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/interpreter/tags/at2dist130208/src/edu/vub/at/objects/natives/grammar/AGSymbol.java

http://ambienttalk.googlecode.com/
Java | 151 lines | 67 code | 24 blank | 60 comment | 4 complexity | f5b702485a3fd739924889cec595afa5 MD5 | raw file
  1/**
  2 * AmbientTalk/2 Project
  3 * AGSymbol.java created on 26-jul-2006 at 16:21:55
  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.grammar;
 29
 30import edu.vub.at.exceptions.InterpreterException;
 31import edu.vub.at.objects.ATBoolean;
 32import edu.vub.at.objects.ATContext;
 33import edu.vub.at.objects.ATObject;
 34import edu.vub.at.objects.ATText;
 35import edu.vub.at.objects.grammar.ATSymbol;
 36import edu.vub.at.objects.natives.NATBoolean;
 37import edu.vub.at.objects.natives.NATText;
 38
 39import java.util.HashMap;
 40
 41/**
 42 * @author tvcutsem
 43 *
 44 * The native implementation of a symbol AG element.
 45 * Symbols should only be created via a call to AGSymbol.alloc
 46 * This ensures that symbols remain unique within one AmbientTalk VM.
 47 */
 48public class AGSymbol extends AGExpression implements ATSymbol {
 49
 50	/** hashmap shared by ALL actors/VMs, hence, thread access should be explicitly synchronized */
 51	protected static final HashMap _STRINGPOOL_ = new HashMap();
 52
 53	private final String txt_;
 54	
 55	protected AGSymbol(String txt) {
 56		txt_ = txt;
 57	}
 58	
 59	/**
 60	 * Allocate and return a unique symbol object denoting the given
 61	 * text string.
 62	 */
 63	public static AGSymbol jAlloc(String name) {
 64		synchronized (_STRINGPOOL_) {
 65			AGSymbol existing = (AGSymbol) _STRINGPOOL_.get(name);
 66			if (existing == null) {
 67				existing = new AGSymbol(name);
 68				_STRINGPOOL_.put(name, existing);
 69			}
 70			return existing;	
 71		}
 72	}
 73	
 74	/**
 75	 * Allocate and return a unique symbol denoting the given native text.
 76	 */
 77	public static final AGSymbol alloc(NATText txt) {
 78		return jAlloc(txt.javaValue);
 79	}
 80	
 81	public ATText base_text() { return NATText.atValue(txt_); }
 82	
 83	/**
 84	 * To evaluate a symbol reference, look up the symbol in the lexical scope.
 85	 * 
 86	 * AGSYM(txt).eval(ctx) = ctx.scope.lookup(AGSYM(txt))
 87	 * 
 88	 * @return the value bound to this symbol in the lexical environment
 89	 */
 90	public ATObject meta_eval(ATContext ctx) throws InterpreterException {
 91		return ctx.base_lexicalScope().impl_callField(this);
 92	}
 93
 94	/**
 95	 * Quoting a symbol results in the same symbol.
 96	 * 
 97	 * sym.quote(ctx) = sym
 98	 */
 99	public ATObject meta_quote(ATContext ctx) throws InterpreterException {
100		return this;
101	}
102	
103	public NATText meta_print() throws InterpreterException {
104		return NATText.atValue(txt_);
105	}
106	
107	public boolean isSymbol() {
108		return true;
109	}
110	
111	public ATSymbol asSymbol() {
112		return this;
113	}
114	
115	public boolean isAssignmentSymbol() {
116		return false;
117	}
118	
119	public AGAssignmentSymbol asAssignmentSymbol() {
120		return (AGAssignmentSymbol) AGAssignmentSymbol.jAlloc(txt_+":=");
121	}
122	
123	// comparison and identity operations
124	
125	public boolean equals(Object other) {
126		// pointer equality is valid for symbols as they are pooled
127		return this == other;
128	}
129	
130    public ATBoolean base__opeql__opeql_(ATObject comparand) throws InterpreterException {
131        return NATBoolean.atValue(this == comparand);
132    }
133	
134	// important as AGSymbols are often used as keys in hash tables
135	
136	public int hashCode() {
137		return this.txt_.hashCode();
138	}
139	
140	public String toString() {
141		return txt_;
142	}
143	
144	/**
145	 * After deserialization, ensure that the symbol remains unique.
146	 */
147	public ATObject meta_resolve() throws InterpreterException {
148		return jAlloc(txt_);
149	}
150
151}