keywordp & :killing-the-cat

keywordp & :killing-the-cat

[MON KEY]

How does one test whether a symbol is a keyword?

(keywordp :killing-the-cat-with-epr) ;=> t
(unintern :killing-the-cat-with-epr) ;=> t

(mapatoms (lambda (x)
	    (when (eq x :killing-the-cat-with-epr)
		(prin1 `(found ,x))))
	    	  obarray)

;=>(found :killing-the-cat-with-epr)

Is this because keywords are self quoting?
And if so, how does one use keywordp to test if a (possibly
non-existent) keyword is interned without interning it?

i.e. (makunbound :killing-the-cat-with-epr) ;-> Lisp error:
(setting-constant :killing-the-cat-with-epr)

s_P

RE: keywordp & :killing-the-cat

[Drew Adams]

> (keywordp :killing-the-cat-with-epr) ;=> t
> (unintern :killing-the-cat-with-epr) ;=> t
> 
> (mapatoms (lambda (x)
> 	    (when (eq x :killing-the-cat-with-epr)
> 		(prin1 `(found ,x))))
> 	    	  obarray)

Evaluating (actually, Lisp reading) that sexp creates and interns a symbol
`:killing-the-cat-with-epr'.

Try this instead:

(mapatoms (lambda (x)
	      (when (string= (symbol-name x)
                           ":killing-the-cat-with-epr")
		  (prin1 `(found ,x))))
          obarray)

Replace ":killing-the-cat-with-epr" by the name of an existing symbol, e.g.
"forward-char", to see the difference.

> how does one use keywordp to test if a (possibly
> non-existent) keyword is interned without interning it?

You don't use keywordp for that. keywordp:

 Return t if OBJECT is a keyword.
 This means that it is a symbol with a print name beginning with `:'
 interned in the initial obarray.

IOW, keywordp returns non-nil only for an interned symbol (whose print name
starts with `:').

If you want to check whether a symbol is interned, use `intern-soft':

(intern-soft ":killing-the-cat-with-epr") -> nil
(intern-soft "forward-char") -> forward-char