/interpreter/tags/at_build150307/src/edu/vub/at/objects/mirrors/PrimitiveMethod.java

  1/**
  2 * AmbientTalk/2 Project
  3 * PrimitiveMethod.java created on 2-feb-2007 at 21:44:00
  4 * (c) Programming Technology Lab, 2006 - 2007
  5 * Authors: Tom Van Cutsem & Stijn Mostinckx
  6 * 
  7 * Permission is hereby granted, free of charge, to any person
  8 * obtaining a copy of this software and associated documentation
  9 * files (the "Software"), to deal in the Software without
 10 * restriction, including without limitation the rights to use,
 11 * copy, modify, merge, publish, distribute, sublicense, and/or
 12 * sell copies of the Software, and to permit persons to whom the
 13 * Software is furnished to do so, subject to the following
 14 * conditions:
 15 *
 16 * The above copyright notice and this permission notice shall be
 17 * included in all copies or substantial portions of the Software.
 18 *
 19 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
 20 * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES
 21 * OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
 22 * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
 23 * HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
 24 * WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
 25 * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
 26 * OTHER DEALINGS IN THE SOFTWARE.
 27 */
 28package edu.vub.at.objects.mirrors;
 29
 30import edu.vub.at.exceptions.InterpreterException;
 31import edu.vub.at.exceptions.XTypeMismatch;
 32import edu.vub.at.objects.ATContext;
 33import edu.vub.at.objects.ATObject;
 34import edu.vub.at.objects.ATTable;
 35import edu.vub.at.objects.grammar.ATBegin;
 36import edu.vub.at.objects.grammar.ATSymbol;
 37import edu.vub.at.objects.natives.NATMethod;
 38import edu.vub.at.objects.natives.NATNil;
 39import edu.vub.at.objects.natives.NATTable;
 40import edu.vub.at.objects.natives.NATText;
 41import edu.vub.at.objects.natives.grammar.NATAbstractGrammar;
 42
 43/**
 44 * A primitive method is the equivalent of a NativeClosure but for methods rather
 45 * than closures. The advantage of PrimtiveMethods is that their base_apply method
 46 * gives access to both arguments as well as to the runtime context in that contains
 47 * the lexical environment in which they were defined.
 48 * 
 49 * Example primitive methods are '==', 'new' and 'init' implemented in NATObject.
 50 *
 51 * Primitive methods should implement this method's base_apply method or invoke the
 52 * constructor taking a PrimitiveBody parameter and implement that class's meta_eval
 53 * method, if they want to make use of AT/2's parameter binding semantics.
 54 * 
 55 * Primitive methods installed in native objects that can be extended should ensure
 56 * that they use the dynamic receiver stored in the application context (the AmbientTalk
 57 * 'self') rather than the Java 'this' variable to perform self-sends. The former will
 58 * properly invoke/select the overridden methods/fields of a child AT object, the latter
 59 * will simply refer to the native instance, disregarding any modifications by child objects.
 60 *
 61 * @author tvcutsem
 62 */
 63public class PrimitiveMethod extends NATMethod {
 64	
 65	/**
 66	 * Instances of this helper class represent primitive method bodies. To the
 67	 * AT programmer, they look like empty methods (i.e. { nil }). The native Java
 68	 * implementation is specified by overriding the meta_eval method.
 69	 */
 70	public static abstract class PrimitiveBody extends NATAbstractGrammar implements ATBegin {
 71		
 72		/**
 73		 * A primitive can override this method and has access to:
 74		 * - ctx.lexicalScope = the call frame for this method invocation
 75		 * - ctx.lexicalScope.lexicalParent = the object in which the method was found
 76		 * - ctx.dynamicReceiver = the object on which the method was invoked
 77		 */
 78		public abstract ATObject meta_eval(ATContext ctx) throws InterpreterException;
 79
 80		public ATObject meta_quote(ATContext ctx) throws InterpreterException {
 81			return this;
 82		}
 83		
 84		public ATTable base_getStatements() { return NATTable.of(NATNil._INSTANCE_); }
 85		
 86		public NATText meta_print() throws InterpreterException {
 87			return NATText.atValue("<primitive body>");
 88		}
 89		
 90		public ATBegin asBegin() throws XTypeMismatch {
 91			return this;
 92		}
 93		
 94	}
 95	
 96	public PrimitiveMethod(ATSymbol name, ATTable formals, PrimitiveBody body) {
 97		super(name, formals, body);
 98	}
 99
100	/**
101	 * Constructor for the creation of primitive methods where the body is left empty.
102	 * The idea is that the creator of such primitive methods overrides the base_apply
103	 * method because the primitive method has no need for a call frame or parameter binding.
104	 */
105	public PrimitiveMethod(ATSymbol name, ATTable formals) {
106		super(name, formals, new PrimitiveBody() {
107			public ATObject meta_eval(ATContext ctx) throws InterpreterException {
108				return NATNil._INSTANCE_;
109			}
110		});
111	}
112	
113	public NATText meta_print() throws InterpreterException {
114		return NATText.atValue("<primitive method:"+base_getName()+">");
115	}
116	
117}