Functional Problem Solving (CSC 151 2014F) : EBoards
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What are the potential topics for tomorow's quiz?
drawing-render
image-new
display
image-height
image-show
image-width
load-image
Can we talk about procedures with side effects?
> (define x 5) > (define y (square x)) > y 25 > x 5 > (define d (scale-drawing 10 drawing-unit-circle)) > (define d2 (hshift-drawing 20 d)) > (drawing-left d2) 15 > (drawing-left d) -5
> (define kitten (image-load "/home/rebelsky/Desktop/kitten.jpg")) > kitten 1 > (image-get-pixel kitten 0 0) 3037011 > (irgb->string (image-get-pixel kitten 0 0)) "46/87/83" > (image-set-pixel! kitten 0 0 "yellow") > (irgb->string (image-get-pixel kitten 0 0)) "255/255/0" > (image-show kitten) 1
> (define silly (lambda (name) (display "Hello ") (display name) (display ".") (newline) 5)) > (silly "Sam") Hello Sam. 5
* Note: We see output *and* we get a value back.
* We say that the second and third models have "side effects".
* What about that !?
* Custom is to use the ! when you write a procedure with side effects.
* But custom is not always followed. E.g., display doesn't have a !.
* And then there's image-show
.
* It doesn't change the pixels.
* But it changes the state, perhaps dangerously.
What's the relationship between image-show
and drawing-render!
?
image-show
- take the grid of pixels and display it in GIMP.drawing-render!
- takes the description, convert it to pixels, and
set those pixels to the appropriate values on the image.What about drawing->image
?
(drawing-render! drawing (image-new width height))
Can you talk to us about check and test and the rest?
What's the difference between check-= and check-eq?
check-=
check-eq?
Example
> (define prof "SamR") > (define sam (string-append "Sam" "R")) > prof "SamR" > sam "SamR" > (require rackunit) > (check-= prof sam 0) -------------------- ERROR . . -: contract violation expected: number? given: "SamR" argument position: 1st other arguments...: "SamR" -------------------- > (check-eq? prof sam 0) -------------------- FAILURE actual: "SamR" expected: "SamR" name: check-eq? location: (unsaved-editor331 43 2 840 22) expression: (check-eq? prof sam) message: 0 . . Check failure -------------------- > (check-equal? prof sam 0)
(define sqrt-tests (test-suite "Tests of the square root method" (test-case "If you square the square root (or vv), you get the original" (check-= (sqrt (square 2)) 2 0.000001) (check-= (square (sqrt 2)) 2 0.000001)) (test-case "Easy test: sqrt 4. If this doesn't work, things are broken." (check-= (sqrt 4) 2 0)) (test-case "When sqrt can have an exact result, it should" (check-equal? (exact? (sqrt 4)) #t)) (test-case "Check zero" (check-= (sqrt 0) 0 0)) (test-case "Imaginary sqrt(-1)" (check-= (sqrt -1) 0+i 0.0000001)))) (define ss-test (lambda (num) (test-suite "Checking square roots" (check-= (sqrt (square num)) num 0.000001) (check-= (square (sqrt num)) num 0.000001) (check-= (square (square (sqrt (sqrt num)))) num 0.0000001)))) (define sqrt-tests (test-suite "Tests of the square root method" (test-suite "Roots of 2" (ss-test 2)) (test-suite "Roots of 9273" (ss-test 9273))
Given documentation for a procedure, how do you write the procedure?
;;; Procedure: ;;; whatever ;;; Parameters: ;;; alpha, a number ;;; beta, another number ;;; image, an image ;;; Purpose: ;;; Put a blue ellipse on image. ;;; ... ;;; Postconditions: ;;; The width of the ellipse is alpha ;;; The height of the ellipse is beta ...
(define whatever (lambda (alpha beta image) ...))
Will you send me my responses to the prologue?