/* 
 * Kodkod -- Copyright (c) 2005-2011, Emina Torlak
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 * THE SOFTWARE.
 */
package kodkod.ast;

/** 
 * An expression with no children.  
 * {@link kodkod.ast.Relation Relation} and {@link kodkod.ast.Variable Variable} 
 * are examples of leaf exressions.  Two leaf expressions are equal 
 * if and only if they refer to the same object.  That is, 
 * leaf1.eauls(leaf2) <=> leaf1 == leaf2.  A leaf has a name, which is 
 * basically a comment for the purpose of printing, viewing, etc.  The name 
 * has no meaning otherwise.  
 * 
 * @specfield name: String
 * @specfield arity: int
 * @specfield no children
 * @author Emina Torlak 
 */
public abstract class LeafExpression extends Expression {

	private final int arity;
	private final String name;

	/**
	 * Constructs a leaf with the specified name and arity
	 * 
	 * @ensures  this.name' = name && this.arity' = arity 
	 * @throws IllegalArgumentException  arity < 1
	 */
	LeafExpression(String name, int arity) {
		if (arity < 1) {
			throw new IllegalArgumentException("Arity must be at least 1: " + arity);
		}
		this.name = name;
		this.arity = arity;
	}


	/**
	 * Returns the arity of this leaf.
	 * @return this.arity
	 */
	public final int arity() {
		return arity;
	}

	/**
	 * Returns the name of this leaf.
	 * @return this.name
	 */
	public final String name() {
		return name;
	}

	/**
	 * {@inheritDoc}
	 * @see kodkod.ast.Node#toString()
	 */
	public String toString() {
		return name;
	}

}
