https://github.com/doowb/composer/issues/30

assemblefile.js

const app = require('assemble')();
app.use(require('./task-namespace')());

// Shared init task for all sources.
app.task('init', function(next) {
  //app.layouts(abs(config.layouts));
  //app.partials(abs(config.partials));
  next();
});

// Shared build task for all sources.
app.task('build', ['init']);

app.use(require('./source-guide')('guide', {}));

module.exports = app;

source-guide.js

module.exports = function(name, options) {

  return function run(app) {
    const addTask = app.taskNamespace(name);

    const collection = app.create(name, {
      engine: 'hbs',
    });

    addTask('init', function(next) {
      //collection.addViews(options.src);
      next();
    });

    addTask('build', ['init'], function(next) {
      return collection.toStream();
      // .pipe(app.renderFile())
      // .pipe(app.dest(options.dest));
    });

  }

};

task-namespace.js

module.exports = function(options) {
  return function(app) {

    app.define('taskNamespace', function(namespace) {
      return function(taskName, deps, fn) {
        if(!fn && typeof deps === 'function') {
          fn = deps;
        }
        if(!Array.isArray(deps)) {
          deps = [];
        }

        deps = deps.map(fullName);
        app.task(fullName(taskName), deps, fn);
        if(!app.tasks.hasOwnProperty(taskName)) {
          app.task(taskName, []);
        }
        app.tasks[taskName].deps.push(fullName(taskName));
      };

      function fullName(taskName) {
        return taskName + ':' + namespace;
      }
    });
  };

};