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340 lines
9.3 KiB
Python
340 lines
9.3 KiB
Python
# Natural Language Toolkit: Combinatory Categorial Grammar
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#
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# Copyright (C) 2001-2020 NLTK Project
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# Author: Graeme Gange <ggange@csse.unimelb.edu.au>
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# URL: <http://nltk.org/>
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# For license information, see LICENSE.TXT
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"""
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CCG Lexicons
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"""
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import re
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from collections import defaultdict
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from nltk.ccg.api import PrimitiveCategory, Direction, CCGVar, FunctionalCategory
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from nltk.internals import deprecated
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from nltk.sem.logic import Expression
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# ------------
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# Regular expressions used for parsing components of the lexicon
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# ------------
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# Parses a primitive category and subscripts
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PRIM_RE = re.compile(r"""([A-Za-z]+)(\[[A-Za-z,]+\])?""")
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# Separates the next primitive category from the remainder of the
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# string
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NEXTPRIM_RE = re.compile(r"""([A-Za-z]+(?:\[[A-Za-z,]+\])?)(.*)""")
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# Separates the next application operator from the remainder
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APP_RE = re.compile(r"""([\\/])([.,]?)([.,]?)(.*)""")
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# Parses the definition of the right-hand side (rhs) of either a word or a family
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LEX_RE = re.compile(r"""([\S_]+)\s*(::|[-=]+>)\s*(.+)""", re.UNICODE)
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# Parses the right hand side that contains category and maybe semantic predicate
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RHS_RE = re.compile(r"""([^{}]*[^ {}])\s*(\{[^}]+\})?""", re.UNICODE)
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# Parses the semantic predicate
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SEMANTICS_RE = re.compile(r"""\{([^}]+)\}""", re.UNICODE)
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# Strips comments from a line
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COMMENTS_RE = re.compile("""([^#]*)(?:#.*)?""")
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class Token(object):
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"""
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Class representing a token.
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token => category {semantics}
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e.g. eat => S\\var[pl]/var {\\x y.eat(x,y)}
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* `token` (string)
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* `categ` (string)
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* `semantics` (Expression)
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"""
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def __init__(self, token, categ, semantics=None):
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self._token = token
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self._categ = categ
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self._semantics = semantics
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def categ(self):
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return self._categ
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def semantics(self):
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return self._semantics
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def __str__(self):
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semantics_str = ""
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if self._semantics is not None:
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semantics_str = " {" + str(self._semantics) + "}"
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return "" + str(self._categ) + semantics_str
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def __cmp__(self, other):
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if not isinstance(other, Token):
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return -1
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return cmp((self._categ, self._semantics), other.categ(), other.semantics())
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class CCGLexicon(object):
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"""
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Class representing a lexicon for CCG grammars.
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* `primitives`: The list of primitive categories for the lexicon
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* `families`: Families of categories
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* `entries`: A mapping of words to possible categories
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"""
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def __init__(self, start, primitives, families, entries):
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self._start = PrimitiveCategory(start)
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self._primitives = primitives
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self._families = families
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self._entries = entries
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def categories(self, word):
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"""
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Returns all the possible categories for a word
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"""
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return self._entries[word]
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def start(self):
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"""
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Return the target category for the parser
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"""
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return self._start
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def __str__(self):
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"""
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String representation of the lexicon. Used for debugging.
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"""
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string = ""
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first = True
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for ident in sorted(self._entries):
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if not first:
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string = string + "\n"
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string = string + ident + " => "
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first = True
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for cat in self._entries[ident]:
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if not first:
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string = string + " | "
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else:
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first = False
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string = string + "%s" % cat
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return string
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# -----------
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# Parsing lexicons
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# -----------
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def matchBrackets(string):
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"""
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Separate the contents matching the first set of brackets from the rest of
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the input.
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"""
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rest = string[1:]
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inside = "("
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while rest != "" and not rest.startswith(")"):
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if rest.startswith("("):
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(part, rest) = matchBrackets(rest)
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inside = inside + part
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else:
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inside = inside + rest[0]
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rest = rest[1:]
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if rest.startswith(")"):
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return (inside + ")", rest[1:])
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raise AssertionError("Unmatched bracket in string '" + string + "'")
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def nextCategory(string):
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"""
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Separate the string for the next portion of the category from the rest
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of the string
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"""
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if string.startswith("("):
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return matchBrackets(string)
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return NEXTPRIM_RE.match(string).groups()
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def parseApplication(app):
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"""
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Parse an application operator
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"""
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return Direction(app[0], app[1:])
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def parseSubscripts(subscr):
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"""
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Parse the subscripts for a primitive category
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"""
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if subscr:
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return subscr[1:-1].split(",")
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return []
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def parsePrimitiveCategory(chunks, primitives, families, var):
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"""
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Parse a primitive category
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If the primitive is the special category 'var', replace it with the
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correct `CCGVar`.
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"""
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if chunks[0] == "var":
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if chunks[1] is None:
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if var is None:
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var = CCGVar()
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return (var, var)
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catstr = chunks[0]
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if catstr in families:
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(cat, cvar) = families[catstr]
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if var is None:
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var = cvar
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else:
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cat = cat.substitute([(cvar, var)])
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return (cat, var)
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if catstr in primitives:
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subscrs = parseSubscripts(chunks[1])
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return (PrimitiveCategory(catstr, subscrs), var)
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raise AssertionError(
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"String '" + catstr + "' is neither a family nor primitive category."
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)
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def augParseCategory(line, primitives, families, var=None):
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"""
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Parse a string representing a category, and returns a tuple with
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(possibly) the CCG variable for the category
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"""
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(cat_string, rest) = nextCategory(line)
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if cat_string.startswith("("):
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(res, var) = augParseCategory(cat_string[1:-1], primitives, families, var)
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else:
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(res, var) = parsePrimitiveCategory(
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PRIM_RE.match(cat_string).groups(), primitives, families, var
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)
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while rest != "":
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app = APP_RE.match(rest).groups()
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direction = parseApplication(app[0:3])
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rest = app[3]
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(cat_string, rest) = nextCategory(rest)
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if cat_string.startswith("("):
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(arg, var) = augParseCategory(cat_string[1:-1], primitives, families, var)
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else:
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(arg, var) = parsePrimitiveCategory(
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PRIM_RE.match(cat_string).groups(), primitives, families, var
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)
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res = FunctionalCategory(res, arg, direction)
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return (res, var)
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def fromstring(lex_str, include_semantics=False):
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"""
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Convert string representation into a lexicon for CCGs.
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"""
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CCGVar.reset_id()
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primitives = []
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families = {}
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entries = defaultdict(list)
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for line in lex_str.splitlines():
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# Strip comments and leading/trailing whitespace.
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line = COMMENTS_RE.match(line).groups()[0].strip()
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if line == "":
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continue
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if line.startswith(":-"):
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# A line of primitive categories.
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# The first one is the target category
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# ie, :- S, N, NP, VP
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primitives = primitives + [
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prim.strip() for prim in line[2:].strip().split(",")
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]
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else:
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# Either a family definition, or a word definition
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(ident, sep, rhs) = LEX_RE.match(line).groups()
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(catstr, semantics_str) = RHS_RE.match(rhs).groups()
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(cat, var) = augParseCategory(catstr, primitives, families)
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if sep == "::":
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# Family definition
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# ie, Det :: NP/N
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families[ident] = (cat, var)
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else:
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semantics = None
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if include_semantics is True:
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if semantics_str is None:
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raise AssertionError(
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line
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+ " must contain semantics because include_semantics is set to True"
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)
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else:
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semantics = Expression.fromstring(
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SEMANTICS_RE.match(semantics_str).groups()[0]
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)
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# Word definition
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# ie, which => (N\N)/(S/NP)
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entries[ident].append(Token(ident, cat, semantics))
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return CCGLexicon(primitives[0], primitives, families, entries)
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@deprecated("Use fromstring() instead.")
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def parseLexicon(lex_str):
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return fromstring(lex_str)
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openccg_tinytiny = fromstring(
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"""
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# Rather minimal lexicon based on the openccg `tinytiny' grammar.
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# Only incorporates a subset of the morphological subcategories, however.
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:- S,NP,N # Primitive categories
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Det :: NP/N # Determiners
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Pro :: NP
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IntransVsg :: S\\NP[sg] # Tensed intransitive verbs (singular)
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IntransVpl :: S\\NP[pl] # Plural
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TransVsg :: S\\NP[sg]/NP # Tensed transitive verbs (singular)
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TransVpl :: S\\NP[pl]/NP # Plural
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the => NP[sg]/N[sg]
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the => NP[pl]/N[pl]
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I => Pro
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me => Pro
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we => Pro
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us => Pro
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book => N[sg]
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books => N[pl]
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peach => N[sg]
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peaches => N[pl]
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policeman => N[sg]
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policemen => N[pl]
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boy => N[sg]
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boys => N[pl]
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sleep => IntransVsg
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sleep => IntransVpl
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eat => IntransVpl
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eat => TransVpl
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eats => IntransVsg
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eats => TransVsg
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see => TransVpl
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sees => TransVsg
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"""
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)
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