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Get rid of the first_terminal variable in the grammar generator

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Dave Halter
2018-06-26 09:48:13 +02:00
parent 5d46c3e18b
commit 7b7b66eb3c
1 changed files with 15 additions and 15 deletions
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30
parso/pgen2/grammar.py
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@@ -46,13 +46,12 @@ class Grammar(object):
def _make_grammar(self):
# Map from grammar rule (nonterminal) name to a set of tokens.
self._first_terminals = {}
self._first_plans = {}
nonterminals = list(self._nonterminal_to_dfas.keys())
nonterminals.sort()
for nonterminal in nonterminals:
if nonterminal not in self._first_terminals:
if nonterminal not in self._first_plans:
self._calculate_first_terminals(nonterminal)
# Now that we have calculated the first terminals, we are sure that
@@ -66,34 +65,35 @@ class Grammar(object):
def _calculate_first_terminals(self, nonterminal):
dfas = self._nonterminal_to_dfas[nonterminal]
self._first_terminals[nonterminal] = None # dummy to detect left recursion
first_plans = self._first_plans[nonterminal] = {}
new_first_plans = {}
self._first_plans[nonterminal] = None # dummy to detect left recursion
# We only need to check the first dfa. All the following ones are not
# interesting to find first terminals.
state = dfas[0]
for transition, next_ in state.ilabel_to_plan.items():
# It's a string. We have finally found a possible first token.
first_plans[transition] = [next_.next_dfa]
for nonterminal2, next_ in state.nonterminal_arcs.items():
# It's a nonterminal and we have either a left recursion issue
# in the grammar or we have to recurse.
try:
fset = self._first_terminals[nonterminal2]
first_plans2 = self._first_plans[nonterminal2]
except KeyError:
self._calculate_first_terminals(nonterminal2)
first_plans2 = self._calculate_first_terminals(nonterminal2)
else:
if fset is None:
if first_plans2 is None:
raise ValueError("left recursion for rule %r" % nonterminal)
for t, pushes in self._first_plans[nonterminal2].items():
check = first_plans.get(t)
for t, pushes in first_plans2.items():
check = new_first_plans.get(t)
if check is not None:
raise ValueError(
"Rule %s is ambiguous; %s is the"
" start of the rule %s as well as %s."
% (nonterminal, t, nonterminal2, check[-1].from_rule)
)
first_plans[t] = [next_] + pushes
new_first_plans[t] = [next_] + pushes
self._first_terminals[nonterminal] = 1
for transition, next_ in state.ilabel_to_plan.items():
# It's a string. We have finally found a possible first token.
new_first_plans[transition] = [next_.next_dfa]
self._first_plans[nonterminal] = new_first_plans
return new_first_plans