sync

src/grammar.py

@@ -2,15 +2,16 @@ from terminal import Terminal
 from nonTerminal import NonTerminal
 
 class Grammar:
-    __atomKeyMapping = []
-    __productions = []
-    __first = {}
+    def __init__(self):
+        self.__nonTerminals = {}
+        self.__terminals = {}
+        self.__startSymbol = None;
+        self.__endMarker = Terminal("$")
 
-    __nonTerminals = {}
-    __terminals = {}
-    
     def addProduction(self, nonTerminal, atoms):
-
+        if self.__startSymbol == None:
+            self.__startSymbol = nonTerminal;
+            self.__startSymbol.addToFollowSet(self.__endMarker);
 
         self.__addAtom(nonTerminal);
 
@@ -45,6 +46,7 @@ class Grammar:
 
     def generateMetrics(self):
         self.__generateFirstSets()
+        self.__generateFollowSets()
 
 
     def __generateFirstSets(self):
@@ -52,6 +54,9 @@ class Grammar:
             nonTerminal = self.__nonTerminals[key]
             nonTerminal.generateFirstSet();
 
+    def __generateFollowSets(self):
+        for key in self.__nonTerminals:
+            self.__nonTerminals[key].generateFollowSet()
 
     def printNullableSet(self):
         output = "Nullable = { "

src/nonTerminal.py

@@ -6,6 +6,7 @@ class NonTerminal:
         self.__isNullable = False
         self.__productions = []
         self.__first = []
+        self.__follow = []
         self.__firstSetIsGenerated = False;
 
         self.__string = string
@@ -49,6 +50,45 @@ class NonTerminal:
 
         self.__firstSetIsGenrated = True;
 
+    def addToFollowSet(self, marker):
+        self.__follow.append(marker)
+
+    def generateFollowSet(self):
+        for production in self.__productions:
+            self.__extendFollowSetsBasedOnProduction(production)
+
+    def __extendFollowSetsBasedOnProduction(self, production):
+        for i in range(len(production)):
+            atom = production[i]
+
+            if isinstance(atom, NonTerminal):
+                if self.__isPossiblyLastInProduction(i, production):
+                    atom.extendFollowWithFollowOf(self)
+                else:
+                    atom.extendFollowWithFirstOf(production[i + 1])
+
+    def __isPossiblyLastInProduction(self, index, production):
+        for j in range(index, len(production)):
+            if isinstance(production[j], Terminal):
+                return False
+
+            if not production[j].isNullable():
+                return False
+
+        return True
+
+    def extendFollowWithFollowOf(self, atom):
+        for el in atom.getFollowSet():
+            self.addToFollowSet(el)
+
+    def extendFollowWithFirstOf(self, atom):
+        for el in atom.getFirstSet():
+            if not el.isEmptyString():
+                self.addToFollowSet(el)
+
+    def getFollowSet(self):
+        return self.__follow
+
     def __addFirsSetForProduction(self, production):
         stillNullable = True
         lenProd = len(production)

src/testParser.py

@@ -18,5 +18,3 @@ grm.printNullableSet()
 
 print("----------------")
 grm.printFirstSets()
-
-#prs.printGrammar();