怎样使用JavaScript实现一个简单的编译器（如将子集语言编译成JS）？

function tokenize(input) {
  const tokens = [];
  let i = 0;

  while (i < input.length) {
    let char = input[i];

    if (char === ' ') {
      i++;
      continue;
    }

    if (/[0-9]/.test(char)) {
      let value = '';
      while (i < input.length && /[0-9\.]/.test(input[i])) {
        value += input[i++];
      }
      tokens.push({ type: 'number', value });
      continue;
    }

    if (/[a-z]/i.test(char)) {
      let value = '';
      while (i < input.length && /[a-z_]/i.test(input[i])) {
        value += input[i++];
      }
      tokens.push({ type: 'identifier', value });
      continue;
    }

    if (char === '+') {
      tokens.push({ type: 'plus', value: '+' });
      i++;
      continue;
    }
    if (char === '-') {
      tokens.push({ type: 'minus', value: '-' });
      i++;
      continue;
    }
    if (char === '*') {
      tokens.push({ type: 'asterisk', value: '*' });
      i++;
      continue;
    }
    if (char === '/') {
      tokens.push({ type: 'slash', value: '/' });
      i++;
      continue;
    }
    if (char === '(') {
      tokens.push({ type: 'paren', value: '(' });
      i++;
      continue;
    }
    if (char === ')') {
      tokens.push({ type: 'paren', value: ')' });
      i++;
      continue;
    }

    throw new Error('未知字符: ' + char);
  }

  return tokens;
}

function parse(tokens) {
  let current = 0;

  function walk() {
    let token = tokens[current];

    if (token.type === 'number') {
      current++;
      return {
        type: 'NumberLiteral',
        value: token.value,
      };
    }

    if (token.type === 'identifier') {
      current++;
      return {
        type: 'Identifier',
        name: token.value,
      };
    }

    if (token.type === 'paren' && token.value === '(') {
      current++; // 跳过 '('
      let expr = walk();
      token = tokens[current];
      if (token.type === 'paren' && token.value === ')') {
        current++;
      } else {
        throw new Error('缺少右括号');
      }
      return expr;
    }

    // 处理二元表达式，简单左递归处理
    let left = walk();
    token = tokens[current];

    if (token && ['plus', 'minus', 'asterisk', 'slash'].includes(token.type)) {
      current++;
      let operator = token.value;
      let right = walk();

      return {
        type: 'BinaryExpression',
        operator,
        left,
        right,
      };
    }

    return left;
  }

  const ast = {
    type: 'Program',
    body: walk(),
  };

  return ast;
}

function generate(ast) {
  if (ast.type === 'NumberLiteral') {
    return ast.value;
  }

  if (ast.type === 'Identifier') {
    return ast.name;
  }

  if (ast.type === 'BinaryExpression') {
    return `(${generate(ast.left)} ${ast.operator} ${generate(ast.right)})`;
  }

  if (ast.type === 'Program') {
    return generate(ast.body);
  }

  throw new Error('不支持的节点类型: ' + ast.type);
}

function compile(input) {
  const tokens = tokenize(input);
  const ast = parse(tokens);
  const output = generate(ast);
  return output;
}

console.log(compile("(x + 5) * y - 3"));
// 输出: ((((x + 5)) * y) - 3)