LET and SETF in commonLISP

Question

From what my teacher told me, I should use let to declare local variables and setf to declare global variables.

I'm tried running the following code:

(let (state-list (problem-initial-state problem))
  (print state-list))

and I get NIL.

However, when I try the following:

(setf state-list (problem-initial-state problem))
  (print final-list)

I get the desired value (the value in problem-initial-state problem).

Why is that?

PS: I apologize for these begginer questions, I'm getting a hard time getting into LISP, coming from a C background.

Answer 1

You are missing a couple of parens in your let forms:

(let ((a 1)
      (b 2))
  (print (list a b)))

will print (1 2).

Your form

(let (state-list (problem-initial-state problem))
  (print state-list))

binds state-list to nil and problem-initial-state to problem.