; Chapter 7.5
; Let the missing

; What is "let"?           It's that bit of scheme that's not in the book.
;
; What is "let" for?       It's a way of giving a name to something that you're
;                          going to use more than once.
;
; Do you have to use it?   No.  But your program will become even
;                          harder to read.
;
; Give an example of let
                            (let ((x 2))
                              (+ x x))

; What would have been a    (+ 2 2)
; shorter way to write
; that?
;
; Even shorter?             4
;
; Why is that?             Because scheme gives "x" the value of 2 inside
;                          the let.
;
; Could you have used a    Yes.
; define for that?
;
; Why not then?            Except in the simplest cases, you can't use a define
;                          inside a define.  Plus, it leads to scary programs.
;
; Why not just use 2       You could, but if "x" has a complicated value, then
; twice, then?             it makes it a lot easier to read.
;
; Give an example of that   
                            (let ((x (+ 4 (* 3 5))))
                              (+ x x))
;                       which is a lot easier to read than this:
                             (+ (+ 4 (* 3 5)) (+ 4 (* 3 5)))