def test_can_lookup_variable_from_the_environment(self):
env = Environment()
env.set("a", 2.0)
env.set("b", 3.0)
parse_tree = [ OperatorFactory.make_operator("*"), Symbol("a"), Symbol("b") ]
result = Evaluator.evaluate(parse_tree, env)
self.assertEqual(result, 6.0)
def test_can_handle_nested_arithmetic(self):
parse_tree = [ OperatorFactory.make_operator("*"),
Number(2.0),
[ OperatorFactory.make_operator("+"), Number(4.0), Number(5.0) ] ]
result = Evaluator.evaluate(parse_tree)
self.assertEqual(result, 18.0)
def test_raises_exception_on_unknown_operator(self):
with self.assertRaises(Exception) as context:
OperatorFactory.make_operator("#")
self.assertEqual(str(context.exception), 'Unknown operator: #')
def test_can_evaluate_simple_subtraction(self):
parse_tree = [ OperatorFactory.make_operator("-"), Number(8.0), Number(4.0), Number(1.0) ]
result = Evaluator.evaluate(parse_tree)
self.assertEqual(result, 3.0)
def test_can_evaluate_simple_division(self):
parse_tree = [ OperatorFactory.make_operator("/"), Number(8.0), Number(2.0) ]
result = Evaluator.evaluate(parse_tree)
self.assertEqual(result, 4.0)
def test_can_evaluate_simple_addition(self):
parse_tree = [ OperatorFactory.make_operator("+"), Number(2.0), Number(3.0) ]
result = Evaluator.evaluate(parse_tree)
self.assertEqual(result, 5.0)
def test_can_set_variable_to_the_environment(self):
env = Environment()
parse_tree = [ OperatorFactory.make_operator("set!"), Symbol("x"), Number(19) ]
Evaluator.evaluate(parse_tree, env)
self.assertEqual(env.get("x"), 19)
