Scripting Languages G22.3033-002 Summer 2008

• hw10: Homework 10.

Scripting Languages G22.3033-002 Summer 2008 hw10

Assigned Th 7/24/2008, due Fr 8/1 at 9pm. 50 points.

http://www.cs.nyu.edu/courses/summer08/G22.3033-002/

• Instructions: Homework instructions.
• hw10-concepts: Concept questions.
• hw10-programming: Programming exercises.

Homework instructions

Homeworks are due on Fridays at 9pm. This deadline will be strictly enforced.

Email your answers to Robert Soulé robert.soule@gmail.com. Please put your solutions to VBA programming problems in a powerpoint presentation. For all other questions (including programming problems in other languages), just send a simple text file, such as what you get when using Emacs, Vi, Notepad, or the "save as text only" feature in Word.

Please make sure that your code works with the compilers and tools installed at CIWW. Specifically, please test:

JavaScript

Your JavaScript code must run with both Mozilla's Firefox browser and with Microsoft's Internet Explorer browser.

Php

Your PHP code must run with PHP 5.1.6 on the CIMS web servers, see http://www.cims.nyu.edu/systems/userservices/webhosting/.

Perl

Your Perl code must run with Perl 5.8.8 for Linux/x86, for example on doowop1 (see http://www.cims.nyu.edu/systems/resources/computeservers/).

Vba

Your VBA code must run with Microsoft Office 2003 for Windows on the machines in the labs CIWW 502 or CIWW 624.

Concept questions

• hw10-1: hw10-1 Iterating with Coroutines
• hw10-2: hw10-1 Iterating with Block Parameters
• hw10-3: hw10-1 Coroutines vs. Block Parameters

hw10-1 Iterating with Coroutines

(4+6 = 10 points) Consider the following Python script.

     #!/usr/bin/env python
     class Tree:
         def __init__(self, value, left=None, right=None):
             self.value = value
             self.left = left
             self.right = right
         def preorder(self):
             yield self.value
             if self.left:
                 for v in self.left.preorder():
                     yield v
             if self.right:
                 for v in self.right.preorder():
                     yield v
     
     my_tree = Tree(1,
                 Tree(2,Tree(4),Tree(5)),
                 Tree(3,Tree(6),Tree(7)))
     
     def print_preorder(tree):
         print 'preorder:'
         for y in my_tree.preorder():
             print y
     
     print_preorder(my_tree)

1. Predict what the code should print. Then run it. What does it print?
2. Add another generator method Tree.inorder that walks the tree in-order instead of pre-order. An in-order walk first visits all nodes in the left subtree, then the current node, then all nodes in the right subtree. The following picture shows a tree for which an in-order walk would visit nodes in alphabetical order:

                  d
                /   \
               b     f
              / \   / \
             a   c e   g
        

   After you write the generator Tree.inorder, the following code:

             def print_inorder(tree):
                 print 'inorder:'
                 for y in my_tree.inorder():
                     print y
             
             print_inorder(my_tree)
        

   should cause the following output to be printed:

             inorder:
             4
             2
             5
             1
             6
             3
             7
        

hw10-2 Iterating with Block Parameters

(4+6 = 10 points) Consider the following Ruby script.

     #!/usr/bin/env ruby
     class Tree
       attr_accessor :value, :left, :right
       def initialize(value, *leftRight)
         @value = value
         if 0 < leftRight.length()
           @left = leftRight[0]
           @right = leftRight[1]
         end
       end
       def preorder()
         yield @value
         if @left
           @left.preorder {|v| yield v }
         end
         if @right
           @right.preorder {|v| yield v }
         end
       end
     end
     
     $my_tree = Tree.new(1,
                  Tree.new(2, Tree.new(4), Tree.new(5)),
                  Tree.new(3, Tree.new(6), Tree.new(7)))
     
     def print_preorder(tree)
       puts 'preorder:'
       tree.preorder {|y| puts y.to_s + "\n" }
     end
     
     print_preorder($my_tree)

1. Predict what the code should print. Then run it. What does it print?
2. Add another top-level function print_sum that uses the iterator to compute the sum of all values in the tree. For example, the following call:

             print_sum($my_tree)
        

   should cause the following output to be printed:

             sum:
             28
        

hw10-3 Coroutines vs. Block Parameters

(7+4+4=15 points)

1. Briefly explain the difference between coroutines and block parameters.
2. Give an advantage of coroutines compared to block parameters.
3. Give an advantage of block parameters compared to coroutines.

Programming exercises

• hw10-4: hw10-4 Iterating with Closure Parameters (PHP)

hw10-4 Iterating with Closure Parameters (PHP)

(15 points) Consider the following skeleton PHP script:

     #!/usr/bin/env php
     <?php
     class Tree {
       # --- add your code here ---
     }
     
     $myTree = new Tree(1,
                      new Tree(2, new Tree(4), new Tree(5)),
                      new Tree(3, new Tree(6), new Tree(7)));
     
     function printPreorder($tree) {
       echo "preorder:\n";
       $tree->preorder(create_function('$v', 'echo "$v\n";'));
     }
     
     printPreorder($myTree);
     ?>

Implement the body of class Tree so that the construction (new Tree(...)) and iteration ($tree->preorder(...)) at the bottom of the script work, and produce the same output as the equivalent Python and Ruby scripts above.