def kstar(graph, id_alloc):
""" Kleene Star operator """
new_start = NFAState(id_alloc.create_id())
new_start.add_path(create_epsilon_trans(), graph.start)
new_end = NFAState(id_alloc.create_id())
new_start.add_path(create_epsilon_trans(), new_end)
graph.end.add_path(create_epsilon_trans(), new_end)
graph.end.add_path(create_epsilon_trans(), graph.start)
return NFA(new_start, new_end)
def union(graph1, graph2, id_alloc):
""" A union is represented by the pipe operator ('|')
"""
new_start = NFAState(id_alloc.create_id())
new_start.add_path(create_epsilon_trans(), graph1.start)
new_start.add_path(create_epsilon_trans(), graph2.start)
new_end = NFAState(id_alloc.create_id())
graph1.end.add_path(create_epsilon_trans(), new_end)
graph2.end.add_path(create_epsilon_trans(), new_end)
return NFA(new_start, new_end)
def test_epsilon_transition_always_passes(self):
transition = create_epsilon_trans()
self.assertTrue(transition.is_available('a'))
self.assertTrue(transition.is_available('A'))
self.assertTrue(transition.is_available('0'))
self.assertTrue(transition.is_available('-'))
self.assertTrue(transition.is_available('\n'))
def trans_desc_to_trans(desc_str):
""" Takes a description str and converts it into an actual transition
"""
if desc_str == "epsilon":
return create_epsilon_trans()
elif desc_str == "metachar":
return create_metachar_trans()
elif desc_str[0:6] == "char: ":
return create_char_trans(desc_str[6])
else:
Exception("cannot convert " + desc_str + " to a transition")
def repeater(graph, repeater_tok, id_alloc):
""" Constructs an nfa for '*', '+', '?'
"""
if repeater_tok.has_val('*'):
return kstar(graph, id_alloc)
elif repeater_tok.has_val('+'):
kstar_graph = kstar(graph, id_alloc)
return concat(graph, kstar_graph)
elif repeater_tok.has_val('?'):
empty_graph = construct_graph(create_epsilon_trans(), id_alloc)
return union(graph, empty_graph)
else:
raise Exception("repeater not recognized: " + repeater_tok)