Purpose The purpose of this problem set is to internalize design skills. Topically, the problem set focuses on functions that process structures and arbitrary unions of data.
Finger Exercises HtDP/2e: 65, 67, 68, 69, 70, 71, 77, 78, 79, 86, 94, 102, 104, 123, 124, 125
(define-struct dist (yards feet inches)) ; A Distance is a structure: ; (make-dist Number Number Number) ; interpretation: (make-dist y f i) is the distance between two ; points expressed in yards, feet, and inches ; Constraints: ; – yards is greater or equal than 0 ; – feet is always between 0 and 2 ; – inches is always between 0 and 11
Design the function absolute, which converts a Distance to the number of inches it represents.
Design the function plus1, which adds one inch to a given Distance.
Design the function dist->string, which expresses a given Distance as a String. For example, (make-dist 10 2 5) maps to "10yd. 2' 5''".
Problem 2 You have been hired by the local psychology department to assist with the software for a perception experiment. For the first step, the lab director would like you to design a world program that records the first two mouse clicks ("button-down" mouse events) and draws the two clicks and a line between them on the canvas. The experimenter must be able to specify for how many seconds the world program runs.
The program should draw the first mouse click as a five-pointed, solid-red star and the second one as a five-pointed, solid-blue star.
Read the documentation for on-tick to understand how a world program can run for a specified number of seconds.
Challenge Have the program add a green mid-point between the two stars. See Problem Set 2, problem 4 for inspiration.
Problem 3 The second step of your employment is to design a world program that records a specified number of key strokes with string representation of length 1. That is, the experimenter launches the program on some natural number n and when the “subject”Psychologists use the word “subject” for the victims that participate in their experiments. has struck n keys (with good representations), the program returns the string that is made up of these keys.
Challenge You can’t trust psychologists with computers. Design a checked version of the program that rejects all inputs other than natural numbers.
Problem 4 Design the function downward. It consumes a list of strings and produces the string of all first characters in these strings. You do not need to worry about empty strings in the list.