title: “Observed Errors” date: 2022-12-08T22:50:36-06:00 draft: false weight: 90 summary: “Errors observed in student work.”

A catalog of mistakes seen while writing this project.

Quotient of Doubles

The quot and div functions only work on integers. That is, quot 1.7 0.5 does not give 3.

Rouding gives an Integer

The result of round 1.7 is the integer 2, not the double 2.0.

Recursive Rendering

Recursion in general can be a mess without an example to guide the coding.

draw :: [Double] -> Picture
draw [] = []
draw (x:xs) = pictures [translated x 0 (circle 2.5) : draw xs ]

Clicked Point

Not returning the intended coordinates. No check-expects.

ck = clickedPoint (1.7, 4.3) == Just (2,4) -- Missing a line like this

clickedPt (x,y)
   | not $ null (findCircle (x,y)) = Just (x,y)
   | otherwise = Nothing

Ignoring Logical Coordinates

Plenty of people are spacing out their circles so each coordinate in the model is a multiple of 4, in direct contradiction to the instructions.