Emacs Lisp: If then else (Conditional)

The form for “if” expression is:

(if test body)

or

(if test true_body false_body)

(if (< 3 2)
    (progn 8)
  (progn 7))
;; 8

;; no false clause, return nil
(if (< 3 2)
    (message "yes")) ; nil

when

If you do not need a “else” part, you should use the function when instead, because it is more clear. The form is:

(when test expr1 expr2 etc)

Its meaning is the same as

(if test (progn expr1 expr2 etc) nil)

(info "(elisp) Control Structures")

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