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venv/lib/python3.7/site-packages/nltk/sem/cooper_storage.py

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+# Natural Language Toolkit: Cooper storage for Quantifier Ambiguity
+#
+# Copyright (C) 2001-2019 NLTK Project
+# Author: Ewan Klein <ewan@inf.ed.ac.uk>
+# URL: <http://nltk.org/>
+# For license information, see LICENSE.TXT
+from __future__ import print_function
+
+from nltk.sem.logic import LambdaExpression, ApplicationExpression, Variable
+from nltk.parse import load_parser
+from nltk.parse.featurechart import InstantiateVarsChart
+
+
+class CooperStore(object):
+    """
+    A container for handling quantifier ambiguity via Cooper storage.
+    """
+
+    def __init__(self, featstruct):
+        """
+        :param featstruct: The value of the ``sem`` node in a tree from
+            ``parse_with_bindops()``
+        :type featstruct: FeatStruct (with features ``core`` and ``store``)
+
+        """
+        self.featstruct = featstruct
+        self.readings = []
+        try:
+            self.core = featstruct['CORE']
+            self.store = featstruct['STORE']
+        except KeyError:
+            print("%s is not a Cooper storage structure" % featstruct)
+
+    def _permute(self, lst):
+        """
+        :return: An iterator over the permutations of the input list
+        :type lst: list
+        :rtype: iter
+        """
+        remove = lambda lst0, index: lst0[:index] + lst0[index + 1 :]
+        if lst:
+            for index, x in enumerate(lst):
+                for y in self._permute(remove(lst, index)):
+                    yield (x,) + y
+        else:
+            yield ()
+
+    def s_retrieve(self, trace=False):
+        """
+        Carry out S-Retrieval of binding operators in store. If hack=True,
+        serialize the bindop and core as strings and reparse. Ugh.
+
+        Each permutation of the store (i.e. list of binding operators) is
+        taken to be a possible scoping of quantifiers. We iterate through the
+        binding operators in each permutation, and successively apply them to
+        the current term, starting with the core semantic representation,
+        working from the inside out.
+
+        Binding operators are of the form::
+
+             bo(\P.all x.(man(x) -> P(x)),z1)
+        """
+        for perm, store_perm in enumerate(self._permute(self.store)):
+            if trace:
+                print("Permutation %s" % (perm + 1))
+            term = self.core
+            for bindop in store_perm:
+                # we just want the arguments that are wrapped by the 'bo' predicate
+                quant, varex = tuple(bindop.args)
+                # use var to make an abstraction over the current term and then
+                # apply the quantifier to it
+                term = ApplicationExpression(
+                    quant, LambdaExpression(varex.variable, term)
+                )
+                if trace:
+                    print("  ", term)
+                term = term.simplify()
+            self.readings.append(term)
+
+
+def parse_with_bindops(sentence, grammar=None, trace=0):
+    """
+    Use a grammar with Binding Operators to parse a sentence.
+    """
+    if not grammar:
+        grammar = 'grammars/book_grammars/storage.fcfg'
+    parser = load_parser(grammar, trace=trace, chart_class=InstantiateVarsChart)
+    # Parse the sentence.
+    tokens = sentence.split()
+    return list(parser.parse(tokens))
+
+
+def demo():
+    from nltk.sem import cooper_storage as cs
+
+    sentence = "every girl chases a dog"
+    # sentence = "a man gives a bone to every dog"
+    print()
+    print("Analyis of sentence '%s'" % sentence)
+    print("=" * 50)
+    trees = cs.parse_with_bindops(sentence, trace=0)
+    for tree in trees:
+        semrep = cs.CooperStore(tree.label()['SEM'])
+        print()
+        print("Binding operators:")
+        print("-" * 15)
+        for s in semrep.store:
+            print(s)
+        print()
+        print("Core:")
+        print("-" * 15)
+        print(semrep.core)
+        print()
+        print("S-Retrieval:")
+        print("-" * 15)
+        semrep.s_retrieve(trace=True)
+        print("Readings:")
+        print("-" * 15)
+
+        for i, reading in enumerate(semrep.readings):
+            print("%s: %s" % (i + 1, reading))
+
+
+if __name__ == '__main__':
+    demo()