// CS 2510, Assignment 3

import tester.*;

// to represent a list of Strings
interface ILoString {
    // combine all Strings in this list into one
    String combine();
}

// to represent an empty list of Strings
class MtLoString implements ILoString {
    MtLoString(){}
    
    // combine all Strings in this list into one
    public String combine() {
       return "";
    }  
}

// to represent a nonempty list of Strings
class ConsLoString implements ILoString {
    String first;
    ILoString rest;
    
    ConsLoString(String first, ILoString rest){
        this.first = first;
        this.rest = rest;  
    }
    
    /*
     TEMPLATE
     FIELDS:
     ... this.first ...         -- String
     ... this.rest ...          -- ILoString
     
     METHODS
     ... this.combine() ...     -- String
     
     METHODS FOR FIELDS
     ... this.first.concat(String) ...        -- String
     ... this.first.compareTo(String) ...     -- int
     ... this.rest.combine() ...              -- String
     
     */
    
    // combine all Strings in this list into one
    public String combine(){
        return this.first.concat(this.rest.combine());
    }  
    
}

// to represent examples for lists of strings
class ExamplesStrings{
    
    ILoString mary = new ConsLoString("Mary ",
                    new ConsLoString("had ",
                        new ConsLoString("a ",
                            new ConsLoString("little ",
                                new ConsLoString("lamb.", new MtLoString())))));
    
    // test the method combine for the lists of Strings
    boolean testCombine(Tester t){
        return 
            t.checkExpect(this.mary.combine(), "Mary had a little lamb.");
    }
}