?? readme.html
字號:
<?xml version="1.0" encoding="iso-8859-1"?><!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1//EN" "http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd"><html xmlns="http://www.w3.org/1999/xhtml"><head> <meta http-equiv="content-type" content="text/html; charset=iso-8859-1" /> <title>COMP151 Programming Assignment 1, Spring 2006</title> <meta name="generator" content="amaya 8.8.3, see http://www.w3.org/Amaya/" /></head><body><h1>COMP151 Programming Assignment 2, Spring 2007</h1><p><strong>Author:</strong> <a href="http://www.cs.ust.hk/~dekai/">DekaiWu</a></p><p><strong>Date:</strong> Due 2007.03.28 at 23:00 by CASS</p><p><strong>Download:</strong> <ahref="http://www.cs.ust.hk/~dekai/151/assignments/a2.tar.gz">http://www.cs.ust.hk/~dekai/151/assignments/a2.tar.gz</a></p><p><strong>Assignment page:</strong> <ahref="http://www.cs.ust.hk/~dekai/151/assignments/a2/html/">http://www.cs.ust.hk/~dekai/151/assignments/a2/html/</a></p><p><strong>Course page:</strong> <ahref="http://www.cs.ust.hk/~dekai/151/">http://www.cs.ust.hk/~dekai/151/</a></p><h3>Your assignment</h3><p>You are assigned to maintain and extend the expression evaluator codebuilt in <a href="http://www.cs.ust.hk/~dekai/151/assignments/a1/html/">Assignment 1</a>.Your job this time is to take the following steps.</p><h3>Step 1: Re-design Cell using polymorphism</h3><p>Completely re-implement the <tt>Cell</tt> class, to eliminate the use of atagged union, by instead making use of polymorphism virtual functions. The<tt>Cell</tt> class is to become an abstract base class (ABC). Derivedclasses should include <tt>IntCell</tt>, <tt>DoubleCell</tt>,<tt>SymbolCell</tt>, and <tt>ConsCell</tt>.</p><p>After this step, your <tt>eval()</tt> implementation from Assignment 1should still work (assuming you didn't break encapsulation!) Note that theinterface specified in <tt>cons.hpp</tt> has <em>not</em> changed. Thefunction <em>definitions</em> in <tt>cons.hpp</tt> may have changed to fitthe new <tt>Cell</tt> implementation's use of late binding, but the<em>declarations</em> have not. This means that <tt>parse()</tt> and<tt>eval()</tt> and any other functions that made proper use of the interfaceencapsulated by <tt>cons.hpp</tt> should all still work.</p><h3>Step 2: Do a cleaner re-design of eval() to take advantage ofpolymorphism</h3><p>Re-design your <tt>eval()</tt> implementation to be much cleaner, takingadvantage of the polymorphism to get rid of all those ugly<tt>if-then-else</tt> and/or <tt>switch</tt> statements from your Assignment1 version, by instead making appropriate use of function overriding and/oroverloading.</p><p>To accomplish this step, you will have to extend the interface in<tt>Cell.hpp</tt>. Because of this, note that after this step, your new<tt>eval()</tt> implementation may no longer work with your oldimplementation of the <tt>Cell</tt> class from Assignment 1.</p><h3>Step 3: Generalize to add more arithmetic operators</h3><p>Take advantage of the cleaner polymorphic implementation, to add morearithmetic operators <em>neatly</em>. Besides the <tt>+</tt> and<tt>ceiling</tt> operators from Assignment 1, you should add the <tt>-</tt>,<tt>*</tt>, <tt>/</tt>, and <tt>floor</tt> arithmetic operators for<tt>int</tt> and <tt>double</tt> operands.</p><p>Note that the <tt>-</tt>, <tt>*</tt>, and <tt>/</tt> operators aregeneralized similarly to the <tt>+</tt> operator. The <tt>-</tt>, <tt>*</tt>,and <tt>/</tt> operators can also be called with more than two arguments; forexample, <tt>(- 11 2 3)</tt> means the same thing as <tt>(- (- 11 2) 3)</tt>.The same holds for the <tt>*</tt> and <tt>/</tt> operators, so for example,<tt>(* 11 2 3)</tt> means the same thing as <tt>(* (* 11 2) 3)</tt>, while<tt>(/ 11 2 3)</tt> means the same thing as <tt>(/ (/ 11 2) 3)</tt>.</p><p>If the <tt>*</tt> operator is called with zero arguments, then it simplyreturns 1, which is the identity value for multiplication (just like 0 forthe <tt>+</tt> operator). If the <tt>*</tt> operator is called with oneargument, then it returns the same value.</p><p>If the <tt>-</tt> operator is called with one argument, then it simplyreturns the negative of the argument. If the <tt>/</tt> operator is calledwith one argument, then it simply returns the inverse of the argument.</p><p>To avoid ambiguity, the <tt>-</tt> and <tt>/</tt> operators<em>cannot</em> be called with zero arguments, unlike the <tt>+</tt> and<tt>*</tt> operators. So, for example <tt>(-)</tt> is considered to be asemantically ill-formed expression.</p><p>If you've done things correctly, you should notice how much easier it isto add all these operators, now that you have polymorphism.</p><h3>Step 4: Implement quoted expressions</h3><p>Next you will add support for <em>quoted expressions</em>, which allow youto prevent <tt>eval()</tt> from trying to evaluate s-expressions. The special<tt>quote</tt> operator takes exactly one operand, which can be <em>any</em>s-expression, and simply returns the exact same expression. The operand is<em>not</em> evaluated, so it just needs to be a syntactically valid tree(including empty lists as well as leaf nodes representing atomic ints,doubles, or symbols). It does <em>not</em> need to be a semantically validexpression. For example:</p><p><tt>> (quote (a b c))<br />(a b c)<br />> (quote (+ 2 3))<br />(+ 2 3)<br />> (quote (if if 5))<br />(if if 5)<br />> (quote ())<br />()<br />> (quote (quote (a b c)))<br />(quote (a b c))<br />> (quote hello)<br />hello<br />> (quote 6)<br />6<br />> (quote 3.14)<br />3.14<br />> (+ 4 (quote 2))<br />6<br />> (+ 4 (quote (* 2 3)))<br />ERROR: operand of + cannot be a list<br />> (+ 4 (* 2 3))<br />10</tt></p><h3>Step 5: Expose <tt>cons</tt>, <tt>car</tt>, <tt>cdr</tt>, and<tt>nullp</tt> in Scheme</h3><p>Finally, you will expose your existing <tt>cons.hpp</tt> C++implementation of <tt>cons</tt>, <tt>car</tt>, <tt>cdr</tt>, and<tt>nullp</tt> so that they can be called from Scheme just like otheroperators such as <tt>ceiling</tt>:</p><p><tt>> (cons 4 (quote ()))<br />(4)<br />> (cons (quote hello) (cons 4 (quote ())))<br />(hello 4)<br />> (cons 2 (cons (quote hello) (cons 4 (quote ()))))<br />(2 hello 4)<br />> (car (cons 2 (cons (quote hello) (cons 4 (quote ())))))<br />2<br />> (cdr (cons 2 (cons (quote hello) (cons 4 (quote ())))))<br />(hello 4)<br />> (nullp foo)<br />0<br />> (nullp 0)<br />0<br />> (nullp 1)<br />0<br />> (nullp (quote ()))<br />1<br />> (nullp (quote (a b c)))<br />0</tt></p><h3>Putting it all together</h3><p>This time, we are not including any dummy implementation of<tt>Cell.hpp</tt>, <tt>Cell.cpp</tt> or <tt>eval.cpp</tt> at all. Theimplementation is up to you. But be careful! You must make sure your<tt>Cell</tt> interface fits what <tt>cons.hpp</tt> expects!</p><p>We're again including <tt>parse.cpp</tt> for your convenience, in case youwant to build your assignment on some other machine outside the lab. Butremember you shouldn't look inside <tt>parse.cpp</tt> at all. (In the realworld, you would only get the separately-compiled <tt>parse.o</tt>, so you<em>couldn't</em> look inside <tt>parse.cpp</tt> even if you wanted to!)</p><h3>Important reminders</h3><p>You must follow the design approach outlined in this document. Do<em>not</em> just implement the required functionality using a differentdesign.</p><p>You are expected to make best possible use of polymorphism and virtualfunctions. For example, of course your old <tt>eval()</tt> from Assignment 1should still work, but without making correct use of polymorphism throughout,it will not be considered a solution to Assignment 2 (even if it implementsthe additional operators).</p><p>This time you <em>must</em> use virtual functions in this assignment, butyou still may <em>not</em> use templates. This assignment is about dynamic OOsupport in C++. (You'll get a chance to use templates in the followingassignment...)</p><p>Remember we are focusing on proper use of encapsulation. So you stillshould <em>not</em> edit the files <tt>parse.hpp</tt>, <tt>parse.cpp</tt>,<tt>cons.hpp</tt>, <tt>eval.hpp</tt>, or <tt>main.cpp</tt>. Again, theprogramming assignments are mini-exercises in how multiple programmers aresupposed to interact and communicate in the real world; these files are<em>owned</em> and <em>maintained</em> by the other author(s).</p><p>You will need to turn in a tar file <tt>a2.tar.gz</tt> containing allsource files including your own implementation of <tt>Cell.hpp</tt>,<tt>Cell.cpp</tt>, and <tt>eval.cpp</tt>. Depending on your approach, you mayor may not also wish to add more files. You should also make sure to includeall doxygen generated HTML documentation.</p><p>Depending on your approach, you may or may not need to change the<tt>Makefile</tt>. Whether you changed it or not, always make sure youinclude whatever <tt>Makefile</tt> is needed to build your program, when yousubmit assignment. Otherwise, the graders cannot build your program.</p><p>You must write the final version of the program on your own. Sophisticatedplagiarism detection systems are in operation, and they are pretty good atcatching copying! If you worked in study groups, you must also acknowledgeyour collaborators in the write-up for each problem, whether or not they areclassmates. Other cases will be dealt with as plagiarism. Re-read the policyon the course home page, and note the University's tougher policy this yearregarding cheating.</p><p><strong>Your programming style (how clearly and how well you speak C++) iswhat will be graded. Correct functioning of your program is necessary but notsufficient!</strong></p><hr /><p style="text-align: right"><i>Last updated: 2007.03.19 dekai</i></p></body></html>?? 快捷鍵說明
復制代碼
Ctrl + C
搜索代碼
Ctrl + F
全屏模式
F11
切換主題
Ctrl + Shift + D
顯示快捷鍵
?
增大字號
Ctrl + =
減小字號
Ctrl + -