Function argument with maps in Clojure

Question

I'm getting my feet wet with Clojure the past couple of day and came across this piece of code:

(defn reduce-example
  [new-map [key val]]
  (assoc new-map key (inc val)))

(reduce reduce-example
        {}
        {:max 30 :min 10})
; => {:max 31, :min 11}

I am confused about the function argument in reduce-example, more specifically this: new-map [key value]

From what I studied so far and after the function name, you can declare the number of arguments (arities). For example [x y z], but what does [new-map [key value]] mean? of course it can extract the key and value but how? how should I interpret this function argument?

Thank you

Have a look at clojure.org/guides/destructuring#_sequential_destructuring ; the [key value] takes a parameter which is a sequence and assigns the first value to key and the second to value. Also note that when passing a map to a function like reduce, it is automatically converted into a sequence of vectors. Try (seq {:max 30 :min 30}) and you'll see what I mean. This also shows you where the [key value] that is being passed into reduce-example is coming from. — optevo
– optevo, Commented Nov 2, 2019 at 8:22

Shawn Zhang · Accepted Answer · 2019-11-02 08:18:53Z

6

[new-map [key value]] mean the function expect two argument:

first one will bind to name new-map
second one (should be a sequential type with 2 elements inside) . The elements inside will bind to key and value

Clojure has an ability of destructuring

answered Nov 2, 2019 at 8:18

Shawn Zhang

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1 Comment

Thumbnail Over a year ago

Slightly more accurate: second one should be a sequential type, Its first element will bind to key, its second to value.

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