/interpreter/tags/at2dist170907/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.ATSymbol;
 40
 41/**
 42 * A 'closure method' is literally a function that sits in between of a full closure and a method.
 43 * It is a method that captures only its lexical scope of definition, but not the value of 'self'
 44 * and 'super' which are active at that time. When invoked, the method is evaluated in its lexical
 45 * scope, but with the values of 'self' and 'super' equal to those given to it at method invocation time.
 46 * 
 47 * Closure methods are used to implement 'externally added' methods to objects. In such cases,
 48 * the external methods can only access their own surrounding lexical scope (and not that of the actual
 49 * object to which they are added), but their values for 'self' and 'super' will act as if the method
 50 * was actually defined within the object itself.
 51 * 
 52 * See the description of the ATDefExternalMethod interface for more information.
 53 * 
 54 * @author tvcutsem
 55 */
 56public class NATClosureMethod extends NATByRef implements ATMethod {
 57	
 58	private final ATObject lexicalScope_;
 59	private final ATMethod method_;
 60	
 61	/** construct a new closure method */
 62	public NATClosureMethod(ATObject scope, ATMethod method) throws InterpreterException {
 63		lexicalScope_ = scope;
 64		method_ = method;
 65	}
 66	
 67	/**
 68	 * A closure method application acts exactly like a regular direct method application, except that
 69	 * the given lexical scope is disregarded and replaced by the lexical scope encapsulated by the
 70	 * closure method. The bindings for 'self' and 'super' remain intact.
 71	 * 
 72	 * Closure methods are a result of external method definitions.
 73	 * 
 74	 * @param arguments the evaluated actual arguments
 75	 * @param ctx the context whose 'self' binding will be used during the execution of the method.
 76	 * The lexical scope, however, will be replaced by the closure method's own lexical scope. A call frame will
 77	 * be inserted into this lexical scope before executing the method body.
 78	 * To ensure that 'super' points to the parent of the actual 'self' and not the parent of the object
 79	 * performing the external method definition, a 'super' field is added to the call frame shadowing
 80	 * the defining object's 'super' field.
 81	 * @return the value of evaluating the function body
 82	 */
 83	public ATObject base_apply(ATTable arguments, ATContext ctx) throws InterpreterException {
 84		// should be: method_.base_apply(arguments, ctx.base_withLexicalEnvironment(lexicalScope_),
 85		// but this version is more efficient, as we immediately create the right context, rather than
 86		// creating a temporary context which will in turn be modified by method_.base_apply
 87		
 88		// hostObject = the object to which the external method was added (actually the object in which
 89		// the external method was now found)
 90		ATObject hostObject = ctx.base_lexicalScope();
 91		ATObject hostParent = hostObject.base_super();
 92		
 93		NATCallframe externalFrame = new NATCallframe(lexicalScope_);
 94		// super = the parent of the object to which this method was added
 95		externalFrame.meta_defineField(NATObject._SUPER_NAME_, hostParent);
 96		
 97		return method_.base_applyInScope(arguments, ctx.base_withLexicalEnvironment(externalFrame));
 98	}
 99
100	public ATObject base_applyInScope(ATTable arguments, ATContext ctx) throws InterpreterException {
101		return method_.base_applyInScope(arguments, ctx);
102	}
103
104	public ATBegin base_bodyExpression() throws InterpreterException {
105		return method_.base_bodyExpression();
106	}
107
108	public ATSymbol base_name() throws InterpreterException {
109		return method_.base_name();
110	}
111
112	public ATTable base_parameters() throws InterpreterException {
113		return method_.base_parameters();
114	}
115	
116	/**
117	 * When wrapping a closure method, return a closure that is bound to the given lexical scope.
118	 */
119	public ATClosure base_wrap(ATObject lexicalScope, ATObject dynamicReceiver) throws InterpreterException {
120		return method_.base_wrap(lexicalScope_, dynamicReceiver);
121	}
122	
123	public NATText meta_print() throws InterpreterException {
124		return NATText.atValue("<closure:"+method_.base_name()+">");
125	}
126
127	public ATMethod asMethod() throws XTypeMismatch {
128		return this;
129	}
130	
131    public ATTable meta_typeTags() throws InterpreterException {
132    	return NATTable.of(NativeTypeTags._METHOD_);
133    }
134	
135}