/interpreter/tags/at2-build060407/src/edu/vub/at/objects/natives/NATNamespace.java
Java | 209 lines | 101 code | 21 blank | 87 comment | 6 complexity | d6c80d4ca80b3125204d891f67762fce MD5 | raw file
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.ATObject; 37import edu.vub.at.objects.ATStripe; 38import edu.vub.at.objects.grammar.ATSymbol; 39import edu.vub.at.objects.mirrors.Reflection; 40import edu.vub.at.parser.NATParser; 41 42import java.io.File; 43import java.io.IOException; 44import java.util.LinkedList; 45import java.util.Vector; 46 47/** 48 * Instances of the class NATNamespace represent namespace objects. 49 * 50 * Namespace objects act as regular AmbientTalk objects with the following differences and conventions: 51 * - Behaviourally, a namespace object is mirrored by a mirror whose doesNotUnderstand 52 * method reacts differently from the standard semantics of raising a 'selector not found' exception. 53 * - Structurally, a namespace has the lexical root as its lexical parent and the dynamic root as its dynamic parent. 54 * Furthermore, a namespace object encapsulates an absolute file system path and a relative 'path name'. 55 * The name should correspond to a portion of the tail of the absolute path. 56 * These variables are not visible to AmbientTalk code. 57 * 58 * When a slot is looked up in a namespace NS for a path P (via meta_select) and not found, the namespace object 59 * queries the local file system to see whether the selector corresponds to a directory or file in the 60 * directory P. Either the selector: 61 * - corresponds to a directory, in which case the missing slot is bound to a new namespace object corresponding to the path P/selector 62 * - corresponds to a file named selector.at, in which case: 63 * 1) the slot is temporarily bound to nil 64 * (this is to prevent loops when the code to be evaluated would refer to itself; 65 * it also means there can be no circular dependencies, because referring to a slot still under construction yields nil) 66 * 2) a new object FS (the 'file scope') is created. 67 * This object acts as the local scope for the file and has access to its 'enclosing' namespace via the '~' slot. 68 * Hence, it can refer to other files in the 'current directory' using ~.filename 69 * 3) the code in the file is loaded and evaluated in the context (current=FS, self=FS, super=FS.parent=dynroot) 70 * 4) the result of the evaluated code is bound to the missing slot. 71 * The next time the slot is queried for in the namespace, the value is immediately returned. This prevents 72 * files from being loaded twice. 73 * - does not correspond to any file or directory, resulting in a selector not found exception as usual. 74 * 75 * @author tvcutsem 76 * @author smostinc 77 */ 78public final class NATNamespace extends NATObject { 79 80 private static final String _AT_EXT_ = ".at"; 81 private final File path_; 82 private final String name_; 83 84 /** 85 * A namespace object encapsulates a given absolute path and represents the given relative path. 86 * 87 * @param name the name of this namespace (corresponding to a certain depth to the tail of the absolute path) 88 * @param path an absolute path referring to a local file system directory. 89 */ 90 public NATNamespace(String name, File path) { 91 super(); 92 name_ = name; 93 path_ = path; 94 } 95 96 /** 97 * Private constructor used only for cloning 98 */ 99 private NATNamespace(FieldMap map, 100 Vector state, 101 LinkedList customFields, 102 MethodDictionary methodDict, 103 ATObject dynamicParent, 104 ATObject lexicalParent, 105 byte flags, 106 ATStripe[] stripes, 107 File path, 108 String name) throws InterpreterException { 109 super(map, state, customFields, methodDict, dynamicParent, lexicalParent, flags, stripes); 110 path_ = path; 111 name_ = name; 112 } 113 114 /** 115 * For a namespace object, doesNotUnderstand triggers the querying of the local file system 116 * to load files corresponding to the missing selector. 117 */ 118 public ATObject meta_doesNotUnderstand(ATSymbol selector) throws InterpreterException { 119 // first, convert the AmbientTalk name to a Java selector. Java selectors are always valid filenames because 120 // they do not contain special operator characters 121 String javaSelector = Reflection.upSelector(selector); 122 123 // first, try to see if the file exists and corresponds to a directory 124 File dir = new File(path_, javaSelector); 125 if (dir.exists() && dir.isDirectory()) { 126 // create a new namespace object for this directory 127 NATNamespace childNS = new NATNamespace(name_ + "/" + javaSelector, dir); 128 129 // bind the new child namespace to the selector 130 this.meta_defineField(selector, childNS); 131 return childNS; 132 133 } else { 134 // try to see if a file with extension .at exists corresponding to the selector 135 File src = new File(path_, javaSelector + _AT_EXT_); 136 if (src.exists() && src.isFile()) { 137 138 // bind the missing slot to nil to prevent calling this dNU recursively when evaluating the code in the file 139 this.meta_defineField(selector, NATNil._INSTANCE_); 140 141 // create a new file scope object for this file 142 NATObject fileScope = createFileScopeFor(this); 143 144 try { 145 // load the code from the file 146 String code = Evaluator.loadContentOfFile(src); 147 148 // construct the proper evaluation context for the code 149 NATContext ctx = new NATContext(fileScope, fileScope); 150 151 // parse and evaluate the code in the proper context and bind its result to the missing slot 152 ATAbstractGrammar source = NATParser.parse(src.getName(), code); 153 ATObject result = source.meta_eval(ctx); 154 this.meta_assignField(this, selector, result); 155 156 return result; 157 } catch (IOException e) { 158 throw new XIOProblem(e); 159 } 160 161 } else { // neither a matching directory nor a matching file.at were found 162 // perform the default dNU behaviour, which means raising a 'selector not found' exception 163 return super.meta_doesNotUnderstand(selector); 164 } 165 } 166 } 167 168 public NATText meta_print() throws InterpreterException { 169 return NATText.atValue("<ns:"+name_+">"); 170 } 171 172 public static NATObject createFileScopeFor(NATNamespace ns) { 173 NATObject fileScope = new NATObject(); 174 // a fileScope object is empty, save for a reference to its creating namespace 175 try { 176 fileScope.meta_defineField(Evaluator._CURNS_SYM_, ns); 177 } catch (XDuplicateSlot e) { 178 // impossible: the object is empty 179 e.printStackTrace(); 180 } catch (XTypeMismatch e) { 181 // impossible: the given selector is native 182 e.printStackTrace(); 183 } catch (InterpreterException e) { 184 // impossible : call cannot be intercepted : namespaces are not mirages 185 e.printStackTrace(); 186 } 187 return fileScope; 188 } 189 190 protected NATObject createClone(FieldMap map, 191 Vector state, 192 LinkedList customFields, 193 MethodDictionary methodDict, 194 ATObject dynamicParent, 195 ATObject lexicalParent, 196 byte flags, ATStripe[] stripes) throws InterpreterException { 197 return new NATNamespace(map, 198 state, 199 customFields, 200 methodDict, 201 dynamicParent, 202 lexicalParent, 203 flags, 204 stripes, 205 path_, 206 name_); 207 } 208 209}