Clojure threading macors

thread.cljs

;Retuns 5
(-> 25
    (/ 5))

;Return 1/5
(->> 25
     (/ 5))

Clojure's threading macros were initially slightly confusing to me, but the above example should make things a bit clearer. Simply, -> will pass evaluated elements in a list as the FIRST method argument to the next item in the list; ->> will pass evaluated elements in a list as the LAST method argument to the next item in the list.

In the first example, 25 evaluates to 25, and is passed as the first argument to the next item - essentially creating the function call (/ 25 5), which returns 5.

In the second example, 25 still evaluates to 25, but it's passed as the LAST argument to the next item - creating the call (/ 5 25), which evaluates to and returns 1/5.