# Natural Language Toolkit: Combinatory Categorial Grammar
#
# Copyright (C) 2001-2017 NLTK Project
# Author: Tanin Na Nakorn (@tanin)
# URL: <http://nltk.org/>
# For license information, see LICENSE.TXT
"""
Helper functions for CCG semantics computation
"""

from nltk.sem.logic import *

def compute_type_raised_semantics(semantics):
    core = semantics
    parent = None
    while isinstance(core, LambdaExpression):
        parent = core
        core = core.term
        
    var = Variable("F")
    while var in core.free():
        var = unique_variable(pattern=var)
    core = ApplicationExpression(FunctionVariableExpression(var), core)
    
    if parent is not None:
        parent.term = core
    else:
        semantics = core
    
    return LambdaExpression(var, semantics)

def compute_function_semantics(function, argument):
    return ApplicationExpression(function, argument).simplify()

def compute_composition_semantics(function, argument):
    assert isinstance(argument, LambdaExpression), "`" + str(argument) + "` must be a lambda expression"
    return LambdaExpression(argument.variable, ApplicationExpression(function, argument.term).simplify())

def compute_substitution_semantics(function, argument):
    assert isinstance(function, LambdaExpression) and isinstance(function.term, LambdaExpression), "`" + str(function) + "` must be a lambda expression with 2 arguments"
    assert isinstance(argument, LambdaExpression), "`" + str(argument) + "` must be a lambda expression"

    new_argument = ApplicationExpression(argument, VariableExpression(function.variable)).simplify()
    new_term = ApplicationExpression(function.term, new_argument).simplify() 

    return LambdaExpression(function.variable, new_term)
