How to use the harp.compile function in harp

gulp.task('build', ['copy'], function(cb) {
    // This task is for production, so BASE_URL should be a project name.
    // $BASE_URL is referenced in harp.json, and it will be replaced by harp (envy).
    process.env.BASE_URL = '/' + project.name
    harp.compile(paths.harp.project, paths.harp.output, function(err) {
        if (err) {
            gutil.log('build failed: ' + err);
        }
        gutil.log('Compile done');
        cb();
    });
});

function compileHarp () {
  harp.compile(__dirname + '/' + options.publicPath, '../www', function (err) {
    if (err) throw err;
    events.emit('harp:compiled')
  })
}