Using a quote before a symbol inside a function?

Question

I am a bit confused about when to NOT use the quote before a symbol.

For example if I want to remove a function from my image:

> (fmakunbound 'func-name)
FUNC-NAME

but, if i create a function for doing the same thing, it looks like this:

(defun remove-func (symbol)
  (fmakunbound symbol))

In the second example, why does the fmakunbound in the remove-func function not need the quoted symbol?

Answer 1

You might want to make sure you understand evaluation rules.

> foo    ; -> this is a variable, the result is its value

> 'foo   ; -> this is the expression (QUOTE FOO), the result is the symbol FOO

and

> (sin x)   ; -> calls the function SIN with the value of the variable X

> (sin 'x)  ; -> calls the function SIN with the symbol X.
            ;  ==> this is an ERROR, since SIN expects a number

> (fmakunbound FOO)   ; calls FMAKUNBOUND with the value of the variable FOO
                      ; , whatever it is


> (fmakunbound 'FOO)  ; calls FMAKUNBOUND with the result of evaluating 'FOO
                      ; 'FOO evaluates to the symbol FOO.
                      ; thus FMAKUNBOUND is called with the symbol FOO
                      ; thus FMAKUNBOUND removes the function binding 
                      ; from the symbol FOO