How do I execute a Lisp program which has been stored in a variable?

Question

I have this code:

(setf prg '(+ 1 n)) ; define a very simple program
(print prg) ; print the program

I need to add more code so that when the above code is executed, it should set n to 1 and execute the program stored in variable prg.

Answer 1

I think you want to do this:

(setf prg (lambda (n) + 1 n)) ; define a very simple program
(print (funcall prg 1))       ; print the program

In your example: (+ 1 n) is not a valid Common Lisp program.

EDIT: If you wanted to play with variables binding, you could also declare a variable:

(setf prg '(+ 1 n)) ; define a Common Lisp expression
(defparameter n 1)  ; bind a variable to the value 1
(print (eval prg))  ; evaluate the Common Lisp expression
> 2