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clr.py
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clr.py
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from com import AUG_SYMBOL_EOF
class GrammarBase():
pass
class GrammarClr(GrammarBase):
def __init__(self):
# grammar definition
self.prods = []
self.terminals = []
self.nonterminals = []
# grammar table
self._table_goto = None
self._table_action = None
def set_grammar(self, *, productions, terminals, nonterminals):
self.prods = productions
self.terminals = terminals
self.nonterminals = nonterminals
self.compute_grammar_cache()
def compute_grammar_cache(self):
_prod_map = self._prod_map = [[] for _ in self.nonterminals]
for prod_idx, prod_exp in enumerate(self.prods):
_prod_map[prod_exp[0]].append(prod_idx)
self.terminal_map = {'EOF': ~self.terminals.index(AUG_SYMBOL_EOF)}
self._first_map = {}
def _first(self, X, lookup_cache=True, trace=None):
if lookup_cache and X in self._first_map:
return self._first_map[X]
if trace is None:
trace = []
# X is a terminal symbol
if X < 0:
fst = self._first_map[X] = [X]
return fst
# X is an nonterminal symbol
fst = []
for p in (p for p in self.prods if p[0] == X):
# for empty productions
if len(p) == 1 or p[1] is None:
fst.append(None)
continue
# Remember to skip left-recursive productions
fst += self._first_beta(p[1:], left=X, trace=trace+[X])
self._first_map[X] = fst
return fst
def _first_beta(self, beta, left=None, trace=None):
ret = []
for X in beta:
if X == left or (trace is not None and X in trace):
break
X_first = self._first(X, trace=trace)
ret += (s for s in X_first if s is not None)
if None not in X_first:
break
else:
ret.append(None)
return ret
def closure(self, I):
I = I[:]
v, w = 0, len(I)
while v < w:
prod, dot_pos, lasym = I[v]
prod_exp = self.prods[prod]
if dot_pos < len(prod_exp):
firsts = self._first_beta(prod_exp[dot_pos+1:] + (lasym,))
dot_sym = prod_exp[dot_pos]
if dot_sym >= 0:
dot_prods = self._prod_map[dot_sym]
for y in dot_prods:
for b in firsts:
if (new_item := (y, 1, b)) not in I:
I.append(new_item)
w += 1
v += 1
I.sort(key=lambda t: (t[0], t[1], ~t[2]))
return I
def goto(self, I, X):
J = []
for prod, dot_pos, lasym in I:
prod_exp = self.prods[prod]
if dot_pos < len(prod_exp) and prod_exp[dot_pos] == X:
J.append((prod, dot_pos+1, lasym))
return self.closure(J)
def items(self):
C = [self.closure([(0, 1, self.terminal_map['EOF'])])]
v, w = 0, len(C)
while v < w:
I = C[v]
# seek possible goto symbol
dot_symbols = []
for prod, dot_pos, _ in I:
prod_exp = self.prods[prod]
if dot_pos < len(prod_exp):
if (s := prod_exp[dot_pos]) not in dot_symbols:
dot_symbols.append(s)
# compute and append new item sets
for X in dot_symbols:
g = self.goto(I, X)
if len(g) and g not in C:
C.append(g)
w += 1
v += 1
self.itemset_collection = C # "collection"?
return C
def construct_table(self):
itemset_collection = self.itemset_collection
n_s = len(self.itemset_collection)
n_t = len(self.terminals)
n_n = len(self.nonterminals)
table_action = self._table_action =\
memoryview(bytearray(n_s * n_t * 4)).cast('L', (n_s, n_t))
table_goto = self._table_goto =\
memoryview(bytearray(n_s * n_n * 4)).cast('L', (n_s, n_n))
for i, I_i in enumerate(itemset_collection):
for prod, dot_pos, lasym in I_i:
prod_exp = self.prods[prod]
# case: shift
if dot_pos < len(prod_exp) and (a := prod_exp[dot_pos]) < 0:
I_j = self.goto(I_i, prod_exp[dot_pos])
j = itemset_collection.index(I_j)
table_action[i, ~a] = j << 2 | 3
# case: accept
elif dot_pos == len(prod_exp) and\
prod_exp[0] == 0 and lasym == self.terminal_map['EOF']:
table_action[i, ~lasym] = 1
# case: reduce
elif dot_pos == len(prod_exp):
table_action[i, ~lasym] = prod << 2 | 2
else:
pass
for i, I_i in enumerate(itemset_collection):
for A in range(len(self.nonterminals)):
I_j = self.goto(I_i, A)
try:
j = itemset_collection.index(I_j)
table_goto[i, A] = j
except ValueError:
pass # Do nothing
def stringify_item(self, item):
prod, dot_pos, lasym = item
prod_exp = self.prods[prod]
def wrap_symbol(s):
if s < 0:
return '[' + str(self.terminals[~s]) + ']'
else:
return '(' + str(self.nonterminals[s]) + ')'
ss = []
ss.append('%s -> ' % wrap_symbol(prod_exp[0]))
for i, r in enumerate(prod_exp[1:]):
ss.append(('\u25AA' if i + 1 == dot_pos else ' ') + str(wrap_symbol(r)))
ss.append('\u25AA' if dot_pos == len(prod_exp) else ' ')
return ''.join(ss) + ' , ' + wrap_symbol(lasym)
def print_itemset_collection(self):
for i, itemset in enumerate(self.itemset_collection):
print(f'C[{i}]')
print(*(' '*4 + self.stringify_item(t) for t in itemset), sep='\n')
def print_analysis_table(self, terminal_formatter=lambda x: x):
if self._table_action is None or self._table_goto is None:
return
size_state, size_action = self._table_action.shape
_, size_goto = self._table_goto.shape
def str_val(n):
if n & 3 == 0:
return ''
elif n & 3 == 1:
return 'acc'
elif n & 3 == 2:
return 'r' + str(n >> 2)
elif n & 3 == 3:
return 's' + str(n >> 2)
table_str_list = []
def format_terminal(t):
if not getattr(t, '_augmented', False):
t = terminal_formatter(t)
return f'{t:<8}'
table_header_str = ' | '
table_header_str += ' '.join(map(format_terminal, self.terminals))
table_header_str += ' | '
table_header_str += ' '.join(f'{x:<8}' for x in self.nonterminals)
table_str_list.append('-' * len(table_header_str))
table_str_list.append(table_header_str)
table_str_list.append('-' * len(table_header_str))
for i in range(size_state):
table_body_str = f'{i:>3} | '
table_body_str += ' '.join(
'{:<8}'.format(str_val(self._table_action[i, j]))
for j in range(size_action))
table_body_str += ' | '
table_body_str += ' '.join(
'{:<8}'.format(self._table_goto[i, j] or '')
for j in range(size_goto))
table_str_list.append(table_body_str)
table_str_list.append('-' * len(table_header_str))
final_str = '\n'.join(table_str_list)
print(final_str)