def remove_rules_with_epsilon(grammar: Grammar,
transform_grammar=False) -> Grammar:
"""
Remove epsilon rules.
:param grammar: Grammar where rules remove
:param transform_grammar: True if transformation should be performed in place, false otherwise.
False by default.
:return: Grammar without epsilon rules.
"""
# Copy if required
if transform_grammar is False: grammar = copy(grammar)
# Find nonterminals rewritable to epsilon
rewritable = find_nonterminals_rewritable_to_epsilon(grammar)
# Create list from rules
rules = list(grammar.rules())
index = 0
# Iterate thought rules
while index < len(rules):
rule = rules[index]
index += 1
right = rule.right
if right == [EPSILON]:
if not grammar.start_isSet(
) or rule.fromSymbol != grammar.start_get():
grammar.remove_rule(rule)
# Continue IS executed, but due optimalization line is marked as missed.
continue #pragma: no cover
for rule_index in range(len(right)):
symbol = right[rule_index]
if symbol in rewritable:
new_rule = _create_rule(rule, rule_index, rewritable)
rules.append(new_rule)
grammar.add_rule(new_rule)
return grammar
def remove_unreachable_symbols(grammar: Grammar,
transform_grammar=False) -> Grammar:
"""
Remove unreachable symbols from the gramar
:param grammar: Grammar where to symbols remove
:param transform_grammar: True if transformation should be performed in place, false otherwise.
False by default.
:return: Grammar without unreachable symbols.
"""
# Copy if required
if transform_grammar is False: grammar = copy(grammar)
# Check if start symbol is set
if not grammar.start_isSet(): raise StartSymbolNotSpecifiedException()
# Create process sets
reachable = {grammar.start_get()}
rules = grammar.rules()
# Begin iterations
while True:
# Create sets for current iteration
active = reachable.copy()
processedRules = []
# Loop rest of rules
for rule in rules:
# If left part of rule already in reachable symbols
if rule.fromSymbol in reachable:
# Set symbols as reachable
processedRules.append(rule)
for symbol in rule.right:
active.add(symbol)
# End of rules loop
# Remove processed rules
for item in processedRules:
rules.remove(item)
# If current and previous iterations are same, than end iterations
if active == reachable: break
reachable = active
# End of iterations
# Set symbols to remove
allSymbols = set(grammar.nonterms()).union(
set(x.s for x in grammar.terms()))
for symbol in allSymbols.difference(reachable):
try:
grammar.remove_nonterm(symbol)
except NotNonterminalException:
grammar.remove_term(symbol)
return grammar
