def _non_nullable_head(self, symbol):
"Returns the non-nullable subset of the FIRST set of the given symbol."
if symbol == '':
return set_new()
elif is_nonterminal(symbol):
return [s for s in self._first[symbol] if s != '']
else:
return set_new([symbol])
def _fill_table(self, nonterminal, terminal, production):
"""Adds the given production to the entry (nonterminal, terminal) of
the parsing table."""
key = (nonterminal, terminal)
if key not in self._parse_table:
self._parse_table[key] = set_new()
self._parse_table[key][id(production)] = production
def first(self, alpha):
"""Returns the FIRST set of a string alpha (FIRST(alpha)).
A terminal symbol x is in FIRST(alpha) iff alpha =>* x...
The empty string '' is in FIRST(alpha) iff alpha =>* ''"""
first_set = set_new()
self._build_first_seq(first_set, alpha)
return first_set
def _build_table(self):
"Builds the LL(1) parsing table."
self._parse_table = {}
for nonterminal in self.all_nonterminals():
for production in self.syntax[nonterminal]:
follow = set_new()
self._build_follow_seq(nonterminal, follow, production.rule)
for terminal in follow:
self._fill_table(nonterminal, terminal, production)
def _build_follow(self):
"Builds a table that associates each nonterminal with its FOLLOW set."
self._follow = {}
for nonterminal in self.all_nonterminals():
self._follow[nonterminal] = set_new()
self._follow['<start>'] = set_new(['EOF'])
change = True
while change:
change = False
for nonterminal in self.all_nonterminals():
for production in self.syntax[nonterminal]:
for i in range(len(production.rule)):
rule = production.rule[i]
if not is_nonterminal(rule):
continue
beta = production.rule[i + 1:]
if self._build_follow_seq(nonterminal,
self._follow[rule],
beta):
change = True
def _build_first(self):
"""Builds a table that associates each nonterminal with
its FIRST set."""
self._first = {}
for nonterminal in self.all_nonterminals():
self._first[nonterminal] = set_new()
change = True
while change:
change = False
for nonterminal in self.all_nonterminals():
for production in self.syntax[nonterminal]:
if self._build_first_seq(self._first[nonterminal],
production.rule):
change = True
def push_env(self):
"Push an empty environment into the stack of environment ribs."
self.ribs.append(set_new())
def __init__(self, enable_errors):
self.ribs = [set_new()]
self.global_context = {}
self.context = {}
self.init_builtins()
self.enable_errors = enable_errors