text: var stream = require('stream');
  
  exports.sequence = function sequence(before, after) {
    var s = new stream.PassThrough();
    before
      .then(function(result) {
        after(result)
          .on('error', function(e) { s.emit('error', e) })
          .pipe(s);
      })
      .catch(function(error) {
        s.emit("error", error);
      });
    return s;
  };
  