def apply_substitution_to_term(term: Term, substitution: Dict[str,
Term]) -> Term:
complete_substitution = {}
# NOTE: all variables in the term need to be defined in the substitution
for var in term.variables():
complete_substitution[var.name] = Var(var.name)
complete_substitution.update(substitution)
term_substitution = term.apply(complete_substitution)
return term_substitution
def unify_value_different_contexts(value1: Term, value2: Term, source_values, target_values):
"""
Unify two values that exist in different contexts.
Updates the mapping of variables from value1 to values from value2.
:param value1:
:param value2:
:param source_values: mapping of source variable to target value
:param target_values: mapping of target variable to TARGET value
"""
# Variables are negative numbers or None
if is_variable(value1) and is_variable(value2):
if value1 is None: # value1 is anonyous var
pass
elif value2 is None: # value2 is anonymous
pass
else:
# Two named variables
# Check whether value2 is already linked to another value in the target context
sv2 = target_values.get(value2, value2)
if sv2 == value2: # no
# Check whether value1 is already linked to a value
sv1 = source_values.get(value1)
if sv1 is None: # no
# We can link variable 1 with variable 2
source_values[value1] = value2
else:
# yes: we need to unify sv1 and value2 (they both are in target scope)
unify_value(sv1, value2, target_values)
else:
# value2 is already linked to another value
# we need to unify value1 with that value
unify_value_different_contexts(value1, sv2, source_values, target_values)
# only value1 is a variable; value2 is a nonvar term
elif is_variable(value1):
if value1 is None:
pass
else:
sv1 = source_values.get(value1)
if sv1 is None:
source_values[value1] = value2
elif is_variable(sv1):
if sv1 in value2.variables():
raise OccursCheck()
if sv1 != value2:
target_values[sv1] = value2
source_values[value1] = value2
else:
# unify in same context target_values
source_values[value1] = unify_value(source_values[value1], value2, target_values)
# only value2 is a variable; value1 is a nonvar term
elif is_variable(value2):
sv2 = target_values.get(value2)
if sv2 is None:
target_values[value2] = value1.apply(source_values)
elif is_variable(sv2):
pass
else:
unify_value_different_contexts(value1, sv2, source_values, target_values)
# value1 and value2 are both not variables
# but they are terms with the same signature
elif value1.signature == value2.signature: # Assume Term
for a1, a2 in zip(value1.args, value2.args):
unify_value_different_contexts(a1, a2, source_values, target_values)
# they don't have the same signature
else:
raise UnifyError()
