def test_ex433(self):
p = {"S" : [("i", "E", "t", "S", "S'"), ("a", )],
"S'" : [("e", "S"), ("epsilon",)],
"E" : [("b",)]}
g = Grammar("S", p, ["S", "S'", "E"], ["a", "b", "e", "i", "t"])
g.compute_first()
g.compute_follow()
g.compute_pred_parsing_tab()
self.assertEqual(g.first_tab, {'S': {'a', 'i'}, "S'": {'e', 'epsilon'}, 'E': {'b'}, 'a': {'a'}, 'b': {'b'}, 'e': {'e'}, 'i': {'i'}, 't': {'t'}})
self.assertEqual(g.follow_tab, {'S': {'e', '$'}, "S'": {'e', '$'}, 'E': {'t'}})
self.assertEqual(g.pred_parsing_tab, {'S': {'a': ['S -> a'], 'b': [], 'e': [], 'i': ["S -> iEtSS'"], 't': [], '$': []}, "S'": {'a': [], 'b': [], 'e': ["S' -> eS", "S' -> epsilon"], 'i': [], 't': [], '$': ["S' -> epsilon"]}, 'E': {'a': [], 'b': ['E -> b'], 'e': [], 'i': [], 't': [], '$': []}})
def test_ex430(self):
p = {"E" : [("T", "E'")],
"E'" : [("+", "T", "E'"), ("epsilon",)],
"T" : [("F", "T'")],
"T'" : [("*", "F", "T'"), ("epsilon",)],
"F" : [("(", "E", ")"), ("id",)]}
g = Grammar("E", p, ["E", "E'", "T", "T'", "F"], ["+", "*", "(", ")", "id"])
g.compute_first()
g.compute_follow()
g.compute_pred_parsing_tab()
self.assertEqual(g.first_tab, {'E': {'id', '('}, "E'": {'+', 'epsilon'}, 'T': {'id', '('}, "T'": {'*', 'epsilon'}, 'F': {'id', '('}, '+': {'+'}, '*': {'*'}, '(': {'('}, ')': {')'}, 'id': {'id'}})
self.assertEqual(g.follow_tab, {'E': {')', '$'}, "E'": {')', '$'}, 'T': {'+', ')', '$'}, "T'": {'+', '$', ')'}, 'F': {'+', '$', ')', '*'}})
self.assertEqual(g.pred_parsing_tab, {'E': {'+': [], '*': [], '(': ["E -> TE'"], ')': [], 'id': ["E -> TE'"], '$': []}, "E'": {'+': ["E' -> +TE'"], '*': [], '(': [], ')': ["E' -> epsilon"], 'id': [], '$': ["E' -> epsilon"]}, 'T': {'+': [], '*': [], '(': ["T -> FT'"], ')': [], 'id': ["T -> FT'"], '$': []}, "T'": {'+': ["T' -> epsilon"], '*': ["T' -> *FT'"], '(': [], ')': ["T' -> epsilon"], 'id': [], '$': ["T' -> epsilon"]}, 'F': {'+': [], '*': [], '(': ['F -> (E)'], ')': [], 'id': ['F -> id'], '$': []}})
class TestSlrParsing(unittest.TestCase):
def setUp(self):
p = {"E" : [("E", "+", "T"), tuple("T")],
"T" : [("T", "*", "F"), tuple("F")],
"F" : [("(", "E", ")"), ("id",)]}
self.g = Grammar("E", p, ["E", "T", "F"],
["+", "*", "(", ")", "id"])
def test_closure(self):
self.assertEqual(closure({("E'", "E", 0)}, self.g),
{("E'", 'E', 0),
('T', ('F',), 0),
('F', ('(', 'E', ')'), 0),
('F', ('id',), 0),
('E', ('E', '+', 'T'), 0),
('T', ('T', '*', 'F'), 0),
('E', ('T',), 0)})
def test_goto(self):
self.assertEqual(
goto({("E'", "E", 1), ("E", ("E","+","T"), 1)}, "+", self.g),
{('T', ('F',), 0),
('E', ('E', '+', 'T'), 2),
('F', ('id',), 0),
('F', ('(', 'E', ')'), 0),
('T', ('T', '*', 'F'), 0)})
def test_canonical_items(self):
augment(self.g)
self.assertEqual(canonical_items(self.g),
[{('E', ('E', '+', 'T'), 0),
('E', ('T',), 0),
("E'", 'E', 0),
('F', ('(', 'E', ')'), 0),
('F', ('id',), 0),
('T', ('F',), 0),
('T', ('T', '*', 'F'), 0)},
{("E'", 'E', 1), ('E', ('E', '+', 'T'), 1)},
{('E', ('T',), 1), ('T', ('T', '*', 'F'), 1)},
{('T', ('F',), 1)},
{('E', ('E', '+', 'T'), 0),
('E', ('T',), 0),
('F', ('(', 'E', ')'), 0),
('F', ('(', 'E', ')'), 1),
('F', ('id',), 0),
('T', ('F',), 0),
('T', ('T', '*', 'F'), 0)},
{('F', ('id',), 1)},
{('E', ('E', '+', 'T'), 2),
('F', ('(', 'E', ')'), 0),
('F', ('id',), 0),
('T', ('F',), 0),
('T', ('T', '*', 'F'), 0)},
{('T', ('T', '*', 'F'), 2),
('F', ('id',), 0), ('F', ('(', 'E', ')'), 0)},
{('E', ('E', '+', 'T'), 1),
('F', ('(', 'E', ')'), 2)},
{('E', ('E', '+', 'T'), 3),
('T', ('T', '*', 'F'), 1)},
{('T', ('T', '*', 'F'), 3)},
{('F', ('(', 'E', ')'), 3)}])
def test_slr_parsing_table(self):
augment(self.g)
self.g.compute_first()
self.g.compute_follow()
act_tb, goto_tb = slr_parsing_table(self.g)
self.assertEqual(act_tb,
{0: {'$': [],
'(': [('shift', 4)],
')': [],
'*': [],
'+': [],
'id': [('shift', 5)]},
1: {'$': [('accept',)],
'(': [],
')': [],
'*': [],
'+': [('shift', 6)],
'id': []},
2: {'$': [('reduce', ('E', ('T',)))],
'(': [],
')': [('reduce', ('E', ('T',)))],
'*': [('shift', 7)],
'+': [('reduce', ('E', ('T',)))],
'id': []},
3: {'$': [('reduce', ('T', ('F',)))],
'(': [],
')': [('reduce', ('T', ('F',)))],
'*': [('reduce', ('T', ('F',)))],
'+': [('reduce', ('T', ('F',)))],
'id': []},
4: {'$': [],
'(': [('shift', 4)],
')': [],
'*': [],
'+': [],
'id': [('shift', 5)]},
5: {'$': [('reduce', ('F', ('id',)))],
'(': [],
')': [('reduce', ('F', ('id',)))],
'*': [('reduce', ('F', ('id',)))],
'+': [('reduce', ('F', ('id',)))],
'id': []},
6: {'$': [],
'(': [('shift', 4)],
')': [],
'*': [],
'+': [],
'id': [('shift', 5)]},
7: {'$': [],
'(': [('shift', 4)],
')': [],
'*': [],
'+': [],
'id': [('shift', 5)]},
8: {'$': [],
'(': [],
')': [('shift', 11)],
'*': [],
'+': [('shift', 6)],
'id': []},
9: {'$': [('reduce', ('E', ('E', '+', 'T')))],
'(': [],
')': [('reduce', ('E', ('E', '+', 'T')))],
'*': [('shift', 7)],
'+': [('reduce', ('E', ('E', '+', 'T')))],
'id': []},
10: {'$': [('reduce', ('T', ('T', '*', 'F')))],
'(': [],
')': [('reduce', ('T', ('T', '*', 'F')))],
'*': [('reduce', ('T', ('T', '*', 'F')))],
'+': [('reduce', ('T', ('T', '*', 'F')))],
'id': []},
11: {'$': [('reduce', ('F', ('(', 'E', ')')))],
'(': [],
')': [('reduce', ('F', ('(', 'E', ')')))],
'*': [('reduce', ('F', ('(', 'E', ')')))],
'+': [('reduce', ('F', ('(', 'E', ')')))],
'id': []}})
self.assertEqual(goto_tb,
{0: {'E': [1], "E'": [], 'F': [3], 'T': [2]},
1: {'E': [], "E'": [], 'F': [], 'T': []},
2: {'E': [], "E'": [], 'F': [], 'T': []},
3: {'E': [], "E'": [], 'F': [], 'T': []},
4: {'E': [8], "E'": [], 'F': [3], 'T': [2]},
5: {'E': [], "E'": [], 'F': [], 'T': []},
6: {'E': [], "E'": [], 'F': [3], 'T': [9]},
7: {'E': [], "E'": [], 'F': [10], 'T': []},
8: {'E': [], "E'": [], 'F': [], 'T': []},
9: {'E': [], "E'": [], 'F': [], 'T': []},
10: {'E': [], "E'": [], 'F': [], 'T': []},
11: {'E': [], "E'": [], 'F': [], 'T': []}})
"T": [("T", "*", "F"), tuple("F")],
"F": [("(", "E", ")"), ("id", )]
}
g = Grammar("E", p, ["E", "T", "F"], ["+", "*", "(", ")", "id"])
print("Example 4.40, 244")
pp = pprint.PrettyPrinter()
pp.pprint(closure({("E'", "E", 0)}, g))
print("Example 4.4.1, pg 246")
pp.pprint(goto({("E'", "E", 1), ("E", ("E", "+", "T"), 1)}, "+", g))
augment(g)
pp.pprint(canonical_items(g))
print("\n# Production rules for Example 4.45, pg 251, Exp. Grammar 4.1.")
g.print_productions()
g.compute_first()
g.compute_follow()
act_tb, goto_tb = slr_parsing_table(g)
print_slr_table(act_tb, goto_tb)
print("\n# Production rules for grammar 4.28")
p = {
"E": [("T", "E2")],
"E2": [("+", "T", "E2"), ("epsilon", )],
"T": [("F", "T'")],
"T'": [("*", "F", "T'"), ("epsilon", )],
"F": [("(", "E", ")"), ("id", )]
}
# Grammar 4.28
g = Grammar("E", p, ["E", "E2", "T", "T'", "F"],
["+", "*", "(", ")", "id"])
def goto(s, x, g):
'''
Calculates GOTO(s, x) as defined to be the closure of the set of all items
[A -> alpha X * beta] such that [A -> alpha * X beta] is in s.
'''
goto_sx = set()
for lhs, rhs, dot_idx in s:
# Do your magic here!
return goto_sx
def augment(g):
new_start_symbol = g.start_symbol + "'"
assert(not new_start_symbol in g.non_terminals)
g.production_rules[new_start_symbol] = [tuple(g.start_symbol)]
g.start_symbol = new_start_symbol
g.non_terminals.append(new_start_symbol)
g.first_tab[new_start_symbol] = set()
g.follow_tab[new_start_symbol] = set()
def canonical_items(g):
'''
Calculates the canonical collection of sets of LR(0) items.
'''
# Dragon book, 2nd ed, pg 246
# void items(G') {
# C = {closure({[S'-> * S]})}
# repeat
# for each set of items I in C
# for each grammar symbol X
# if GOTO(I, X) is not empty and not in C
# add GOTO(I, X) to C
# until no new set of items are added to C on a round
# }
# Grammar g is assumed augmented
s = g.start_symbol # S'
orig_s = s[:len(s) - 1] # S
start_item = (s, orig_s, 0) # S' -> * S
# I chose to represent C as a list of set of items
# instead of a set so we can assign a natural number to
# each set of items I beig its position in the
# list representing C.
can = [closure({start_item}, g)]
while True:
can_size = len(can)
# Do your magic here!
new_can_size = len(can)
if new_can_size == can_size:
break
return can
def slr_parsing_table(g):
'''
Computes SLR parsing table according to Dragon 2nd ed. pgs 253, 254.
'''
# Grammar g is assumed to augmented.
assert(g.follow_computed)
# 1. Construct C = {I0, I1, ... In}, the collection of sets of LR(0)
# items for G.
can = canonical_items(g)
# Initializes ACTION and GOTO tables.
action_tab = {}
goto_tab = {}
for st in range(len(can)):
d = {}
for t in g.terminals:
d[t] = []
d["$"] = []
action_tab[st] = d
d = {}
for v in g.non_terminals:
d[v] = []
goto_tab[st] = d
# 2. State i is constructed from Ii.
# (They are encoded as the indices of 'can'.)
# The parsing actions for state i are deter mined as follows:
for state_l, l in enumerate(can):
for i, item in enumerate(l):
lhs = item[0]
rhs = item[1]
dot_idx = item[2]
if dot_idx < len(rhs):
a = rhs[dot_idx]
# (a) If [A -> alpha * a beta]is in Ii
# and GOTO(Ii, a) = Ij then
# set ACTION[i,a] =shift j.
# Here a must be a terminal.
# Do your magic here!
else:
# (b) If [A -> alpha *] is in Ii, then set
# ACTION[i, a] = "reduce A -> alpha" to
# all a in FOLLOW(A); here A may not be S'.
# (c) If [S' -> S *] is in Ii, then set
# ACTION[i, $] = "accept".
# Do your magic here!
# 3. The goto transitions for state i are constructed for all
# nonterminals A using the rule If GOTO(Ii, A) = Ij
# then GOTO[i,A] = j.
# Do your magic here!
return (action_tab, goto_tab)
def print_slr_table(act_tb, goto_tb):
print("ACTION table")
df = pd.DataFrame(act_tb).T
df.fillna(0, inplace=True)
print(tabulate(df, headers='keys', tablefmt='psql'))
print("GOTO table")
df = pd.DataFrame(goto_tb).T
df.fillna(0, inplace=True)
print(tabulate(df, headers='keys', tablefmt='psql'))
if __name__ == '__main__':
# Production rules for Expression Grammar 4.1
p = {"E" : [("E", "+", "T"), tuple("T")],
"T" : [("T", "*", "F"), tuple("F")],
"F" : [("(", "E", ")"), ("id",)]}
g = Grammar("E", p, ["E", "T", "F"],
["+", "*", "(", ")", "id"])
print("Example 4.40, 244")
pp = pprint.PrettyPrinter()
pp.pprint(closure({("E'", "E", 0)}, g))
print("Example 4.4.1, pg 246")
pp.pprint(goto({("E'", "E", 1), ("E", ("E","+","T"), 1)}, "+", g))
augment(g)
pp.pprint(canonical_items(g))
print("\n# Production rules for Example 4.45, pg 251, Exp. Grammar 4.1.")
g.print_productions()
g.compute_first()
g.compute_follow()
act_tb, goto_tb = slr_parsing_table(g)
print_slr_table(act_tb, goto_tb)
print("\n# Production rules for grammar 4.28")
p = {"E" : [("T", "E2")],
"E2" : [("+", "T", "E2"), ("epsilon",)],
"T" : [("F", "T'")],
"T'" : [("*", "F", "T'"), ("epsilon",)],
"F" : [("(", "E", ")"), ("id",)]}
# Grammar 4.28
g = Grammar("E", p, ["E", "E2", "T", "T'", "F"],
["+", "*", "(", ")", "id"])
augment(g)
print("\n# Production rules for Example 4.32, pg. 225, Grammar 4.28.")
g.print_productions()
g.compute_first()
g.compute_follow()
act_tb, goto_tb = slr_parsing_table(g)
print_slr_table(act_tb, goto_tb)