675 lines
21 KiB
Python
675 lines
21 KiB
Python
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# Natural Language Toolkit: Chart Parser for Feature-Based Grammars
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#
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# Copyright (C) 2001-2023 NLTK Project
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# Author: Rob Speer <rspeer@mit.edu>
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# Peter Ljunglöf <peter.ljunglof@heatherleaf.se>
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# URL: <https://www.nltk.org/>
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# For license information, see LICENSE.TXT
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"""
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Extension of chart parsing implementation to handle grammars with
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feature structures as nodes.
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"""
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from time import perf_counter
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from nltk.featstruct import TYPE, FeatStruct, find_variables, unify
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from nltk.grammar import (
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CFG,
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FeatStructNonterminal,
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Nonterminal,
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Production,
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is_nonterminal,
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is_terminal,
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)
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from nltk.parse.chart import (
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BottomUpPredictCombineRule,
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BottomUpPredictRule,
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CachedTopDownPredictRule,
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Chart,
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ChartParser,
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EdgeI,
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EmptyPredictRule,
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FundamentalRule,
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LeafInitRule,
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SingleEdgeFundamentalRule,
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TopDownInitRule,
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TreeEdge,
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)
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from nltk.sem import logic
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from nltk.tree import Tree
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# ////////////////////////////////////////////////////////////
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# Tree Edge
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# ////////////////////////////////////////////////////////////
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class FeatureTreeEdge(TreeEdge):
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"""
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A specialized tree edge that allows shared variable bindings
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between nonterminals on the left-hand side and right-hand side.
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Each ``FeatureTreeEdge`` contains a set of ``bindings``, i.e., a
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dictionary mapping from variables to values. If the edge is not
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complete, then these bindings are simply stored. However, if the
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edge is complete, then the constructor applies these bindings to
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every nonterminal in the edge whose symbol implements the
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interface ``SubstituteBindingsI``.
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"""
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def __init__(self, span, lhs, rhs, dot=0, bindings=None):
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"""
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Construct a new edge. If the edge is incomplete (i.e., if
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``dot<len(rhs)``), then store the bindings as-is. If the edge
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is complete (i.e., if ``dot==len(rhs)``), then apply the
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bindings to all nonterminals in ``lhs`` and ``rhs``, and then
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clear the bindings. See ``TreeEdge`` for a description of
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the other arguments.
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"""
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if bindings is None:
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bindings = {}
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# If the edge is complete, then substitute in the bindings,
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# and then throw them away. (If we didn't throw them away, we
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# might think that 2 complete edges are different just because
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# they have different bindings, even though all bindings have
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# already been applied.)
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if dot == len(rhs) and bindings:
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lhs = self._bind(lhs, bindings)
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rhs = [self._bind(elt, bindings) for elt in rhs]
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bindings = {}
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# Initialize the edge.
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TreeEdge.__init__(self, span, lhs, rhs, dot)
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self._bindings = bindings
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self._comparison_key = (self._comparison_key, tuple(sorted(bindings.items())))
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@staticmethod
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def from_production(production, index):
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"""
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:return: A new ``TreeEdge`` formed from the given production.
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The new edge's left-hand side and right-hand side will
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be taken from ``production``; its span will be
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``(index,index)``; and its dot position will be ``0``.
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:rtype: TreeEdge
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"""
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return FeatureTreeEdge(
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span=(index, index), lhs=production.lhs(), rhs=production.rhs(), dot=0
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)
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def move_dot_forward(self, new_end, bindings=None):
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"""
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:return: A new ``FeatureTreeEdge`` formed from this edge.
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The new edge's dot position is increased by ``1``,
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and its end index will be replaced by ``new_end``.
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:rtype: FeatureTreeEdge
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:param new_end: The new end index.
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:type new_end: int
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:param bindings: Bindings for the new edge.
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:type bindings: dict
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"""
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return FeatureTreeEdge(
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span=(self._span[0], new_end),
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lhs=self._lhs,
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rhs=self._rhs,
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dot=self._dot + 1,
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bindings=bindings,
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)
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def _bind(self, nt, bindings):
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if not isinstance(nt, FeatStructNonterminal):
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return nt
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return nt.substitute_bindings(bindings)
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def next_with_bindings(self):
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return self._bind(self.nextsym(), self._bindings)
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def bindings(self):
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"""
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Return a copy of this edge's bindings dictionary.
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"""
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return self._bindings.copy()
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def variables(self):
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"""
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:return: The set of variables used by this edge.
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:rtype: set(Variable)
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"""
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return find_variables(
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[self._lhs]
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+ list(self._rhs)
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+ list(self._bindings.keys())
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+ list(self._bindings.values()),
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fs_class=FeatStruct,
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)
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def __str__(self):
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if self.is_complete():
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return super().__str__()
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else:
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bindings = "{%s}" % ", ".join(
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"%s: %r" % item for item in sorted(self._bindings.items())
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)
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return f"{super().__str__()} {bindings}"
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# ////////////////////////////////////////////////////////////
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# A specialized Chart for feature grammars
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# ////////////////////////////////////////////////////////////
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# TODO: subsumes check when adding new edges
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class FeatureChart(Chart):
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"""
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A Chart for feature grammars.
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:see: ``Chart`` for more information.
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"""
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def select(self, **restrictions):
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"""
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Returns an iterator over the edges in this chart.
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See ``Chart.select`` for more information about the
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``restrictions`` on the edges.
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"""
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# If there are no restrictions, then return all edges.
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if restrictions == {}:
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return iter(self._edges)
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# Find the index corresponding to the given restrictions.
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restr_keys = sorted(restrictions.keys())
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restr_keys = tuple(restr_keys)
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# If it doesn't exist, then create it.
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if restr_keys not in self._indexes:
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self._add_index(restr_keys)
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vals = tuple(
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self._get_type_if_possible(restrictions[key]) for key in restr_keys
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)
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return iter(self._indexes[restr_keys].get(vals, []))
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def _add_index(self, restr_keys):
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"""
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A helper function for ``select``, which creates a new index for
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a given set of attributes (aka restriction keys).
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"""
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# Make sure it's a valid index.
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for key in restr_keys:
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if not hasattr(EdgeI, key):
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raise ValueError("Bad restriction: %s" % key)
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# Create the index.
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index = self._indexes[restr_keys] = {}
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# Add all existing edges to the index.
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for edge in self._edges:
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vals = tuple(
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self._get_type_if_possible(getattr(edge, key)()) for key in restr_keys
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)
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index.setdefault(vals, []).append(edge)
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def _register_with_indexes(self, edge):
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"""
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A helper function for ``insert``, which registers the new
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edge with all existing indexes.
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"""
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for (restr_keys, index) in self._indexes.items():
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vals = tuple(
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self._get_type_if_possible(getattr(edge, key)()) for key in restr_keys
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)
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index.setdefault(vals, []).append(edge)
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def _get_type_if_possible(self, item):
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"""
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Helper function which returns the ``TYPE`` feature of the ``item``,
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if it exists, otherwise it returns the ``item`` itself
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"""
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if isinstance(item, dict) and TYPE in item:
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return item[TYPE]
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else:
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return item
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def parses(self, start, tree_class=Tree):
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for edge in self.select(start=0, end=self._num_leaves):
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if (
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(isinstance(edge, FeatureTreeEdge))
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and (edge.lhs()[TYPE] == start[TYPE])
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and (unify(edge.lhs(), start, rename_vars=True))
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):
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yield from self.trees(edge, complete=True, tree_class=tree_class)
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# ////////////////////////////////////////////////////////////
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# Fundamental Rule
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# ////////////////////////////////////////////////////////////
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class FeatureFundamentalRule(FundamentalRule):
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r"""
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A specialized version of the fundamental rule that operates on
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nonterminals whose symbols are ``FeatStructNonterminal``s. Rather
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than simply comparing the nonterminals for equality, they are
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unified. Variable bindings from these unifications are collected
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and stored in the chart using a ``FeatureTreeEdge``. When a
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complete edge is generated, these bindings are applied to all
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nonterminals in the edge.
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The fundamental rule states that:
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- ``[A -> alpha \* B1 beta][i:j]``
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- ``[B2 -> gamma \*][j:k]``
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licenses the edge:
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- ``[A -> alpha B3 \* beta][i:j]``
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assuming that B1 and B2 can be unified to generate B3.
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"""
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def apply(self, chart, grammar, left_edge, right_edge):
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# Make sure the rule is applicable.
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if not (
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left_edge.end() == right_edge.start()
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and left_edge.is_incomplete()
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and right_edge.is_complete()
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and isinstance(left_edge, FeatureTreeEdge)
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):
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return
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found = right_edge.lhs()
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nextsym = left_edge.nextsym()
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if isinstance(right_edge, FeatureTreeEdge):
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if not is_nonterminal(nextsym):
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return
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if left_edge.nextsym()[TYPE] != right_edge.lhs()[TYPE]:
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return
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# Create a copy of the bindings.
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bindings = left_edge.bindings()
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# We rename vars here, because we don't want variables
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# from the two different productions to match.
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found = found.rename_variables(used_vars=left_edge.variables())
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# Unify B1 (left_edge.nextsym) with B2 (right_edge.lhs) to
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# generate B3 (result).
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result = unify(nextsym, found, bindings, rename_vars=False)
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if result is None:
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return
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else:
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if nextsym != found:
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return
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# Create a copy of the bindings.
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bindings = left_edge.bindings()
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# Construct the new edge.
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new_edge = left_edge.move_dot_forward(right_edge.end(), bindings)
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# Add it to the chart, with appropriate child pointers.
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if chart.insert_with_backpointer(new_edge, left_edge, right_edge):
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yield new_edge
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class FeatureSingleEdgeFundamentalRule(SingleEdgeFundamentalRule):
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"""
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A specialized version of the completer / single edge fundamental rule
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that operates on nonterminals whose symbols are ``FeatStructNonterminal``.
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Rather than simply comparing the nonterminals for equality, they are
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unified.
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"""
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_fundamental_rule = FeatureFundamentalRule()
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def _apply_complete(self, chart, grammar, right_edge):
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fr = self._fundamental_rule
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for left_edge in chart.select(
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end=right_edge.start(), is_complete=False, nextsym=right_edge.lhs()
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):
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yield from fr.apply(chart, grammar, left_edge, right_edge)
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def _apply_incomplete(self, chart, grammar, left_edge):
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fr = self._fundamental_rule
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for right_edge in chart.select(
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start=left_edge.end(), is_complete=True, lhs=left_edge.nextsym()
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):
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yield from fr.apply(chart, grammar, left_edge, right_edge)
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# ////////////////////////////////////////////////////////////
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# Top-Down Prediction
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# ////////////////////////////////////////////////////////////
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class FeatureTopDownInitRule(TopDownInitRule):
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def apply(self, chart, grammar):
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for prod in grammar.productions(lhs=grammar.start()):
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new_edge = FeatureTreeEdge.from_production(prod, 0)
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if chart.insert(new_edge, ()):
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yield new_edge
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class FeatureTopDownPredictRule(CachedTopDownPredictRule):
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r"""
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A specialized version of the (cached) top down predict rule that operates
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on nonterminals whose symbols are ``FeatStructNonterminal``. Rather
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than simply comparing the nonterminals for equality, they are
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unified.
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The top down expand rule states that:
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- ``[A -> alpha \* B1 beta][i:j]``
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licenses the edge:
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- ``[B2 -> \* gamma][j:j]``
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for each grammar production ``B2 -> gamma``, assuming that B1
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and B2 can be unified.
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"""
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def apply(self, chart, grammar, edge):
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if edge.is_complete():
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return
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nextsym, index = edge.nextsym(), edge.end()
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if not is_nonterminal(nextsym):
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return
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# If we've already applied this rule to an edge with the same
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# next & end, and the chart & grammar have not changed, then
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# just return (no new edges to add).
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nextsym_with_bindings = edge.next_with_bindings()
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done = self._done.get((nextsym_with_bindings, index), (None, None))
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if done[0] is chart and done[1] is grammar:
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return
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for prod in grammar.productions(lhs=nextsym):
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# If the left corner in the predicted production is
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# leaf, it must match with the input.
|
||
|
|
if prod.rhs():
|
||
|
|
first = prod.rhs()[0]
|
||
|
|
if is_terminal(first):
|
||
|
|
if index >= chart.num_leaves():
|
||
|
|
continue
|
||
|
|
if first != chart.leaf(index):
|
||
|
|
continue
|
||
|
|
|
||
|
|
# We rename vars here, because we don't want variables
|
||
|
|
# from the two different productions to match.
|
||
|
|
if unify(prod.lhs(), nextsym_with_bindings, rename_vars=True):
|
||
|
|
new_edge = FeatureTreeEdge.from_production(prod, edge.end())
|
||
|
|
if chart.insert(new_edge, ()):
|
||
|
|
yield new_edge
|
||
|
|
|
||
|
|
# Record the fact that we've applied this rule.
|
||
|
|
self._done[nextsym_with_bindings, index] = (chart, grammar)
|
||
|
|
|
||
|
|
|
||
|
|
# ////////////////////////////////////////////////////////////
|
||
|
|
# Bottom-Up Prediction
|
||
|
|
# ////////////////////////////////////////////////////////////
|
||
|
|
|
||
|
|
|
||
|
|
class FeatureBottomUpPredictRule(BottomUpPredictRule):
|
||
|
|
def apply(self, chart, grammar, edge):
|
||
|
|
if edge.is_incomplete():
|
||
|
|
return
|
||
|
|
for prod in grammar.productions(rhs=edge.lhs()):
|
||
|
|
if isinstance(edge, FeatureTreeEdge):
|
||
|
|
_next = prod.rhs()[0]
|
||
|
|
if not is_nonterminal(_next):
|
||
|
|
continue
|
||
|
|
|
||
|
|
new_edge = FeatureTreeEdge.from_production(prod, edge.start())
|
||
|
|
if chart.insert(new_edge, ()):
|
||
|
|
yield new_edge
|
||
|
|
|
||
|
|
|
||
|
|
class FeatureBottomUpPredictCombineRule(BottomUpPredictCombineRule):
|
||
|
|
def apply(self, chart, grammar, edge):
|
||
|
|
if edge.is_incomplete():
|
||
|
|
return
|
||
|
|
found = edge.lhs()
|
||
|
|
for prod in grammar.productions(rhs=found):
|
||
|
|
bindings = {}
|
||
|
|
if isinstance(edge, FeatureTreeEdge):
|
||
|
|
_next = prod.rhs()[0]
|
||
|
|
if not is_nonterminal(_next):
|
||
|
|
continue
|
||
|
|
|
||
|
|
# We rename vars here, because we don't want variables
|
||
|
|
# from the two different productions to match.
|
||
|
|
used_vars = find_variables(
|
||
|
|
(prod.lhs(),) + prod.rhs(), fs_class=FeatStruct
|
||
|
|
)
|
||
|
|
found = found.rename_variables(used_vars=used_vars)
|
||
|
|
|
||
|
|
result = unify(_next, found, bindings, rename_vars=False)
|
||
|
|
if result is None:
|
||
|
|
continue
|
||
|
|
|
||
|
|
new_edge = FeatureTreeEdge.from_production(
|
||
|
|
prod, edge.start()
|
||
|
|
).move_dot_forward(edge.end(), bindings)
|
||
|
|
if chart.insert(new_edge, (edge,)):
|
||
|
|
yield new_edge
|
||
|
|
|
||
|
|
|
||
|
|
class FeatureEmptyPredictRule(EmptyPredictRule):
|
||
|
|
def apply(self, chart, grammar):
|
||
|
|
for prod in grammar.productions(empty=True):
|
||
|
|
for index in range(chart.num_leaves() + 1):
|
||
|
|
new_edge = FeatureTreeEdge.from_production(prod, index)
|
||
|
|
if chart.insert(new_edge, ()):
|
||
|
|
yield new_edge
|
||
|
|
|
||
|
|
|
||
|
|
# ////////////////////////////////////////////////////////////
|
||
|
|
# Feature Chart Parser
|
||
|
|
# ////////////////////////////////////////////////////////////
|
||
|
|
|
||
|
|
TD_FEATURE_STRATEGY = [
|
||
|
|
LeafInitRule(),
|
||
|
|
FeatureTopDownInitRule(),
|
||
|
|
FeatureTopDownPredictRule(),
|
||
|
|
FeatureSingleEdgeFundamentalRule(),
|
||
|
|
]
|
||
|
|
BU_FEATURE_STRATEGY = [
|
||
|
|
LeafInitRule(),
|
||
|
|
FeatureEmptyPredictRule(),
|
||
|
|
FeatureBottomUpPredictRule(),
|
||
|
|
FeatureSingleEdgeFundamentalRule(),
|
||
|
|
]
|
||
|
|
BU_LC_FEATURE_STRATEGY = [
|
||
|
|
LeafInitRule(),
|
||
|
|
FeatureEmptyPredictRule(),
|
||
|
|
FeatureBottomUpPredictCombineRule(),
|
||
|
|
FeatureSingleEdgeFundamentalRule(),
|
||
|
|
]
|
||
|
|
|
||
|
|
|
||
|
|
class FeatureChartParser(ChartParser):
|
||
|
|
def __init__(
|
||
|
|
self,
|
||
|
|
grammar,
|
||
|
|
strategy=BU_LC_FEATURE_STRATEGY,
|
||
|
|
trace_chart_width=20,
|
||
|
|
chart_class=FeatureChart,
|
||
|
|
**parser_args,
|
||
|
|
):
|
||
|
|
ChartParser.__init__(
|
||
|
|
self,
|
||
|
|
grammar,
|
||
|
|
strategy=strategy,
|
||
|
|
trace_chart_width=trace_chart_width,
|
||
|
|
chart_class=chart_class,
|
||
|
|
**parser_args,
|
||
|
|
)
|
||
|
|
|
||
|
|
|
||
|
|
class FeatureTopDownChartParser(FeatureChartParser):
|
||
|
|
def __init__(self, grammar, **parser_args):
|
||
|
|
FeatureChartParser.__init__(self, grammar, TD_FEATURE_STRATEGY, **parser_args)
|
||
|
|
|
||
|
|
|
||
|
|
class FeatureBottomUpChartParser(FeatureChartParser):
|
||
|
|
def __init__(self, grammar, **parser_args):
|
||
|
|
FeatureChartParser.__init__(self, grammar, BU_FEATURE_STRATEGY, **parser_args)
|
||
|
|
|
||
|
|
|
||
|
|
class FeatureBottomUpLeftCornerChartParser(FeatureChartParser):
|
||
|
|
def __init__(self, grammar, **parser_args):
|
||
|
|
FeatureChartParser.__init__(
|
||
|
|
self, grammar, BU_LC_FEATURE_STRATEGY, **parser_args
|
||
|
|
)
|
||
|
|
|
||
|
|
|
||
|
|
# ////////////////////////////////////////////////////////////
|
||
|
|
# Instantiate Variable Chart
|
||
|
|
# ////////////////////////////////////////////////////////////
|
||
|
|
|
||
|
|
|
||
|
|
class InstantiateVarsChart(FeatureChart):
|
||
|
|
"""
|
||
|
|
A specialized chart that 'instantiates' variables whose names
|
||
|
|
start with '@', by replacing them with unique new variables.
|
||
|
|
In particular, whenever a complete edge is added to the chart, any
|
||
|
|
variables in the edge's ``lhs`` whose names start with '@' will be
|
||
|
|
replaced by unique new ``Variable``.
|
||
|
|
"""
|
||
|
|
|
||
|
|
def __init__(self, tokens):
|
||
|
|
FeatureChart.__init__(self, tokens)
|
||
|
|
|
||
|
|
def initialize(self):
|
||
|
|
self._instantiated = set()
|
||
|
|
FeatureChart.initialize(self)
|
||
|
|
|
||
|
|
def insert(self, edge, child_pointer_list):
|
||
|
|
if edge in self._instantiated:
|
||
|
|
return False
|
||
|
|
self.instantiate_edge(edge)
|
||
|
|
return FeatureChart.insert(self, edge, child_pointer_list)
|
||
|
|
|
||
|
|
def instantiate_edge(self, edge):
|
||
|
|
"""
|
||
|
|
If the edge is a ``FeatureTreeEdge``, and it is complete,
|
||
|
|
then instantiate all variables whose names start with '@',
|
||
|
|
by replacing them with unique new variables.
|
||
|
|
|
||
|
|
Note that instantiation is done in-place, since the
|
||
|
|
parsing algorithms might already hold a reference to
|
||
|
|
the edge for future use.
|
||
|
|
"""
|
||
|
|
# If the edge is a leaf, or is not complete, or is
|
||
|
|
# already in the chart, then just return it as-is.
|
||
|
|
if not isinstance(edge, FeatureTreeEdge):
|
||
|
|
return
|
||
|
|
if not edge.is_complete():
|
||
|
|
return
|
||
|
|
if edge in self._edge_to_cpls:
|
||
|
|
return
|
||
|
|
|
||
|
|
# Get a list of variables that need to be instantiated.
|
||
|
|
# If there are none, then return as-is.
|
||
|
|
inst_vars = self.inst_vars(edge)
|
||
|
|
if not inst_vars:
|
||
|
|
return
|
||
|
|
|
||
|
|
# Instantiate the edge!
|
||
|
|
self._instantiated.add(edge)
|
||
|
|
edge._lhs = edge.lhs().substitute_bindings(inst_vars)
|
||
|
|
|
||
|
|
def inst_vars(self, edge):
|
||
|
|
return {
|
||
|
|
var: logic.unique_variable()
|
||
|
|
for var in edge.lhs().variables()
|
||
|
|
if var.name.startswith("@")
|
||
|
|
}
|
||
|
|
|
||
|
|
|
||
|
|
# ////////////////////////////////////////////////////////////
|
||
|
|
# Demo
|
||
|
|
# ////////////////////////////////////////////////////////////
|
||
|
|
|
||
|
|
|
||
|
|
def demo_grammar():
|
||
|
|
from nltk.grammar import FeatureGrammar
|
||
|
|
|
||
|
|
return FeatureGrammar.fromstring(
|
||
|
|
"""
|
||
|
|
S -> NP VP
|
||
|
|
PP -> Prep NP
|
||
|
|
NP -> NP PP
|
||
|
|
VP -> VP PP
|
||
|
|
VP -> Verb NP
|
||
|
|
VP -> Verb
|
||
|
|
NP -> Det[pl=?x] Noun[pl=?x]
|
||
|
|
NP -> "John"
|
||
|
|
NP -> "I"
|
||
|
|
Det -> "the"
|
||
|
|
Det -> "my"
|
||
|
|
Det[-pl] -> "a"
|
||
|
|
Noun[-pl] -> "dog"
|
||
|
|
Noun[-pl] -> "cookie"
|
||
|
|
Verb -> "ate"
|
||
|
|
Verb -> "saw"
|
||
|
|
Prep -> "with"
|
||
|
|
Prep -> "under"
|
||
|
|
"""
|
||
|
|
)
|
||
|
|
|
||
|
|
|
||
|
|
def demo(
|
||
|
|
print_times=True,
|
||
|
|
print_grammar=True,
|
||
|
|
print_trees=True,
|
||
|
|
print_sentence=True,
|
||
|
|
trace=1,
|
||
|
|
parser=FeatureChartParser,
|
||
|
|
sent="I saw John with a dog with my cookie",
|
||
|
|
):
|
||
|
|
import sys
|
||
|
|
import time
|
||
|
|
|
||
|
|
print()
|
||
|
|
grammar = demo_grammar()
|
||
|
|
if print_grammar:
|
||
|
|
print(grammar)
|
||
|
|
print()
|
||
|
|
print("*", parser.__name__)
|
||
|
|
if print_sentence:
|
||
|
|
print("Sentence:", sent)
|
||
|
|
tokens = sent.split()
|
||
|
|
t = perf_counter()
|
||
|
|
cp = parser(grammar, trace=trace)
|
||
|
|
chart = cp.chart_parse(tokens)
|
||
|
|
trees = list(chart.parses(grammar.start()))
|
||
|
|
if print_times:
|
||
|
|
print("Time: %s" % (perf_counter() - t))
|
||
|
|
if print_trees:
|
||
|
|
for tree in trees:
|
||
|
|
print(tree)
|
||
|
|
else:
|
||
|
|
print("Nr trees:", len(trees))
|
||
|
|
|
||
|
|
|
||
|
|
def run_profile():
|
||
|
|
import profile
|
||
|
|
|
||
|
|
profile.run("for i in range(1): demo()", "/tmp/profile.out")
|
||
|
|
import pstats
|
||
|
|
|
||
|
|
p = pstats.Stats("/tmp/profile.out")
|
||
|
|
p.strip_dirs().sort_stats("time", "cum").print_stats(60)
|
||
|
|
p.strip_dirs().sort_stats("cum", "time").print_stats(60)
|
||
|
|
|
||
|
|
|
||
|
|
if __name__ == "__main__":
|
||
|
|
from nltk.data import load
|
||
|
|
|
||
|
|
demo()
|
||
|
|
print()
|
||
|
|
grammar = load("grammars/book_grammars/feat0.fcfg")
|
||
|
|
cp = FeatureChartParser(grammar, trace=2)
|
||
|
|
sent = "Kim likes children"
|
||
|
|
tokens = sent.split()
|
||
|
|
trees = cp.parse(tokens)
|
||
|
|
for tree in trees:
|
||
|
|
print(tree)
|