/interpreter/tags/at2dist170907/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.grammar.ATSymbol;
 41import edu.vub.at.objects.mirrors.NativeClosure;
 42import edu.vub.at.objects.mirrors.Reflection;
 43import edu.vub.at.parser.NATParser;
 44
 45import java.io.File;
 46import java.io.IOException;
 47import java.util.LinkedList;
 48import java.util.Vector;
 49
 50/**
 51 * Instances of the class NATNamespace represent namespace objects.
 52 * 
 53 * Namespace objects act as regular AmbientTalk objects with the following differences and conventions:
 54 *  - Behaviourally, a namespace object is mirrored by a mirror whose doesNotUnderstand
 55 *    method reacts differently from the standard semantics of raising a 'selector not found' exception.
 56 *  - Structurally, a namespace has the lexical root as its lexical parent and the dynamic root as its dynamic parent.
 57 *    Furthermore, a namespace object encapsulates an absolute file system path and a relative 'path name'.
 58 *    The name should correspond to a portion of the tail of the absolute path.
 59 *    These variables are not visible to AmbientTalk code.
 60 *         
 61 * When a slot is looked up in a namespace NS for a path P (via meta_select) and not found, the namespace object
 62 * queries the local file system to see whether the selector corresponds to a directory or file in the
 63 * directory P. Either the selector:
 64 *  - corresponds to a directory, in which case the missing slot is bound to a new namespace object corresponding to the path P/selector
 65 *  - corresponds to a file named selector.at, in which case:
 66 *    1) the slot is temporarily bound to nil
 67 *       (this is to prevent loops when the code to be evaluated would refer to itself;
 68 *        it also means there can be no circular dependencies, because referring to a slot still under construction yields nil)
 69 *    2) a new object FS (the 'file scope') is created.
 70 *       This object acts as the local scope for the file and has access to its 'enclosing' namespace via the '~' slot.
 71 *       Hence, it can refer to other files in the 'current directory' using ~.filename
 72 *    3) the code in the file is loaded and evaluated in the context (current=FS, self=FS, super=FS.parent=dynroot)
 73 *    4) the result of the evaluated code is bound to the missing slot.
 74 *       The next time the slot is queried for in the namespace, the value is immediately returned. This prevents
 75 *       files from being loaded twice.
 76 *  - does not correspond to any file or directory, resulting in a selector not found exception as usual.
 77 * 
 78 * @author tvcutsem
 79 * @author smostinc
 80 */
 81public final class NATNamespace extends NATObject {
 82
 83	private static final String _AT_EXT_ = ".at";
 84	private final File path_;
 85	private final String name_;
 86	
 87	/**
 88	 * A namespace object encapsulates a given absolute path and represents the given relative path.
 89	 * 
 90	 * @param name the name of this namespace (corresponding to a certain depth to the tail of the absolute path)
 91	 * @param path an absolute path referring to a local file system directory.
 92	 */
 93	public NATNamespace(String name, File path) {
 94		super();
 95		name_ = name;
 96		path_ = path;
 97	}
 98	
 99	/**
100	 * Private constructor used only for cloning
101	 */
102	private NATNamespace(FieldMap map,
103			  Vector state,
104			  LinkedList customFields,
105			  MethodDictionary methodDict,
106			  ATObject dynamicParent,
107			  ATObject lexicalParent,
108			  byte flags,
109			  ATTypeTag[] types,
110			  File path,
111			  String name) throws InterpreterException {
112	  super(map, state, customFields, methodDict, dynamicParent, lexicalParent, flags, types);
113	  path_ = path;
114	  name_ = name;
115	}
116	
117	/**
118	 * For a namespace object, doesNotUnderstand triggers the querying of the local file system
119	 * to load files corresponding to the missing selector.
120	 */
121	public ATClosure meta_doesNotUnderstand(ATSymbol selector) throws InterpreterException {
122		// first, convert the AmbientTalk name to a Java selector. Java selectors are always valid filenames because
123		// they do not contain special operator characters
124		String javaSelector = Reflection.upSelector(selector);
125		
126		// first, try to see if the file exists and corresponds to a directory
127		File dir = new File(path_, javaSelector);
128		if (dir.exists() && dir.isDirectory()) {
129             // create a new namespace object for this directory
130			final NATNamespace childNS = new NATNamespace(name_ + "/" + javaSelector, dir);
131
132			// bind the new child namespace to the selector
133			this.meta_defineField(selector, childNS);
134			return new NativeClosure(this) {
135				public ATObject base_apply(ATTable args) {
136					return childNS;
137				}
138			};
139		} else {
140			// try to see if a file with extension .at exists corresponding to the selector
141			File src = new File(path_, javaSelector + _AT_EXT_);
142			if (src.exists() && src.isFile()) {
143			
144                 // bind the missing slot to nil to prevent calling this dNU recursively when evaluating the code in the file
145				this.meta_defineField(selector, OBJNil._INSTANCE_);
146				
147	             // create a new file scope object for this file
148				NATObject fileScope = createFileScopeFor(this);
149				
150				try {
151                     // load the code from the file
152					String code = Evaluator.loadContentOfFile(src);
153				
154				    // construct the proper evaluation context for the code
155				    NATContext ctx = new NATContext(fileScope, fileScope);
156				    
157				    // parse and evaluate the code in the proper context and bind its result to the missing slot
158					ATAbstractGrammar source = NATParser.parse(src.getName(), code);
159					final ATObject result = source.meta_eval(ctx);
160					this.impl_invokeMutator(this, selector.asAssignmentSymbol(), NATTable.of(result));
161					//this.meta_assignField(this, selector, result);
162					
163					return new NativeClosure(this) {
164						public ATObject base_apply(ATTable args) {
165							return result;
166						}
167					};
168				} catch (IOException e) {
169					throw new XIOProblem(e);
170				}
171				
172			} else { // neither a matching directory nor a matching file.at were found
173                 // perform the default dNU behaviour, which means raising a 'selector not found' exception
174				return super.meta_doesNotUnderstand(selector);
175			}
176		}
177	}
178
179	public NATText meta_print() throws InterpreterException {
180		return NATText.atValue("<ns:"+name_+">");
181	}
182	
183	public static NATObject createFileScopeFor(NATNamespace ns) {
184		NATObject fileScope = new NATObject();
185		// a fileScope object is empty, save for a reference to its creating namespace
186		try {
187			fileScope.meta_defineField(Evaluator._CURNS_SYM_, ns);
188		} catch (XDuplicateSlot e) {
189			// impossible: the object is empty
190			e.printStackTrace();
191		} catch (XTypeMismatch e) {
192			// impossible: the given selector is native
193			e.printStackTrace();
194		} catch (InterpreterException e) {
195			// impossible : call cannot be intercepted : namespaces are not mirages
196			e.printStackTrace();			
197		}
198		return fileScope;
199	}
200	
201	protected NATObject createClone(FieldMap map,
202			  Vector state,
203			  LinkedList customFields,
204			  MethodDictionary methodDict,
205			  ATObject dynamicParent,
206			  ATObject lexicalParent,
207			  byte flags, ATTypeTag[] types) throws InterpreterException {
208      return new NATNamespace(map,
209    		  				    state,
210    		  				    customFields,
211    		  				    methodDict,
212    		  				    dynamicParent,
213    		  				    lexicalParent,
214    		  				    flags,
215    		  				    types,
216    		  				    path_,
217    		  				    name_);
218	}
219	
220}