Let, eval, and quote behavior

Question

I tried to understand the behavior let. Why did case2 give me an error?

;; case1: worked fine.
(let ((NF 5)) NF)
5

;; case2: got an error
(let ((NF 5)) (eval 'NF))
error: The variable NF is unbound

Answer 1

EVALdoes not have access to lexical variables. CLHS says:

Computes the form in the current dynamic environment and zero lexical environment.

If you declare a variable special, it will work because it performs dynamic binding, not lexical binding.

(let ((NF 5))
  (declare (special NF))
  (eval 'NF))
5