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Began refactoring of lalr_analysis -> grammar_analysis

This commit is contained in:
Erez Shinan 2017-02-20 00:11:56 +02:00
parent 07df4b80eb
commit 972034fd2d
1 changed files with 54 additions and 52 deletions
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106
lark/parsers/lalr_analysis.py
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@ -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):