CODEWITHSUNDEEP
clojure
Claudio Ferreira
Claudio Ferreira

Reputation: 45

Function doesn't print the integers inside her

I'm a begginer with clojure and i were reading a book that contained that function:

(defn illustrative-function [] (+ 1 304) 30 "joe")

And if you invoke that function without an argument it returns only "joe", as you can see:

(illustrative-function )
=> "joe"

My question:

Why the numbers inside the function aren't printed? 305 and 30? Even when i use and argument (and a parameter) it doesn't return nothing:

(defn illustrative-function [x] x (+ 1 304) 30 "joe")
=> #'dev-projects.core/illustrative-function

(illustrative-function 3)
=> "joe"

(illustrative-function [3])
=> "joe"

Can someone explain why does that happens?

Why the integers and the arguments are not printed?

Thanks!

Upvotes: 0

Views: 60

Answers (1)

cfrick
cfrick

Reputation: 37008

The body of a defn is wrapped in an do. do allows you to execute multiple instructions usually for side-effects. The last statement in the do is the return. So this looks like this:

(defn illustrative-function 
  [] 
  (do
    (+ 1 304) ; no-op
    30        ; no-op
    "joe"))   ; return

(+ 1 304) is read and calculated, then thrown aways. 30 is just read and thrown away. "joe" then is the return of do and by that the return of the function.

If you want to "print" something, you have to explicitly print it. E.g. replace 30 with (println 30). Also note, that in the REPL, the return value is printed into the REPL - if you call that function from somewhere else, nothing is printed unless you print explicitly.

Upvotes: 2

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