Question
Implement Lisp-like list in Java. Write basic operations such as 'car', 'cdr', and 'cons'. If L is a list [3, 0, 2, 5], L.car() returns 3, while L.cdr() returns [0,2,5].
Lisp Operations
Car
The car of a list is, quite simply, the first item in the list. For Ex: car of L.car() of a list [3 0 2 5] returns 3.
Cdr
The cdr of a list is the rest of the list, that is, the cdr function returns the part of the list that follows the first item. For ex: cdr of a list [3 0 2 5] returns [0 2 5]
Cons
The cons function constructs lists. It is useful to add element to the front of the list; it is the inverse of car and cdr. For example, cons can be used to make a five element list from the four element list.
(source – Wikipedia)
Length
Returns the length of the list.
Program
import java.util.*;
import java.io.*;
// To implement LISP-like List in Java to perform functions like car, cdr, cons.
class Lisp
{
Vector v = new Vector(4,1);
int i;
InputStreamReader isr = new InputStreamReader(System.in);
BufferedReader inData = new BufferedReader(isr);
String str;
//Create a LISP-Like List using VECTOR
public void create()
{
int n;
System.out.print("\n Enter the Size of the list:");
//Get Input from the user...Use I/p stream reader for it...
try
{
str = inData.readLine();
n = Integer.parseInt(str);
for(i=0;i
{
int temp;
System.out.print("\n Enter the element " + (i+1) + " of the list:");
str = inData.readLine();
temp=Integer.parseInt(str);
v.addElement(new Integer(temp));
}
}
catch (IOException e)
{
System.out.println("Error!");
System.exit(1);
}
}
//Display the content of LISP-List
public void display()
{
int n=v.size();
System.out.print("[ ");
for(i=0;i
{
System.out.print(v.elementAt(i) + " ");
}
System.out.println("]");
}
/*
The car of a list is, quite simply, the first item in the list.
For Ex: car of L.car() of a list [3 0 2 5] returns 3.
Gives the CAR of LISP-List
*/
public void car()
{
System.out.println("\n CAR of the List: " + v.elementAt(0));
}
/*
The cdr of a list is the rest of the list, that is, the cdr function returns the part of the list that follows the first item.
For ex: cdr of a list [3 0 2 5] returns [0 2 5]
*/
public void cdr()
{
int n=v.size();
System.out.print("\n The CDR of the List is:");
System.out.print("[ ");
for(i=1;i
{
System.out.print(v.elementAt(i) + " ");
}
System.out.println("]");
}
/*
The cons function constructs lists. It is useful to add element to the front of the list; it is the inverse of car and cdr. For example, cons can be used to make a five element list from the four element list.
For ex: adding 7 to [3 0 2 5], cons(7) gives [7 3 0 2 5]
*/
public void cons(int x)
{
v.insertElementAt(x,0);
System.out.print("\n The List after using CONS and adding an element:");
display();
}
// Returns the length of the LISP-List
public int length()
{
return v.size();
}
}
class Lisp_List
{
public static void main(String[] args)
{
Lisp a = new Lisp();
a.create();
System.out.print("\n The contents of the List are:");
a.display();
a.car();
a.cdr();
a.cons(5);
System.out.println("\n\n The length of the list is " + a.length());
}
}
Output
Enter the Size of the list:4
Enter the element 1 of the list:3
Enter the element 2 of the list:0
Enter the element 3 of the list:2
Enter the element 4 of the list:5
The contents of the List are:[ 3 0 2 5 ]
CAR of the List: 3
The CDR of the List is:[ 0 2 5 ]
The List after using CONS and adding an element:[ 5 3 0 2 5 ]
The length of the list is 5
