How to pass function as argument in elisp

Question

I am reading SICP recently to learn lisp programming.

There is an example in the book to make a high level function sum as below.

 (define (sum term a next b)
   ...
   (term a)
   ...
   (next a)
   ...

In this function, term and next are functions.

I want to write the same function in elisp like this.

 (defun sum (term a next b)
    ....
    (funcall term a)
    ...
    (func next a)
    ....

Then I define some test functions to test sum

 (defun inc-test (x) (+ x 1))

 sum inc-test 1 inc-test 10 

but it show errors like this: Invalid function: inc-test

As I am new to elisp, can anyone call tell me how to fix it? very appreciate

Answer 1

To recap what is in the comments, funcall unquotes its argument (by just accessing the argument). And before that, we also need to make sure that we don't try to evaluate or access the value of the function name parameter that is passed in the call to the function.

Therefore, an acceptable answer seems to be:

(defun sum (term a next b)
    (funcall term a)
    (funcall next a))

(defun inc-test (x) (+ x 1))

(sum 'inc-test 1 'inc-test 10 )

Or basically call with 'inc-test or (quote inctest) rather than inc-test.