/interpreter/tags/at2dist030708/src/edu/vub/at/objects/natives/NATClosureMethod.java

  1/**
  2 * AmbientTalk/2 Project
  3 * NATClosureMethod.java created on 16-nov-2006 at 9:12:46
  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.natives;
 29
 30import edu.vub.at.exceptions.InterpreterException;
 31import edu.vub.at.exceptions.XTypeMismatch;
 32import edu.vub.at.objects.ATClosure;
 33import edu.vub.at.objects.ATContext;
 34import edu.vub.at.objects.ATMethod;
 35import edu.vub.at.objects.ATObject;
 36import edu.vub.at.objects.ATTable;
 37import edu.vub.at.objects.coercion.NativeTypeTags;
 38import edu.vub.at.objects.grammar.ATBegin;
 39import edu.vub.at.objects.grammar.ATDefExternalMethod;
 40import edu.vub.at.objects.grammar.ATSymbol;
 41
 42/**
 43 * A 'closure method' is literally a function that sits in between of a full closure and a method.
 44 * It is a method that captures only its lexical scope of definition, but not the value of 'self'
 45 * and 'super' which are active at that time. When invoked, the method is evaluated in its lexical
 46 * scope, but with the values of 'self' and 'super' equal to those given to it at method invocation time.
 47 * 
 48 * Closure methods are used to implement 'externally added' methods to objects. In such cases,
 49 * the external methods can only access their own surrounding lexical scope (and not that of the actual
 50 * object to which they are added), but their values for 'self' and 'super' will act as if the method
 51 * was actually defined within the object itself.
 52 * 
 53 * See the description of the {@link ATDefExternalMethod} interface for more information.
 54 * 
 55 * @author tvcutsem
 56 */
 57public class NATClosureMethod extends NATByRef implements ATMethod {
 58	
 59	private final ATObject lexicalScope_;
 60	private final ATMethod method_;
 61	
 62	/** construct a new closure method */
 63	public NATClosureMethod(ATObject scope, ATMethod method) throws InterpreterException {
 64		lexicalScope_ = scope;
 65		method_ = method;
 66	}
 67	
 68	/**
 69	 * A closure method application acts exactly like a regular direct method application, except that
 70	 * the given lexical scope is disregarded and replaced by the lexical scope encapsulated by the
 71	 * closure method. The bindings for 'self' and 'super' remain intact.
 72	 * 
 73	 * Closure methods are a result of external method definitions.
 74	 * 
 75	 * @param arguments the evaluated actual arguments
 76	 * @param ctx the context whose 'self' binding will be used during the execution of the method.
 77	 * The lexical scope, however, will be replaced by the closure method's own lexical scope. A call frame will
 78	 * be inserted into this lexical scope before executing the method body.
 79	 * To ensure that 'super' points to the parent of the actual 'self' and not the parent of the object
 80	 * performing the external method definition, a 'super' field is added to the call frame shadowing
 81	 * the defining object's 'super' field.
 82	 * @return the value of evaluating the function body
 83	 */
 84	public ATObject base_apply(ATTable arguments, ATContext ctx) throws InterpreterException {
 85		// should be: method_.base_apply(arguments, ctx.base_withLexicalEnvironment(lexicalScope_),
 86		// but this version is more efficient, as we immediately create the right context, rather than
 87		// creating a temporary context which will in turn be modified by method_.base_apply
 88		
 89		// hostObject = the object to which the external method was added (actually the object in which
 90		// the external method was now found)
 91		ATObject hostObject = ctx.base_lexicalScope();
 92		ATObject hostParent = hostObject.base_super();
 93		
 94		NATCallframe externalFrame = new NATCallframe(lexicalScope_);
 95		// super = the parent of the object to which this method was added
 96		externalFrame.meta_defineField(NATObject._SUPER_NAME_, hostParent);
 97		
 98		return method_.base_applyInScope(arguments, ctx.base_withLexicalEnvironment(externalFrame));
 99	}
100
101	public ATObject base_applyInScope(ATTable arguments, ATContext ctx) throws InterpreterException {
102		return method_.base_applyInScope(arguments, ctx);
103	}
104
105	public ATBegin base_bodyExpression() throws InterpreterException {
106		return method_.base_bodyExpression();
107	}
108
109	public ATSymbol base_name() throws InterpreterException {
110		return method_.base_name();
111	}
112
113	public ATTable base_parameters() throws InterpreterException {
114		return method_.base_parameters();
115	}
116	
117	public ATTable base_annotations() throws InterpreterException {
118		return method_.base_annotations();
119	}
120	
121	/**
122	 * When wrapping a closure method, return a closure that is bound to my own lexical scope.
123	 * The lexical scope passed to wrap is ignored.
124	 */
125	public ATClosure base_wrap(ATObject lexicalScope, ATObject dynamicReceiver) throws InterpreterException {
126		return method_.base_wrap(lexicalScope_, dynamicReceiver);
127	}
128	
129	public NATText meta_print() throws InterpreterException {
130		return NATText.atValue("<closure:"+method_.base_name()+">");
131	}
132
133	public ATMethod asMethod() throws XTypeMismatch {
134		return this;
135	}
136	
137    public ATTable meta_typeTags() throws InterpreterException {
138    	return NATTable.of(NativeTypeTags._METHOD_);
139    }
140	
141}