|
1
22
23 package org.javacc.parser;
24
25 import java.util.Vector  ;
26
27 public class LookaheadCalc extends JavaCCGlobals {
28
29 static MatchInfo overlap(Vector v1, Vector v2) {
30 MatchInfo m1, m2, m3;
31 int size;
32 boolean diff;
33 for (int i = 0; i < v1.size(); i++) {
34 m1 = (MatchInfo)v1.elementAt(i);
35 for (int j = 0; j < v2.size(); j++) {
36 m2 = (MatchInfo)v2.elementAt(j);
37 size = m1.firstFreeLoc; m3 = m1;
38 if (size > m2.firstFreeLoc) {
39 size = m2.firstFreeLoc; m3 = m2;
40 }
41 if (size == 0) return null;
42 diff = false;
44 for (int k = 0; k < size; k++) {
45 if (m1.match[k] != m2.match[k]) {
46 diff = true;
47 break;
48 }
49 }
50 if (!diff) return m3;
51 }
52 }
53 return null;
54 }
55
56 static boolean javaCodeCheck(Vector v) {
57 for (int i = 0; i < v.size(); i++) {
58 if (((MatchInfo)v.elementAt(i)).firstFreeLoc == 0) {
59 return true;
60 }
61 }
62 return false;
63 }
64
65 static String image(MatchInfo m) {
66 String ret = "";
67 for (int i = 0; i < m.firstFreeLoc; i++) {
68 if (m.match[i] == 0) {
69 ret += " <EOF>";
70 } else {
71 RegularExpression re = (RegularExpression)rexps_of_tokens.get(new Integer (m.match[i]));
72 if (re instanceof RStringLiteral) {
73 ret += " \"" + add_escapes(((RStringLiteral)re).image) + "\"";
74 } else if (re.label != null && !re.label.equals("")) {
75 ret += " <" + re.label + ">";
76 } else {
77 ret += " <token of kind " + i + ">";
78 }
79 }
80 }
81 if (m.firstFreeLoc == 0) {
82 return "";
83 } else {
84 return ret.substring(1);
85 }
86 }
87
88 public static void choiceCalc(Choice ch) {
89 int first = firstChoice(ch);
90 Vector [] dbl = new Vector [ch.choices.size()];
94 Vector [] dbr = new Vector [ch.choices.size()];
95 int[] minLA = new int[ch.choices.size()-1];
96 MatchInfo[] overlapInfo = new MatchInfo[ch.choices.size()-1];
97 int[] other = new int[ch.choices.size()-1];
98 MatchInfo m;
99 Vector v;
100 boolean overlapDetected;
101 for (int la = 1; la <= Options.getChoiceAmbiguityCheck(); la++) {
102 MatchInfo.laLimit = la;
103 LookaheadWalk.considerSemanticLA = !Options.getForceLaCheck();
104 for (int i = first; i < ch.choices.size()-1; i++) {
105 LookaheadWalk.sizeLimitedMatches = new java.util.Vector ();
106 m = new MatchInfo();
107 m.firstFreeLoc = 0;
108 v = new java.util.Vector ();
109 v.addElement(m);
110 LookaheadWalk.genFirstSet(v, (Expansion)ch.choices.elementAt(i));
111 dbl[i] = LookaheadWalk.sizeLimitedMatches;
112 }
113 LookaheadWalk.considerSemanticLA = false;
114 for (int i = first+1; i < ch.choices.size(); i++) {
115 LookaheadWalk.sizeLimitedMatches = new java.util.Vector ();
116 m = new MatchInfo();
117 m.firstFreeLoc = 0;
118 v = new java.util.Vector ();
119 v.addElement(m);
120 LookaheadWalk.genFirstSet(v, (Expansion)ch.choices.elementAt(i));
121 dbr[i] = LookaheadWalk.sizeLimitedMatches;
122 }
123 if (la == 1) {
124 for (int i = first; i < ch.choices.size()-1; i++) {
125 Expansion exp = (Expansion)ch.choices.elementAt(i);
126 if (Semanticize.emptyExpansionExists(exp)) {
127 JavaCCErrors.warning(exp, "This choice can expand to the empty token sequence and will therefore always be taken in favor of the choices appearing later.");
128 break;
129 } else if (javaCodeCheck(dbl[i])) {
130 JavaCCErrors.warning(exp, "JAVACODE non-terminal will force this choice to be taken in favor of the choices appearing later.");
131 break;
132 }
133 }
134 }
135 overlapDetected = false;
136 for (int i = first; i < ch.choices.size()-1; i++) {
137 for (int j = i+1; j < ch.choices.size(); j++) {
138 if ((m = overlap(dbl[i], dbr[j])) != null) {
139 minLA[i] = la+1;
140 overlapInfo[i] = m;
141 other[i] = j;
142 overlapDetected = true;
143 break;
144 }
145 }
146 }
147 if (!overlapDetected) {
148 break;
149 }
150 }
151 for (int i = first; i < ch.choices.size()-1; i++) {
152 if (explicitLA((Expansion)ch.choices.elementAt(i)) && !Options.getForceLaCheck()) {
153 continue;
154 }
155 if (minLA[i] > Options.getChoiceAmbiguityCheck()) {
156 JavaCCErrors.warning("Choice conflict involving two expansions at");
157 System.err.print(" line " + ((Expansion)ch.choices.elementAt(i)).line);
158 System.err.print(", column " + ((Expansion)ch.choices.elementAt(i)).column);
159 System.err.print(" and line " + ((Expansion)ch.choices.elementAt(other[i])).line);
160 System.err.print(", column " + ((Expansion)ch.choices.elementAt(other[i])).column);
161 System.err.println(" respectively.");
162 System.err.println(" A common prefix is: " + image(overlapInfo[i]));
163 System.err.println(" Consider using a lookahead of " + minLA[i] + " or more for earlier expansion.");
164 } else if (minLA[i] > 1) {
165 JavaCCErrors.warning("Choice conflict involving two expansions at");
166 System.err.print(" line " + ((Expansion)ch.choices.elementAt(i)).line);
167 System.err.print(", column " + ((Expansion)ch.choices.elementAt(i)).column);
168 System.err.print(" and line " + ((Expansion)ch.choices.elementAt(other[i])).line);
169 System.err.print(", column " + ((Expansion)ch.choices.elementAt(other[i])).column);
170 System.err.println(" respectively.");
171 System.err.println(" A common prefix is: " + image(overlapInfo[i]));
172 System.err.println(" Consider using a lookahead of " + minLA[i] + " for earlier expansion.");
173 }
174 }
175 }
176
177 static boolean explicitLA(Expansion exp) {
178 if (!(exp instanceof Sequence)) {
179 return false;
180 }
181 Sequence seq = (Sequence)exp;
182 Object obj = seq.units.elementAt(0);
183 if (!(obj instanceof Lookahead)) {
184 return false;
185 }
186 Lookahead la = (Lookahead)obj;
187 return la.isExplicit;
188 }
189
190 static int firstChoice(Choice ch) {
191 if (Options.getForceLaCheck()) {
192 return 0;
193 }
194 for (int i = 0; i < ch.choices.size(); i++) {
195 if (!explicitLA((Expansion)ch.choices.elementAt(i))) {
196 return i;
197 }
198 }
199 return ch.choices.size();
200 }
201
202 private static String image(Expansion exp) {
203 if (exp instanceof OneOrMore) {
204 return "(...)+";
205 } else if (exp instanceof ZeroOrMore) {
206 return "(...)*";
207 } else {
208 return "[...]";
209 }
210 }
211
212 public static void ebnfCalc(Expansion exp, Expansion nested) {
213 MatchInfo m, m1 = null;
215 Vector v, first, follow;
216 int la;
217 for (la = 1; la <= Options.getOtherAmbiguityCheck(); la++) {
218 MatchInfo.laLimit = la;
219 LookaheadWalk.sizeLimitedMatches = new java.util.Vector ();
220 m = new MatchInfo();
221 m.firstFreeLoc = 0;
222 v = new java.util.Vector ();
223 v.addElement(m);
224 LookaheadWalk.considerSemanticLA = !Options.getForceLaCheck();
225 LookaheadWalk.genFirstSet(v, nested);
226 first = LookaheadWalk.sizeLimitedMatches;
227 LookaheadWalk.sizeLimitedMatches = new java.util.Vector ();
228 LookaheadWalk.considerSemanticLA = false;
229 LookaheadWalk.genFollowSet(v, exp, Expansion.nextGenerationIndex++);
230 follow = LookaheadWalk.sizeLimitedMatches;
231 if (la == 1) {
232 if (javaCodeCheck(first)) {
233 JavaCCErrors.warning(nested, "JAVACODE non-terminal within " + image(exp) + " construct will force this construct to be entered in favor of expansions occurring after construct.");
234 }
235 }
236 if ((m = overlap(first, follow)) == null) {
237 break;
238 }
239 m1 = m;
240 }
241 if (la > Options.getOtherAmbiguityCheck()) {
242 JavaCCErrors.warning("Choice conflict in " + image(exp) + " construct at line " + exp.line + ", column " + exp.column + ".");
243 System.err.println(" Expansion nested within construct and expansion following construct");
244 System.err.println(" have common prefixes, one of which is: " + image(m1));
245 System.err.println(" Consider using a lookahead of " + la + " or more for nested expansion.");
246 } else if (la > 1) {
247 JavaCCErrors.warning("Choice conflict in " + image(exp) + " construct at line " + exp.line + ", column " + exp.column + ".");
248 System.err.println(" Expansion nested within construct and expansion following construct");
249 System.err.println(" have common prefixes, one of which is: " + image(m1));
250 System.err.println(" Consider using a lookahead of " + la + " for nested expansion.");
251 }
252 }
253
254 }
255 |
Popular Tags |
Java API By Example, From Geeks To Geeks.