content: /* 
   * Kodkod -- Copyright (c) 2005-present, 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;
  	}
  
  }
  