Question

As we should know, Clojure’s map can be applied to a sequence:

(map #(* %1 %1) [1 2 3])           ; (1)

..or to more than one, in this way:

(map vector [0 1] [2 1])           ; (2)
;=> ([0 2] [1 1])

Now I want to obtain the same result as (2), but I have the arguments stored inside a sequence. In other words, the following does not give the desired result:

(map vector [[0 1] [2 1]])         ; (3)
;=> ([[0 1]] [[2 1]])

So I’ve written this simple macro, where umap stands for “unsplice map”:

(defmacro umap [fun args-list]
  "umap stands for unspliced map.
  Let args-list be a list of args [a1 a2 ... an].
  umap is the same of (map fun a1 a2 .. an)"
  `(map ~fun ~@args-list))

Obviously it works like a charm:

(umap vector [[0 1] [2 1]])        ; (4)
;=> ([0 2] [1 1])

So here’s my question: am I reinventing the wheel?
Is there another way to do the same as (4)?

Bye and thanks in advance,

Alfredo

Answer 1

apply unpacks all of the elements in the sequence at the end of the argument list.

user> (apply map vector [[0 1] [2 1]])
([0 2] [1 1])