// -- Challenge 3 -------------------------
// There is more to point-free programming
// than compose! Let's build ourselves
// another function that combines functions
// to let us write code without glue variables.

var fork = _.curry(function(lastly, f, g, x) {
  return lastly(f(x), g(x));
});

The task is to get the average from a list. You need to get two facts about the list: the length and the sum. 

​fork​

  // As you can see, the fork function is a
// pipeline like compose, except it duplicates
// its value, sends it to two functions, then
// sends the results to a combining function.
//
// Your challenge: implement a function to
// compute the average values in a list using
// only fork, _.divide, _.sum, and _.size.

var avg = _.identity; // change this
assertEqual(3, avg([1,2,3,4,5]));

The solution with ​fork​

  var avg = fork(_.divide, _.sum, _.size)

Curried (here) means that the function has been called, but was not given all of the arguments (​x​) and waiting for the last one. 

Brian explains that this fork stuff will be replaced by other applicative functors later in the course.