/interpreter/tags/at2dist220411/src/edu/vub/at/objects/natives/grammar/AGSymbol.java

  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.ATTable;
 35import edu.vub.at.objects.ATText;
 36import edu.vub.at.objects.coercion.NativeTypeTags;
 37import edu.vub.at.objects.grammar.ATSymbol;
 38import edu.vub.at.objects.natives.NATBoolean;
 39import edu.vub.at.objects.natives.NATTable;
 40import edu.vub.at.objects.natives.NATText;
 41import edu.vub.at.parser.SourceLocation;
 42import edu.vub.util.TempFieldGenerator;
 43
 44import java.util.HashMap;
 45import java.util.HashSet;
 46import java.util.Set;
 47
 48/**
 49 * @author tvcutsem
 50 *
 51 * The native implementation of a symbol AG element.
 52 * Symbols should only be created via a call to AGSymbol.alloc
 53 * This ensures that symbols remain unique within one AmbientTalk VM.
 54 */
 55public class AGSymbol extends AGExpression implements ATSymbol {
 56
 57	/** hashmap shared by ALL actors/VMs, hence, thread access should be explicitly synchronized */
 58	protected static final HashMap _STRINGPOOL_ = new HashMap();
 59
 60	private final String txt_;
 61	
 62	protected AGSymbol(String txt) {
 63		txt_ = txt;
 64	}
 65	
 66	/**
 67	 * Allocate and return a unique symbol object denoting the given
 68	 * text string.
 69	 */
 70	public static AGSymbol jAlloc(String name) {
 71		synchronized (_STRINGPOOL_) {
 72			AGSymbol existing = (AGSymbol) _STRINGPOOL_.get(name);
 73			if (existing == null) {
 74				existing = new AGSymbol(name);
 75				_STRINGPOOL_.put(name, existing);
 76			}
 77			return existing;	
 78		}
 79	}
 80	
 81	/**
 82	 * Allocate and return a unique symbol denoting the given native text.
 83	 */
 84	public static final AGSymbol alloc(NATText txt) {
 85		return jAlloc(txt.javaValue);
 86	}
 87	
 88	public ATText base_text() { return NATText.atValue(txt_); }
 89	
 90	/**
 91	 * To evaluate a symbol reference, look up the symbol in the lexical scope.
 92	 * 
 93	 * AGSYM(txt).eval(ctx) = ctx.scope.lookup(AGSYM(txt))
 94	 * 
 95	 * @return the value bound to this symbol in the lexical environment
 96	 */
 97	public ATObject meta_eval(ATContext ctx) throws InterpreterException {
 98		return ctx.base_lexicalScope().impl_callField(this);
 99	}
100
101	/**
102	 * Quoting a symbol results in the same symbol.
103	 * 
104	 * sym.quote(ctx) = sym
105	 */
106	public ATObject meta_quote(ATContext ctx) throws InterpreterException {
107		return this;
108	}
109	
110	public NATText meta_print() throws InterpreterException {
111		return NATText.atValue(txt_);
112	}
113	
114	public ATTable meta_typeTags() throws InterpreterException {
115		return NATTable.of(NativeTypeTags._SYMBOL_, NativeTypeTags._ISOLATE_);
116	}
117	
118	public NATText impl_asCode(TempFieldGenerator objectMap) throws InterpreterException {
119		return NATText.atValue("`" + txt_);
120	}
121	
122	public NATText impl_asUnquotedCode(TempFieldGenerator objectMap) throws InterpreterException {
123		return NATText.atValue(txt_);
124	}
125	
126	public boolean isSymbol() {
127		return true;
128	}
129	
130	public ATSymbol asSymbol() {
131		return this;
132	}
133	
134	public boolean isAssignmentSymbol() {
135		return false;
136	}
137	
138	public AGAssignmentSymbol asAssignmentSymbol() {
139		return (AGAssignmentSymbol) AGAssignmentSymbol.jAlloc(txt_+":=");
140	}
141	
142	// comparison and identity operations
143	
144	public boolean equals(Object other) {
145		// pointer equality is valid for symbols as they are pooled
146		return this == other;
147	}
148	
149    public ATBoolean base__opeql__opeql_(ATObject comparand) throws InterpreterException {
150        return NATBoolean.atValue(this == comparand);
151    }
152	
153	// important as AGSymbols are often used as keys in hash tables
154	
155	public int hashCode() {
156		return this.txt_.hashCode();
157	}
158	
159	public String toString() {
160		return txt_;
161	}
162	
163	/**
164	 * After deserialization, ensure that the symbol remains unique.
165	 */
166	public ATObject meta_resolve() throws InterpreterException {
167		return jAlloc(txt_);
168	}
169	
170	/**
171	 * FV(nam) = { nam }
172	 */
173	public Set impl_freeVariables() throws InterpreterException {
174        HashSet singleton = new HashSet();
175        singleton.add(this);
176        return singleton;
177	}
178	
179	/**
180	 * Within a quoted expression, a variable reference is not considered
181	 * a free variable, e.g. `(x)
182	 */
183	public Set impl_quotedFreeVariables() throws InterpreterException {
184		return new HashSet();
185	}
186	
187	// since symbols are interned, they are shared among parse trees
188	// (even among actors!) so their source location is meaningless
189    public SourceLocation impl_getLocation() { return null; }
190    public void impl_setLocation(SourceLocation loc) {}
191
192}