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class Production(object):
def __init__(self, *terms):
self.terms = terms
def __len__(self):
return len(self.terms)
def __getitem__(self, index):
return self.terms[index]
def __iter__(self):
return iter(self.terms)
def __repr__(self):
return " ".join(str(t) for t in self.terms)
def __eq__(self, other):
if not isinstance(other, Production):
return False
return self.terms == other.terms
def __ne__(self, other):
return not (self == other)
def __hash__(self):
return hash(self.terms)
class Rule(object):
def __init__(self, name, *productions): = name = list(productions)
def __str__(self):
def __repr__(self):
return "%s -> %s" % (, " | ".join(repr(p) for p in
def add(self, *productions):
class State(object):
def __init__(self, name, production, dot_index, start_column): = name
self.production = production
self.start_column = start_column
self.end_column = None
self.dot_index = dot_index
self.rules = [t for t in production if isinstance(t, Rule)]
def __repr__(self):
terms = [str(p) for p in self.production]
terms.insert(self.dot_index, u"$")
return "%-5s -> %-16s [%s-%s]" % (, " ".join(terms), self.start_column, self.end_column)
def __eq__(self, other):
return (, self.production, self.dot_index, self.start_column) == \
(, other.production, other.dot_index, other.start_column)
def __ne__(self, other):
return not (self == other)
def __hash__(self):
return hash((, self.production))
def completed(self):
return self.dot_index >= len(self.production)
def next_term(self):
if self.completed():
return None
return self.production[self.dot_index]
class Column(object):
def __init__(self, index, token):
self.index = index
self.token = token
self.states = []
self._unique = set()
def __str__(self):
return str(self.index)
def __len__(self):
return len(self.states)
def __iter__(self):
return iter(self.states)
def __getitem__(self, index):
return self.states[index]
def enumfrom(self, index):
for i in range(index, len(self.states)):
yield i, self.states[i]
def add(self, state):
if state not in self._unique:
state.end_column = self
return True
return False
def print_(self, completedOnly = False):
print "[%s] %r" % (self.index, self.token)
print "=" * 35
for s in self.states:
if completedOnly and not s.completed():
print repr(s)
class Node(object):
def __init__(self, value, children):
self.value = value
self.children = children
def print_(self, level = 0):
print " " * level + str(self.value)
for child in self.children:
child.print_(level + 1)
def predict(col, rule):
for prod in
col.add(State(, prod, 0, col))
def scan(col, state, token):
if token != col.token:
col.add(State(, state.production, state.dot_index + 1, state.start_column))
def complete(col, state):
if not state.completed():
for st in state.start_column:
term = st.next_term()
if not isinstance(term, Rule):
if ==
col.add(State(, st.production, st.dot_index + 1, st.start_column))
def parse(rule, text):
table = [Column(i, tok) for i, tok in enumerate([None] + text.lower().split())]
table[0].add(State(GAMMA_RULE, Production(rule), 0, table[0]))
for i, col in enumerate(table):
for state in col:
if state.completed():
complete(col, state)
term = state.next_term()
if isinstance(term, Rule):
predict(col, term)
elif i + 1 < len(table):
scan(table[i+1], state, term)
#col.print_(completedOnly = True)
# find gamma rule in last table column (otherwise fail)
for st in table[-1]:
if == GAMMA_RULE and st.completed():
return st
raise ValueError("parsing failed")
def build_trees(state):
return build_trees_helper([], state, len(state.rules) - 1, state.end_column)
def build_trees_helper(children, state, rule_index, end_column):
if rule_index < 0:
return [Node(state, children)]
elif rule_index == 0:
start_column = state.start_column
start_column = None
rule = state.rules[rule_index]
outputs = []
for st in end_column:
if st is state:
if st is state or not st.completed() or !=
if start_column is not None and st.start_column != start_column:
for sub_tree in build_trees(st):
for node in build_trees_helper([sub_tree] + children, state, rule_index - 1, st.start_column):
return outputs
SYM = Rule("SYM", Production("a"))
OP = Rule("OP", Production("+"))
EXPR = Rule("EXPR", Production(SYM))
EXPR.add(Production(EXPR, OP, EXPR))
for i in range(1,9):
text = " + ".join(["a"] * i)
q0 = parse(EXPR, text)
forest = build_trees(q0)
print len(forest), text
N = Rule("N", Production("time"), Production("flight"), Production("banana"),
Production("flies"), Production("boy"), Production("telescope"))
D = Rule("D", Production("the"), Production("a"), Production("an"))
V = Rule("V", Production("book"), Production("eat"), Production("sleep"), Production("saw"))
P = Rule("P", Production("with"), Production("in"), Production("on"), Production("at"),
PP = Rule("PP")
NP = Rule("NP", Production(D, N), Production("john"), Production("houston"))
NP.add(Production(NP, PP))
PP.add(Production(P, NP))
VP = Rule("VP", Production(V, NP))
VP.add(Production(VP, PP))
S = Rule("S", Production(NP, VP), Production(VP))
for tree in build_trees(parse(S, "book the flight through houston")):
print "--------------------------"
for tree in build_trees(parse(S, "john saw the boy with the telescope")):
print "--------------------------"
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