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feat: Add listContains and firstWhereOrNull

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This commit is contained in:
PapaTutuWawa 2022-11-05 13:21:17 +01:00
parent 96edecdf2a
commit c1087fe12e
5 changed files with 18 additions and 179 deletions
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99
lib/automaton.dart
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@ -1,99 +0,0 @@
class NoTransitionPossibleException implements Exception {
@override
String errMsg() => "The transition graph allows no transition";
}
/// A deterministic finite automaton. [T] is the state type while
/// [I] is the input type.
/// Edges of the node must be added with [addTransition]. If a trap state
/// is required, it can be set in the constructor.
class DeterministicFiniteAutomaton<T, I> {
/// The current state of the DFA
T _state;
/// The edges of the DFA: State x Input -> State
Map<T, Map<I, T>> _transitions;
/// Trap state
T? trapState;
/// The argument is the initial state
DeterministicFiniteAutomaton(this._state, { this.trapState }) : _transitions = {};
T get state => _state;
void addTransition(T oldState, I input, T newState) {
assert(oldState != trapState);
// These are handled implicitly if no transition has been found
assert(newState != trapState);
if (!_transitions.containsKey(oldState)) {
_transitions[oldState] = {};
}
_transitions[oldState]![input] = newState;
}
/// Transition the DFA based on its current state and the input [input].
void onInput(I input) {
final newState = _transitions[_state]?[input];
if (newState == null) {
// Go to the trap state if we can
if (trapState != null) {
_state = trapState!;
return;
} else {
throw NoTransitionPossibleException();
}
}
_state = newState;
}
/// Returns where [input] would take the automaton to. Returns null if no transition
/// is possible, ignoring trap transitions.
T? peekTransition(I input) {
if (!_transitions.containsKey(_state) || !_transitions[_state]!.containsKey(input)) {
return null;
}
return _transitions[_state]![input]!;
}
}
typedef MealyAutomatonCallback<T, I> = void Function(T oldState, I input);
class MealyAutomaton<T, I> {
/// The base automaton
final DeterministicFiniteAutomaton<T, I> _automaton;
/// Mapping of State x Input -> Output callback
Map<T, Map<I, MealyAutomatonCallback<T, I>>> _outputs;
/// Trap state
MealyAutomatonCallback<T, I>? trapCallback;
// TODO: Assert that trapState != null implies trapCallback != null.
MealyAutomaton(T initialState, { T? trapState, this.trapCallback })
: _outputs = {},
_automaton = DeterministicFiniteAutomaton(initialState, trapState: trapState);
T get state => _automaton.state;
void addTransition(T oldState, I input, T newState, MealyAutomatonCallback<T, I> callback) {
_automaton.addTransition(oldState, input, newState);
if (!_outputs.containsKey(oldState)) {
_outputs[oldState] = {};
}
_outputs[oldState]![input] = callback;
}
void onInput(I input) {
final _state = _automaton.state;
if (_automaton.peekTransition(input) == null && trapCallback == null) {
throw new NoTransitionPossibleException();
}
final callback = _outputs[_state]?[input] ?? trapCallback!;
_automaton.onInput(input);
callback(_state, input);
}
}

1
lib/awaitabledatasender.dart
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@ -72,6 +72,7 @@ abstract class AwaitableDataSender<
/// Future will be returned that can be used to await a response. If it
/// is false, then null will be imediately resolved.
Future<R?> sendData(S data, { bool awaitable = true, @visibleForTesting String? id }) async {
// ignore: no_leading_underscores_for_local_identifiers
final _id = id ?? _uuid.v4();
Future<R?> future = Future.value(null);
_log.fine("sendData: Waiting to acquire lock...");

16
lib/lists.dart Normal file
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@ -0,0 +1,16 @@
/// A wrapper around List<T>.firstWhere that does not throw but instead just
/// returns true if [test] returns true for an element or false if [test] never
/// returned true.
bool listContains<T>(List<T> list, bool Function(T element) test) {
return firstWhereOrNull<T>(list, test) != null;
}
/// A wrapper around [List<T>.firstWhere] that does not throw but instead just
/// return null if [test] never returned true
T? firstWhereOrNull<T>(List<T> list, bool Function(T element) test) {
try {
return list.firstWhere(test);
} catch(e) {
return null;
}
}

2
lib/moxlib.dart
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@ -1,5 +1,5 @@
library moxlib;
export "awaitabledatasender.dart";
export "automaton.dart";
export "lists.dart";
export "math.dart";

79
test/automaton_test.dart
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@ -1,79 +0,0 @@
import "package:moxlib/automaton.dart";
import "package:test/test.dart";
enum States {
a, b, c, trap
}
void main() {
test("Test a simple DFA", () {
final automaton = DeterministicFiniteAutomaton<States, int>(States.a);
automaton.addTransition(States.a, 1, States.b);
automaton.addTransition(States.b, 2, States.c);
automaton.addTransition(States.c, 3, States.a);
expect(automaton.state, States.a);
automaton.onInput(1);
expect(automaton.state, States.b);
automaton.onInput(2);
expect(automaton.state, States.c);
automaton.onInput(3);
expect(automaton.state, States.a);
});
test("Test a simple DFA with a trap state", () {
final automaton = DeterministicFiniteAutomaton<States, int>(States.a, trapState: States.trap);
automaton.addTransition(States.a, 1, States.b);
automaton.addTransition(States.b, 2, States.c);
automaton.addTransition(States.c, 3, States.a);
expect(automaton.state, States.a);
automaton.onInput(1);
expect(automaton.state, States.b);
automaton.onInput(2);
expect(automaton.state, States.c);
automaton.onInput(4);
expect(automaton.state, States.trap);
// Transitioning away from the trap state should not be possible
automaton.onInput(5);
expect(automaton.state, States.trap);
});
test("Test a simple Mealy Automaton", () {
bool called = false;
final callback = (state, input) {
called = true;
};
final automaton = MealyAutomaton<States, int>(States.a);
automaton.addTransition(States.a, 1, States.b, callback);
automaton.onInput(1);
expect(automaton.state, States.b);
expect(called, true);
});
test("Test a simple Mealy Automaton with a trap state", () {
bool called = false;
bool trapCalled = false;
final callback = (state, input) {
called = true;
};
final trapCallback = (state, input) {
trapCalled = true;
};
final automaton = MealyAutomaton<States, int>(States.a, trapState: States.trap, trapCallback: trapCallback);
automaton.addTransition(States.a, 1, States.b, callback);
automaton.onInput(1);
expect(called, true);
automaton.onInput(1);
expect(automaton.state, States.trap);
expect(trapCalled, true);
});
}