CODEWITHSUNDEEP
common-lisp
Bohulenkov Artem
Bohulenkov Artem

Reputation: 59

Common lisp Error: the value is not of the expected type number

i am new to lisp, and have some troubles with my function:

(setf (symbol-function 'reduce-our)
    #'(lambda(new-expression)
            (setf expression nil)
              (loop while (not (equal new-expression expression)) do
                        (setf expression new-expression)
                        (setf new-expression (reduce-once-our expression))
                        (if (not (equal 'new-expression 'expression))
                            (format t " ==> ~A Further reductions are impossible.~%"
                             new-expression)
            new-expression))))

(reduce-our '(^ x => x))

This thows next error:

Error: The value ^ is not of the expected type NUMBER.

I thought that lisp is trying to evaluate my input list in while loop, but 

(not (equal nil '(^ x => x)))

works just fine, and i am sure that my function does the same check. So. i don't understand where and why happens this error.

Upvotes: 1

Views: 2166

Answers (1)

Rainer Joswig
Rainer Joswig

Reputation: 139321

Are you sure that the error happens in this function? You should look at the backtrace.

Additionally:

(setf (symbol-function 'reduce-our)
   #'(lambda (new-expression)
      ...))

is typically written as

(defun reduce-our (new-expression)
   ...)

Then:

(setf (symbol-function 'reduce-our)
  #'(lambda(new-expression)
      (setf expression nil) ...

Where is the variable expression introduced? It is undeclared. Setting the value does not declare a variable.

Then:

while (not (foo ...))

is just

until (foo ...)

And

(if (not (foo)) a b)

is

(if (foo) b a)

Also: improve the indentation. The editor in Lisp will do that for you. It increases readability for you and others.

Upvotes: 3

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