def evaluate(self, context):
if self.op == 'or':
if to_boolean(self.left.evaluate(context)):
return True
return to_boolean(self.right.evaluate(context))
elif self.op == 'and':
if not to_boolean(self.left.evaluate(context)):
return False
return to_boolean(self.right.evaluate(context))
elif self.op in ['=', '!=', '<', '>', '<=', '>=']:
return compare(self.op, self.left.evaluate(context),
self.right.evaluate(context))
elif self.op in ['+', '-', '*', 'div', 'mod']:
x = to_number(self.left.evaluate(context))
y = to_number(self.right.evaluate(context))
if self.op == '+':
return x + y
elif self.op == '-':
return x - y
elif self.op == '*':
return x * y
elif self.op == 'div':
return x / y
elif self.op == 'mod':
z = abs(x) % abs(y)
if x >= 0:
return z
else:
return -z
else:
assert False
elif self.op == '|':
x = self.left.evaluate(context)
y = self.right.evaluate(context)
if is_node_set(x) and is_node_set(y):
# XXX This is incorrect, because it neither preserves
# document order nor removes duplicates.
return join_node_sets(x, y)
else:
raise XPathEvaluationError, "Operands of '|' must be node sets."
else:
assert False
def evaluate(self, context):
assert self.op == '-'
return - to_number(self.right.evaluate(context))