One of the most common problems when first starting out with Lisp is 
deciding when to use the QUOTE ('). A couple of hints in that regard:

(A) If you quote a form containing a local variable, that is almost always
a mistake.

(defun Foo (A B C)
  (first (Bar (Boo 'A) '(2 3 C))))   ; A and C are arguments to the function,
                   ^^        ^^      ; you WANT their values.

Local variables either quoted directly or inside quoted lists are almost
always an error unless by some wild coincidence you wanted a specific symbol
that looked just like the real variable name. That is silly; in such a
bizarre case you would just rename your local variables to avoid confusion.

(B) If your function is processing numbers, it is probably an error
to use QUOTE at all. Numeric operators act on numbers, not symbols or lists, 
and you only need QUOTE to make symbols [FOO] or lists [(A B C)]. 

Anyhow, cases like this are clearly wrong:

(defun Square (X)
  (* 'X 'X))       ; You can't multiply symbols, only numbers

(defun Root-Mean-Square-Variation (X Y Z)
  (* (+ Y (Foo Z))
     (/ Z 3)
     (Baz Y 'pi)) )
             ^^

Since * expects all numbers as arguments, BAZ must return a number. Even
though we have no idea what BAZ does, it is a good guess it expects numbers
as input, not symbols. So the QUOTE in front of the PI is misplaced.

C) Beginners put QUOTE in when they shouldn't much more often than 
they leave it off when it is needed. Assume you won't use QUOTE at all
in your functions, and only in the cases where you specifically see
"Oh, I want LITERALLY such and such a form and don't want this evaluated"
do you make an exception and use QUOTE.


Marty Hall
Milton S. Eisenhower Research Center
The Johns Hopkins University Applied Physics Lab
Johns Hopkins Rd. 
Laurel, MD 20723
hall@aplcenmp.apl.jhu.edu