Question

I’m trying to read up a bit on Clojure, but I hit a brick wall with the following basic example:

(defn make-adder [x]
  (let [y x]
    (fn [z] (+ y z))))
(def add2 (make-adder 2))
(add2 4)
-> 6

What I don’t understand is how is add2 passing the number 4 to the make-adder function, and how does that function turn assigns that number to z.

Thanks in advance!

Answer 1

make-adder returns a function that takes one parameter (z), the parameter passed in to make-adder is used to assign a value to y. add2 is set equal to the result of evaluating make-adder with a parameter of 2. So add2 is set equal to the function returned from make-adder, which (since y has been assigned to the parameter from make-adder) looks like

(fn [z] (+ 2 z))

So (add2 4) calls this function which evaluates to 6. Does that help?