[lispm]

> (1 2 3) is syntactic sugar for (cons 1 (cons 2 (cons 3 nil)))

Not really.

(1 2 3) is a list in Lisp.

(cons 1 (cons 2 (cons 3 nil))) is code to produce a list.

if we have

  (append '(1 2 3)
          (cond 1 (cons 2 (cons 3 nil))))

The first is a literal list and the second one is code, which produces a list at some point in time - maybe at runtime.