Began refactoring of lalr_analysis -> grammar_analysis

lark/parsers/lalr_analysis.py

@@ -57,6 +57,58 @@ def update_set(set1, set2):
     set1 |= set2
     return set1 != copy
 
+def calculate_sets(rules):
+    """Calculate FOLLOW sets.
+
+    Adapted from: http://lara.epfl.ch/w/cc09:algorithm_for_first_and_follow_sets"""
+    symbols = {sym for rule in rules for sym in rule.expansion} | {rule.origin for rule in rules}
+    symbols.add('$root')    # what about other unused rules?
+
+    # foreach grammar rule X ::= Y(1) ... Y(k)
+    # if k=0 or {Y(1),...,Y(k)} subset of NULLABLE then
+    #   NULLABLE = NULLABLE union {X}
+    # for i = 1 to k
+    #   if i=1 or {Y(1),...,Y(i-1)} subset of NULLABLE then
+    #     FIRST(X) = FIRST(X) union FIRST(Y(i))
+    #   for j = i+1 to k
+    #     if i=k or {Y(i+1),...Y(k)} subset of NULLABLE then
+    #       FOLLOW(Y(i)) = FOLLOW(Y(i)) union FOLLOW(X)
+    #     if i+1=j or {Y(i+1),...,Y(j-1)} subset of NULLABLE then
+    #       FOLLOW(Y(i)) = FOLLOW(Y(i)) union FIRST(Y(j))
+    # until none of NULLABLE,FIRST,FOLLOW changed in last iteration
+
+    NULLABLE = set()
+    FIRST = {}
+    FOLLOW = {}
+    for sym in symbols:
+        FIRST[sym]={sym} if is_terminal(sym) else set()
+        FOLLOW[sym]=set()
+
+    changed = True
+    while changed:
+        changed = False
+
+        for rule in rules:
+            if set(rule.expansion) <= NULLABLE:
+                if update_set(NULLABLE, {rule.origin}):
+                    changed = True
+
+            for i, sym in enumerate(rule.expansion):
+                if set(rule.expansion[:i]) <= NULLABLE:
+                    if update_set(FIRST[rule.origin], FIRST[sym]):
+                        changed = True
+                if i==len(rule.expansion)-1 or set(rule.expansion[i:]) <= NULLABLE:
+                    if update_set(FOLLOW[sym], FOLLOW[rule.origin]):
+                        changed = True
+
+                for j in range(i+1, len(rule.expansion)):
+                    if set(rule.expansion[i+1:j]) <= NULLABLE:
+                        if update_set(FOLLOW[sym], FIRST[rule.expansion[j]]):
+                            changed = True
+
+    return FIRST, FOLLOW, NULLABLE
+
+
 class GrammarAnalyzer(object):
     def __init__(self, rule_tuples, start_symbol, debug=False):
         self.start_symbol = start_symbol
@@ -79,6 +131,8 @@ class GrammarAnalyzer(object):
 
         self.init_state = self.expand_rule(start_symbol)
 
+        self.FIRST, self.FOLLOW, self.NULLABLE = calculate_sets(self.rules)
+
     def expand_rule(self, rule):
         "Returns all init_ptrs accessible by rule (recursive)"
         init_ptrs = set()
@@ -104,59 +158,7 @@ class GrammarAnalyzer(object):
         else:
             return {rp.next for rp in self.expand_rule(r) if is_terminal(rp.next)}
 
-    def _calc(self):
-        """Calculate FOLLOW sets.
-
-        Adapted from: http://lara.epfl.ch/w/cc09:algorithm_for_first_and_follow_sets"""
-        symbols = {sym for rule in self.rules for sym in rule.expansion} | {rule.origin for rule in self.rules}
-        symbols.add('$root')    # what about other unused rules?
-
-        # foreach grammar rule X ::= Y(1) ... Y(k)
-        # if k=0 or {Y(1),...,Y(k)} subset of NULLABLE then
-        #   NULLABLE = NULLABLE union {X}
-        # for i = 1 to k
-        #   if i=1 or {Y(1),...,Y(i-1)} subset of NULLABLE then
-        #     FIRST(X) = FIRST(X) union FIRST(Y(i))
-        #   for j = i+1 to k
-        #     if i=k or {Y(i+1),...Y(k)} subset of NULLABLE then
-        #       FOLLOW(Y(i)) = FOLLOW(Y(i)) union FOLLOW(X)
-        #     if i+1=j or {Y(i+1),...,Y(j-1)} subset of NULLABLE then
-        #       FOLLOW(Y(i)) = FOLLOW(Y(i)) union FIRST(Y(j))
-        # until none of NULLABLE,FIRST,FOLLOW changed in last iteration
-
-        NULLABLE = set()
-        FIRST = {}
-        FOLLOW = {}
-        for sym in symbols:
-            FIRST[sym]={sym} if is_terminal(sym) else set()
-            FOLLOW[sym]=set()
-
-        changed = True
-        while changed:
-            changed = False
-
-            for rule in self.rules:
-                if set(rule.expansion) <= NULLABLE:
-                    if update_set(NULLABLE, {rule.origin}):
-                        changed = True
-
-                for i, sym in enumerate(rule.expansion):
-                    if set(rule.expansion[:i]) <= NULLABLE:
-                        if update_set(FIRST[rule.origin], FIRST[sym]):
-                            changed = True
-                    if i==len(rule.expansion)-1 or set(rule.expansion[i:]) <= NULLABLE:
-                        if update_set(FOLLOW[sym], FOLLOW[rule.origin]):
-                            changed = True
-
-                    for j in range(i+1, len(rule.expansion)):
-                        if set(rule.expansion[i+1:j]) <= NULLABLE:
-                            if update_set(FOLLOW[sym], FIRST[rule.expansion[j]]):
-                                changed = True
-
-        self.FOLLOW = FOLLOW
-
     def analyze(self):
-        self._calc()
 
         self.states = {}
         def step(state):