Helpers are the Variants

Main Visitor ToString1

Tail-recursive helper ToString1Help

package listFW.visitor;
import listFW.*;
public class ToString1 implements IListAlgo {
public static final ToString1 Singleton = new ToString1();
private ToString1() {
}
public Object emptyCase(IMTList host, Object... nu) {
return "()";
}
public Object nonEmptyCase(INEList host, Object... nu) {
return host.getRest().execute(ToString1Help.Singleton, 
"(" + host.getFirst());
}
}
 

/**
* Helps ToString1 compute the String representation of the rest of the list.
* It takes as input the accumulated string representation of the preceding
* list.  This accumulated string contains the left most parenthesis and all
* the elements of the preceding list, each separated by a comma.
*/
class ToString1Help implements IListAlgo {
public static final ToString1Help Singleton = new ToString1Help();
private ToString1Help() {
}
public Object emptyCase(IMTList host, Object... acc) {
return acc[0] + ")";
}
public Object nonEmptyCase(INEList host, Object... acc) {
return host.getRest().execute(this, acc[0] + ", " 
+ host.getFirst());
}
}
 

Main Visitor ToString2

Tail-recursive helper ToString2Help

package listFW.visitor;
import listFW.*;
public class ToString2 implements IListAlgo { 
public static final ToString2 Singleton = new ToString2();
private ToString2() {
}
public Object emptyCase(IMTList host, Object... nu) {
return "()";
}
public Object nonEmptyCase(INEList host, Object... nu) {
return host.getRest().execute(ToString2Help.Singleton, 
host.getFirst().toString());
}
}
 

/**
* Helps ToString2 compute the String representation of the rest of the list.
*/
class ToString2Help implements IListAlgo {
public static final ToString2Help Singleton = new ToString2Help();
private ToString2Help() {
}
public Object emptyCase(IMTList host, Object... acc) {
return "(" + acc[0] + ")";
}
public Object nonEmptyCase(INEList host, Object... acc) {
return host.getRest().execute(this, 
acc[0] + ", " + host.getFirst());
}
}
 

Main Visitor ToString3

Non tail-recursive helper ToString3Help

package listFW.visitor;
import listFW.*;
public class ToString3 implements IListAlgo {
public static final ToString3 Singleton = new ToString3();
private ToString3() {
}
public Object emptyCase(IMTList host, Object... nu) {
return "()";
}
public Object nonEmptyCase(INEList host, Object... nu) {
return "(" + host.getFirst() 
+ host.getRest().execute(ToString3Help.Singleton);
}
}
 

/**
* Helps ToString3 compute the String representation of the rest of the list.
*/
class ToString3Help implements IListAlgo {
public static final ToString3Help Singleton = new ToString3Help();
private ToString3Help() {
}
public Object emptyCase(IMTList host, Object... nu) {
return ")";
}
public Object nonEmptyCase(INEList host, Object... nu) {
return ", " + host.getFirst() 
+ host.getRest().execute(this);
}
}