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Unformatted text preview: CS 135 Winter 2012 Brad Lushman Assignment: 4 Due: Wednesday, February 8, 2012 9:15am Language level: Beginning Student Allowed recursion: Structural recursion Files to submit: list.rkt , dailybalance.rkt , area.rkt Warmup exercises: HtDP 8.7.2, 9.1.1 (but use boxandpointer diagrams), 9.1.2, 9.5.3 Practise exercises: HtDP 8.7.3, 9.5.4, 9.5.6, 9.5.7 Overall instructions for this assignment are the same as previous assignments except you will note a new addition at the top: “Allowed recursion” restricts you to structural recursion – recursion that follows the data definition of the data it consumes. Here are the assignment questions you need to submit. 1. Perform the Assignment 4 questions using the online evaluation “Stepping Problems” tool linked to the course web page and available at https://www.student.cs.uwaterloo.ca/ ˜ cs135/stepping The instructions are the same as A03; check there for more information, if necessary. Re minder: You should not use DrRacket’s Stepper to help you with this question, for a few reasons. First, as mentioned in class, DrRacket’s evaluation rules are slightly different from the ones presented in class; you are to use the ones presented in class. Second, in an exam sit uation, of course, you will not have the Stepper to help you. Third, you can reenter steps as many times as necessary to get them correct, so you might as well maximize the educational benefit. 2. This problem involves lists. Of the builtin list functions, you may only use cons , first , rest , empty? , and cons? . In the file list.rkt : (a) Use the template for functions that consume a ( listof Num ) to write countpositives , which consumes a ( listof Num ) and produces a count of all of the positive numbers in the list. (b) Use the template to write the predicate somenegative? , which consumes a ( listof Num ) and produces true if and only if at least one number in the list is negative. (c) Use the template to write the function reciprocals , which consumes a ( listof Num ) and produces the list resulting from transforming each number in the list into its reciprocal. Every occurrence of 0 in the original list should be transformed to ’ error . For example, ( reciprocals ( cons 1 ( cons ( cons 2 empty )))) should produce ( cons 1 ( cons ’ error ( cons 0.5 empty ))). CS 135 — Winter 2012 Assignment 4 1 (d) For this subquestion, you should use the template for functions that process a non empty list. Write the Scheme function differences , which consumes a nonempty list of Num , and produces the list of differences between consecutive entries. For exam ple, ( differences ( cons 1 ( cons 4 ( cons 5 empty )))) should produce ( cons 5 ( cons 1 empty )). Note that the list produced will always be one element shorter than the list))....
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