error.log

c:\Users\Aweesome\AppData\Roaming\npm\node_modules\learnyounode\node_modules\workshopper-exercise\exercise.js:152
    processors[i].call(self, mode, function (err, pass) {
                  ^
TypeError: Cannot call method 'call' of undefined
    at next (c:\Users\Aweesome\AppData\Roaming\npm\node_modules\learnyounode\node_modules\workshopper-exercise\exercise.js:152:19)
    at c:\Users\Aweesome\AppData\Roaming\npm\node_modules\learnyounode\node_modules\workshopper-exercise\exercise.js:159:7
    at callback (c:\Users\Aweesome\AppData\Roaming\npm\node_modules\learnyounode\exercises\make_it_modular\verify.js:25:15)
    at modFileError (c:\Users\Aweesome\AppData\Roaming\npm\node_modules\learnyounode\exercises\make_it_modular\verify.js:30:5)
    at c:\Users\Aweesome\AppData\Roaming\npm\node_modules\learnyounode\exercises\make_it_modular\verify.js:103:18
    at g:\sites\hello\exercise6\mymodule.js:14:17
    at Array.forEach (native)
    at callback (g:\sites\hello\exercise6\mymodule.js:12:14)
    at Object.oncomplete (fs.js:107:15)

mymodule.js

var fs = require('fs');
var path = require('path');

module.exports = function(folder, ext, cb) {
    var extension = '.' + ext;

    fs.readdir(folder, function callback(err, list) {
        if (err) {
            console.log(err);
            return cb(err);
        }
        list.forEach(function(file) {
            if (path.extname(file) === extension) {
                cb(file);
            }
        })
    });
}

program.js

var mymodule = require('./mymodule.js');

mymodule(process.argv[2], process.argv[3], function(file) {
    console.log(file);
})