import java.util.*;

public abstract class Expression {

	public static Expression parse(Scanner tokens) throws Exception {
		if (tokens.hasNext("\\(")) { 		// if next token is a left paren
			return FunCall.parse(tokens); // then it must be a FunCall
		} else {
			return Literal.parse(tokens); // else it must be a Literal
		}
	}

	abstract public double eval() throws Exception;
	public void accept(ExpVisitor v) { }
}