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01-toys.ss
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01-toys.ss
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;
; Chapter 1 of The Little Schemer:
; Toys
;
; Code examples assemled by Peteris Krumins (peter@catonmat.net).
; His blog is at http://www.catonmat.net -- good coders code, great reuse.
;
; Get yourself this wonderful book at Amazon: http://bit.ly/4GjWdP
;
; Examples of atoms:
;
'atom
(quote atom)
'turkey
1492
'*abc$
(quote *abc$)
; Examples of lists and s-expressions
;
'(atom)
(quote (atom))
'(atom turkey or)
'((atom turkey) or)
'xyz
'(x y z)
'((x y z))
'(how are you doing so far)
'(((how) are) ((you) (doing so)) far)
'()
'(() () () ())
; Example of not-lists
;
'(atom turkey) 'or ; because it's two separate s-expressions
; Example of not-atoms
;
'() ; because it's a list
; Examples of car
;
(car '(a b c)) ; 'a
(car '((a b c) x y z)) ; '(a b c)
; Examples of not-applicable car
;
; (car 'hotdog) ; not-applicable because 'hotdog is not a list
; (car '()) ; not-applicable because '() is an empty list
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
; The law of car: ;
; ;
; The primitive /car/ is defined only for non-empty lists. ;
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
; More examples of car
;
(car '(((hotdogs)) (and) (pickle) relish)) ; '((hotdogs))
(car (car '(((hotdogs)) (and)))) ; '(hotdogs)
; Examples of cdr
;
(cdr '(a b c)) ; '(b c)
(cdr '((a b c) x y z)) ; '(x y z)
(cdr '(hamburger)) ; '()
(cdr '((x) t r)) ; '(t r)
; Examples of not-applicable cdr
;
; (cdr 'hotdogs) ; not-applicable because 'hotdogs is not a list
; (cdr '()) ; not-applicable because '() is an empty list
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
; The law of cdr: ;
; ;
; The primitive /cdr/ is defined only for non-empty lists. ;
; The /cdr/ of any non-empty list is always another list. ;
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
; Examples of car and cdr
;
(car (cdr '((b) (x y) ((c))))) ; '(x y)
(cdr (cdr '((b) (x y) ((c))))) ; '(((c)))
; Examples of cons
;
(cons 'peanut '(butter and jelly)) ; '(peanut butter and jelly)
(cons '(banana and) '(peanut butter and jelly)) ; '((banana and) peanut butter and jelly)
(cons '((help) this) '(is very ((hard) to learn))) ; '(((help) this) is very ((hard) to learn))
(cons '(a b (c)) '()) ; '((a b (c)))
(cons 'a '()) ; '(a)
; Examples of not-applicable cons
;
; (cons '((a b c)) 'b) ; not-applicable because 'b is not a list
; (cons 'a 'b) ; not-applicable because 'b is not a list
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
; The law of cons ;
; ;
; The primitive /cons/ takes two arguments. ;
; The second argument to /cons/ must be a list. ;
; The result is a list. ;
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
; Examples of cons, car and cdr
;
(cons 'a (car '((b) c d))) ; (a b)
(cons 'a (cdr '((b) c d))) ; (a c d)
; Example of the null-list
;
'()
; Examples of null?
;
(null? '()) ; true
(null? '(a b c)) ; false
; Example of not-applicable null?
;
; (null? 'spaghetti) ; not-applicable because 'spaghetti is not a list
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
; The law of null? ;
; ;
; The primitive /null?/ is defined only for lists ;
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
; We first need to define atom? for Scheme as it's not a primitive
;
(define atom?
(lambda (x)
(and (not (pair? x)) (not (null? x)))))
; Examples of atom?
;
(atom? 'Harry) ; true
(atom? '(Harry had a heap of apples)) ; false
; Examples of atom?, car and cdr
;
(atom? (car '(Harry had a heap of apples))) ; true
(atom? (cdr '(Harry had a heap of apples))) ; false
(atom? (cdr '(Harry))) ; false
(atom? (car (cdr '(swing low sweet cherry oat)))) ; true
(atom? (car (cdr '(swing (low sweet) cherry oat)))) ; false
; Examples of eq?
;
(eq? 'Harry 'Harry) ; true
(eq? 'margarine 'butter) ; false
; Example of not-applicable eq?
;
; (eq? '() '(strawberry)) ; not-applicable because eq? works only on atoms
; (eq? 5 6) ; not-applicable because eq? works only on non-numeric atoms
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
; The law of eq? ;
; ;
; The primitive /eq?/ takes two arguments. ;
; Each must be a non-numeric atom. ;
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
; Examples of eq?, car and cdr
;
(eq? (car '(Mary had a little lamb chop)) 'Mary) ; true
(eq? (car '(beans beans)) (car (cdr '(beans beans)))) ; true
; Examples of not-applicable eq?, car and cdr
;
; (eq? (cdr '(soured milk)) 'milk) ; not-applicable because (cdr '(...)) is a list
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
; ;
; This space reserved for ;
; JELLY STAINS! ;
; ;
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;
; Go get yourself this wonderful book and have fun with these examples!
;
; Shortened URL to the book at Amazon.com: http://bit.ly/4GjWdP
;
; Sincerely,
; Peteris Krumins
; http://www.catonmat.net
;