Submission Instructions:

• The assignment is due Thursday December 1, 2005 at 5:00pm
• You must do both of the following:
  1. Hand in a printed version of your completed assignmet:
     • Print, fill in and sign the CS342 Assignment Submission Form.
     • Attach the submission form to a printed copy of your completed assignment and place it in the CS342 locker.
  2. Submit an electronic version of your completed assignment:
     • Save all of the files for your completed assignment in a directory called Assignment1. This directory should contain a subdirectory for each question, i.e. Question1, Question2, etc. Make sure there are no files you don't want in the directory.
     • Make sure the directories with the answers contain what they should. For questions that require written answers, save the answer as a plain text or pdf file. Word .doc files will not be accepted. For questions that require programs, make sure that you have a working version of the program, all of its parts, documentation, test inputs and outputs, or whatever is specified in the question. Make sure there is only one version of the answer saved.
     • cd to the parent directory of Assignment1 (i.e. Assignment1 should show up when you do an ls).
     • Run the command submit cs342 Assignment1 to submit your assignment.
     • Check (and keep) your email receipt. Make sure the file name and file size information is correct.

Assignment:

This assignment is out of 100 points. The bonus question can give you an extra 40 points.

• Question 1 [25 points]

  Do problems 5 and 7 on pages 423 to 424 of the text (Sebesta, 7th edition).

• Question 2 [40 points]
  • Question 2a [15 points]

    Define macros my-lambda and my-return that use continuations to implement a return statement in Scheme. More specifically, my-lambda should be usable in exactly the same way as a normal Scheme lambda (in fact, you should use a lambda as part of its implementation.) However, a function f, created by a my-lambda, contains a sub-expression (my-return result), and this expression is evaluated, then result should be returned immediately as the result of the call to f.

  • Question 2b [25 points]

    Use continuations to implement a iterator/yield construct that can be used to make generic iterators. You must also define functions has-next? and get-next to access the values of the iterator. These should be used together as follows:

    • iterator takes a number of expressions arguments and returns an iterator. This iterator produces values by evaluating the expressions.
    • When the body of the iterator evaluates a (yield result) sub-expression, then this value is returned from the iterator. The iterator may later resume its calculation following the yield to produce further values, if needed.
    • The function has-next? is used to ask an iterator object whether it has another value to return.
    • The function get-next obtains the next value from the iterator. If has-next? did not return true, then the value of get-next is undefined.

    Example:

        ;; Create an iterator
        (define my-it  (iterator
                ;; Sprinkle some yield statements throughout
                (yield 7)
                (if (> a b) (yield a))
                (do ((i 0 (+ i 1)))
                    ((> i b))
                    (yield i) )
                (yield 8) ))
    
        ;; Add up the values it returns
        (do ((s 0))                      ;; local variable for sum
            ((not (has-next? my-it))  s) ;; return sum when done
    
            (set! s (+ s (get-next my-it))) )
    

• Question 3 [35 points]

  XSLT can be used to in web servers to customize the web-pages that are served to different kinds of devices. For example, web pages served to cell-phones should be laid yout in a compact manner. In this exercise you will write a simple XSLT stylesheet which performs such a task.

  Write an XSLT stylesheet to replace <img> elements with the text that is present in their alt="..." attribute (if one is given), or their src="..." attribute (if no alt is given). Your stylesheet should replace only the img tags, and leave the page otherwise unchanged.

  Provide a suitable set of input test cases, and show the resulting outputs. Note that your input HTML must also be legal XML. For this reason, your img tags should be written as

  <img src="..." alt="..."> </img>

• Question 4 (Bonus) [40 points]

  Write an XSLT style sheet to transpose a rectangular HTML table of arbitrary size. E.g. the table

  <table>
  <tr> <td>a</td> <td>b</td> <td>c</td> </tr>
  <tr> <td>d</td> <td>e</td> <td>f</td> </tr>
  </table>
  

  should be transformed to

  <table>
  <tr> <td>a</td> <td>d</td> </tr>
  <tr> <td>b</td> <td>e</td> </tr>
  <tr> <td>c</td> <td>f</td> </tr>
  </table>
  

  Provide a test file and output showing the stylesheet transposing a matrix of size 2x3 and also of size 4x3.