/*  File Succ.java

    Part of Natural Number Example
    H. Conrad Cunningham, Professor

1234567890123456789012345678901234567890123456789012345678901234567890

2004-01-17: Original
2016-10-26: Formatting changes, compilation check
    
Class Succ represents the successor function in the natural number
definition.  It maps its argument (i.e., contained Nat value) to its
successor (i.e., one larger value).  It is a composite subclass in the
Composite pattern.

 */

public class Succ extends Nat
{   
    public Succ(Nat n)
    {   val = n;   }

    public Nat pred()  // operation of Succ, not Nat 
    {   return val;   }

    public Nat add(Nat n)
    {   return val.add(new Succ(n));   }  // m + n = (m-1)+(n+1)

    public Nat sub(Nat n)
    {   if (n == Zero.getZero()) {   return this;  }  // m - 0 = m
        return val.sub(((Succ)n).pred());  // m - n = (m-1) - (n-1)
    }

    public boolean isLess(Nat n)
    {   if (n == Zero.getZero()) {   return false;   }  // m > 0S
        return val.isLess(((Succ)n).pred());  // m < n = (m-1)<(n-1)  
    }

    // Normally we should avoid use of instanceof in OO code, but
    // it is often necessary in comparisons.
    public boolean equals(Object n)  // method from class Object
    {   if (!(n instanceof Succ)) {   return false;   }
        return val.equals(((Succ)n).pred());  // (m=n) = ((m-1)=(n-1))
    }

    public String toString()  // method from class Object
    {   return ("1+" + val);   }

    private Nat val;  // predecessor value
}