def test_book_example(self):
"""
S -> i E t S | i E t S e S | a
E -> b
"""
solved = f.parse_bnf(test_data.solved_left_factoring)
unsolved = f.parse_bnf(test_data.unsolved_left_factoring)
g = f.remove_left_factoring(unsolved)
self.assertEqual(solved, g)
def test_cases(self):
try:
for case in test_data.examples:
g = f.parse_bnf(case)
h = f.remove_left_recursion(g)
i = f.remove_left_factoring(h)
for x in i.nonterminals:
i.first(x)
except Exception as e:
self.fail(str(e))
def do_the_whole_thing(grammar_text,
epsilon='ε',
eof='$',
output=None,
verbose=True):
file = None
if output:
file = open(output, 'w')
sys.stdout = file
vprint = print if verbose else lambda *a, **key: None # Only print if verbose is True
vprint("Original:")
g = parse_bnf(grammar_text, epsilon=epsilon, eof=eof)
vprint(g)
vprint("\nAfter removing left-recursion:")
g = remove_left_recursion(g)
vprint(g)
vprint("\nAfter removing left-factoring:")
g = remove_left_factoring(g)
vprint(g)
vprint()
for nt in g.nonterminals:
vprint('FIRST({}) = {}'.format(nt, g.first(nt)))
vprint()
follow = [(nt, g.follow(nt)) for nt in g.nonterminals]
for nt, f in follow:
vprint('FOLLOW({}) = {}'.format(nt, f))
vprint()
table, ambiguous = g.parsing_table()
vprint("Parsing Table: ")
if ambiguous:
vprint(
"El lenguaje de entrada no es LL(1) debido a que se encontraron ambigüedades."
)
vprint()
pprint_table(g, table)
if file:
file.close()
def parsing_table(self, is_clean=True):
"""
Compute LL(1) predictive parsing table
:param is_clean: If False, will remove left factoring and left recursions.
:return: parsing table
"""
from parser.functions import remove_left_recursion, remove_left_factoring # To avoid cyclic import
equiv = self if is_clean else remove_left_recursion(remove_left_factoring(copy(self)))
table = {}
ambigous = False
for r in equiv.iter_productions():
terminals = equiv.first(r.body)
for t in terminals:
if not equiv.is_terminal(t):
continue
if t == equiv.epsilon:
f = equiv.follow(r.head)
for ef in f:
if (table.get((r.head, ef))):
ls = []
ls.append(table[(r.head, ef)])
ls.append(r)
table[(r.head, ef)] = ls
ambigous = True
else:
table[(r.head, ef)] = r
else:
if (table.get((r.head, t))):
ls = []
ls.append(table[(r.head, t)])
ls.append(r)
table[(r.head, t)] = ls
ambigous = True
else:
table[(r.head, t)] = r
return (table, ambigous)
def just_do_it(req):
errors = []
g = None
grammar_not_recursive = None
grammar_not_factor = None
parsing_table = None
try:
g = parse_bnf(req.form['bnf'],
epsilon=req.form['epsilon'],
eof=req.form['eof'])
grammar_not_recursive = remove_left_recursion(g)
grammar_not_factor = remove_left_factoring(grammar_not_recursive)
table, ambiguous = grammar_not_factor.parsing_table()
if ambiguous:
errors.append(
'El lenguaje de entrada no es LL(1) debido a que se encontraron ambigüedades.'
)
parsing_table = {
'table': table,
'terminals': sorted(set(g.terminals) - {g.epsilon}) + [g.eof],
'nonterminals': [nt for nt in grammar_not_factor.nonterminals]
}
except InvalidGrammar:
errors.append(
'Gramática inválida. Revise las especificaciones de BNF.')
except InvalidProduction as e:
errors.append('Produccion invalida: {}.'.format(e.production))
return render_template('results.html',
grammar=g,
no_recursion=grammar_not_recursive,
no_factor=grammar_not_factor,
parsing_table=parsing_table,
errors=errors)
def test_cases(self):
for case in test_data.examples:
g = f.parse_bnf(case)
g = f.remove_left_factoring(g)
self.assertFalse(f.check_left_factors(g),
msg='{} has left factors'.format(g))