Lisp- "[Function name] Is not a Number"

Question

So I have this simple expression to evaluate and list the two roots of a quadratic equation:

(defun QUADRATIC (A B C) (list (/  (+  (- B) (sqrt(- (* B B) - (* 4 A C)))) (* 2 A)) (/  (- (- B) (sqrt(- (* B B) - (* 4 A C)))) (* 2 A))))

But when I evaluate it in CLISP with any three numbers for parameters, say

(quadratic 2 2 2)

I get the following error: (quadratic 2 2 2) is not a number

I am sure there is an easy fix but I can't figure it out!

Answer 1

There is a syntactic error in your definition (and using an editor that format properly the code help in finding this kind of errors).

The correct definition is:

 (defun quadratic (A B C) 
    (list (/  (+ (- B) (sqrt(- (* B B) (* 4 A C)))) 
              (* 2 A)) 
          (/  (- (- B) (sqrt(- (* B B) (* 4 A C)))) 
              (* 2 A))))

while you have an extra - in the sqrt call: (sqrt(- (* B B) - (* 4 A C)))) (* 2 A)) (the second -).

The reason for the particular error message is that - used not in function position is a special variable that refer to the current form (see the specification).