Fix architecture issues

[bygu4]

Some modules of pyformlang have a strange design that makes this project hard to maintain and develop, and we should think about what we can do to make the architecture cleaner and more concise.

[bygu4]

This should be in EpsilonNFA:

pyformlang/pyformlang/finite_automaton/finite_automaton.py

Lines 497 to 504 in 176a609

	@classmethod
	def from_networkx(cls, graph):
	"""
	Import a networkx graph into an finite state automaton. \
	The imported graph requires to have the good format, i.e. to come \
	from the function to_networkx

pyformlang/pyformlang/finite_automaton/finite_automaton.py

Lines 531 to 533 in 176a609

	"""
	enfa = finite_automaton.EpsilonNFA()
	for s_from in graph:

[bygu4]

We have to get rid of this abstract method, otherwise we are bound to have cyclic imports:

pyformlang/pyformlang/finite_automaton/finite_automaton.py

Lines 644 to 648 in 176a609

	def to_deterministic(self):
	""" Turns the automaton into a deterministic one"""
	raise NotImplementedError

[bygu4]

This shouldn't return None:

pyformlang/pyformlang/finite_automaton/finite_automaton.py

Lines 688 to 702 in 176a609

	def to_state(given: Any) -> State:
	""" Transforms the input into a state
	Parameters
	----------
	given : any
	What we want to transform
	"""
	if given is None:
	return None
	if isinstance(given, State):
	return given
	return State(given)

[bygu4]

Probably should be for Any type, because we cast these parameters to State and Symbol anyway:

pyformlang/pyformlang/finite_automaton/finite_automaton.py

Lines 46 to 49 in 176a609

	def add_transition(self, s_from: State, symb_by: Symbol,
	s_to: State) -> int:
	""" Adds a transition to the nfa

pyformlang/pyformlang/finite_automaton/finite_automaton.py

Lines 77 to 81 in 176a609

	"""
	s_from = to_state(s_from)
	symb_by = to_symbol(symb_by)
	s_to = to_state(s_to)
	temp = self._transition_function.add_transition(s_from, symb_by, s_to)

[bygu4]

Same as previous:

pyformlang/pyformlang/finite_automaton/finite_automaton.py

Lines 121 to 124 in 176a609

	def remove_transition(self, s_from: State, symb_by: Symbol,
	s_to: State) -> int:
	""" Remove a transition of the nfa

[bygu4]

Maybe it's a good idea to rename TransitionFunction to DeterministicTransitionFunction, and also create an interface TransitionFunction from which we can inherit both transition function classes

pyformlang/pyformlang/finite_automaton/transition_function.py

Lines 17 to 22 in 176a609

	class TransitionFunction:
	""" A transition function in a finite automaton.
	This is a deterministic transition function.

[bygu4]

I think it would be better to make an overload for this method, as it's output type is different depending on the number of input parameters:

pyformlang/pyformlang/finite_automaton/transition_function.py

Lines 123 to 126 in 176a609

	def __call__(self, s_from: State, symb_by: Symbol = None) -> List[State]:
	""" Calls the transition function as a real function

Also probably should return Set rather than List

[bygu4]

Iterable[Any] as we cast it to Symbols:

pyformlang/pyformlang/finite_automaton/epsilon_nfa.py

Lines 121 to 123 in 176a609

	def accepts(self, word: Iterable[Symbol]) -> bool:
	""" Checks whether the epsilon nfa accepts a given word

[bygu4]

Add same method for TransitionFunction (but it always returns True):

pyformlang/pyformlang/finite_automaton/nondeterministic_transition_function.py

Lines 149 to 152 in 176a609

	def is_deterministic(self):
	""" Whether the transition function is deterministic

[bygu4]

I think we can try moving this to NFA and making it a classmethod (like NondeterministicFiniteAutomaton.remove_epsilon_transitions(enfa))

pyformlang/pyformlang/finite_automaton/epsilon_nfa.py

Lines 253 to 266 in 176a609

	def remove_epsilon_transitions(self) -> "NondeterministicFiniteAutomaton":
	""" Removes the epsilon transitions from the automaton
	Returns
	----------
	dfa : :class:`~pyformlang.finite_automaton.\
	NondeterministicFiniteAutomaton`
	A non-deterministic finite automaton equivalent to the current \
	nfa, with no epsilon transition
	"""
	from pyformlang.finite_automaton import NondeterministicFiniteAutomaton
	nfa = NondeterministicFiniteAutomaton()
	for state in self._start_state:

[bygu4]

Same here with DeterministicFiniteAutomaton.from_epsilon_nfa(enfa)

pyformlang/pyformlang/finite_automaton/epsilon_nfa.py

Lines 332 to 341 in 176a609

	def to_deterministic(self) -> "DeterministicFiniteAutomaton":
	""" Transforms the epsilon-nfa into a dfa
	Returns
	----------
	dfa : :class:`~pyformlang.finite_automaton\
	.DeterministicFiniteAutomaton`
	A dfa equivalent to the current nfa

But it will require some refactoring to make sure we don't use protected enfa members

[bygu4]

Same story:

pyformlang/pyformlang/finite_automaton/nondeterministic_finite_automaton.py

Lines 118 to 127 in 176a609

	def to_deterministic(self) -> "DeterministicFiniteAutomaton":
	""" Transforms the nfa into a dfa
	Returns
	----------
	dfa : :class:`~pyformlang.deterministic_finite_automaton\
	.DeterministicFiniteAutomaton`
	A dfa equivalent to the current nfa

[bygu4]

Cyclic import here between Regex and EpsilonNFA

pyformlang/pyformlang/finite_automaton/epsilon_nfa.py

Lines 398 to 421 in 176a609

	def to_regex(self) -> "Regex":
	""" Transforms the EpsilonNFA to a regular expression
	Returns
	----------
	regex : :class:`~pyformlang.regular_expression.Regex`
	A regular expression equivalent to the current Epsilon NFA
	Examples
	--------
	>>> enfa = EpsilonNFA()
	>>> enfa.add_transitions([(0, "abc", 1), (0, "d", 1), \
	(0, "epsilon", 2)])
	>>> enfa.add_start_state(0)
	>>> enfa.add_final_state(1)
	>>> regex = enfa.to_regex()
	>>> regex.accepts(["abc"])
	True
	"""
	from pyformlang.regular_expression import Regex
	enfas = [self.copy() for _ in self._final_states]

[bygu4]

I think it would be better to make an overload for this method, as it's output type is different depending on the number of input parameters:

pyformlang/pyformlang/finite_automaton/transition_function.py

Lines 123 to 126 in 176a609

	def __call__(self, s_from: State, symb_by: Symbol = None) -> List[State]:
	""" Calls the transition function as a real function

Also probably should return Set rather than List

Same in NondeterministicTransitionFunction and FiniteAutomaton

[bygu4]

We should also rework DoublyLinkedList because Node can access List

pyformlang/pyformlang/finite_automaton/doubly_linked_node.py

Lines 6 to 20 in 176a609

	def __init__(self,
	list_in,
	next_node=None,
	previous_node=None,
	value=None):
	self.next_node = next_node
	self.previous_node = previous_node
	self.value = value
	self.list_in = list_in
	def delete(self):
	"""Delete the current node"""
	self.list_in.delete(self)