(macroexpand-1 '(Square-Sum2 1 First))
==> (LET* ((#:FIRST-590 1)
(#:SECOND-591 FIRST)
(#:SUM-592 (+ #:FIRST-590 #:SECOND-591)))
(* #:SUM-592 #:SUM-592))
Lecture Notes: Macros(三)
-Sum2 (X Y)
(let ((First (gensym FIRST-))
(Second (gensym SECOND-))
(Sum (gensym SUM-)))
'(let* ((,First ,X)
(,Second ,Y)
(,Sum (+ ,First ,Second)))
(* ,Sum ,Sum))
))
Now
This expansion has no dependence on any local variable names in the macro definition itself, and since the generated ones are guaranteed to be unique, is safe from name collisions.