by @yokolet

Level: easy

Comment

Programmers often add comments for various reasons, such as explaining code or temporarily disabling code.

Clojure has three ways to add comments or comment out a section.

  • comment macro
  • ; reader macro
  • #_ reader macro

comment macro

The syntax is like a function: (comment & body).

With this comment style, we can write multi-line comments or comment out multi-line code blocks.


; (semicolon) reader macro

This is used to comment out a single line. Clojure ignores everything from the ; (semicolon) to the end of the line.

user> (+ 1 2) ; the answer is 3
3

user> (def my-number
           ;; this is used later
           123)
#'user/my-number
user> my-number
123


#_ reader macro

This is used to comment out a form. For example, a corresponding pair of ( and ), or [ and ]. The form can be nested.

user> (def my-vec #_[1 2 3] [3 4 5])
#'user/my-vec
user> my-vec
[3 4 5]
user> ; [1 2 3] was ignored

user> (take 5 #_(iterate inc 0) (range))
(0 1 2 3 4)
user> ; (iterate inc 0) was ignored

user> (defn reverse-word
        [five-letter-word]
        #_(let [[a b c d e] five-letter-word]
          (str e d c b a))
        (clojure.string/reverse five-letter-word))
#'user/reverse-word
user> (reverse-word "hello")
"olleh"
user> ; let form  was ignored


References