Why does if-not call "not", rather than just inverting arguments?

Question

I'm studying the source of clojure.core.

(defmacro if-not
  ([test then] `(if-not ~test ~then nil))
  ([test then else]
  `(if (not ~test) ~then ~else)))

As to the second form, why not just

([test then else] `(if ~test ~else ~then)

Answer 1

This looks just a style of coding.

(if-not test then else)

(if (not test) then else)

(if test else then)

The above code will work the same way. There are multiple way to write code to do the same thing.

The author of if-not macro might have thought that it would be better to write the code that way.

(defmacro if-not
  ...
  ([test then else]
    `(if (not ~test) ~then ~else)))

When we read this code (above), we can think in the order of if, then, else, quite straightforward.

(defmacro if-not
  ...    
  ([test then else]
    `(if ~test ~else ~then)

Yes, this will work fine. However, in terms of readability, the order then and else are swapped, and it might cause confusing.

That's why (in my guess) the author implemented if-not in that way.