University of Toronto

csc324H Programming Languages, Fall 1996

Assignment 3 [10 of mark]

Objective

In this project, you will use virtual function mechanism of C++.

Background

  ("abc", 1, 3.2, 'a')

   ("abc", (1, 2), 3)

    cons (1, (2, 3, 4)) = (1, 2, 3, 4)
    cons (1, (1, 2, 3)) = (1, 1, 2, 3)
    cons ((1, 2), (2, 3)) = ((1, 2), (2, 3))
    car ((1, 2, 3)) = 1
    car (((1, 2), 3, 4)) = (1, 2)
    cdr ((1)) = ()  /* empty list, i.e., list with no elements */
    cdr (((1, 2), 3, 4)) = (3, 4)
    null ((1, 2)) = false
    null (()) = true
    append ((1), (2, 3)) = (1, 2, 3)
    append (((1)), (2, 3)) = ((1), 2, 3)
    append ((), (2, (3))) = (2, (3))

In functional languages like Scheme or ML, lists are represented using a dotted notation. All lists are constructed using cons, and a "dot" is put in place where cons was called. For example, a list (1, 2, 3) could be constructed starting with an empty list () using a constructor cons as follows:

   cons (1, cons (2, cons (3, ())))

i.e., first construct a list (3), then insert 2 in front of it, and then insert 1 in front of the resulting list. So, in functional languages a list (1, 2, 3) would be represented as

  (1. (2 . (3. ())))

Project Description

You are to implement lists in C++. The elements consist of strings, integers and other lists. Implement cons, car, cdr, null and append ( append makes a new list which consists of concatenation of the previous lists). In addition, implement operations print and clone. The print operation should produce the ``dotted'' notation form of lists. clone makes a copy of the list and returns a reference to it.

The program skeleton appears below. It is broken down into two files here, the file containing class definitions and implementation of member functions, and the file containing main program. In your projects, please break up the solutions into at least 3 files.

// File classdef.h
// This file contains a definition and an implementation for
// lists.

class Object;
typedef Object* PObject;  // we do this so that we can define
                          // a pointer to class Object


class Object { /* an abstract class */
public:
  virtual PObject clone() = 0;
  virtual ~Object() {};
  friend  ostream &operator<<(ostream &, const Object &);
private:
  virtual ostream &printTo(ostream &o) const=0;
};

ostream &operator << (ostream &o, const Object &s) {
   return s.printTo(o);
}

// You will need to provide definitions for classes
// String and Int, and implementations for classes
// String, Int and List.

class String;
class Int;
class List;
typedef List* PList;

// This is the definition of class List
class List: public Object
{
public:
  List(); 
  ~List();
  PObject car() const;
  List& cons(PObject);
  List& cdr() const;
  int null() const;
  ostream &printTo(ostream &o) const;
  PObject clone();
private:
  PObject car_part;
  PList cdr_part;
};

// Notice that append is not a member function!
List& append (List* X, List* Z) { }

And now the file which contains main:

// main.C.  This file contains test cases for the
// implementation of lists.

#include < iostream.h >
#include "classdef.h"

int main()
{
    String V1("Hello");
    Int V2(7);

    Object *p1 = &V1, *p2 = &V2;

    List L1;
    List L2;

    List L3 = L2.cons(&Int(1)).cons(&String("Two")).cons(&Int(3)).cons(&String("Four")).cons(&Int(5)).cons(&Int(6));
    List L4 = L2.cons(&Int(25)).cons(&String("Fleas")).cons(&String("has")).cons(&Int(24));

    List L5 = append(&L3,&L4);

    for(; !L3.null(); L3= L3.cdr()) {
      cout << *L3.car() << endl << L3 << endl << L3.cdr()t << endl;
    }
    cout << L3 << endl << endl << endl;
    cout << V1 << endl;
    cout << V2 << endl;

    p1 = V1.clone(); 
    cout << *p1 << endl;
    p2 = V2.clone();
    cout << *p2 << endl;

    cout << "(L1.cons(&V1))=" << (L1.cons(&V1)) << endl;   
    cout << "(L1.cons(p1))=" << (L1.cons(p1)) << endl;

    p1 = (L1.cons(&V1)).clone();
    p2 = (L1.cons(&V2)).clone();
    cout << "append((PList)p1,(PList)p2)=" 
         << append((PList)p1,(PList)p2) << endl;

    cout << "(L1.cons(&V2).cons(&V1))=" << (L1.cons(&V2).cons(&V1)) << endl;
    if ( (L1.cons(&V2).cdr()).null() ) 
      cout << "null list\n";

    cout << L4 << endl;
    cout << L5 << endl;
}

Int: 6
(Int: 6 . (Int: 5 . (String: "Four" . (Int: 3 . (String: "Two" . (Int: 1 . ( )))))))
(Int: 5 . (String: "Four" . (Int: 3 . (String: "Two" . (Int: 1 . ( ))))))
Int: 5
(Int: 5 . (String: "Four" . (Int: 3 . (String: "Two" . (Int: 1 . ( ))))))
(String: "Four" . (Int: 3 . (String: "Two" . (Int: 1 . ( )))))
String: "Four"
(String: "Four" . (Int: 3 . (String: "Two" . (Int: 1 . ( )))))
(Int: 3 . (String: "Two" . (Int: 1 . ( ))))
Int: 3
(Int: 3 . (String: "Two" . (Int: 1 . ( ))))
(String: "Two" . (Int: 1 . ( )))
String: "Two"
(String: "Two" . (Int: 1 . ( )))
(Int: 1 . ( ))
Int: 1
(Int: 1 . ( ))
( )
( )


String: "Hello"
Int: 7
String: "Hello"
Int: 7
(L1.cons(&V1))=(String: "Hello" . ( ))
(L1.cons(p1))=(String: "Hello" . ( ))
append((PList)p1,(PList)p2)=(String: "Hello" . (Int: 7 . ( )))
(L1.cons(&V2).cons(&V1))=(String: "Hello" . (Int: 7 . ( )))
null list
(Int: 24 . (String: "has" . (String: "Fleas" . (Int: 25 . ( )))))
(Int: 6 . (Int: 5 . (String: "Four" . (Int: 3 . (String: "Two" . (Int: 1 . (Int: 24 . (String: "has" . (String: "Fleas" . (Int: 25 . ( )))))))))))

Submission

Submit (electronically) a tar file with

1. Well-documented source code (broken down into several files)
2. Test programs
3. Makefile
4. Output showing the operation of your program.
5. (Optional) README file with instructions on how to run your program.

Note that we will rerun your program with, so please do not change the output of your program!!!!!

Bring a paper copy with your programs, test cases, output, etc. to class

Marking

Marking scheme for this project is as follows:

Notes