20.N Inventory

Practice writing inventories and examples.

Good check-expects have no coincidences. Specifically, none of the inputs should be the same.

A. Linecheck

The function linecheck returns true if a posn is on the graph of a particular line. The line is y=m*x+b, where m and b are inputs to the fuction. The posn gives (x,y).

    ; linecheck : number(m) number(b) posn(p) -> boolean

  1. Write two good check-expect statements, one with a true answer and one with a false answer.

  2. Write an inventory for linecheck.

  3. Without using a conditional, write the code for linecheck.

B. Distance-based Coloring

The bg-color function takes in a number(xline) and a posn, and returns a color: “light blue” if the point is close to a specific line, “orange” otherwise.

A star is on the line $y=\frac{3}{4}x+100$. The x-coordinate of the star is given by the input xline. The input circle-p gives the posn of the center of a circle. Return “orange” if the center of the circle is less than 50 pixels from the center. Otherwise return “light blue”.

An example function is below:

;; bg-color: number posn -> color
(define (bg-color xline circle-p)
  (cond [(< (posn-distance (make-posn 80 160)
                           (make-posn 110 120))
            50)
         "orange"]
         [else
         "light blue"]))