/interpreter/tags/at2dist041108/src/edu/vub/at/objects/natives/NATNamespace.java

  1/**
  2 * AmbientTalk/2 Project
  3 * NATNamespace.java created on 6-sep-2006 at 14:33:41
  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.eval.Evaluator;
 31import edu.vub.at.exceptions.InterpreterException;
 32import edu.vub.at.exceptions.XDuplicateSlot;
 33import edu.vub.at.exceptions.XIOProblem;
 34import edu.vub.at.exceptions.XTypeMismatch;
 35import edu.vub.at.objects.ATAbstractGrammar;
 36import edu.vub.at.objects.ATClosure;
 37import edu.vub.at.objects.ATObject;
 38import edu.vub.at.objects.ATTable;
 39import edu.vub.at.objects.ATTypeTag;
 40import edu.vub.at.objects.coercion.NativeTypeTags;
 41import edu.vub.at.objects.grammar.ATSymbol;
 42import edu.vub.at.objects.mirrors.NativeClosure;
 43import edu.vub.at.objects.mirrors.Reflection;
 44import edu.vub.at.parser.NATParser;
 45
 46import java.io.File;
 47import java.io.IOException;
 48import java.util.LinkedList;
 49import java.util.Vector;
 50
 51/**
 52 * Instances of the class NATNamespace represent namespace objects.
 53 * 
 54 * Namespace objects act as regular AmbientTalk objects with the following differences and conventions:
 55 *  - Behaviourally, a namespace object is mirrored by a mirror whose doesNotUnderstand
 56 *    method reacts differently from the standard semantics of raising a 'selector not found' exception.
 57 *  - Structurally, a namespace has the lexical root as its lexical parent and the dynamic root as its dynamic parent.
 58 *    Furthermore, a namespace object encapsulates an absolute file system path and a relative 'path name'.
 59 *    The name should correspond to a portion of the tail of the absolute path.
 60 *    These variables are not visible to AmbientTalk code.
 61 *         
 62 * When a slot is looked up in a namespace NS for a path P (via meta_select) and not found, the namespace object
 63 * queries the local file system to see whether the selector corresponds to a directory or file in the
 64 * directory P. Either the selector:
 65 *  - corresponds to a directory, in which case the missing slot is bound to a new namespace object corresponding to the path P/selector
 66 *  - corresponds to a file named selector.at, in which case:
 67 *    1) the slot is temporarily bound to nil
 68 *       (this is to prevent loops when the code to be evaluated would refer to itself;
 69 *        it also means there can be no circular dependencies, because referring to a slot still under construction yields nil)
 70 *    2) a new object FS (the 'file scope') is created.
 71 *       This object acts as the local scope for the file and has access to its 'enclosing' namespace via the '~' slot.
 72 *       Hence, it can refer to other files in the 'current directory' using ~.filename
 73 *    3) the code in the file is loaded and evaluated in the context (current=FS, self=FS, super=FS.parent=dynroot)
 74 *    4) the result of the evaluated code is bound to the missing slot.
 75 *       The next time the slot is queried for in the namespace, the value is immediately returned. This prevents
 76 *       files from being loaded twice.
 77 *  - does not correspond to any file or directory, resulting in a selector not found exception as usual.
 78 * 
 79 * @author tvcutsem
 80 * @author smostinc
 81 */
 82public final class NATNamespace extends NATObject {
 83
 84	private static final String _AT_EXT_ = ".at";
 85	private final File path_;
 86	private final String name_;
 87	
 88	/**
 89	 * A namespace object encapsulates a given absolute path and represents the given relative path.
 90	 * 
 91	 * @param name the name of this namespace (corresponding to a certain depth to the tail of the absolute path)
 92	 * @param path an absolute path referring to a local file system directory.
 93	 */
 94	public NATNamespace(String name, File path) {
 95		super();
 96		name_ = name;
 97		path_ = path;
 98	}
 99	
100	/**
101	 * Private constructor used only for cloning
102	 */
103	private NATNamespace(FieldMap map,
104			  Vector state,
105			  LinkedList customFields,
106			  MethodDictionary methodDict,
107			  ATObject dynamicParent,
108			  ATObject lexicalParent,
109			  byte flags,
110			  ATTypeTag[] types,
111			  File path,
112			  String name) throws InterpreterException {
113	  super(map, state, customFields, methodDict, dynamicParent, lexicalParent, flags, types);
114	  path_ = path;
115	  name_ = name;
116	}
117	
118	/**
119	 * For a namespace object, doesNotUnderstand triggers the querying of the local file system
120	 * to load files corresponding to the missing selector.
121	 */
122	public ATClosure meta_doesNotUnderstand(ATSymbol selector) throws InterpreterException {
123		// first, convert the AmbientTalk name to a Java selector. Java selectors are always valid filenames because
124		// they do not contain special operator characters
125		String javaSelector = Reflection.upSelector(selector);
126		
127		// first, try to see if the file exists and corresponds to a directory
128		File dir = new File(path_, javaSelector);
129		if (dir.exists() && dir.isDirectory()) {
130             // create a new namespace object for this directory
131			final NATNamespace childNS = new NATNamespace(name_ + File.separator + javaSelector, dir);
132
133			// bind the new child namespace to the selector
134			this.meta_defineField(selector, childNS);
135			return new NativeClosure(this) {
136				public ATObject base_apply(ATTable args) {
137					return childNS;
138				}
139			};
140		} else {
141			// try to see if a file with extension .at exists corresponding to the selector
142			File src = new File(path_, javaSelector + _AT_EXT_);
143			if (src.exists() && src.isFile()) {
144			
145                 // bind the missing slot to nil to prevent calling this dNU recursively when evaluating the code in the file
146				this.meta_defineField(selector, Evaluator.getNil());
147				
148	             // create a new file scope object for this file
149				NATObject fileScope = createFileScopeFor(this);
150				
151				try {
152                     // load the code from the file
153					String code = Evaluator.loadContentOfFile(src);
154				
155				    // construct the proper evaluation context for the code
156				    NATContext ctx = new NATContext(fileScope, fileScope);
157				    
158				    // parse and evaluate the code in the proper context and bind its result to the missing slot
159					ATAbstractGrammar source = NATParser.parse(src.getName(), code);
160					final ATObject result = source.meta_eval(ctx);
161					this.impl_invokeMutator(this, selector.asAssignmentSymbol(), NATTable.of(result));
162					//this.meta_assignField(this, selector, result);
163					
164					// keeping up with the UAP: if the return value of a module is
165					// a function, the function itself is returned (and most presumably
166					// applied immediately). This allows modules to be parameterized easily.
167					if (result.meta_isTaggedAs(NativeTypeTags._CLOSURE_).asNativeBoolean().javaValue) {
168						return result.asClosure();
169					} else {
170						return new NativeClosure(this) {
171							public ATObject base_apply(ATTable args) {
172								return result;
173							}
174						};	
175					}
176				} catch (IOException e) {
177					throw new XIOProblem(e);
178				}
179				
180			} else { // neither a matching directory nor a matching file.at were found
181                 // perform the default dNU behaviour, which means raising a 'selector not found' exception
182				return super.meta_doesNotUnderstand(selector);
183			}
184		}
185	}
186
187	public NATText meta_print() throws InterpreterException {
188		return NATText.atValue("<ns:"+name_+">");
189	}
190	
191	public static NATObject createFileScopeFor(NATNamespace ns) {
192		NATObject fileScope = new NATObject();
193		// a fileScope object is empty, save for a reference to its creating namespace
194		try {
195			fileScope.meta_defineField(Evaluator._CURNS_SYM_, ns);
196		} catch (XDuplicateSlot e) {
197			// impossible: the object is empty
198			e.printStackTrace();
199		} catch (XTypeMismatch e) {
200			// impossible: the given selector is native
201			e.printStackTrace();
202		} catch (InterpreterException e) {
203			// impossible : call cannot be intercepted : namespaces are not mirages
204			e.printStackTrace();			
205		}
206		return fileScope;
207	}
208	
209	protected NATObject createClone(FieldMap map,
210			  Vector state,
211			  LinkedList customFields,
212			  MethodDictionary methodDict,
213			  ATObject dynamicParent,
214			  ATObject lexicalParent,
215			  byte flags, ATTypeTag[] types) throws InterpreterException {
216      return new NATNamespace(map,
217    		  				    state,
218    		  				    customFields,
219    		  				    methodDict,
220    		  				    dynamicParent,
221    		  				    lexicalParent,
222    		  				    flags,
223    		  				    types,
224    		  				    path_,
225    		  				    name_);
226	}
227	
228}