diff --git "a/llmeval-env/lib/python3.10/site-packages/nltk/featstruct.py" "b/llmeval-env/lib/python3.10/site-packages/nltk/featstruct.py" new file mode 100644--- /dev/null +++ "b/llmeval-env/lib/python3.10/site-packages/nltk/featstruct.py" @@ -0,0 +1,2779 @@ +# Natural Language Toolkit: Feature Structures +# +# Copyright (C) 2001-2023 NLTK Project +# Author: Edward Loper , +# Rob Speer, +# Steven Bird +# URL: +# For license information, see LICENSE.TXT + +""" +Basic data classes for representing feature structures, and for +performing basic operations on those feature structures. A feature +structure is a mapping from feature identifiers to feature values, +where each feature value is either a basic value (such as a string or +an integer), or a nested feature structure. There are two types of +feature structure, implemented by two subclasses of ``FeatStruct``: + + - feature dictionaries, implemented by ``FeatDict``, act like + Python dictionaries. Feature identifiers may be strings or + instances of the ``Feature`` class. + - feature lists, implemented by ``FeatList``, act like Python + lists. Feature identifiers are integers. + +Feature structures are typically used to represent partial information +about objects. A feature identifier that is not mapped to a value +stands for a feature whose value is unknown (*not* a feature without +a value). Two feature structures that represent (potentially +overlapping) information about the same object can be combined by +unification. When two inconsistent feature structures are unified, +the unification fails and returns None. + +Features can be specified using "feature paths", or tuples of feature +identifiers that specify path through the nested feature structures to +a value. Feature structures may contain reentrant feature values. A +"reentrant feature value" is a single feature value that can be +accessed via multiple feature paths. Unification preserves the +reentrance relations imposed by both of the unified feature +structures. In the feature structure resulting from unification, any +modifications to a reentrant feature value will be visible using any +of its feature paths. + +Feature structure variables are encoded using the ``nltk.sem.Variable`` +class. The variables' values are tracked using a bindings +dictionary, which maps variables to their values. When two feature +structures are unified, a fresh bindings dictionary is created to +track their values; and before unification completes, all bound +variables are replaced by their values. Thus, the bindings +dictionaries are usually strictly internal to the unification process. +However, it is possible to track the bindings of variables if you +choose to, by supplying your own initial bindings dictionary to the +``unify()`` function. + +When unbound variables are unified with one another, they become +aliased. This is encoded by binding one variable to the other. + +Lightweight Feature Structures +============================== +Many of the functions defined by ``nltk.featstruct`` can be applied +directly to simple Python dictionaries and lists, rather than to +full-fledged ``FeatDict`` and ``FeatList`` objects. In other words, +Python ``dicts`` and ``lists`` can be used as "light-weight" feature +structures. + + >>> from nltk.featstruct import unify + >>> unify(dict(x=1, y=dict()), dict(a='a', y=dict(b='b'))) # doctest: +SKIP + {'y': {'b': 'b'}, 'x': 1, 'a': 'a'} + +However, you should keep in mind the following caveats: + + - Python dictionaries & lists ignore reentrance when checking for + equality between values. But two FeatStructs with different + reentrances are considered nonequal, even if all their base + values are equal. + + - FeatStructs can be easily frozen, allowing them to be used as + keys in hash tables. Python dictionaries and lists can not. + + - FeatStructs display reentrance in their string representations; + Python dictionaries and lists do not. + + - FeatStructs may *not* be mixed with Python dictionaries and lists + (e.g., when performing unification). + + - FeatStructs provide a number of useful methods, such as ``walk()`` + and ``cyclic()``, which are not available for Python dicts and lists. + +In general, if your feature structures will contain any reentrances, +or if you plan to use them as dictionary keys, it is strongly +recommended that you use full-fledged ``FeatStruct`` objects. +""" + +import copy +import re +from functools import total_ordering + +from nltk.internals import raise_unorderable_types, read_str +from nltk.sem.logic import ( + Expression, + LogicalExpressionException, + LogicParser, + SubstituteBindingsI, + Variable, +) + +###################################################################### +# Feature Structure +###################################################################### + + +@total_ordering +class FeatStruct(SubstituteBindingsI): + """ + A mapping from feature identifiers to feature values, where each + feature value is either a basic value (such as a string or an + integer), or a nested feature structure. There are two types of + feature structure: + + - feature dictionaries, implemented by ``FeatDict``, act like + Python dictionaries. Feature identifiers may be strings or + instances of the ``Feature`` class. + - feature lists, implemented by ``FeatList``, act like Python + lists. Feature identifiers are integers. + + Feature structures may be indexed using either simple feature + identifiers or 'feature paths.' A feature path is a sequence + of feature identifiers that stand for a corresponding sequence of + indexing operations. In particular, ``fstruct[(f1,f2,...,fn)]`` is + equivalent to ``fstruct[f1][f2]...[fn]``. + + Feature structures may contain reentrant feature structures. A + "reentrant feature structure" is a single feature structure + object that can be accessed via multiple feature paths. Feature + structures may also be cyclic. A feature structure is "cyclic" + if there is any feature path from the feature structure to itself. + + Two feature structures are considered equal if they assign the + same values to all features, and have the same reentrancies. + + By default, feature structures are mutable. They may be made + immutable with the ``freeze()`` method. Once they have been + frozen, they may be hashed, and thus used as dictionary keys. + """ + + _frozen = False + """:ivar: A flag indicating whether this feature structure is + frozen or not. Once this flag is set, it should never be + un-set; and no further modification should be made to this + feature structure.""" + + ##//////////////////////////////////////////////////////////// + # { Constructor + ##//////////////////////////////////////////////////////////// + + def __new__(cls, features=None, **morefeatures): + """ + Construct and return a new feature structure. If this + constructor is called directly, then the returned feature + structure will be an instance of either the ``FeatDict`` class + or the ``FeatList`` class. + + :param features: The initial feature values for this feature + structure: + + - FeatStruct(string) -> FeatStructReader().read(string) + - FeatStruct(mapping) -> FeatDict(mapping) + - FeatStruct(sequence) -> FeatList(sequence) + - FeatStruct() -> FeatDict() + :param morefeatures: If ``features`` is a mapping or None, + then ``morefeatures`` provides additional features for the + ``FeatDict`` constructor. + """ + # If the FeatStruct constructor is called directly, then decide + # whether to create a FeatDict or a FeatList, based on the + # contents of the `features` argument. + if cls is FeatStruct: + if features is None: + return FeatDict.__new__(FeatDict, **morefeatures) + elif _is_mapping(features): + return FeatDict.__new__(FeatDict, features, **morefeatures) + elif morefeatures: + raise TypeError( + "Keyword arguments may only be specified " + "if features is None or is a mapping." + ) + if isinstance(features, str): + if FeatStructReader._START_FDICT_RE.match(features): + return FeatDict.__new__(FeatDict, features, **morefeatures) + else: + return FeatList.__new__(FeatList, features, **morefeatures) + elif _is_sequence(features): + return FeatList.__new__(FeatList, features) + else: + raise TypeError("Expected string or mapping or sequence") + + # Otherwise, construct the object as normal. + else: + return super().__new__(cls, features, **morefeatures) + + ##//////////////////////////////////////////////////////////// + # { Uniform Accessor Methods + ##//////////////////////////////////////////////////////////// + # These helper functions allow the methods defined by FeatStruct + # to treat all feature structures as mappings, even if they're + # really lists. (Lists are treated as mappings from ints to vals) + + def _keys(self): + """Return an iterable of the feature identifiers used by this + FeatStruct.""" + raise NotImplementedError() # Implemented by subclasses. + + def _values(self): + """Return an iterable of the feature values directly defined + by this FeatStruct.""" + raise NotImplementedError() # Implemented by subclasses. + + def _items(self): + """Return an iterable of (fid,fval) pairs, where fid is a + feature identifier and fval is the corresponding feature + value, for all features defined by this FeatStruct.""" + raise NotImplementedError() # Implemented by subclasses. + + ##//////////////////////////////////////////////////////////// + # { Equality & Hashing + ##//////////////////////////////////////////////////////////// + + def equal_values(self, other, check_reentrance=False): + """ + Return True if ``self`` and ``other`` assign the same value to + to every feature. In particular, return true if + ``self[p]==other[p]`` for every feature path *p* such + that ``self[p]`` or ``other[p]`` is a base value (i.e., + not a nested feature structure). + + :param check_reentrance: If True, then also return False if + there is any difference between the reentrances of ``self`` + and ``other``. + :note: the ``==`` is equivalent to ``equal_values()`` with + ``check_reentrance=True``. + """ + return self._equal(other, check_reentrance, set(), set(), set()) + + def __eq__(self, other): + """ + Return true if ``self`` and ``other`` are both feature structures, + assign the same values to all features, and contain the same + reentrances. I.e., return + ``self.equal_values(other, check_reentrance=True)``. + + :see: ``equal_values()`` + """ + return self._equal(other, True, set(), set(), set()) + + def __ne__(self, other): + return not self == other + + def __lt__(self, other): + if not isinstance(other, FeatStruct): + # raise_unorderable_types("<", self, other) + # Sometimes feature values can be pure strings, + # so we need to be able to compare with non-featstructs: + return self.__class__.__name__ < other.__class__.__name__ + else: + return len(self) < len(other) + + def __hash__(self): + """ + If this feature structure is frozen, return its hash value; + otherwise, raise ``TypeError``. + """ + if not self._frozen: + raise TypeError("FeatStructs must be frozen before they " "can be hashed.") + try: + return self._hash + except AttributeError: + self._hash = self._calculate_hashvalue(set()) + return self._hash + + def _equal( + self, other, check_reentrance, visited_self, visited_other, visited_pairs + ): + """ + Return True iff self and other have equal values. + + :param visited_self: A set containing the ids of all ``self`` + feature structures we've already visited. + :param visited_other: A set containing the ids of all ``other`` + feature structures we've already visited. + :param visited_pairs: A set containing ``(selfid, otherid)`` pairs + for all pairs of feature structures we've already visited. + """ + # If we're the same object, then we're equal. + if self is other: + return True + + # If we have different classes, we're definitely not equal. + if self.__class__ != other.__class__: + return False + + # If we define different features, we're definitely not equal. + # (Perform len test first because it's faster -- we should + # do profiling to see if this actually helps) + if len(self) != len(other): + return False + if set(self._keys()) != set(other._keys()): + return False + + # If we're checking reentrance, then any time we revisit a + # structure, make sure that it was paired with the same + # feature structure that it is now. Note: if check_reentrance, + # then visited_pairs will never contain two pairs whose first + # values are equal, or two pairs whose second values are equal. + if check_reentrance: + if id(self) in visited_self or id(other) in visited_other: + return (id(self), id(other)) in visited_pairs + + # If we're not checking reentrance, then we still need to deal + # with cycles. If we encounter the same (self, other) pair a + # second time, then we won't learn anything more by examining + # their children a second time, so just return true. + else: + if (id(self), id(other)) in visited_pairs: + return True + + # Keep track of which nodes we've visited. + visited_self.add(id(self)) + visited_other.add(id(other)) + visited_pairs.add((id(self), id(other))) + + # Now we have to check all values. If any of them don't match, + # then return false. + for (fname, self_fval) in self._items(): + other_fval = other[fname] + if isinstance(self_fval, FeatStruct): + if not self_fval._equal( + other_fval, + check_reentrance, + visited_self, + visited_other, + visited_pairs, + ): + return False + else: + if self_fval != other_fval: + return False + + # Everything matched up; return true. + return True + + def _calculate_hashvalue(self, visited): + """ + Return a hash value for this feature structure. + + :require: ``self`` must be frozen. + :param visited: A set containing the ids of all feature + structures we've already visited while hashing. + """ + if id(self) in visited: + return 1 + visited.add(id(self)) + + hashval = 5831 + for (fname, fval) in sorted(self._items()): + hashval *= 37 + hashval += hash(fname) + hashval *= 37 + if isinstance(fval, FeatStruct): + hashval += fval._calculate_hashvalue(visited) + else: + hashval += hash(fval) + # Convert to a 32 bit int. + hashval = int(hashval & 0x7FFFFFFF) + return hashval + + ##//////////////////////////////////////////////////////////// + # { Freezing + ##//////////////////////////////////////////////////////////// + + #: Error message used by mutating methods when called on a frozen + #: feature structure. + _FROZEN_ERROR = "Frozen FeatStructs may not be modified." + + def freeze(self): + """ + Make this feature structure, and any feature structures it + contains, immutable. Note: this method does not attempt to + 'freeze' any feature value that is not a ``FeatStruct``; it + is recommended that you use only immutable feature values. + """ + if self._frozen: + return + self._freeze(set()) + + def frozen(self): + """ + Return True if this feature structure is immutable. Feature + structures can be made immutable with the ``freeze()`` method. + Immutable feature structures may not be made mutable again, + but new mutable copies can be produced with the ``copy()`` method. + """ + return self._frozen + + def _freeze(self, visited): + """ + Make this feature structure, and any feature structure it + contains, immutable. + + :param visited: A set containing the ids of all feature + structures we've already visited while freezing. + """ + if id(self) in visited: + return + visited.add(id(self)) + self._frozen = True + for (fname, fval) in sorted(self._items()): + if isinstance(fval, FeatStruct): + fval._freeze(visited) + + ##//////////////////////////////////////////////////////////// + # { Copying + ##//////////////////////////////////////////////////////////// + + def copy(self, deep=True): + """ + Return a new copy of ``self``. The new copy will not be frozen. + + :param deep: If true, create a deep copy; if false, create + a shallow copy. + """ + if deep: + return copy.deepcopy(self) + else: + return self.__class__(self) + + # Subclasses should define __deepcopy__ to ensure that the new + # copy will not be frozen. + def __deepcopy__(self, memo): + raise NotImplementedError() # Implemented by subclasses. + + ##//////////////////////////////////////////////////////////// + # { Structural Information + ##//////////////////////////////////////////////////////////// + + def cyclic(self): + """ + Return True if this feature structure contains itself. + """ + return self._find_reentrances({})[id(self)] + + def walk(self): + """ + Return an iterator that generates this feature structure, and + each feature structure it contains. Each feature structure will + be generated exactly once. + """ + return self._walk(set()) + + def _walk(self, visited): + """ + Return an iterator that generates this feature structure, and + each feature structure it contains. + + :param visited: A set containing the ids of all feature + structures we've already visited while freezing. + """ + raise NotImplementedError() # Implemented by subclasses. + + def _walk(self, visited): + if id(self) in visited: + return + visited.add(id(self)) + yield self + for fval in self._values(): + if isinstance(fval, FeatStruct): + yield from fval._walk(visited) + + # Walk through the feature tree. The first time we see a feature + # value, map it to False (not reentrant). If we see a feature + # value more than once, then map it to True (reentrant). + def _find_reentrances(self, reentrances): + """ + Return a dictionary that maps from the ``id`` of each feature + structure contained in ``self`` (including ``self``) to a + boolean value, indicating whether it is reentrant or not. + """ + if id(self) in reentrances: + # We've seen it more than once. + reentrances[id(self)] = True + else: + # This is the first time we've seen it. + reentrances[id(self)] = False + + # Recurse to contained feature structures. + for fval in self._values(): + if isinstance(fval, FeatStruct): + fval._find_reentrances(reentrances) + + return reentrances + + ##//////////////////////////////////////////////////////////// + # { Variables & Bindings + ##//////////////////////////////////////////////////////////// + + def substitute_bindings(self, bindings): + """:see: ``nltk.featstruct.substitute_bindings()``""" + return substitute_bindings(self, bindings) + + def retract_bindings(self, bindings): + """:see: ``nltk.featstruct.retract_bindings()``""" + return retract_bindings(self, bindings) + + def variables(self): + """:see: ``nltk.featstruct.find_variables()``""" + return find_variables(self) + + def rename_variables(self, vars=None, used_vars=(), new_vars=None): + """:see: ``nltk.featstruct.rename_variables()``""" + return rename_variables(self, vars, used_vars, new_vars) + + def remove_variables(self): + """ + Return the feature structure that is obtained by deleting + any feature whose value is a ``Variable``. + + :rtype: FeatStruct + """ + return remove_variables(self) + + ##//////////////////////////////////////////////////////////// + # { Unification + ##//////////////////////////////////////////////////////////// + + def unify(self, other, bindings=None, trace=False, fail=None, rename_vars=True): + return unify(self, other, bindings, trace, fail, rename_vars) + + def subsumes(self, other): + """ + Return True if ``self`` subsumes ``other``. I.e., return true + If unifying ``self`` with ``other`` would result in a feature + structure equal to ``other``. + """ + return subsumes(self, other) + + ##//////////////////////////////////////////////////////////// + # { String Representations + ##//////////////////////////////////////////////////////////// + + def __repr__(self): + """ + Display a single-line representation of this feature structure, + suitable for embedding in other representations. + """ + return self._repr(self._find_reentrances({}), {}) + + def _repr(self, reentrances, reentrance_ids): + """ + Return a string representation of this feature structure. + + :param reentrances: A dictionary that maps from the ``id`` of + each feature value in self, indicating whether that value + is reentrant or not. + :param reentrance_ids: A dictionary mapping from each ``id`` + of a feature value to a unique identifier. This is modified + by ``repr``: the first time a reentrant feature value is + displayed, an identifier is added to ``reentrance_ids`` for it. + """ + raise NotImplementedError() + + +# Mutation: disable if frozen. +_FROZEN_ERROR = "Frozen FeatStructs may not be modified." +_FROZEN_NOTICE = "\n%sIf self is frozen, raise ValueError." + + +def _check_frozen(method, indent=""): + """ + Given a method function, return a new method function that first + checks if ``self._frozen`` is true; and if so, raises ``ValueError`` + with an appropriate message. Otherwise, call the method and return + its result. + """ + + def wrapped(self, *args, **kwargs): + if self._frozen: + raise ValueError(_FROZEN_ERROR) + else: + return method(self, *args, **kwargs) + + wrapped.__name__ = method.__name__ + wrapped.__doc__ = (method.__doc__ or "") + (_FROZEN_NOTICE % indent) + return wrapped + + +###################################################################### +# Feature Dictionary +###################################################################### + + +class FeatDict(FeatStruct, dict): + """ + A feature structure that acts like a Python dictionary. I.e., a + mapping from feature identifiers to feature values, where a feature + identifier can be a string or a ``Feature``; and where a feature value + can be either a basic value (such as a string or an integer), or a nested + feature structure. A feature identifiers for a ``FeatDict`` is + sometimes called a "feature name". + + Two feature dicts are considered equal if they assign the same + values to all features, and have the same reentrances. + + :see: ``FeatStruct`` for information about feature paths, reentrance, + cyclic feature structures, mutability, freezing, and hashing. + """ + + def __init__(self, features=None, **morefeatures): + """ + Create a new feature dictionary, with the specified features. + + :param features: The initial value for this feature + dictionary. If ``features`` is a ``FeatStruct``, then its + features are copied (shallow copy). If ``features`` is a + dict, then a feature is created for each item, mapping its + key to its value. If ``features`` is a string, then it is + processed using ``FeatStructReader``. If ``features`` is a list of + tuples ``(name, val)``, then a feature is created for each tuple. + :param morefeatures: Additional features for the new feature + dictionary. If a feature is listed under both ``features`` and + ``morefeatures``, then the value from ``morefeatures`` will be + used. + """ + if isinstance(features, str): + FeatStructReader().fromstring(features, self) + self.update(**morefeatures) + else: + # update() checks the types of features. + self.update(features, **morefeatures) + + # //////////////////////////////////////////////////////////// + # { Dict methods + # //////////////////////////////////////////////////////////// + _INDEX_ERROR = "Expected feature name or path. Got %r." + + def __getitem__(self, name_or_path): + """If the feature with the given name or path exists, return + its value; otherwise, raise ``KeyError``.""" + if isinstance(name_or_path, (str, Feature)): + return dict.__getitem__(self, name_or_path) + elif isinstance(name_or_path, tuple): + try: + val = self + for fid in name_or_path: + if not isinstance(val, FeatStruct): + raise KeyError # path contains base value + val = val[fid] + return val + except (KeyError, IndexError) as e: + raise KeyError(name_or_path) from e + else: + raise TypeError(self._INDEX_ERROR % name_or_path) + + def get(self, name_or_path, default=None): + """If the feature with the given name or path exists, return its + value; otherwise, return ``default``.""" + try: + return self[name_or_path] + except KeyError: + return default + + def __contains__(self, name_or_path): + """Return true if a feature with the given name or path exists.""" + try: + self[name_or_path] + return True + except KeyError: + return False + + def has_key(self, name_or_path): + """Return true if a feature with the given name or path exists.""" + return name_or_path in self + + def __delitem__(self, name_or_path): + """If the feature with the given name or path exists, delete + its value; otherwise, raise ``KeyError``.""" + if self._frozen: + raise ValueError(_FROZEN_ERROR) + if isinstance(name_or_path, (str, Feature)): + return dict.__delitem__(self, name_or_path) + elif isinstance(name_or_path, tuple): + if len(name_or_path) == 0: + raise ValueError("The path () can not be set") + else: + parent = self[name_or_path[:-1]] + if not isinstance(parent, FeatStruct): + raise KeyError(name_or_path) # path contains base value + del parent[name_or_path[-1]] + else: + raise TypeError(self._INDEX_ERROR % name_or_path) + + def __setitem__(self, name_or_path, value): + """Set the value for the feature with the given name or path + to ``value``. If ``name_or_path`` is an invalid path, raise + ``KeyError``.""" + if self._frozen: + raise ValueError(_FROZEN_ERROR) + if isinstance(name_or_path, (str, Feature)): + return dict.__setitem__(self, name_or_path, value) + elif isinstance(name_or_path, tuple): + if len(name_or_path) == 0: + raise ValueError("The path () can not be set") + else: + parent = self[name_or_path[:-1]] + if not isinstance(parent, FeatStruct): + raise KeyError(name_or_path) # path contains base value + parent[name_or_path[-1]] = value + else: + raise TypeError(self._INDEX_ERROR % name_or_path) + + clear = _check_frozen(dict.clear) + pop = _check_frozen(dict.pop) + popitem = _check_frozen(dict.popitem) + setdefault = _check_frozen(dict.setdefault) + + def update(self, features=None, **morefeatures): + if self._frozen: + raise ValueError(_FROZEN_ERROR) + if features is None: + items = () + elif hasattr(features, "items") and callable(features.items): + items = features.items() + elif hasattr(features, "__iter__"): + items = features + else: + raise ValueError("Expected mapping or list of tuples") + + for key, val in items: + if not isinstance(key, (str, Feature)): + raise TypeError("Feature names must be strings") + self[key] = val + for key, val in morefeatures.items(): + if not isinstance(key, (str, Feature)): + raise TypeError("Feature names must be strings") + self[key] = val + + ##//////////////////////////////////////////////////////////// + # { Copying + ##//////////////////////////////////////////////////////////// + + def __deepcopy__(self, memo): + memo[id(self)] = selfcopy = self.__class__() + for (key, val) in self._items(): + selfcopy[copy.deepcopy(key, memo)] = copy.deepcopy(val, memo) + return selfcopy + + ##//////////////////////////////////////////////////////////// + # { Uniform Accessor Methods + ##//////////////////////////////////////////////////////////// + + def _keys(self): + return self.keys() + + def _values(self): + return self.values() + + def _items(self): + return self.items() + + ##//////////////////////////////////////////////////////////// + # { String Representations + ##//////////////////////////////////////////////////////////// + + def __str__(self): + """ + Display a multi-line representation of this feature dictionary + as an FVM (feature value matrix). + """ + return "\n".join(self._str(self._find_reentrances({}), {})) + + def _repr(self, reentrances, reentrance_ids): + segments = [] + prefix = "" + suffix = "" + + # If this is the first time we've seen a reentrant structure, + # then assign it a unique identifier. + if reentrances[id(self)]: + assert id(self) not in reentrance_ids + reentrance_ids[id(self)] = repr(len(reentrance_ids) + 1) + + # sorting note: keys are unique strings, so we'll never fall + # through to comparing values. + for (fname, fval) in sorted(self.items()): + display = getattr(fname, "display", None) + if id(fval) in reentrance_ids: + segments.append(f"{fname}->({reentrance_ids[id(fval)]})") + elif ( + display == "prefix" and not prefix and isinstance(fval, (Variable, str)) + ): + prefix = "%s" % fval + elif display == "slash" and not suffix: + if isinstance(fval, Variable): + suffix = "/%s" % fval.name + else: + suffix = "/%s" % repr(fval) + elif isinstance(fval, Variable): + segments.append(f"{fname}={fval.name}") + elif fval is True: + segments.append("+%s" % fname) + elif fval is False: + segments.append("-%s" % fname) + elif isinstance(fval, Expression): + segments.append(f"{fname}=<{fval}>") + elif not isinstance(fval, FeatStruct): + segments.append(f"{fname}={repr(fval)}") + else: + fval_repr = fval._repr(reentrances, reentrance_ids) + segments.append(f"{fname}={fval_repr}") + # If it's reentrant, then add on an identifier tag. + if reentrances[id(self)]: + prefix = f"({reentrance_ids[id(self)]}){prefix}" + return "{}[{}]{}".format(prefix, ", ".join(segments), suffix) + + def _str(self, reentrances, reentrance_ids): + """ + :return: A list of lines composing a string representation of + this feature dictionary. + :param reentrances: A dictionary that maps from the ``id`` of + each feature value in self, indicating whether that value + is reentrant or not. + :param reentrance_ids: A dictionary mapping from each ``id`` + of a feature value to a unique identifier. This is modified + by ``repr``: the first time a reentrant feature value is + displayed, an identifier is added to ``reentrance_ids`` for + it. + """ + # If this is the first time we've seen a reentrant structure, + # then tack on an id string. + if reentrances[id(self)]: + assert id(self) not in reentrance_ids + reentrance_ids[id(self)] = repr(len(reentrance_ids) + 1) + + # Special case: empty feature dict. + if len(self) == 0: + if reentrances[id(self)]: + return ["(%s) []" % reentrance_ids[id(self)]] + else: + return ["[]"] + + # What's the longest feature name? Use this to align names. + maxfnamelen = max(len("%s" % k) for k in self.keys()) + + lines = [] + # sorting note: keys are unique strings, so we'll never fall + # through to comparing values. + for (fname, fval) in sorted(self.items()): + fname = ("%s" % fname).ljust(maxfnamelen) + if isinstance(fval, Variable): + lines.append(f"{fname} = {fval.name}") + + elif isinstance(fval, Expression): + lines.append(f"{fname} = <{fval}>") + + elif isinstance(fval, FeatList): + fval_repr = fval._repr(reentrances, reentrance_ids) + lines.append(f"{fname} = {repr(fval_repr)}") + + elif not isinstance(fval, FeatDict): + # It's not a nested feature structure -- just print it. + lines.append(f"{fname} = {repr(fval)}") + + elif id(fval) in reentrance_ids: + # It's a feature structure we've seen before -- print + # the reentrance id. + lines.append(f"{fname} -> ({reentrance_ids[id(fval)]})") + + else: + # It's a new feature structure. Separate it from + # other values by a blank line. + if lines and lines[-1] != "": + lines.append("") + + # Recursively print the feature's value (fval). + fval_lines = fval._str(reentrances, reentrance_ids) + + # Indent each line to make room for fname. + fval_lines = [(" " * (maxfnamelen + 3)) + l for l in fval_lines] + + # Pick which line we'll display fname on, & splice it in. + nameline = (len(fval_lines) - 1) // 2 + fval_lines[nameline] = ( + fname + " =" + fval_lines[nameline][maxfnamelen + 2 :] + ) + + # Add the feature structure to the output. + lines += fval_lines + + # Separate FeatStructs by a blank line. + lines.append("") + + # Get rid of any excess blank lines. + if lines[-1] == "": + lines.pop() + + # Add brackets around everything. + maxlen = max(len(line) for line in lines) + lines = ["[ {}{} ]".format(line, " " * (maxlen - len(line))) for line in lines] + + # If it's reentrant, then add on an identifier tag. + if reentrances[id(self)]: + idstr = "(%s) " % reentrance_ids[id(self)] + lines = [(" " * len(idstr)) + l for l in lines] + idline = (len(lines) - 1) // 2 + lines[idline] = idstr + lines[idline][len(idstr) :] + + return lines + + +###################################################################### +# Feature List +###################################################################### + + +class FeatList(FeatStruct, list): + """ + A list of feature values, where each feature value is either a + basic value (such as a string or an integer), or a nested feature + structure. + + Feature lists may contain reentrant feature values. A "reentrant + feature value" is a single feature value that can be accessed via + multiple feature paths. Feature lists may also be cyclic. + + Two feature lists are considered equal if they assign the same + values to all features, and have the same reentrances. + + :see: ``FeatStruct`` for information about feature paths, reentrance, + cyclic feature structures, mutability, freezing, and hashing. + """ + + def __init__(self, features=()): + """ + Create a new feature list, with the specified features. + + :param features: The initial list of features for this feature + list. If ``features`` is a string, then it is paresd using + ``FeatStructReader``. Otherwise, it should be a sequence + of basic values and nested feature structures. + """ + if isinstance(features, str): + FeatStructReader().fromstring(features, self) + else: + list.__init__(self, features) + + # //////////////////////////////////////////////////////////// + # { List methods + # //////////////////////////////////////////////////////////// + _INDEX_ERROR = "Expected int or feature path. Got %r." + + def __getitem__(self, name_or_path): + if isinstance(name_or_path, int): + return list.__getitem__(self, name_or_path) + elif isinstance(name_or_path, tuple): + try: + val = self + for fid in name_or_path: + if not isinstance(val, FeatStruct): + raise KeyError # path contains base value + val = val[fid] + return val + except (KeyError, IndexError) as e: + raise KeyError(name_or_path) from e + else: + raise TypeError(self._INDEX_ERROR % name_or_path) + + def __delitem__(self, name_or_path): + """If the feature with the given name or path exists, delete + its value; otherwise, raise ``KeyError``.""" + if self._frozen: + raise ValueError(_FROZEN_ERROR) + if isinstance(name_or_path, (int, slice)): + return list.__delitem__(self, name_or_path) + elif isinstance(name_or_path, tuple): + if len(name_or_path) == 0: + raise ValueError("The path () can not be set") + else: + parent = self[name_or_path[:-1]] + if not isinstance(parent, FeatStruct): + raise KeyError(name_or_path) # path contains base value + del parent[name_or_path[-1]] + else: + raise TypeError(self._INDEX_ERROR % name_or_path) + + def __setitem__(self, name_or_path, value): + """Set the value for the feature with the given name or path + to ``value``. If ``name_or_path`` is an invalid path, raise + ``KeyError``.""" + if self._frozen: + raise ValueError(_FROZEN_ERROR) + if isinstance(name_or_path, (int, slice)): + return list.__setitem__(self, name_or_path, value) + elif isinstance(name_or_path, tuple): + if len(name_or_path) == 0: + raise ValueError("The path () can not be set") + else: + parent = self[name_or_path[:-1]] + if not isinstance(parent, FeatStruct): + raise KeyError(name_or_path) # path contains base value + parent[name_or_path[-1]] = value + else: + raise TypeError(self._INDEX_ERROR % name_or_path) + + # __delslice__ = _check_frozen(list.__delslice__, ' ') + # __setslice__ = _check_frozen(list.__setslice__, ' ') + __iadd__ = _check_frozen(list.__iadd__) + __imul__ = _check_frozen(list.__imul__) + append = _check_frozen(list.append) + extend = _check_frozen(list.extend) + insert = _check_frozen(list.insert) + pop = _check_frozen(list.pop) + remove = _check_frozen(list.remove) + reverse = _check_frozen(list.reverse) + sort = _check_frozen(list.sort) + + ##//////////////////////////////////////////////////////////// + # { Copying + ##//////////////////////////////////////////////////////////// + + def __deepcopy__(self, memo): + memo[id(self)] = selfcopy = self.__class__() + selfcopy.extend(copy.deepcopy(fval, memo) for fval in self) + return selfcopy + + ##//////////////////////////////////////////////////////////// + # { Uniform Accessor Methods + ##//////////////////////////////////////////////////////////// + + def _keys(self): + return list(range(len(self))) + + def _values(self): + return self + + def _items(self): + return enumerate(self) + + ##//////////////////////////////////////////////////////////// + # { String Representations + ##//////////////////////////////////////////////////////////// + + # Special handling for: reentrances, variables, expressions. + def _repr(self, reentrances, reentrance_ids): + # If this is the first time we've seen a reentrant structure, + # then assign it a unique identifier. + if reentrances[id(self)]: + assert id(self) not in reentrance_ids + reentrance_ids[id(self)] = repr(len(reentrance_ids) + 1) + prefix = "(%s)" % reentrance_ids[id(self)] + else: + prefix = "" + + segments = [] + for fval in self: + if id(fval) in reentrance_ids: + segments.append("->(%s)" % reentrance_ids[id(fval)]) + elif isinstance(fval, Variable): + segments.append(fval.name) + elif isinstance(fval, Expression): + segments.append("%s" % fval) + elif isinstance(fval, FeatStruct): + segments.append(fval._repr(reentrances, reentrance_ids)) + else: + segments.append("%s" % repr(fval)) + + return "{}[{}]".format(prefix, ", ".join(segments)) + + +###################################################################### +# Variables & Bindings +###################################################################### + + +def substitute_bindings(fstruct, bindings, fs_class="default"): + """ + Return the feature structure that is obtained by replacing each + variable bound by ``bindings`` with its binding. If a variable is + aliased to a bound variable, then it will be replaced by that + variable's value. If a variable is aliased to an unbound + variable, then it will be replaced by that variable. + + :type bindings: dict(Variable -> any) + :param bindings: A dictionary mapping from variables to values. + """ + if fs_class == "default": + fs_class = _default_fs_class(fstruct) + fstruct = copy.deepcopy(fstruct) + _substitute_bindings(fstruct, bindings, fs_class, set()) + return fstruct + + +def _substitute_bindings(fstruct, bindings, fs_class, visited): + # Visit each node only once: + if id(fstruct) in visited: + return + visited.add(id(fstruct)) + + if _is_mapping(fstruct): + items = fstruct.items() + elif _is_sequence(fstruct): + items = enumerate(fstruct) + else: + raise ValueError("Expected mapping or sequence") + for (fname, fval) in items: + while isinstance(fval, Variable) and fval in bindings: + fval = fstruct[fname] = bindings[fval] + if isinstance(fval, fs_class): + _substitute_bindings(fval, bindings, fs_class, visited) + elif isinstance(fval, SubstituteBindingsI): + fstruct[fname] = fval.substitute_bindings(bindings) + + +def retract_bindings(fstruct, bindings, fs_class="default"): + """ + Return the feature structure that is obtained by replacing each + feature structure value that is bound by ``bindings`` with the + variable that binds it. A feature structure value must be + identical to a bound value (i.e., have equal id) to be replaced. + + ``bindings`` is modified to point to this new feature structure, + rather than the original feature structure. Feature structure + values in ``bindings`` may be modified if they are contained in + ``fstruct``. + """ + if fs_class == "default": + fs_class = _default_fs_class(fstruct) + (fstruct, new_bindings) = copy.deepcopy((fstruct, bindings)) + bindings.update(new_bindings) + inv_bindings = {id(val): var for (var, val) in bindings.items()} + _retract_bindings(fstruct, inv_bindings, fs_class, set()) + return fstruct + + +def _retract_bindings(fstruct, inv_bindings, fs_class, visited): + # Visit each node only once: + if id(fstruct) in visited: + return + visited.add(id(fstruct)) + + if _is_mapping(fstruct): + items = fstruct.items() + elif _is_sequence(fstruct): + items = enumerate(fstruct) + else: + raise ValueError("Expected mapping or sequence") + for (fname, fval) in items: + if isinstance(fval, fs_class): + if id(fval) in inv_bindings: + fstruct[fname] = inv_bindings[id(fval)] + _retract_bindings(fval, inv_bindings, fs_class, visited) + + +def find_variables(fstruct, fs_class="default"): + """ + :return: The set of variables used by this feature structure. + :rtype: set(Variable) + """ + if fs_class == "default": + fs_class = _default_fs_class(fstruct) + return _variables(fstruct, set(), fs_class, set()) + + +def _variables(fstruct, vars, fs_class, visited): + # Visit each node only once: + if id(fstruct) in visited: + return + visited.add(id(fstruct)) + if _is_mapping(fstruct): + items = fstruct.items() + elif _is_sequence(fstruct): + items = enumerate(fstruct) + else: + raise ValueError("Expected mapping or sequence") + for (fname, fval) in items: + if isinstance(fval, Variable): + vars.add(fval) + elif isinstance(fval, fs_class): + _variables(fval, vars, fs_class, visited) + elif isinstance(fval, SubstituteBindingsI): + vars.update(fval.variables()) + return vars + + +def rename_variables( + fstruct, vars=None, used_vars=(), new_vars=None, fs_class="default" +): + """ + Return the feature structure that is obtained by replacing + any of this feature structure's variables that are in ``vars`` + with new variables. The names for these new variables will be + names that are not used by any variable in ``vars``, or in + ``used_vars``, or in this feature structure. + + :type vars: set + :param vars: The set of variables that should be renamed. + If not specified, ``find_variables(fstruct)`` is used; i.e., all + variables will be given new names. + :type used_vars: set + :param used_vars: A set of variables whose names should not be + used by the new variables. + :type new_vars: dict(Variable -> Variable) + :param new_vars: A dictionary that is used to hold the mapping + from old variables to new variables. For each variable *v* + in this feature structure: + + - If ``new_vars`` maps *v* to *v'*, then *v* will be + replaced by *v'*. + - If ``new_vars`` does not contain *v*, but ``vars`` + does contain *v*, then a new entry will be added to + ``new_vars``, mapping *v* to the new variable that is used + to replace it. + + To consistently rename the variables in a set of feature + structures, simply apply rename_variables to each one, using + the same dictionary: + + >>> from nltk.featstruct import FeatStruct + >>> fstruct1 = FeatStruct('[subj=[agr=[gender=?y]], obj=[agr=[gender=?y]]]') + >>> fstruct2 = FeatStruct('[subj=[agr=[number=?z,gender=?y]], obj=[agr=[number=?z,gender=?y]]]') + >>> new_vars = {} # Maps old vars to alpha-renamed vars + >>> fstruct1.rename_variables(new_vars=new_vars) + [obj=[agr=[gender=?y2]], subj=[agr=[gender=?y2]]] + >>> fstruct2.rename_variables(new_vars=new_vars) + [obj=[agr=[gender=?y2, number=?z2]], subj=[agr=[gender=?y2, number=?z2]]] + + If new_vars is not specified, then an empty dictionary is used. + """ + if fs_class == "default": + fs_class = _default_fs_class(fstruct) + + # Default values: + if new_vars is None: + new_vars = {} + if vars is None: + vars = find_variables(fstruct, fs_class) + else: + vars = set(vars) + + # Add our own variables to used_vars. + used_vars = find_variables(fstruct, fs_class).union(used_vars) + + # Copy ourselves, and rename variables in the copy. + return _rename_variables( + copy.deepcopy(fstruct), vars, used_vars, new_vars, fs_class, set() + ) + + +def _rename_variables(fstruct, vars, used_vars, new_vars, fs_class, visited): + if id(fstruct) in visited: + return + visited.add(id(fstruct)) + if _is_mapping(fstruct): + items = fstruct.items() + elif _is_sequence(fstruct): + items = enumerate(fstruct) + else: + raise ValueError("Expected mapping or sequence") + for (fname, fval) in items: + if isinstance(fval, Variable): + # If it's in new_vars, then rebind it. + if fval in new_vars: + fstruct[fname] = new_vars[fval] + # If it's in vars, pick a new name for it. + elif fval in vars: + new_vars[fval] = _rename_variable(fval, used_vars) + fstruct[fname] = new_vars[fval] + used_vars.add(new_vars[fval]) + elif isinstance(fval, fs_class): + _rename_variables(fval, vars, used_vars, new_vars, fs_class, visited) + elif isinstance(fval, SubstituteBindingsI): + # Pick new names for any variables in `vars` + for var in fval.variables(): + if var in vars and var not in new_vars: + new_vars[var] = _rename_variable(var, used_vars) + used_vars.add(new_vars[var]) + # Replace all variables in `new_vars`. + fstruct[fname] = fval.substitute_bindings(new_vars) + return fstruct + + +def _rename_variable(var, used_vars): + name, n = re.sub(r"\d+$", "", var.name), 2 + if not name: + name = "?" + while Variable(f"{name}{n}") in used_vars: + n += 1 + return Variable(f"{name}{n}") + + +def remove_variables(fstruct, fs_class="default"): + """ + :rtype: FeatStruct + :return: The feature structure that is obtained by deleting + all features whose values are ``Variables``. + """ + if fs_class == "default": + fs_class = _default_fs_class(fstruct) + return _remove_variables(copy.deepcopy(fstruct), fs_class, set()) + + +def _remove_variables(fstruct, fs_class, visited): + if id(fstruct) in visited: + return + visited.add(id(fstruct)) + + if _is_mapping(fstruct): + items = list(fstruct.items()) + elif _is_sequence(fstruct): + items = list(enumerate(fstruct)) + else: + raise ValueError("Expected mapping or sequence") + + for (fname, fval) in items: + if isinstance(fval, Variable): + del fstruct[fname] + elif isinstance(fval, fs_class): + _remove_variables(fval, fs_class, visited) + return fstruct + + +###################################################################### +# Unification +###################################################################### + + +class _UnificationFailure: + def __repr__(self): + return "nltk.featstruct.UnificationFailure" + + +UnificationFailure = _UnificationFailure() +"""A unique value used to indicate unification failure. It can be + returned by ``Feature.unify_base_values()`` or by custom ``fail()`` + functions to indicate that unificaiton should fail.""" + + +# The basic unification algorithm: +# 1. Make copies of self and other (preserving reentrance) +# 2. Destructively unify self and other +# 3. Apply forward pointers, to preserve reentrance. +# 4. Replace bound variables with their values. +def unify( + fstruct1, + fstruct2, + bindings=None, + trace=False, + fail=None, + rename_vars=True, + fs_class="default", +): + """ + Unify ``fstruct1`` with ``fstruct2``, and return the resulting feature + structure. This unified feature structure is the minimal + feature structure that contains all feature value assignments from both + ``fstruct1`` and ``fstruct2``, and that preserves all reentrancies. + + If no such feature structure exists (because ``fstruct1`` and + ``fstruct2`` specify incompatible values for some feature), then + unification fails, and ``unify`` returns None. + + Bound variables are replaced by their values. Aliased + variables are replaced by their representative variable + (if unbound) or the value of their representative variable + (if bound). I.e., if variable *v* is in ``bindings``, + then *v* is replaced by ``bindings[v]``. This will + be repeated until the variable is replaced by an unbound + variable or a non-variable value. + + Unbound variables are bound when they are unified with + values; and aliased when they are unified with variables. + I.e., if variable *v* is not in ``bindings``, and is + unified with a variable or value *x*, then + ``bindings[v]`` is set to *x*. + + If ``bindings`` is unspecified, then all variables are + assumed to be unbound. I.e., ``bindings`` defaults to an + empty dict. + + >>> from nltk.featstruct import FeatStruct + >>> FeatStruct('[a=?x]').unify(FeatStruct('[b=?x]')) + [a=?x, b=?x2] + + :type bindings: dict(Variable -> any) + :param bindings: A set of variable bindings to be used and + updated during unification. + :type trace: bool + :param trace: If true, generate trace output. + :type rename_vars: bool + :param rename_vars: If True, then rename any variables in + ``fstruct2`` that are also used in ``fstruct1``, in order to + avoid collisions on variable names. + """ + # Decide which class(es) will be treated as feature structures, + # for the purposes of unification. + if fs_class == "default": + fs_class = _default_fs_class(fstruct1) + if _default_fs_class(fstruct2) != fs_class: + raise ValueError( + "Mixing FeatStruct objects with Python " + "dicts and lists is not supported." + ) + assert isinstance(fstruct1, fs_class) + assert isinstance(fstruct2, fs_class) + + # If bindings are unspecified, use an empty set of bindings. + user_bindings = bindings is not None + if bindings is None: + bindings = {} + + # Make copies of fstruct1 and fstruct2 (since the unification + # algorithm is destructive). Do it all at once, to preserve + # reentrance links between fstruct1 and fstruct2. Copy bindings + # as well, in case there are any bound vars that contain parts + # of fstruct1 or fstruct2. + (fstruct1copy, fstruct2copy, bindings_copy) = copy.deepcopy( + (fstruct1, fstruct2, bindings) + ) + + # Copy the bindings back to the original bindings dict. + bindings.update(bindings_copy) + + if rename_vars: + vars1 = find_variables(fstruct1copy, fs_class) + vars2 = find_variables(fstruct2copy, fs_class) + _rename_variables(fstruct2copy, vars1, vars2, {}, fs_class, set()) + + # Do the actual unification. If it fails, return None. + forward = {} + if trace: + _trace_unify_start((), fstruct1copy, fstruct2copy) + try: + result = _destructively_unify( + fstruct1copy, fstruct2copy, bindings, forward, trace, fail, fs_class, () + ) + except _UnificationFailureError: + return None + + # _destructively_unify might return UnificationFailure, e.g. if we + # tried to unify a mapping with a sequence. + if result is UnificationFailure: + if fail is None: + return None + else: + return fail(fstruct1copy, fstruct2copy, ()) + + # Replace any feature structure that has a forward pointer + # with the target of its forward pointer. + result = _apply_forwards(result, forward, fs_class, set()) + if user_bindings: + _apply_forwards_to_bindings(forward, bindings) + + # Replace bound vars with values. + _resolve_aliases(bindings) + _substitute_bindings(result, bindings, fs_class, set()) + + # Return the result. + if trace: + _trace_unify_succeed((), result) + if trace: + _trace_bindings((), bindings) + return result + + +class _UnificationFailureError(Exception): + """An exception that is used by ``_destructively_unify`` to abort + unification when a failure is encountered.""" + + +def _destructively_unify( + fstruct1, fstruct2, bindings, forward, trace, fail, fs_class, path +): + """ + Attempt to unify ``fstruct1`` and ``fstruct2`` by modifying them + in-place. If the unification succeeds, then ``fstruct1`` will + contain the unified value, the value of ``fstruct2`` is undefined, + and forward[id(fstruct2)] is set to fstruct1. If the unification + fails, then a _UnificationFailureError is raised, and the + values of ``fstruct1`` and ``fstruct2`` are undefined. + + :param bindings: A dictionary mapping variables to values. + :param forward: A dictionary mapping feature structures ids + to replacement structures. When two feature structures + are merged, a mapping from one to the other will be added + to the forward dictionary; and changes will be made only + to the target of the forward dictionary. + ``_destructively_unify`` will always 'follow' any links + in the forward dictionary for fstruct1 and fstruct2 before + actually unifying them. + :param trace: If true, generate trace output + :param path: The feature path that led us to this unification + step. Used for trace output. + """ + # If fstruct1 is already identical to fstruct2, we're done. + # Note: this, together with the forward pointers, ensures + # that unification will terminate even for cyclic structures. + if fstruct1 is fstruct2: + if trace: + _trace_unify_identity(path, fstruct1) + return fstruct1 + + # Set fstruct2's forward pointer to point to fstruct1; this makes + # fstruct1 the canonical copy for fstruct2. Note that we need to + # do this before we recurse into any child structures, in case + # they're cyclic. + forward[id(fstruct2)] = fstruct1 + + # Unifying two mappings: + if _is_mapping(fstruct1) and _is_mapping(fstruct2): + for fname in fstruct1: + if getattr(fname, "default", None) is not None: + fstruct2.setdefault(fname, fname.default) + for fname in fstruct2: + if getattr(fname, "default", None) is not None: + fstruct1.setdefault(fname, fname.default) + + # Unify any values that are defined in both fstruct1 and + # fstruct2. Copy any values that are defined in fstruct2 but + # not in fstruct1 to fstruct1. Note: sorting fstruct2's + # features isn't actually necessary; but we do it to give + # deterministic behavior, e.g. for tracing. + for fname, fval2 in sorted(fstruct2.items()): + if fname in fstruct1: + fstruct1[fname] = _unify_feature_values( + fname, + fstruct1[fname], + fval2, + bindings, + forward, + trace, + fail, + fs_class, + path + (fname,), + ) + else: + fstruct1[fname] = fval2 + + return fstruct1 # Contains the unified value. + + # Unifying two sequences: + elif _is_sequence(fstruct1) and _is_sequence(fstruct2): + # If the lengths don't match, fail. + if len(fstruct1) != len(fstruct2): + return UnificationFailure + + # Unify corresponding values in fstruct1 and fstruct2. + for findex in range(len(fstruct1)): + fstruct1[findex] = _unify_feature_values( + findex, + fstruct1[findex], + fstruct2[findex], + bindings, + forward, + trace, + fail, + fs_class, + path + (findex,), + ) + + return fstruct1 # Contains the unified value. + + # Unifying sequence & mapping: fail. The failure function + # doesn't get a chance to recover in this case. + elif (_is_sequence(fstruct1) or _is_mapping(fstruct1)) and ( + _is_sequence(fstruct2) or _is_mapping(fstruct2) + ): + return UnificationFailure + + # Unifying anything else: not allowed! + raise TypeError("Expected mappings or sequences") + + +def _unify_feature_values( + fname, fval1, fval2, bindings, forward, trace, fail, fs_class, fpath +): + """ + Attempt to unify ``fval1`` and and ``fval2``, and return the + resulting unified value. The method of unification will depend on + the types of ``fval1`` and ``fval2``: + + 1. If they're both feature structures, then destructively + unify them (see ``_destructively_unify()``. + 2. If they're both unbound variables, then alias one variable + to the other (by setting bindings[v2]=v1). + 3. If one is an unbound variable, and the other is a value, + then bind the unbound variable to the value. + 4. If one is a feature structure, and the other is a base value, + then fail. + 5. If they're both base values, then unify them. By default, + this will succeed if they are equal, and fail otherwise. + """ + if trace: + _trace_unify_start(fpath, fval1, fval2) + + # Look up the "canonical" copy of fval1 and fval2 + while id(fval1) in forward: + fval1 = forward[id(fval1)] + while id(fval2) in forward: + fval2 = forward[id(fval2)] + + # If fval1 or fval2 is a bound variable, then + # replace it by the variable's bound value. This + # includes aliased variables, which are encoded as + # variables bound to other variables. + fvar1 = fvar2 = None + while isinstance(fval1, Variable) and fval1 in bindings: + fvar1 = fval1 + fval1 = bindings[fval1] + while isinstance(fval2, Variable) and fval2 in bindings: + fvar2 = fval2 + fval2 = bindings[fval2] + + # Case 1: Two feature structures (recursive case) + if isinstance(fval1, fs_class) and isinstance(fval2, fs_class): + result = _destructively_unify( + fval1, fval2, bindings, forward, trace, fail, fs_class, fpath + ) + + # Case 2: Two unbound variables (create alias) + elif isinstance(fval1, Variable) and isinstance(fval2, Variable): + if fval1 != fval2: + bindings[fval2] = fval1 + result = fval1 + + # Case 3: An unbound variable and a value (bind) + elif isinstance(fval1, Variable): + bindings[fval1] = fval2 + result = fval1 + elif isinstance(fval2, Variable): + bindings[fval2] = fval1 + result = fval2 + + # Case 4: A feature structure & a base value (fail) + elif isinstance(fval1, fs_class) or isinstance(fval2, fs_class): + result = UnificationFailure + + # Case 5: Two base values + else: + # Case 5a: Feature defines a custom unification method for base values + if isinstance(fname, Feature): + result = fname.unify_base_values(fval1, fval2, bindings) + # Case 5b: Feature value defines custom unification method + elif isinstance(fval1, CustomFeatureValue): + result = fval1.unify(fval2) + # Sanity check: unify value should be symmetric + if isinstance(fval2, CustomFeatureValue) and result != fval2.unify(fval1): + raise AssertionError( + "CustomFeatureValue objects %r and %r disagree " + "about unification value: %r vs. %r" + % (fval1, fval2, result, fval2.unify(fval1)) + ) + elif isinstance(fval2, CustomFeatureValue): + result = fval2.unify(fval1) + # Case 5c: Simple values -- check if they're equal. + else: + if fval1 == fval2: + result = fval1 + else: + result = UnificationFailure + + # If either value was a bound variable, then update the + # bindings. (This is really only necessary if fname is a + # Feature or if either value is a CustomFeatureValue.) + if result is not UnificationFailure: + if fvar1 is not None: + bindings[fvar1] = result + result = fvar1 + if fvar2 is not None and fvar2 != fvar1: + bindings[fvar2] = result + result = fvar2 + + # If we unification failed, call the failure function; it + # might decide to continue anyway. + if result is UnificationFailure: + if fail is not None: + result = fail(fval1, fval2, fpath) + if trace: + _trace_unify_fail(fpath[:-1], result) + if result is UnificationFailure: + raise _UnificationFailureError + + # Normalize the result. + if isinstance(result, fs_class): + result = _apply_forwards(result, forward, fs_class, set()) + + if trace: + _trace_unify_succeed(fpath, result) + if trace and isinstance(result, fs_class): + _trace_bindings(fpath, bindings) + + return result + + +def _apply_forwards_to_bindings(forward, bindings): + """ + Replace any feature structure that has a forward pointer with + the target of its forward pointer (to preserve reentrancy). + """ + for (var, value) in bindings.items(): + while id(value) in forward: + value = forward[id(value)] + bindings[var] = value + + +def _apply_forwards(fstruct, forward, fs_class, visited): + """ + Replace any feature structure that has a forward pointer with + the target of its forward pointer (to preserve reentrancy). + """ + # Follow our own forwards pointers (if any) + while id(fstruct) in forward: + fstruct = forward[id(fstruct)] + + # Visit each node only once: + if id(fstruct) in visited: + return + visited.add(id(fstruct)) + + if _is_mapping(fstruct): + items = fstruct.items() + elif _is_sequence(fstruct): + items = enumerate(fstruct) + else: + raise ValueError("Expected mapping or sequence") + for fname, fval in items: + if isinstance(fval, fs_class): + # Replace w/ forwarded value. + while id(fval) in forward: + fval = forward[id(fval)] + fstruct[fname] = fval + # Recurse to child. + _apply_forwards(fval, forward, fs_class, visited) + + return fstruct + + +def _resolve_aliases(bindings): + """ + Replace any bound aliased vars with their binding; and replace + any unbound aliased vars with their representative var. + """ + for (var, value) in bindings.items(): + while isinstance(value, Variable) and value in bindings: + value = bindings[var] = bindings[value] + + +def _trace_unify_start(path, fval1, fval2): + if path == (): + print("\nUnification trace:") + else: + fullname = ".".join("%s" % n for n in path) + print(" " + "| " * (len(path) - 1) + "|") + print(" " + "| " * (len(path) - 1) + "| Unify feature: %s" % fullname) + print(" " + "| " * len(path) + " / " + _trace_valrepr(fval1)) + print(" " + "| " * len(path) + "|\\ " + _trace_valrepr(fval2)) + + +def _trace_unify_identity(path, fval1): + print(" " + "| " * len(path) + "|") + print(" " + "| " * len(path) + "| (identical objects)") + print(" " + "| " * len(path) + "|") + print(" " + "| " * len(path) + "+-->" + repr(fval1)) + + +def _trace_unify_fail(path, result): + if result is UnificationFailure: + resume = "" + else: + resume = " (nonfatal)" + print(" " + "| " * len(path) + "| |") + print(" " + "X " * len(path) + "X X <-- FAIL" + resume) + + +def _trace_unify_succeed(path, fval1): + # Print the result. + print(" " + "| " * len(path) + "|") + print(" " + "| " * len(path) + "+-->" + repr(fval1)) + + +def _trace_bindings(path, bindings): + # Print the bindings (if any). + if len(bindings) > 0: + binditems = sorted(bindings.items(), key=lambda v: v[0].name) + bindstr = "{%s}" % ", ".join( + f"{var}: {_trace_valrepr(val)}" for (var, val) in binditems + ) + print(" " + "| " * len(path) + " Bindings: " + bindstr) + + +def _trace_valrepr(val): + if isinstance(val, Variable): + return "%s" % val + else: + return "%s" % repr(val) + + +def subsumes(fstruct1, fstruct2): + """ + Return True if ``fstruct1`` subsumes ``fstruct2``. I.e., return + true if unifying ``fstruct1`` with ``fstruct2`` would result in a + feature structure equal to ``fstruct2.`` + + :rtype: bool + """ + return fstruct2 == unify(fstruct1, fstruct2) + + +def conflicts(fstruct1, fstruct2, trace=0): + """ + Return a list of the feature paths of all features which are + assigned incompatible values by ``fstruct1`` and ``fstruct2``. + + :rtype: list(tuple) + """ + conflict_list = [] + + def add_conflict(fval1, fval2, path): + conflict_list.append(path) + return fval1 + + unify(fstruct1, fstruct2, fail=add_conflict, trace=trace) + return conflict_list + + +###################################################################### +# Helper Functions +###################################################################### + + +def _is_mapping(v): + return hasattr(v, "__contains__") and hasattr(v, "keys") + + +def _is_sequence(v): + return hasattr(v, "__iter__") and hasattr(v, "__len__") and not isinstance(v, str) + + +def _default_fs_class(obj): + if isinstance(obj, FeatStruct): + return FeatStruct + if isinstance(obj, (dict, list)): + return (dict, list) + else: + raise ValueError( + "To unify objects of type %s, you must specify " + "fs_class explicitly." % obj.__class__.__name__ + ) + + +###################################################################### +# FeatureValueSet & FeatureValueTuple +###################################################################### + + +class SubstituteBindingsSequence(SubstituteBindingsI): + """ + A mixin class for sequence classes that distributes variables() and + substitute_bindings() over the object's elements. + """ + + def variables(self): + return [elt for elt in self if isinstance(elt, Variable)] + sum( + ( + list(elt.variables()) + for elt in self + if isinstance(elt, SubstituteBindingsI) + ), + [], + ) + + def substitute_bindings(self, bindings): + return self.__class__([self.subst(v, bindings) for v in self]) + + def subst(self, v, bindings): + if isinstance(v, SubstituteBindingsI): + return v.substitute_bindings(bindings) + else: + return bindings.get(v, v) + + +class FeatureValueTuple(SubstituteBindingsSequence, tuple): + """ + A base feature value that is a tuple of other base feature values. + FeatureValueTuple implements ``SubstituteBindingsI``, so it any + variable substitutions will be propagated to the elements + contained by the set. A ``FeatureValueTuple`` is immutable. + """ + + def __repr__(self): # [xx] really use %s here? + if len(self) == 0: + return "()" + return "(%s)" % ", ".join(f"{b}" for b in self) + + +class FeatureValueSet(SubstituteBindingsSequence, frozenset): + """ + A base feature value that is a set of other base feature values. + FeatureValueSet implements ``SubstituteBindingsI``, so it any + variable substitutions will be propagated to the elements + contained by the set. A ``FeatureValueSet`` is immutable. + """ + + def __repr__(self): # [xx] really use %s here? + if len(self) == 0: + return "{/}" # distinguish from dict. + # n.b., we sort the string reprs of our elements, to ensure + # that our own repr is deterministic. + return "{%s}" % ", ".join(sorted(f"{b}" for b in self)) + + __str__ = __repr__ + + +class FeatureValueUnion(SubstituteBindingsSequence, frozenset): + """ + A base feature value that represents the union of two or more + ``FeatureValueSet`` or ``Variable``. + """ + + def __new__(cls, values): + # If values contains FeatureValueUnions, then collapse them. + values = _flatten(values, FeatureValueUnion) + + # If the resulting list contains no variables, then + # use a simple FeatureValueSet instead. + if sum(isinstance(v, Variable) for v in values) == 0: + values = _flatten(values, FeatureValueSet) + return FeatureValueSet(values) + + # If we contain a single variable, return that variable. + if len(values) == 1: + return list(values)[0] + + # Otherwise, build the FeatureValueUnion. + return frozenset.__new__(cls, values) + + def __repr__(self): + # n.b., we sort the string reprs of our elements, to ensure + # that our own repr is deterministic. also, note that len(self) + # is guaranteed to be 2 or more. + return "{%s}" % "+".join(sorted(f"{b}" for b in self)) + + +class FeatureValueConcat(SubstituteBindingsSequence, tuple): + """ + A base feature value that represents the concatenation of two or + more ``FeatureValueTuple`` or ``Variable``. + """ + + def __new__(cls, values): + # If values contains FeatureValueConcats, then collapse them. + values = _flatten(values, FeatureValueConcat) + + # If the resulting list contains no variables, then + # use a simple FeatureValueTuple instead. + if sum(isinstance(v, Variable) for v in values) == 0: + values = _flatten(values, FeatureValueTuple) + return FeatureValueTuple(values) + + # If we contain a single variable, return that variable. + if len(values) == 1: + return list(values)[0] + + # Otherwise, build the FeatureValueConcat. + return tuple.__new__(cls, values) + + def __repr__(self): + # n.b.: len(self) is guaranteed to be 2 or more. + return "(%s)" % "+".join(f"{b}" for b in self) + + +def _flatten(lst, cls): + """ + Helper function -- return a copy of list, with all elements of + type ``cls`` spliced in rather than appended in. + """ + result = [] + for elt in lst: + if isinstance(elt, cls): + result.extend(elt) + else: + result.append(elt) + return result + + +###################################################################### +# Specialized Features +###################################################################### + + +@total_ordering +class Feature: + """ + A feature identifier that's specialized to put additional + constraints, default values, etc. + """ + + def __init__(self, name, default=None, display=None): + assert display in (None, "prefix", "slash") + + self._name = name # [xx] rename to .identifier? + self._default = default # [xx] not implemented yet. + self._display = display + + if self._display == "prefix": + self._sortkey = (-1, self._name) + elif self._display == "slash": + self._sortkey = (1, self._name) + else: + self._sortkey = (0, self._name) + + @property + def name(self): + """The name of this feature.""" + return self._name + + @property + def default(self): + """Default value for this feature.""" + return self._default + + @property + def display(self): + """Custom display location: can be prefix, or slash.""" + return self._display + + def __repr__(self): + return "*%s*" % self.name + + def __lt__(self, other): + if isinstance(other, str): + return True + if not isinstance(other, Feature): + raise_unorderable_types("<", self, other) + return self._sortkey < other._sortkey + + def __eq__(self, other): + return type(self) == type(other) and self._name == other._name + + def __ne__(self, other): + return not self == other + + def __hash__(self): + return hash(self._name) + + # //////////////////////////////////////////////////////////// + # These can be overridden by subclasses: + # //////////////////////////////////////////////////////////// + + def read_value(self, s, position, reentrances, parser): + return parser.read_value(s, position, reentrances) + + def unify_base_values(self, fval1, fval2, bindings): + """ + If possible, return a single value.. If not, return + the value ``UnificationFailure``. + """ + if fval1 == fval2: + return fval1 + else: + return UnificationFailure + + +class SlashFeature(Feature): + def read_value(self, s, position, reentrances, parser): + return parser.read_partial(s, position, reentrances) + + +class RangeFeature(Feature): + RANGE_RE = re.compile(r"(-?\d+):(-?\d+)") + + def read_value(self, s, position, reentrances, parser): + m = self.RANGE_RE.match(s, position) + if not m: + raise ValueError("range", position) + return (int(m.group(1)), int(m.group(2))), m.end() + + def unify_base_values(self, fval1, fval2, bindings): + if fval1 is None: + return fval2 + if fval2 is None: + return fval1 + rng = max(fval1[0], fval2[0]), min(fval1[1], fval2[1]) + if rng[1] < rng[0]: + return UnificationFailure + return rng + + +SLASH = SlashFeature("slash", default=False, display="slash") +TYPE = Feature("type", display="prefix") + + +###################################################################### +# Specialized Feature Values +###################################################################### + + +@total_ordering +class CustomFeatureValue: + """ + An abstract base class for base values that define a custom + unification method. The custom unification method of + ``CustomFeatureValue`` will be used during unification if: + + - The ``CustomFeatureValue`` is unified with another base value. + - The ``CustomFeatureValue`` is not the value of a customized + ``Feature`` (which defines its own unification method). + + If two ``CustomFeatureValue`` objects are unified with one another + during feature structure unification, then the unified base values + they return *must* be equal; otherwise, an ``AssertionError`` will + be raised. + + Subclasses must define ``unify()``, ``__eq__()`` and ``__lt__()``. + Subclasses may also wish to define ``__hash__()``. + """ + + def unify(self, other): + """ + If this base value unifies with ``other``, then return the + unified value. Otherwise, return ``UnificationFailure``. + """ + raise NotImplementedError("abstract base class") + + def __eq__(self, other): + return NotImplemented + + def __ne__(self, other): + return not self == other + + def __lt__(self, other): + return NotImplemented + + def __hash__(self): + raise TypeError("%s objects or unhashable" % self.__class__.__name__) + + +###################################################################### +# Feature Structure Reader +###################################################################### + + +class FeatStructReader: + def __init__( + self, + features=(SLASH, TYPE), + fdict_class=FeatStruct, + flist_class=FeatList, + logic_parser=None, + ): + self._features = {f.name: f for f in features} + self._fdict_class = fdict_class + self._flist_class = flist_class + self._prefix_feature = None + self._slash_feature = None + for feature in features: + if feature.display == "slash": + if self._slash_feature: + raise ValueError("Multiple features w/ display=slash") + self._slash_feature = feature + if feature.display == "prefix": + if self._prefix_feature: + raise ValueError("Multiple features w/ display=prefix") + self._prefix_feature = feature + self._features_with_defaults = [ + feature for feature in features if feature.default is not None + ] + if logic_parser is None: + logic_parser = LogicParser() + self._logic_parser = logic_parser + + def fromstring(self, s, fstruct=None): + """ + Convert a string representation of a feature structure (as + displayed by repr) into a ``FeatStruct``. This process + imposes the following restrictions on the string + representation: + + - Feature names cannot contain any of the following: + whitespace, parentheses, quote marks, equals signs, + dashes, commas, and square brackets. Feature names may + not begin with plus signs or minus signs. + - Only the following basic feature value are supported: + strings, integers, variables, None, and unquoted + alphanumeric strings. + - For reentrant values, the first mention must specify + a reentrance identifier and a value; and any subsequent + mentions must use arrows (``'->'``) to reference the + reentrance identifier. + """ + s = s.strip() + value, position = self.read_partial(s, 0, {}, fstruct) + if position != len(s): + self._error(s, "end of string", position) + return value + + _START_FSTRUCT_RE = re.compile(r"\s*(?:\((\d+)\)\s*)?(\??[\w-]+)?(\[)") + _END_FSTRUCT_RE = re.compile(r"\s*]\s*") + _SLASH_RE = re.compile(r"/") + _FEATURE_NAME_RE = re.compile(r'\s*([+-]?)([^\s\(\)<>"\'\-=\[\],]+)\s*') + _REENTRANCE_RE = re.compile(r"\s*->\s*") + _TARGET_RE = re.compile(r"\s*\((\d+)\)\s*") + _ASSIGN_RE = re.compile(r"\s*=\s*") + _COMMA_RE = re.compile(r"\s*,\s*") + _BARE_PREFIX_RE = re.compile(r"\s*(?:\((\d+)\)\s*)?(\??[\w-]+\s*)()") + # This one is used to distinguish fdicts from flists: + _START_FDICT_RE = re.compile( + r"(%s)|(%s\s*(%s\s*(=|->)|[+-]%s|\]))" + % ( + _BARE_PREFIX_RE.pattern, + _START_FSTRUCT_RE.pattern, + _FEATURE_NAME_RE.pattern, + _FEATURE_NAME_RE.pattern, + ) + ) + + def read_partial(self, s, position=0, reentrances=None, fstruct=None): + """ + Helper function that reads in a feature structure. + + :param s: The string to read. + :param position: The position in the string to start parsing. + :param reentrances: A dictionary from reentrance ids to values. + Defaults to an empty dictionary. + :return: A tuple (val, pos) of the feature structure created by + parsing and the position where the parsed feature structure ends. + :rtype: bool + """ + if reentrances is None: + reentrances = {} + try: + return self._read_partial(s, position, reentrances, fstruct) + except ValueError as e: + if len(e.args) != 2: + raise + self._error(s, *e.args) + + def _read_partial(self, s, position, reentrances, fstruct=None): + # Create the new feature structure + if fstruct is None: + if self._START_FDICT_RE.match(s, position): + fstruct = self._fdict_class() + else: + fstruct = self._flist_class() + + # Read up to the open bracket. + match = self._START_FSTRUCT_RE.match(s, position) + if not match: + match = self._BARE_PREFIX_RE.match(s, position) + if not match: + raise ValueError("open bracket or identifier", position) + position = match.end() + + # If there as an identifier, record it. + if match.group(1): + identifier = match.group(1) + if identifier in reentrances: + raise ValueError("new identifier", match.start(1)) + reentrances[identifier] = fstruct + + if isinstance(fstruct, FeatDict): + fstruct.clear() + return self._read_partial_featdict(s, position, match, reentrances, fstruct) + else: + del fstruct[:] + return self._read_partial_featlist(s, position, match, reentrances, fstruct) + + def _read_partial_featlist(self, s, position, match, reentrances, fstruct): + # Prefix features are not allowed: + if match.group(2): + raise ValueError("open bracket") + # Bare prefixes are not allowed: + if not match.group(3): + raise ValueError("open bracket") + + # Build a list of the features defined by the structure. + while position < len(s): + # Check for the close bracket. + match = self._END_FSTRUCT_RE.match(s, position) + if match is not None: + return fstruct, match.end() + + # Reentances have the form "-> (target)" + match = self._REENTRANCE_RE.match(s, position) + if match: + position = match.end() + match = self._TARGET_RE.match(s, position) + if not match: + raise ValueError("identifier", position) + target = match.group(1) + if target not in reentrances: + raise ValueError("bound identifier", position) + position = match.end() + fstruct.append(reentrances[target]) + + # Anything else is a value. + else: + value, position = self._read_value(0, s, position, reentrances) + fstruct.append(value) + + # If there's a close bracket, handle it at the top of the loop. + if self._END_FSTRUCT_RE.match(s, position): + continue + + # Otherwise, there should be a comma + match = self._COMMA_RE.match(s, position) + if match is None: + raise ValueError("comma", position) + position = match.end() + + # We never saw a close bracket. + raise ValueError("close bracket", position) + + def _read_partial_featdict(self, s, position, match, reentrances, fstruct): + # If there was a prefix feature, record it. + if match.group(2): + if self._prefix_feature is None: + raise ValueError("open bracket or identifier", match.start(2)) + prefixval = match.group(2).strip() + if prefixval.startswith("?"): + prefixval = Variable(prefixval) + fstruct[self._prefix_feature] = prefixval + + # If group 3 is empty, then we just have a bare prefix, so + # we're done. + if not match.group(3): + return self._finalize(s, match.end(), reentrances, fstruct) + + # Build a list of the features defined by the structure. + # Each feature has one of the three following forms: + # name = value + # name -> (target) + # +name + # -name + while position < len(s): + # Use these variables to hold info about each feature: + name = value = None + + # Check for the close bracket. + match = self._END_FSTRUCT_RE.match(s, position) + if match is not None: + return self._finalize(s, match.end(), reentrances, fstruct) + + # Get the feature name's name + match = self._FEATURE_NAME_RE.match(s, position) + if match is None: + raise ValueError("feature name", position) + name = match.group(2) + position = match.end() + + # Check if it's a special feature. + if name[0] == "*" and name[-1] == "*": + name = self._features.get(name[1:-1]) + if name is None: + raise ValueError("known special feature", match.start(2)) + + # Check if this feature has a value already. + if name in fstruct: + raise ValueError("new name", match.start(2)) + + # Boolean value ("+name" or "-name") + if match.group(1) == "+": + value = True + if match.group(1) == "-": + value = False + + # Reentrance link ("-> (target)") + if value is None: + match = self._REENTRANCE_RE.match(s, position) + if match is not None: + position = match.end() + match = self._TARGET_RE.match(s, position) + if not match: + raise ValueError("identifier", position) + target = match.group(1) + if target not in reentrances: + raise ValueError("bound identifier", position) + position = match.end() + value = reentrances[target] + + # Assignment ("= value"). + if value is None: + match = self._ASSIGN_RE.match(s, position) + if match: + position = match.end() + value, position = self._read_value(name, s, position, reentrances) + # None of the above: error. + else: + raise ValueError("equals sign", position) + + # Store the value. + fstruct[name] = value + + # If there's a close bracket, handle it at the top of the loop. + if self._END_FSTRUCT_RE.match(s, position): + continue + + # Otherwise, there should be a comma + match = self._COMMA_RE.match(s, position) + if match is None: + raise ValueError("comma", position) + position = match.end() + + # We never saw a close bracket. + raise ValueError("close bracket", position) + + def _finalize(self, s, pos, reentrances, fstruct): + """ + Called when we see the close brace -- checks for a slash feature, + and adds in default values. + """ + # Add the slash feature (if any) + match = self._SLASH_RE.match(s, pos) + if match: + name = self._slash_feature + v, pos = self._read_value(name, s, match.end(), reentrances) + fstruct[name] = v + ## Add any default features. -- handle in unficiation instead? + # for feature in self._features_with_defaults: + # fstruct.setdefault(feature, feature.default) + # Return the value. + return fstruct, pos + + def _read_value(self, name, s, position, reentrances): + if isinstance(name, Feature): + return name.read_value(s, position, reentrances, self) + else: + return self.read_value(s, position, reentrances) + + def read_value(self, s, position, reentrances): + for (handler, regexp) in self.VALUE_HANDLERS: + match = regexp.match(s, position) + if match: + handler_func = getattr(self, handler) + return handler_func(s, position, reentrances, match) + raise ValueError("value", position) + + def _error(self, s, expected, position): + lines = s.split("\n") + while position > len(lines[0]): + position -= len(lines.pop(0)) + 1 # +1 for the newline. + estr = ( + "Error parsing feature structure\n " + + lines[0] + + "\n " + + " " * position + + "^ " + + "Expected %s" % expected + ) + raise ValueError(estr) + + # //////////////////////////////////////////////////////////// + # { Value Readers + # //////////////////////////////////////////////////////////// + + #: A table indicating how feature values should be processed. Each + #: entry in the table is a pair (handler, regexp). The first entry + #: with a matching regexp will have its handler called. Handlers + #: should have the following signature:: + #: + #: def handler(s, position, reentrances, match): ... + #: + #: and should return a tuple (value, position), where position is + #: the string position where the value ended. (n.b.: order is + #: important here!) + VALUE_HANDLERS = [ + ("read_fstruct_value", _START_FSTRUCT_RE), + ("read_var_value", re.compile(r"\?[a-zA-Z_][a-zA-Z0-9_]*")), + ("read_str_value", re.compile("[uU]?[rR]?(['\"])")), + ("read_int_value", re.compile(r"-?\d+")), + ("read_sym_value", re.compile(r"[a-zA-Z_][a-zA-Z0-9_]*")), + ( + "read_app_value", + re.compile(r"<(app)\((\?[a-z][a-z]*)\s*," r"\s*(\?[a-z][a-z]*)\)>"), + ), + # ('read_logic_value', re.compile(r'<([^>]*)>')), + # lazily match any character after '<' until we hit a '>' not preceded by '-' + ("read_logic_value", re.compile(r"<(.*?)(?")), + ("read_set_value", re.compile(r"{")), + ("read_tuple_value", re.compile(r"\(")), + ] + + def read_fstruct_value(self, s, position, reentrances, match): + return self.read_partial(s, position, reentrances) + + def read_str_value(self, s, position, reentrances, match): + return read_str(s, position) + + def read_int_value(self, s, position, reentrances, match): + return int(match.group()), match.end() + + # Note: the '?' is included in the variable name. + def read_var_value(self, s, position, reentrances, match): + return Variable(match.group()), match.end() + + _SYM_CONSTS = {"None": None, "True": True, "False": False} + + def read_sym_value(self, s, position, reentrances, match): + val, end = match.group(), match.end() + return self._SYM_CONSTS.get(val, val), end + + def read_app_value(self, s, position, reentrances, match): + """Mainly included for backwards compat.""" + return self._logic_parser.parse("%s(%s)" % match.group(2, 3)), match.end() + + def read_logic_value(self, s, position, reentrances, match): + try: + try: + expr = self._logic_parser.parse(match.group(1)) + except LogicalExpressionException as e: + raise ValueError from e + return expr, match.end() + except ValueError as e: + raise ValueError("logic expression", match.start(1)) from e + + def read_tuple_value(self, s, position, reentrances, match): + return self._read_seq_value( + s, position, reentrances, match, ")", FeatureValueTuple, FeatureValueConcat + ) + + def read_set_value(self, s, position, reentrances, match): + return self._read_seq_value( + s, position, reentrances, match, "}", FeatureValueSet, FeatureValueUnion + ) + + def _read_seq_value( + self, s, position, reentrances, match, close_paren, seq_class, plus_class + ): + """ + Helper function used by read_tuple_value and read_set_value. + """ + cp = re.escape(close_paren) + position = match.end() + # Special syntax of empty tuples: + m = re.compile(r"\s*/?\s*%s" % cp).match(s, position) + if m: + return seq_class(), m.end() + # Read values: + values = [] + seen_plus = False + while True: + # Close paren: return value. + m = re.compile(r"\s*%s" % cp).match(s, position) + if m: + if seen_plus: + return plus_class(values), m.end() + else: + return seq_class(values), m.end() + + # Read the next value. + val, position = self.read_value(s, position, reentrances) + values.append(val) + + # Comma or looking at close paren + m = re.compile(r"\s*(,|\+|(?=%s))\s*" % cp).match(s, position) + if not m: + raise ValueError("',' or '+' or '%s'" % cp, position) + if m.group(1) == "+": + seen_plus = True + position = m.end() + + +###################################################################### +# { Demo +###################################################################### + + +def display_unification(fs1, fs2, indent=" "): + # Print the two input feature structures, side by side. + fs1_lines = ("%s" % fs1).split("\n") + fs2_lines = ("%s" % fs2).split("\n") + if len(fs1_lines) > len(fs2_lines): + blankline = "[" + " " * (len(fs2_lines[0]) - 2) + "]" + fs2_lines += [blankline] * len(fs1_lines) + else: + blankline = "[" + " " * (len(fs1_lines[0]) - 2) + "]" + fs1_lines += [blankline] * len(fs2_lines) + for (fs1_line, fs2_line) in zip(fs1_lines, fs2_lines): + print(indent + fs1_line + " " + fs2_line) + print(indent + "-" * len(fs1_lines[0]) + " " + "-" * len(fs2_lines[0])) + + linelen = len(fs1_lines[0]) * 2 + 3 + print(indent + "| |".center(linelen)) + print(indent + "+-----UNIFY-----+".center(linelen)) + print(indent + "|".center(linelen)) + print(indent + "V".center(linelen)) + + bindings = {} + + result = fs1.unify(fs2, bindings) + if result is None: + print(indent + "(FAILED)".center(linelen)) + else: + print( + "\n".join(indent + l.center(linelen) for l in ("%s" % result).split("\n")) + ) + if bindings and len(bindings.bound_variables()) > 0: + print(repr(bindings).center(linelen)) + return result + + +def interactive_demo(trace=False): + import random + import sys + + HELP = """ + 1-%d: Select the corresponding feature structure + q: Quit + t: Turn tracing on or off + l: List all feature structures + ?: Help + """ + + print( + """ + This demo will repeatedly present you with a list of feature + structures, and ask you to choose two for unification. Whenever a + new feature structure is generated, it is added to the list of + choices that you can pick from. However, since this can be a + large number of feature structures, the demo will only print out a + random subset for you to choose between at a given time. If you + want to see the complete lists, type "l". For a list of valid + commands, type "?". + """ + ) + print('Press "Enter" to continue...') + sys.stdin.readline() + + fstruct_strings = [ + "[agr=[number=sing, gender=masc]]", + "[agr=[gender=masc, person=3]]", + "[agr=[gender=fem, person=3]]", + "[subj=[agr=(1)[]], agr->(1)]", + "[obj=?x]", + "[subj=?x]", + "[/=None]", + "[/=NP]", + "[cat=NP]", + "[cat=VP]", + "[cat=PP]", + "[subj=[agr=[gender=?y]], obj=[agr=[gender=?y]]]", + "[gender=masc, agr=?C]", + "[gender=?S, agr=[gender=?S,person=3]]", + ] + + all_fstructs = [ + (i, FeatStruct(fstruct_strings[i])) for i in range(len(fstruct_strings)) + ] + + def list_fstructs(fstructs): + for i, fstruct in fstructs: + print() + lines = ("%s" % fstruct).split("\n") + print("%3d: %s" % (i + 1, lines[0])) + for line in lines[1:]: + print(" " + line) + print() + + while True: + # Pick 5 feature structures at random from the master list. + MAX_CHOICES = 5 + if len(all_fstructs) > MAX_CHOICES: + fstructs = sorted(random.sample(all_fstructs, MAX_CHOICES)) + else: + fstructs = all_fstructs + + print("_" * 75) + + print("Choose two feature structures to unify:") + list_fstructs(fstructs) + + selected = [None, None] + for (nth, i) in (("First", 0), ("Second", 1)): + while selected[i] is None: + print( + ( + "%s feature structure (1-%d,q,t,l,?): " + % (nth, len(all_fstructs)) + ), + end=" ", + ) + try: + input = sys.stdin.readline().strip() + if input in ("q", "Q", "x", "X"): + return + if input in ("t", "T"): + trace = not trace + print(" Trace = %s" % trace) + continue + if input in ("h", "H", "?"): + print(HELP % len(fstructs)) + continue + if input in ("l", "L"): + list_fstructs(all_fstructs) + continue + num = int(input) - 1 + selected[i] = all_fstructs[num][1] + print() + except: + print("Bad sentence number") + continue + + if trace: + result = selected[0].unify(selected[1], trace=1) + else: + result = display_unification(selected[0], selected[1]) + if result is not None: + for i, fstruct in all_fstructs: + if repr(result) == repr(fstruct): + break + else: + all_fstructs.append((len(all_fstructs), result)) + + print('\nType "Enter" to continue unifying; or "q" to quit.') + input = sys.stdin.readline().strip() + if input in ("q", "Q", "x", "X"): + return + + +def demo(trace=False): + """ + Just for testing + """ + # import random + + # processor breaks with values like '3rd' + fstruct_strings = [ + "[agr=[number=sing, gender=masc]]", + "[agr=[gender=masc, person=3]]", + "[agr=[gender=fem, person=3]]", + "[subj=[agr=(1)[]], agr->(1)]", + "[obj=?x]", + "[subj=?x]", + "[/=None]", + "[/=NP]", + "[cat=NP]", + "[cat=VP]", + "[cat=PP]", + "[subj=[agr=[gender=?y]], obj=[agr=[gender=?y]]]", + "[gender=masc, agr=?C]", + "[gender=?S, agr=[gender=?S,person=3]]", + ] + all_fstructs = [FeatStruct(fss) for fss in fstruct_strings] + # MAX_CHOICES = 5 + # if len(all_fstructs) > MAX_CHOICES: + # fstructs = random.sample(all_fstructs, MAX_CHOICES) + # fstructs.sort() + # else: + # fstructs = all_fstructs + + for fs1 in all_fstructs: + for fs2 in all_fstructs: + print( + "\n*******************\nfs1 is:\n%s\n\nfs2 is:\n%s\n\nresult is:\n%s" + % (fs1, fs2, unify(fs1, fs2)) + ) + + +if __name__ == "__main__": + demo() + +__all__ = [ + "FeatStruct", + "FeatDict", + "FeatList", + "unify", + "subsumes", + "conflicts", + "Feature", + "SlashFeature", + "RangeFeature", + "SLASH", + "TYPE", + "FeatStructReader", +]