; Symbols and Lists
; a "word" that can stand for something, could be an identifier
; examples

(define dozen 12)
dozen        ; Scheme will evaluate this symbol and return 12
'dozen       ; because of the '  Scheme will not evaluate dozen

; suppose gross is not defined
; what happens if I type 
'gross        ; Scheme will not evaluate and will return gross
; what if I type:   gross
; will get an error message  "reference to undefined identifier: gross"

; LISTS are the main datatype of Scheme
; what are three ways that we can generate the list:  (bert ernie)

(list 'bert 'ernie)  ; way 1, use the LIST command

(cons 'bert (cons 'ernie '()))  ; way 2, use CONS
; note that this is a very cumbersome way to define long lists

'(bert ernie)    ;way 3, just tell Scheme not to evaluate it