Improve the story regarding dialogs

[ivanperez-keera]

Certain reactive constructs like dialogs do not yet integrate well with RVs.

An example, from https://github.com/keera-studios/haskell-titan/blob/develop/titan-gui/src/Controller/Conditions/Buttons.hs#L89, is:

installConditionLoadTrace cenv = void $ do
  btn <- toolButtonActivateField <$> toolBtnLoadTrace (uiBuilder (view cenv))
  btn =:> conditionVMLoadTrace cenv

conditionVMLoadTrace :: CEnv -> IO ()
conditionVMLoadTrace cenv = do
  window <- mainWindow (uiBuilder (view cenv))
  fch <- fileChooserDialogNew (Just "Open Yampa trace") Nothing
                              FileChooserActionOpen
                              [("Cancel", ResponseCancel),
                               ("Load", ResponseAccept)]

  ytrfilt <- fileFilterNew
  fileFilterAddPattern ytrfilt "*.ytr"
  fileFilterSetName ytrfilt "Yampa Trace"
  fileChooserAddFilter fch ytrfilt

  nofilt <- fileFilterNew
  fileFilterAddPattern nofilt "*.*"
  fileFilterSetName nofilt "All Files"
  fileChooserAddFilter fch nofilt

  widgetShow fch
  response <- dialogRun fch
  fp <- case response of
          ResponseCancel -> putStrLn "You cancelled..." >> return Nothing
          ResponseAccept -> do nwf <- fileChooserGetFilename fch
                               case nwf of
                                 Nothing   -> putStrLn "Nothing" >> return Nothing
                                 Just path -> putStrLn ("New file path is:\n" ++ path) >> return (Just path)
          ResponseDeleteEvent -> putStrLn "You closed the dialog window..." >> return Nothing

  widgetDestroy fch
  awhen fp $ \p -> do
    contents <- readFile p
    sendToYampaSocketAsync (extra cenv) (show (LoadTraceFromString contents))

Instead, one could think of this dialog as a sort-of fudget or reactive processor. If synced, it could be described with something like:

(toolButtonActivateField . toolBtnLoadTrace) =>= openFileDialog =>= loadFile  =:> sendNewTrace

[ivanperez-keera]

I guess what this all means is that we can improve the story for any function of the form:
a -> m b, making it a pair of reactive values (a write end of type a, and a read end of type b)