A silly simple lisp parser in javascript

baby-lisper.js

const rules = [
  { type: 'space', regex: /^\s/ },
  { type: 'lParen', regex: /^\(/ },
  { type: 'rParen', regex: /^\)/ },
  { type: 'number', regex: /^[0-9\.]+/ },
  { type: 'string', regex: /^".*?"/ },
  { type: 'variable', regex: /^[^\s\(\)]+/ } // take from the beginning 1+ characters until you hit a ' ', '(', or ')' // TODO - support escaped double quote
];


const tokenizer = rules => input => {
  for (let i = 0; i < rules.length; i += 1) {
    let tokenized = rules[i].regex.exec(input);
    if (tokenized) {
      return {
        token: tokenized[0],
        type: rules[i].type,
        rest: input.slice(tokenized[0].length)
      };
    }
  }

  throw new Error(`no matching tokenize rule for ${JSON.stringify(input)}`);
};


const parser = tokenize => function parse(input, ast, parents = []) {
  if (input === '') {
    return ast;
  }

  const { token, type, rest } = tokenize(input);

  if (type === 'space') {
    // do nothing
    return parse(rest, ast, parents);
  } else if (type === 'variable') {
    ast.push(token);
    return parse(rest, ast, parents);
  } else if (type === 'number') {
    ast.push(Number(token));
    return parse(rest, ast, parents);
  } else if (type === 'string') {
    ast.push(token.replace(/(^"|"$)/g, "'"));
    return parse(rest, ast, parents);
  } else if (type === 'lParen') {
    parents.push(ast)
    return parse(rest, [], parents)
  } else if (type === 'rParen') {
    const parentAst = parents.pop();
    if (parentAst) {
      parentAst.push(ast);
      return parse(rest, parentAst, parents);
    }

    return parse(rest, ast, parents);
  }

  throw new Error(`Missing parse logic for rule ${JSON.stringify(type)}`);
};


const input = `(first
  (list 1(+ 2 (inc 3)) "nine" 10  "ele ven"))`;

console.log(JSON.stringify(
  parser(tokenizer(rules))(input)[0]
));
// ["first",["list",1,["+",2,["inc",3]],"'nine'",10,"'ele ven'"]]