/*              Visitor Pattern Warmup Assignment

   This warmup assignment allows you to review/practice using
   the parameterized visitor pattern.  See the online calculator for
   example.

   Rewrite the truth table program using the visitor pattern:
*/

interface exp
{
    public <R> R accept(expvisitor<R> v);
}

interface expvisitor<T>
{
    public T visit(conste e);
    public T visit(vare e);
    public T visit(ande e);
    public T visit(ore e);
    public T visit(impe e);
    public T visit(note e);
}


/*
   Rewrite the evaluation procedure as an expvisitor<Boolean>.
   The hashtable representing the current truth assignment can now become
   an instance variable of the visitor object instead of being passed
   around as a parameter to eval:
*/

class evaluator implements expvisitor<Boolean>
{
    Hashtable<String,Boolean> Env;
    public evaluator(Hashtable<String,Boolean> h) { Env=h; }

    // ...
}