/**
 * Interface for boolean operators of Propositional Logic. The required methods
 * are to provide a string representation of a proposition, to verify that a
 * proposition is well formed, and to return the precedence of the operation.
 * The first method supplies a string representation of a proposition formed by
 * applying the operator to an array containing its operands. The whole term
 * will be enclosed in brackets if the precedence of the operator is greater
 * than parameter <code>prec</code>; this parameter can be thought of as the
 * precedence of the operator immediately above this proposition, forcing it to
 * be put in brackets if necessary. The second method returns true if the term
 * is well formed; otherwise, it returns false. The third method simply returns
 * the integer that is its precedence.
 *
 */
public interface Operator {

	/**
	 * Give a string representing a proposition with no unnecessary brackets.
	 * The proposition will be formed by applying this operator to the given
	 * operands, and the entire term will be enclosed in brackets if the
	 * precedence of the operator is greater than parameter <code>prec</code>;
	 *
	 * @param args
	 *            the operands; e.g., for "and": this array should be of length
	 *            2
	 * @param prec
	 *            the precedence of the operator above.
	 * @return a string representing the proposition formed by applying the
	 *         operator to the operands in <code>args</code>; the entire string
	 *         will be enclosed in brackets if parameter <code>prec</code> is
	 *         less than the operator's precedence.
	 */
	public String toString(BoolTerm[] args, int prec);

	/**
	 * Checks if the number of subterms of the proposition matches the expected
	 * number of subterms for this operator; for example, a <code>not</code>
	 * operator would only need an array of subterms of size 1, whereas an
	 * <code>or</code> operator would need an array of subterms of size 2.
	 *
	 * @return <code>true</code> if the term is well formed; otherwise,
	 *         <code>false</code>.
	 */
	public boolean isWellFormed(BoolTerm[] args);

	/**
	 * Return the precedence of the operator. The order of precedences of all Boolean
	 * operators are specified in the Lectures and they are:
	 * IMPLIES_PREC > OR_PREC > AND_PREC > NOT_PREC.
	 * 
	 * This program uses:
	 * IMPLIES_PREC = 7;
	 * OR_PREC = 5;
	 * AND_PREC = 4;
	 * NOT_PREC = 1;
	 *
	 * @return the precedence of the operator
	 */
	public int getPrecedence();

}// Operator