def test_derivation_empty(self):
var_s = Variable("S")
productions = [Production(var_s, [Epsilon()])]
cfg = CFG(productions=productions, start_symbol=var_s)
parse_tree = cfg.get_cnf_parse_tree([])
derivation = parse_tree.get_rightmost_derivation()
self.assertEqual([[var_s], []], derivation)
def test_derivation_does_not_exist(self):
var_s = Variable("S")
ter_a = Terminal("a")
ter_b = Terminal("b")
cfg = CFG(productions=[], start_symbol=var_s)
with self.assertRaises(DerivationDoesNotExist):
parse_tree = cfg.get_cnf_parse_tree([ter_a, ter_b])
parse_tree.get_rightmost_derivation()
def test_get_rightmost_derivation(self):
ter_a = Terminal("a")
ter_b = Terminal("b")
var_s = Variable("S")
var_a = Variable("A")
var_b = Variable("B")
var_c = Variable("C")
productions = [
Production(var_s, [var_c, var_b]),
Production(var_c, [var_a, var_a]),
Production(var_a, [ter_a]),
Production(var_b, [ter_b])
]
cfg = CFG(productions=productions, start_symbol=var_s)
parse_tree = cfg.get_cnf_parse_tree([ter_a, ter_a, ter_b])
derivation = parse_tree.get_rightmost_derivation()
self.assertEqual(
derivation,
[[var_s], [var_c, var_b], [var_c, ter_b], [var_a, var_a, ter_b],
[var_a, ter_a, ter_b], [ter_a, ter_a, ter_b]])
