(define title "Using Abstractions")
(define description "")

;;; Admin
;;; - TA meeting
;;;   + Snake & tetris great assignments
;;;     Stressed coding skills, students exhibit classic probs
;;;     + don't do examples first
;;;     + no templates
;;;     + don't do unit testing - big bang debugging
;;;       Writing test cases after.
;;;     + I.e.: not following design recipes
;;;	+ Examples don't have to be complex!
;;;       Simple examples great! They write your code for you.
;;;       Handle simple cases, complex takes care of itself.
;;;     + code too big -- break into pieces
;;;       Easier to think about; *much* easier to debug.
;;;     + partner-slacking shows up. We have mechanisms...

;;; SERPENTINE

;; ------------------------------------------------------
;; PROBLEM:
;; add10-to-all: [Listof Number] -> [Listof Number]
;; add 10 to each number on the list
;; ------------------------------------------------------

;; given: (list  1  2  3)
;; wanted (list 11 12 13)
;; --> test
(define (add10-to-all l)
   ;; (map f (list x y z)) is (list (f x) (f y) (f z))
   ;; use it and what should f do?
   (map add10 l))

;; Number -> Number
;; add 10 to the number
(define (add10 x) (+ x 10))

(equal? (add10-to-all '(1 2 3)) '(11 12 13))

;; why are the contracts working out?
;; map : [X -> Y] [Listof X] -> [Listof Y]
;; X = Number
;; Y = Number

;; ------------------------------------------------------
;; use LOCAL for the ugly function definition

;; [Listof Number] -> [Listof Number]
;; add 10 to each number on the list
;; given: (list 1 2 3)
;; wanted (list 11 12 13)
;; --> test
(define (add10-to-all.v2 l)
   (local ((define (add10 x) (+ x 10)))
     (map add10 l)))

(equal? (add10-to-all.v2 '(1 2 3)) '(11 12 13))


;; ------------------------------------------------------
;; PROBLEM:
;; add-x-to-all: [Listof Number] Number -> [Listof Number]
;; add the given number (x) to each item on the list
;; ------------------------------------------------------

;; given: (list 1 2 3) 5
;; wanted (list 6 7 8)
(define (add-x-to-all l x)
   (local ((define (add10 i) (+ i x)))
     (map add10 l)))

(equal? (add-x-to-all '(1 2 3) 5) '(6 7 8))

;; ------------------------------------------------------
;; PROBLEM:
;; unit? : [Listof Number] -> Boolean
;; are all numbers on the list between -1 and +1 (incl.)?
;; ------------------------------------------------------

;; given: (list -1 0 +.5 -.3 +1)
;; wanted true

(define (unit? l)
   (local ((define (between-1+1 x) (<= -1 x +1)))
     (andmap between-1+1 l)))

(equal? (unit? (list -1 0 +.5 -.3 +1)) true)
(equal? (unit? (list -1 0 +.5   +1.1)) false)

;; andmap : [X -> Boolean] [Listof X] -> Boolean
;; what is X here? X = Number

;; ------------------------------------------------------
;; PROBLEM:
;; in-range? : [Listof Number] Number Number -> Boolean
;; are all numbers on the list between L and R (incl)?
;; ------------------------------------------------------

(define (in-range? lst L R)
   (local ((define (between-1+1 x) (<= L x R)))
     (andmap between-1+1 lst)))

(equal? (in-range? (list -1 0 +.5 -.3 +1) -1 +1) true)
(equal? (in-range? (list -1 0 +.5   +1.1) -1 +1) false)


;; WHAT IS A LOOP?
;; Perform some computation on every element of a collection
;; then combine the results together somehow.
;; Collection: num range, list... but also tree.

;; Why are loops so important?
;; - programs small; data big.
;; - theoretical source of power

;; How many loops in C or Java? 4? 5?
;; How many loops in Scheme? Many as you like.
;; What if I need some "loop" pattern not in std collection?
;;   Write my own loop! In Scheme, can pass computation around.

-------
;;; Now teach lambda,
;;; then go back and redo examples with lambda.
-------

;; ------------------------------------------------------
;; PROBLEM
;; paint : [Listof Posn] -> Image
;; paint red color spots at the given posn-s 
;; on 100 x 100 canvas
;; ------------------------------------------------------

(define (paint l)
  (local ((define (one-dot p i)
            (place-image dot (posn-x p) (posn-y p) i))
          (define dot (circle 3 'solid 'red)))
    (foldr one-dot (empty-scene 100 100) l)))

(equal? (paint (list (make-posn 20 20)))
	(place-image (circle 3 'solid 'red)
		     20 20
		     (empty-scene 100 100)))

;; foldr : [X Y -> Y] Y [Listof X] -> Y
;; what are X and Y? X = Posn, Y = Image