PageRenderTime 23ms CodeModel.GetById 16ms app.highlight 4ms RepoModel.GetById 1ms app.codeStats 0ms

/interpreter/tags/at2-build060407/src/edu/vub/at/objects/natives/grammar/AGSymbol.java

http://ambienttalk.googlecode.com/
Java | 136 lines | 61 code | 22 blank | 53 comment | 4 complexity | e96d66094be166e8eed614e60a34cce5 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	private static final HashMap _STRINGPOOL_ = new HashMap();
 52
 53	private final String txt_;
 54	
 55	protected AGSymbol(String txt) {
 56		txt_ = txt;
 57	}
 58	
 59	public static final AGSymbol jAlloc(String name) {
 60		synchronized (_STRINGPOOL_) {
 61			AGSymbol existing = (AGSymbol) _STRINGPOOL_.get(name);
 62			if (existing == null) {
 63				existing = new AGSymbol(name);
 64				_STRINGPOOL_.put(name, existing);
 65			}
 66			return existing;	
 67		}
 68	}
 69	
 70	public static final AGSymbol alloc(NATText txt) {
 71		return jAlloc(txt.javaValue);
 72	}
 73	
 74	public ATText base_getText() { return NATText.atValue(txt_); }
 75	
 76	/**
 77	 * To evaluate a symbol reference, look up the symbol in the lexical scope.
 78	 * 
 79	 * AGSYM(txt).eval(ctx) = ctx.scope.lookup(AGSYM(txt))
 80	 * 
 81	 * @return the value bound to this symbol in the lexical environment
 82	 */
 83	public ATObject meta_eval(ATContext ctx) throws InterpreterException {
 84		return ctx.base_getLexicalScope().meta_lookup(this);
 85	}
 86
 87	/**
 88	 * Quoting a symbol results in the same symbol.
 89	 * 
 90	 * sym.quote(ctx) = sym
 91	 */
 92	public ATObject meta_quote(ATContext ctx) throws InterpreterException {
 93		return this;
 94	}
 95	
 96	public NATText meta_print() throws InterpreterException {
 97		return NATText.atValue(txt_);
 98	}
 99	
100	public boolean isSymbol() {
101		return true;
102	}
103	
104	public ATSymbol asSymbol() {
105		return this;
106	}
107	
108	// comparison and identity operations
109	
110	public boolean equals(Object other) {
111		// pointer equality is valid for symbols as they are pooled
112		return this == other;
113	}
114	
115    public ATBoolean base__opeql__opeql_(ATObject comparand) throws InterpreterException {
116        return NATBoolean.atValue(this == comparand);
117    }
118	
119	// important as AGSymbols are often used as keys in hash tables
120	
121	public int hashCode() {
122		return this.txt_.hashCode();
123	}
124	
125	public String toString() {
126		return txt_;
127	}
128	
129	/**
130	 * After deserialization, ensure that the symbol remains unique.
131	 */
132	public ATObject meta_resolve() throws InterpreterException {
133		return jAlloc(txt_);
134	}
135
136}