PropertyLocation


1   package gnu.mapping;
2   import gnu.lists.*;
3   
4   /** Used to implement Lisp-style "property lists".
5    * A <code>PropertyLocation</code> is a location whose value is the
6    * <code>car</code> of a property list.
7    * This class also contains a number of static methods useful for
8    * working with property lists.
9    */
10  
11  public class PropertyLocation extends Location
12  {
13    //  Location plist;
14  
15    Pair pair;
16  
17    public final Object   get (Object   defaultValue)
18    {
19      return pair.car;
20    }
21  
22    public boolean isBound ()
23    {
24      return true;
25    }
26  
27    public final void set (Object   newValue)
28    {
29      pair.car = newValue;
30    }
31  
32    /** Get the property list assocated with an object in a given Environment.
33     * @param symbol Usually but not necessarily a Symbol.
34     * (A String is <em>not </em> converted a Symbol by this method.)
35     */
36    public static Object   getPropertyList (Object   symbol, Environment env)
37    {
38      return env.get(Symbol.PLIST, symbol, LList.Empty);
39    }
40  
41    /** Get the property list associated with object in the current Environment.
42     * Corresponds to Common Lisp's <code>symbol-plist</code> function.
43     * @param symbol Usually but not necessarily a Symbol.
44     * (A String is <em>not </em> converted a Symbol by this method.)
45     */
46    public static Object   getPropertyList (Object   symbol)
47    {
48      return Environment.getCurrent().get(Symbol.PLIST, symbol, LList.Empty);
49    }
50  
51    /** Set the property list assocated with an object in a given Environment.
52     * This function should be avoided, since a Symbol's property list may
53     * be used by unknown classes.  It also can be slow.
54     * @param symbol Usually but not necessarily a Symbol.
55     * (A String is <em>not </em> converted a Symbol by this method.)
56     */
57    public static void setPropertyList (Object   symbol, Object   plist,
58                        Environment env)
59    {
60      synchronized (env)
61        {
62      Location lloc = env.lookup(Symbol.PLIST, symbol);
63      if (symbol instanceof Symbol)
64        {
65          Symbol sym = (Symbol) symbol;
66          Object   old = lloc.get(LList.Empty);
67          Object   p = old;
68          // Remove old PropertyLocation bindings not in plist.
69          for (;;)
70            {
71          if (! (p instanceof Pair))
72            break;
73          Pair pair = (Pair) p;
74          Object   property = pair.car;
75          if (plistGet(plist, property, null) != null)
76            env.remove(sym, property);
77          p = ((Pair) pair.cdr).cdr;
78            }
79          // Add/update PropertyLocation bindings from plist.
80          p = plist;
81          for (;;)
82            {
83          if (! (p instanceof Pair))
84            break;
85          Pair pair = (Pair) p;
86          Object   property = pair.car;
87          Location loc = env.lookup(sym, property);
88          PropertyLocation ploc;
89          if (loc != null
90              && (loc = loc.getBase()) instanceof PropertyLocation)
91            {
92              ploc = (PropertyLocation) loc;
93            }
94          else
95            {
96              ploc = new PropertyLocation();
97              env.addLocation(sym, property, ploc);
98            }
99          Pair valuePair = (Pair) pair.cdr;
100         ploc.pair = valuePair;
101         //ploc.plist = plist;
102         p = valuePair.cdr;
103           }
104       }
105     lloc.set(plist);
106       }
107   }
108 
109   /** Set the property list assocated with an object in a given Environment.
110    * Corresponds to Common Lisp's <code>(setf symbol-plist)</code> function.
111    * @see #setPropertyList(Object, Object, Environment).
112    */
113   public static void setPropertyList (Object   symbol, Object   plist)
114   {
115     setPropertyList(symbol, plist, Environment.getCurrent());
116 
117   }
118 
119   /** Gets a property value associated with an object.
120    * @param symbol Usually a <code>Symbol</code>, but can be any
121    *   <code>Object>/code>.  A <code>String</code> is converted to a
122    *   <code>Symbol</code> using <code>env.getSymbol()</code>.
123    *   Symbols require a constant-type hash lookup; other object
124    *   are serached linearly.
125    */
126   public static Object   getProperty (Object   symbol, Object   property,
127                     Object   defaultValue, Environment env)
128   {
129     if (! (symbol instanceof Symbol))
130       {
131     if (symbol instanceof String  )
132       symbol = Namespace.getDefaultSymbol((String  ) symbol);
133     else
134       return plistGet(env.get(Symbol.PLIST, symbol, LList.Empty),
135               property, defaultValue);
136       }
137     return env.get((Symbol) symbol, property, defaultValue);
138   }
139 
140   /** Gets a property value associated with an object.
141    * Corresponds to Common Lisp's <code>get</code> function.
142    * @see #getProperty(Object, Object, Object, Environment).
143    */
144   public static Object   getProperty (Object   symbol, Object   property,
145                     Object   defaultValue)
146   {
147     return getProperty(symbol, property,
148                defaultValue, Environment.getCurrent());
149   }
150 
151   public static void putProperty (Object   symbol, Object   property,
152                   Object   newValue, Environment env)
153   {
154     if (! (symbol instanceof Symbol))
155       {
156     if (symbol instanceof String  )
157       symbol = Namespace.getDefaultSymbol((String  ) symbol);
158     else
159       {
160         Location lloc = env.getLocation(Symbol.PLIST, symbol);
161         lloc.set(plistPut(lloc.get(LList.Empty), property, newValue));
162         return;
163       }
164       }
165     Location loc = env.lookup((Symbol) symbol, property);
166     if (loc != null && (loc = loc.getBase()) instanceof PropertyLocation)
167       ((PropertyLocation) loc).set(newValue);
168     else
169       {
170     Location lloc = env.getLocation(Symbol.PLIST, symbol);
171     Object   plist = lloc.get(LList.Empty);
172     Pair pair = null;
173     /*
174     pair = null;
175     if (plist instanceof Pair)
176       {
177         pair = (Pair) plist;
178         for (;;)
179           {
180         if (pair.car == property)
181           break;
182         if (pair.cdr instanceof Pair)
183           pair = (Pair) pair.cdr;
184         else
185           {
186             pair = null;
187             break;
188           }
189           }
190       }
191     if (pair == null)
192       plist = pair = new Pair(property, new Pair(newValue, plist));
193     */
194     pair = new Pair(newValue, plist);
195     plist = new Pair(property, pair);
196     lloc.set(plist);
197     PropertyLocation ploc = new PropertyLocation();
198     //ploc.plist = lloc;
199     ploc.pair = pair;
200     env.addLocation((Symbol) symbol, property, ploc);
201       }
202   }
203 
204   /** Sets a property value associated with an object.
205    * Corresponds to Common Lisp's <code>(setf get)</code> function.
206    */
207   public static void putProperty (Object   symbol, Object   property,
208                   Object   newValue)
209   {
210     putProperty(symbol, property, newValue, Environment.getCurrent());
211   }
212 
213   /** Remove a properaty assocatied with an object.
214    */
215   public static boolean removeProperty (Object   symbol, Object   property,
216                     Environment env)
217   {
218     Location ploc = env.lookup(Symbol.PLIST, symbol);
219     if (ploc == null)
220       return false;
221     Object   plist = ploc.get(LList.Empty);
222     if (! (plist instanceof Pair))
223       return false;
224     Pair pair = (Pair) plist;
225     Pair prev = null;
226     for (;;)
227       {
228     if (pair.car == property)
229       break;
230     Object   next = pair.cdr;
231     if (! (next instanceof Pair))
232       return false;
233     prev = pair;
234     pair = (Pair) next;
235       }
236     Object   tail = ((Pair) pair.cdr).cdr;
237     if (prev == null)
238       {
239     plist = tail;
240     ploc.set(plist);
241       }
242     else
243       prev.cdr = tail;
244     if (symbol instanceof Symbol)
245       env.remove((Symbol) symbol, property);
246     return true;
247   }
248 
249   /** Remove a properaty assocatied with an object.
250    * Corresponds to Common Lisp's <code>remprop</code> function.
251    */
252   public static boolean removeProperty (Object   symbol, Object   property)
253   {
254     return removeProperty(symbol, property, Environment.getCurrent());
255   }
256 
257   /**
258    * Given a property list and a key, find the corresponding property value.
259    */
260   public static Object   plistGet(Object   plist, Object   prop, Object   dfault)
261   {
262     while (plist instanceof Pair)
263       {
264     Pair pair = (Pair) plist;
265     if (pair.car == prop)
266       return ((Pair) pair.cdr).car;
267       }
268     return dfault;
269   }
270 
271   /** Modify and add a property binding to a property list.
272    * @return The updated property list.
273    */
274   public static Object   plistPut(Object   plist, Object   prop, Object   value)
275   {
276     for (Object   p = plist; p instanceof Pair; )
277       {
278     Pair pair = (Pair) p;
279     Pair next = (Pair) pair.cdr;
280     if (pair.car == prop)
281       {
282         next.car = value;
283         return plist;
284       }
285     p = next.cdr;
286       }
287     return new Pair(prop, new Pair(value, plist));
288   }
289 
290   /** Remove a property binding from a property list.
291    * @return The updated property list.
292    */
293   public static Object   plistRemove(Object   plist, Object   prop)
294   {
295     Pair prev = null;
296     for (Object   p = plist; p instanceof Pair; )
297       {
298     Pair pair = (Pair) p;
299     Pair next = (Pair) pair.cdr;
300     p = next.cdr;
301     if (pair.car == prop)
302       {
303         if (prev == null)
304           return p;
305         prev.cdr = p;
306         return plist;
307       }
308     prev = next;
309       }
310     return plist;
311   }
312 }
313
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