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_throws_exception_when_getting_unbound(self):
env = Environment()
with self.assertRaises(Exception) as context:
env.get("a")
self.assertEqual(str(context.exception), 'Unbound variable: a')
with self.assertRaises(Exception) as context:
env.get("b")
self.assertEqual(str(context.exception), 'Unbound variable: b')
def test_can_create_new_function(self):
# Create a square function (which will be added to the environment)
env = Environment()
square_function = "(defun square(x)(* x x)))"
Evaluator.evaluate(Parser.parse(Tokenizer.tokenize(square_function)), env)
self.assertTrue(env.get("square"))
# Call the square function
call_square_function = "(square 9)"
returned_value = Evaluator.evaluate(Parser.parse(Tokenizer.tokenize(call_square_function)), env)
self.assertEqual(returned_value, 81)
def test_getting_and_setting_variable(self):
env = Environment()
value = 2.3
env.set("a", value)
self.assertEqual(value, env.get("a"))
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)