Ave1

I wanted to check for an empty string, and so came by the Function NULL. Finally, a well specified function. The description;

Returns t if object is the empty list; otherwise, returns nil.

Luckily, in Common LISP the "empty list" and "nil" are one and the same, so this sentence can be written as is¹.

And the examples;

 (null '()) =>  T
 (null nil) =>  T
 (null t) =>  NIL
 (null 1) =>  NIL

Also fine, the four cases you would expect here.

But then, the last line of the notes;

 (null object) ==  (typep object 'null) ==  (eq object '())

Now, how does help? the author could not be bothered to add some text here? Is "==" somehow part of the syntax?

1. Try this; Returns t if object is nil; otherwise, returns nil.

   Or this; Returns t if object is the empty list; otherwise, returns the empty list.

   I seem to also getting infected with this LISP virus to look for the edge cases [↩]

This entry was posted on Tuesday, July 30th, 2019 at 10:07 and is filed under Uncategorized. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.