socketio_tut_error

/Node/chat_ex/index.js:8
http:listen(3000, function(){
     ^
ReferenceError: listen is not defined
    at Object.<anonymous> (/home/rfmonk/Node/chat_ex/index.js:8:6)
    at Module._compile (module.js:456:26)
    at Object.Module._extensions..js (module.js:474:10)
    at Module.load (module.js:356:32)
    at Function.Module._load (module.js:312:12)
    at Function.Module.runMain (module.js:497:10)
    at startup (node.js:119:16)
    at node.js:906:3

var app = require('express')();
var http = require('http').Server(app);

app.get('/', function(req, res){
    res.send('<h1>Hello world</h1>');
});

http:listen(3000, function(){
    console.log('listening on *:3000');
});