Node.js的PEGjs该如何使用

npm install pegjs

start
 = additive
additive
 = left:multiplicative "+" right:additive { return left + right; }
 / multiplicative
multiplicative
 = left:primary "*" right:multiplicative { return left * right; }
 / primary
primary
 = integer
 / "(" additive:additive ")" { return additive; }integer "integer"
 = digits:[0-9]+ { return parseInt(digits.join(""), 10); }

var fs=require('fs');var PEG=require("pegjs");
fs.readFile('./grammer.pegjs','utf8',function(err,data){ var parser=PEG.buildParser(data); var result=parser.parse('1+2*3'); 
 console.log(result); // 7});

npm install pegjs -g
npm install pegjs
pegjs grammer.pegjs parser.js

var parser=require('./parser.js');
parser.parse('1+2*3'); // 7