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"""This module implements useful building blocks for the Earley parser
"""
class Item:
"An Earley Item, the atom of the algorithm."
__slots__ = ('s', 'rule', 'ptr', 'start', 'is_complete', 'expect', 'previous', 'node', '_hash')
def __init__(self, rule, ptr, start):
self.is_complete = len(rule.expansion) == ptr
self.rule = rule # rule
self.ptr = ptr # ptr
self.start = start # j
self.node = None # w
if self.is_complete:
self.s = rule.origin
self.expect = None
self.previous = rule.expansion[ptr - 1] if ptr > 0 and len(rule.expansion) else None
else:
self.s = (rule, ptr)
self.expect = rule.expansion[ptr]
self.previous = rule.expansion[ptr - 1] if ptr > 0 and len(rule.expansion) else None
self._hash = hash((self.s, self.start, self.rule))
def advance(self):
return Item(self.rule, self.ptr + 1, self.start)
def __eq__(self, other):
return self is other or (self.s == other.s and self.start == other.start and self.rule == other.rule)
def __hash__(self):
return self._hash
def __repr__(self):
before = ( expansion.name for expansion in self.rule.expansion[:self.ptr] )
after = ( expansion.name for expansion in self.rule.expansion[self.ptr:] )
symbol = "{} ::= {}* {}".format(self.rule.origin.name, ' '.join(before), ' '.join(after))
return '%s (%d)' % (symbol, self.start)
# class TransitiveItem(Item):
# ... # removed at commit 4c1cfb2faf24e8f8bff7112627a00b94d261b420
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