  constructor(stack = []) {
    this.stacks = stack;
    this.obj = {
      "+": () => this.stacks.push(this.stacks.pop() + this.stacks.pop()),
      "-": () => {
        let minus = this.stacks.pop() - this.stacks.pop();
        if (minus) this.stacks.push(-1 * minus);
        else this.stacks.push(0);
      },
      "*": () => this.stacks.push(this.stacks.pop() * this.stacks.pop()),
      "/": () => {
        let first = this.stacks.pop();
        let second = this.stacks.pop();
        if (first !== 0) this.stacks.push(Math.floor(second / first));
        else throw new Error("Division by zero");
      },
      dup: () => {
        if (this.stacks.length == 0) throw new Error("Stack empty");
        this.stacks.push(this.stacks[this.stacks.length - 1]);
      },
      drop: () => {
        if (this.stacks.length == 0) throw new Error("Stack empty");
        this.stacks.pop();
      },
      swap: () => {
        if (this.stack.length < 2) throw new Error("Stack empty");
        let first = this.stacks.pop();
        let second = this.stacks.pop();
        this.stacks.push(first, second);
      },
      over: () => this.stacks.push(this.stacks[this.stacks.length - 2]),
    };
  }

  evaluate(str) {
    str = str.split(" ").map((a) => a.toLowerCase());
    if (str[0] == ":") {
      if (str[1].match(/\d/)) throw new Error("Invalid definition");
      this.obj[str[1]] = () => {
        for (let i = 2; i < str.length - 1; i++) {
          let temp = str[i];
          if (this.obj[temp]) this.obj[temp]();
          else {
            this.stacks.push(Number(temp));
          }
        }
      };
    } else {
      for (let i = 0; i < str.length; i++) {
        console.log("inside check", str[i], this.stacks, this.obj);
        if (i < 2) {
          if (str[i].match(/([\+\-\*\/]|over)$/))
            throw new Error("Stack empty");
        }
        if (this.obj[str[i]]) {
          this.obj[str[i]]();
          console.log("inside if 2", this.stacks);
          continue;
        } else if (str[i].match(/[a-z]/i)) throw new Error("Unknown command");
        this.stacks.push(Number(str[i]));
      }
    }
  }

  get stack() {
    console.log("inside stack", this.stacks);
    return this.stacks;
  }
}
3

And the failing tests are…?

4

the first one is

forth.evaluate(': foo 5 ;');
forth.evaluate(': bar foo ;');
forth.evaluate(': foo 6 ;');
forth.evaluate('bar foo');
expect(forth.stack).toEqual([5, 6]);

Error: expect(received).toEqual(expected) // deep equality

  • Expected - 1

  • Received + 1

    Array [

  • 5,
  • 6,
    6,
    ]

and second one is

forth.evaluate(': foo 10 ;');
forth.evaluate(': foo foo 1 + ;');
forth.evaluate('foo');
expect(forth.stack).toEqual([11]);

RangeError: Maximum call stack size exceeded

5

The way you are defining new words looks wrong. You want to store them as an array of strings to evaluate later. You are currently creating a function that makes assumptions about what str will be at a future time.

By the way str is not a great name to hold an array of strings.

6

Can you explain me little bit more that what can i do.