Threads the expr through the forms. Inserts x as the
last item in the first form, making a list of it if it is not a
list already. If there are more forms, inserts the first form as the
last item in second form, etc.
;; An example of using the "thread-last" macro to get
;; the sum of the first 10 even squares.
user=> (->> (range)
(map #(* % %))
(filter even?)
(take 10)
(reduce +))
1140
;; This expands to:
user=> (reduce +
(take 10
(filter even?
(map #(* % %)
(range)))))
1140
user=> (def c 5) user=> (->> c (+ 3) (/ 2) (- 1)) 3/4 ;; and if you are curious why user=> (use 'clojure.walk) user=> (macroexpand-all '(->> c (+ 3) (/ 2) (- 1))) (- 1 (/ 2 (+ 3 c)))
Source
clojure/core.clj:1540
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(defmacro ->>
"Threads the expr through the forms. Inserts x as the
last item in the first form, making a list of it if it is not a
list already. If there are more forms, inserts the first form as the
last item in second form, etc."
{:added "1.1"}
([x form] (if (seq? form)
(with-meta `(~(first form) ~@(next form) ~x) (meta form))
(list form x)))
([x form & more] `(->> (->> ~x ~form) ~@more)))
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