TKStateMachine *inboxStateMachine = [TKStateMachine new];

TKState *unread = [TKState stateWithName:@"Unread"];
[unread setDidEnterStateBlock:^(TKState *state, TKTransition *transition) {
    [self incrementUnreadCount];
}];
TKState *read = [TKState stateWithName:@"Read"];
[read setDidExitStateBlock:^(TKState *state, TKTransition *transition) {
    [self decrementUnreadCount];
}];
TKState *deleted = [TKState stateWithName:@"Deleted"];
[deleted setDidEnterStateBlock:^(TKState *state, TKTransition *transition) {
    [self moveMessageToTrash];
}];

[inboxStateMachine addStates:@[ unread, read, deleted ]];
inboxStateMachine.initialState = unread;

TKEvent *viewMessage = [TKEvent eventWithName:@"View Message" transitioningFromStates:@[ unread ] toState:read];
TKEvent *deleteMessage = [TKEvent eventWithName:@"Delete Message" transitioningFromStates:@[ read, unread ] toState:deleted];
TKEvent *markAsUnread = [TKEvent eventWithName:@"Mark as Unread" transitioningFromStates:@[ read, deleted ] toState:unread];

[inboxStateMachine addEvents:@[ viewMessage, deleteMessage, markAsUnread ]];

// Activate the state machine
[inboxStateMachine activate];

[inboxStateMachine isInState:@"Unread"]; // YES, the initial state

// Fire some events
NSDictionary *userInfo = nil;
NSError *error = nil;
BOOL success = [inboxStateMachine fireEvent:@"View Message" userInfo:userInfo error:&error]; // YES
success = [inboxStateMachine fireEvent:@"Delete Message" userInfo:userInfo error:&error]; // YES
success = [inboxStateMachine fireEvent:@"Mark as Unread" userInfo:userInfo error:&error]; // YES

success = [inboxStateMachine canFireEvent:@"Mark as Unread"]; // NO

// Error. Cannot mark an Unread message as Unread
success = [inboxStateMachine fireEvent:@"Mark as Unread" userInfo:nil error:&error]; // NO

// error is an TKInvalidTransitionError with a descriptive error message and failure reason