// file list-tools.choc
// author : E. Duris
// date : 24.04.97
// last update : 20.05.97

class List {

// Constructor (production) declarations

case Cons(int, List);
case Nil ();

// Attributes (methods) declarations

// REVERSE computes the reversed list with an accumulating parameter

List reverse
{

List acc;
List result;

case Cons (a, l) :

l.acc = Cons(a,this.acc);
this.result = l.result;

case Nil ():

this.result = this.acc

case reverse :

this.acc = Nil;
return this.result;

} // end reverse

// APPEND concatenates the parameter list at the end of the current list.

List append (List)
{

List hy;
List result;

case Cons(a, l) :

this.result = Cons(a,l.result);
l.hy = this.hy;

case Nil ():

this.result = this.hy;

case append (y) :

this.hy = y;
return this.result;

} // end append

// LENGTH computes the number of elements of the current list.

int length ()
{

int result;

case Cons(a, l) :

this.result = 1 + l.result;

case Nil ():

this.result = 0;

case length () :

return this.result;

} // end length

// SUM computes the sum of the elements of the current list.

int sum ()
{

int result;

case Cons(a, l) :

this.result = a + l.result;

case Nil ():

this.result = 0;

case sum () :

return this.result;

} // end sum

// AVERAGE concatenates the parameter list at the end of the current list.

float average ()
{

if this.length == 0 return 0; // default value
return this.sum / this.length;

} // end average

} // end class List