parser.js

/**
 * 将tokens转成AST树
 * @param {array} tokens
 */
function parser(tokens) {
  let current = 0;

  function walk() {
    let token = tokens[current];
    // 数字
    if (token.type === 'number') {
      current++;
      return {
        type: 'NumberLiteral',
        value: token.value
      };
    }
    // 字符串
    if (token.type === 'string') {
      current++;

      return {
        type: 'StringLiteral',
        value: token.value
      };
    }
    // callExpression
    if (token.type === 'paren' && token.value === '(') {
      token = tokens[++current];
      let node = {
        type: 'CallExpression',
        name: token.value,
        params: []
      };

      token = tokens[++current];

      while (
        token.type !== 'paren' ||
        (token.type === 'paren' && token.value !== ')')
      ) {
        node.params.push(walk());
        token = tokens[current];
      }
      current++;
      return node;
    }
    throw new TypeError(token.type);
  }

  let ast = {
    type: 'Program',
    body: []
  };

  while (current < tokens.length) {
    ast.body.push(walk());
  }

  return ast;
}

module.exports = parser;