Merge pull request #3 from ironmeld/fix-follow-epsilon

Fix problems with follow sets, epsilon, and the LR0 action table.
amirhossein-hkh · Feb 22, 2020 · 40f1271 · 40f1271
2 parents 1371bf1 + e81d26a
commit 40f1271
Show file tree

Hide file tree

Showing 3 changed files with 19 additions and 11 deletions.
diff --git a/src/lr0/LR0Parser.java b/src/lr0/LR0Parser.java
@@ -141,7 +141,7 @@ private boolean createActionTableForLR0() {
         for (int i = 0; i < canonicalCollection.size(); i++) {
             for (LR0Item item : canonicalCollection.get(i).getItems()) {
                 if (item.getDotPointer() == item.getRightSide().length) {
-                    if (item.getLeftSide().equals("s'")) {
+                    if (item.getLeftSide().equals("S'")) {
                         actionTable[i].put("$", new Action(ActionType.ACCEPT, 0));
                     } else {
                         HashSet<String> terminals = grammar.getTerminals();

diff --git a/src/lr1/LR1State.java b/src/lr1/LR1State.java
@@ -38,7 +38,12 @@ private void closure(Grammar grammar) {
                     }
                     HashSet<Rule> rules = grammar.getRuledByLeftVariable(item.getCurrent());
                     for(Rule rule : rules){
-                        temp.add(new LR1Item(rule.getLeftSide(),rule.getRightSide(),0,lookahead));
+                        String[] rhs = rule.getRightSide();
+                        int finished = 0;
+                        if (rhs.length == 1 && rhs[0].equals("epsilon")) {
+                            finished = 1;
+                        }
+                        temp.add(new LR1Item(rule.getLeftSide(),rhs,finished,lookahead));
                     }
                 }
             }

diff --git a/src/util/Grammar.java b/src/util/Grammar.java
@@ -31,7 +31,9 @@ public Grammar(String s) {
             for (String rule : rulesRightSide) {
                 String[] rightSide = rule.trim().split("\\s+");
                 for (String terminal : rightSide) {
-                    terminals.add(terminal);
+                    if (!terminal.equals("epsilon")) {
+                        terminals.add(terminal);
+                    }
                 }
 
                 if (line == 0) {
@@ -123,18 +125,19 @@ private void computeFollowSet() {
                 for (Rule rule : rules) {
                     for (int i = 0; i < rule.getRightSide().length; i++) {
                         if (rule.getRightSide()[i].equals(variable)) {
+                            HashSet<String> first;
                             if (i == rule.getRightSide().length - 1) {
-                                fallowSets.get(variable).addAll(fallowSets.get(rule.leftSide));
+                                first = fallowSets.get(rule.leftSide);
                             } else {
-                                HashSet<String> first = computeFirst(rule.getRightSide(), i + 1);
+                                first = computeFirst(rule.getRightSide(), i + 1);
                                 if (first.contains("epsilon")) {
                                     first.remove("epsilon");
                                     first.addAll(fallowSets.get(rule.leftSide));
                                 }
-                                if (!fallowSets.get(variable).containsAll(first)) {
-                                    isChange = true;
-                                    fallowSets.get(variable).addAll(first);
-                                }
+                            }
+                            if (!fallowSets.get(variable).containsAll(first)) {
+                                isChange = true;
+                                fallowSets.get(variable).addAll(first);
                             }
                         }
                     }
@@ -151,7 +154,7 @@ public HashSet<String> computeFirst(String[] string, int index) {
         if (index == string.length) {
             return first;
         }
-        if (terminals.contains(string[index])) {
+        if (terminals.contains(string[index]) || string[index].equals("epsilon")) {
             first.add(string[index]);
             return first;
         }
@@ -164,8 +167,8 @@ public HashSet<String> computeFirst(String[] string, int index) {
 
         if (first.contains("epsilon")) {
             if (index != string.length - 1) {
-                first.addAll(computeFirst(string, index + 1));
                 first.remove("epsilon");
+                first.addAll(computeFirst(string, index + 1));
             }
         }
         return first;