ITEC 380 2014fall ibarland

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hw02
defining functions
`cond` for union types

Due:
Section 01: Sep.08 (Mon) 23:59, on D2L and hardcopy on Wednesday
Section 11: Sep.09 (Tue) 23:59, D2L.
Your submitted file should be named “hw02.rkt” as plain-text (which is what DrRacket saves as).

Standard instructions for all homeworks:

• Your name, the assignment-number, and the URL of this assignment must be in a comment at the start of the file.
• Any code which results in syntax errors will generally not earn more than 50% of the points-possible. For grading, I will ignore any commented-out code (unless the problem is explicitly asking for commented-out code, ’course).
• If your hardcopy is more than 1page, it must be stapled.
• Format well (in particular, each open-paren should be preceded by a space or start-of-line, for now).

Open DrRacket (either in labs, or you can download it to your own computer from racket-lang.org). The first time you start DrRacket, it will ask you to choose a language; select Language > Use Language... > Teaching Languages > Beginning Student, for now.

Follow the design recipe, steps 4,5,7,8.

1. (15pts) Write the function has-suffix?, which takes in two strings and returns whether or not the first string ends with (the letters of) the second.¹.

   hint:You can avoid needing if or cond with a clever (but standard) use of min or max.

2. Data definition: A directory-response is one of:

   • a username: a string of lowercase roman letters, whose length is in [1,14) (e.g. "ibarland"), OR
   • #f (indicating no entry), OR
   • 'private (indicating entry exists, but information is non-public).
   NOTE: You are given a directory-response: so if you're given a string, you deduce (from this def'n) that its length is in [1,14). This is not something you need to check for, or handle.

   (15pts) Write a function which, given a directory-response, returns a string: either

   • a radford email address (e.g. “ibarland@radford.edu”, OR
   • “No such person.”, OR
   • “Information not published.”.
   corresponding to the three cases in our data-definition, respectively.

   (You can think of this function as being one part of a larger program which queries a campus-directory, such as radford's, and then has to use the response it gets.)

   To think about: As per the design recipe since our data-definition has three different variants, you will have a cond with how many branches? (You don't need to write a template (step 3a) separately from your final code, for this homework.)

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©2014, Ian Barland, Radford University Last modified 2014.Oct.28 (Tue)

Please mail any suggestions (incl. typos, broken links) to ibarlandradford.edu