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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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