Implementation of comp

Question

I'm trying to understand how this function work, which is an implementation of comp (from the chapter "Functional Programming" in the book Clojure for the Brave and True):

(defn two-comp
  [f g]
  (fn [& args]
    (f (apply g args))))

The idea is that it takes two functions and apply them to args. What I don't understand is how the args reach the anonymous function, since they are not entered as arguments to two-comp? How can be two-comp used this way?

For g that takes just one argument, (defn two-comp [f g] (fn [x] (f (g x)))) returns a function that invokes f upon the result of invoking g upon its argument. As @mipadi explains, The two-comp in the question just modifies this so that g can have any number of arguments. — Thumbnail

mipadi mipadi · Accepted Answer · 2014-12-01T18:15:22

two-comp returns an anonymous function, which in turn takes args. Look at the body of two-comp:

(fn [& args]
  (f (apply g args)))

fn creates a function, and that function definition follows. The return value of fn is what is returned from two-comp.

Implementation of comp

1 Answers