Source Code Cross Referenced for TreeExtractor.java in  » Parser » Rats-Parser-Generators » xtc » parser » Java Source Code / Java DocumentationJava Source Code and Java Documentation

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Java Source Code / Java Documentation » Parser » Rats Parser Generators » xtc.parser 
Source Cross Referenced  Class Diagram Java Document (Java Doc) 


001:        /*
002:         * xtc - The eXTensible Compiler
003:         * Copyright (C) 2007 Robert Grimm
004:         *
005:         * This program is free software; you can redistribute it and/or
006:         * modify it under the terms of the GNU General Public License
007:         * version 2 as published by the Free Software Foundation.
008:         *
009:         * This program is distributed in the hope that it will be useful,
010:         * but WITHOUT ANY WARRANTY; without even the implied warranty of
011:         * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
012:         * GNU General Public License for more details.
013:         *
014:         * You should have received a copy of the GNU General Public License
015:         * along with this program; if not, write to the Free Software
016:         * Foundation, 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301,
017:         * USA.
018:         */
019:        package xtc.parser;
020:
021:        import xtc.tree.Visitor;
022:
023:        import xtc.type.AST;
024:
025:        import xtc.util.Runtime;
026:
027:        /**
028:         * Visitor to pear down a grammar to the structure of its abstract
029:         * syntax tree.  This visitor assumes that the entire grammar is
030:         * contained in a single module.  It also assumes that directly
031:         * left-recursive generic productions have <em>not</em> been
032:         * transformed by {@link DirectLeftRecurser}.  Note that, after this
033:         * visitor has processed the grammar, the grammar violates the code
034:         * generator's requirements.  Also note that this visitor internally
035:         * uses {@link Simplifier} and {@link DeadProductionEliminator}.
036:         *
037:         * @author Robert Grimm
038:         * @version $Revision: 1.11 $
039:         */
040:        public class TreeExtractor extends Visitor {
041:
042:            /** The runtime. */
043:            protected final Runtime runtime;
044:
045:            /** The analyzer utility. */
046:            protected final Analyzer analyzer;
047:
048:            /** The common type operations. */
049:            protected final AST ast;
050:
051:            /** The flag for removing all elements from lexical productions. */
052:            protected final boolean keepLexical;
053:
054:            /** The flag for whether the current production is generic. */
055:            protected boolean isGeneric;
056:
057:            /** The flag for whether the current production is list-valued. */
058:            protected boolean isList;
059:
060:            /** The flag for whether the current production is text-only. */
061:            protected boolean isTextOnly;
062:
063:            /** The flag for whether the current production is token-level. */
064:            protected boolean isToken;
065:
066:            /**
067:             * The flag for whether the current production defines the semantic
068:             * value in an explicit action.
069:             */
070:            protected boolean setsValue;
071:
072:            /**
073:             * Create a new tree extractor.
074:             *
075:             * @param runtime The runtime.
076:             * @param analyzer The analyzer utility.
077:             * @param ast The type operations.
078:             * @param keepLexical The flag for keeping elements of text-only
079:             *   or token-level productions.
080:             */
081:            public TreeExtractor(Runtime runtime, Analyzer analyzer, AST ast,
082:                    boolean keepLexical) {
083:                this .runtime = runtime;
084:                this .analyzer = analyzer;
085:                this .ast = ast;
086:                this .keepLexical = keepLexical;
087:            }
088:
089:            /** Visit the specified module. */
090:            public void visit(Module m) {
091:                // Initialize the per-grammar state.
092:                analyzer.register(this );
093:                analyzer.init(m);
094:
095:                // Process the productions.
096:                for (Production p : m.productions) {
097:                    analyzer.process(p);
098:                }
099:
100:                // Simplify the grammar and eliminate any dead productions.
101:                new Simplifier(runtime, analyzer).dispatch(m);
102:                new DeadProductionEliminator(runtime, analyzer).dispatch(m);
103:
104:                // Eliminate any actions and attributes.
105:                m.header = null;
106:                m.body = null;
107:                m.footer = null;
108:                m.attributes = null;
109:
110:                // Eliminate the production's attributes and internal types.
111:                for (Production p : m.productions) {
112:                    p.attributes = null;
113:                    p.type = null;
114:                }
115:            }
116:
117:            /** Visit the specified full production. */
118:            public void visit(FullProduction p) {
119:                // Initialize the per-production state.
120:                isGeneric = Generifier.isGeneric(p);
121:                isList = AST.isList(p.type);
122:                isTextOnly = p.getBooleanProperty(Properties.TEXT_ONLY);
123:                isToken = p.getBooleanProperty(Properties.TOKEN);
124:                setsValue = false;
125:
126:                // Preprocess directly left-recursive generic productions.
127:                if (isGeneric && DirectLeftRecurser.isTransformable(p)) {
128:                    for (Sequence s : p.choice.alternatives) {
129:                        if (!DirectLeftRecurser.isRecursive(s, p)) {
130:                            Binding b = analyzer.bind(s.elements);
131:                            if (null != b)
132:                                b.name = CodeGenerator.VALUE;
133:                        }
134:                    }
135:                }
136:
137:                // Process the choice.
138:                if ((isTextOnly || isToken) && (!keepLexical)) {
139:                    p.choice = new OrderedChoice(new Sequence());
140:                    p.setProperty(Properties.REDACTED, Boolean.TRUE);
141:                } else {
142:                    dispatch(p.choice);
143:                }
144:
145:                // Patch the type.
146:                final String s = ast.extern(p.type);
147:                if (isGeneric) {
148:                    p.dType = "define<Node>";
149:                } else if (isTextOnly) {
150:                    p.dType = "define<String>";
151:                } else if (isToken) {
152:                    p.dType = "define<Token>";
153:                } else if (isList) {
154:                    p.dType = "define<" + s + '>';
155:                } else if (setsValue) {
156:                    p.dType = "define<" + s + '>';
157:                } else {
158:                    p.dType = "expand<" + s + '>';
159:                }
160:            }
161:
162:            /** Visit the specified ordered choice. */
163:            public void visit(OrderedChoice c) {
164:                for (Sequence alt : c.alternatives)
165:                    dispatch(alt);
166:            }
167:
168:            /** Visit the specified sequence. */
169:            public void visit(Sequence s) {
170:                // Eliminate the sequence name.
171:                s.name = null;
172:
173:                // Process the elements.
174:                for (int i = 0; i < s.size(); i++) {
175:                    Element e = s.get(i);
176:
177:                    // If the element is a trailing choice, process its sequences.
178:                    if ((s.size() - 1 == i) && (e instanceof  OrderedChoice)) {
179:                        dispatch(e);
180:                        continue;
181:                    }
182:
183:                    // If the element is a voided element, semantic predicate, or
184:                    // value element, remove the element and move on to the next
185:                    // element.
186:                    if ((e instanceof  VoidedElement)
187:                            || (e instanceof  SemanticPredicate)
188:                            || (e instanceof  ValueElement)) {
189:                        s.elements.remove(i);
190:                        i--;
191:                        continue;
192:                    }
193:
194:                    // If the element is an action that sets the semantic value,
195:                    // simplify it.  Otherwise, remove the action.
196:                    if (e instanceof  Action) {
197:                        Action a = (Action) e;
198:
199:                        if (a.setsValue()) {
200:                            setsValue = true;
201:
202:                            a.code.clear();
203:                            a.indent.clear();
204:
205:                            a.code.add("yyValue = ...");
206:                            a.indent.add(0);
207:
208:                        } else {
209:                            s.elements.remove(i);
210:                            i--;
211:                        }
212:                        continue;
213:                    }
214:
215:                    // Process bindings.  In generic productions, we get rid of
216:                    // bindings unless they bind yyValue (since they indicate a
217:                    // passed-through value).  In productions that are neither
218:                    // generic, text-valued, or text-only, we get rid of elements if
219:                    // they are not bound (since they cannot contribute to a
220:                    // semantic value).
221:                    if (e instanceof  Binding) {
222:                        Binding b = (Binding) e;
223:
224:                        if ((!isGeneric)
225:                                || (isGeneric && (!CodeGenerator.VALUE
226:                                        .equals(b.name)))) {
227:                            e = b.element;
228:                            s.elements.set(i, e);
229:                        }
230:                        // Continue processing the element.
231:
232:                    } else if ((!isGeneric) && (!isList) && (!isTextOnly)
233:                            && (!isToken)) {
234:                        s.elements.remove(i);
235:                        i--;
236:                        continue;
237:                    }
238:
239:                    // Remove any void nonterminals.
240:                    if (e instanceof  NonTerminal) {
241:                        FullProduction p = analyzer.lookup((NonTerminal) e);
242:
243:                        if (AST.isVoid(p.type)) {
244:                            s.elements.remove(i);
245:                            i--;
246:                            continue;
247:                        }
248:                    }
249:
250:                    // Process the element.
251:                    dispatch(e);
252:                }
253:            }
254:
255:            /** Visit the specified character case. */
256:            public void visit(CharCase c) {
257:                dispatch(c.element);
258:            }
259:
260:            /** Visit the specified character switch. */
261:            public void visit(CharSwitch s) {
262:                for (CharCase c : s.cases) {
263:                    dispatch(c);
264:                }
265:                dispatch(s.base);
266:            }
267:
268:            /** Visit the specified unary operator. */
269:            public void visit(UnaryOperator op) {
270:                dispatch(op.element);
271:
272:                // Strip any unnecessary choices and sequences.
273:                op.element = Analyzer.strip(op.element);
274:            }
275:
276:            /** Visit the specified element. */
277:            public void visit(Element e) {
278:                // Nothing to do.
279:            }
280:
281:        }
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