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.operator;
  
  /**
   * Enumerates unary (~, ^, *), binary (+, &, ++, ->, -, .) and nary (+, &, ++, ->) expression operators.
   * @specfield op: (int->lone Expression) -> Expression
   * @invariant all args: seq Expression, out: Expression | args->out in op => (out.children = args && out.op = this)
   */
  public enum ExprOperator {
  	/** Relational union (+) operator. */
  	UNION 				{ public String toString() { return "+"; } },
  	/** Relational intersection (&) operator. */
  	INTERSECTION		{ public String toString() { return "&"; } },
  	/** Relational override (++) operator. */
  	OVERRIDE			{ public String toString() { return "++"; } },
  	/** Relational product (->) operator. */
  	PRODUCT				{ public String toString() { return "->"; } },
  	/** Relational difference (-) operator. */
  	DIFFERENCE			{ public String toString() { return "-"; } },
  	/** Relational join (.) operator. */
  	JOIN 				{ public String toString() { return "."; } },
  	/** Transpose (~) operator. */
      TRANSPOSE 			{ public String toString() { return "~";} },
      /** Transitive closure (^) operator. */
      CLOSURE 			{ public String toString() { return "^";} },
      /** Reflexive transitive closure (*) operator. */
      REFLEXIVE_CLOSURE 	{ public String toString() { return "*";} };
    	
      static final int unary = TRANSPOSE.index() | CLOSURE.index() | REFLEXIVE_CLOSURE.index();
      
      static final int binary = ~unary;
      
      static final int nary = UNION.index() | INTERSECTION.index() | OVERRIDE.index() | PRODUCT.index();
      
      private final int index() { return 1<<ordinal(); }
      
      /**
       * Returns true if this is a unary operator.
       * @return true if this is a unary operator.
       */
      public final boolean unary() { return (unary & index())!=0; }
      
      /**
       * Returns true if this is a binary operator.
       * @return true if this is a binary operator.
       */
      public final boolean binary() { return (binary & index())!=0; }
      
      /**
       * Returns true if this is an nary operator.
       * @return true if this is an nary operator.
       */
      public final boolean nary() { return (nary & index())!=0; }
      
  }