Signal's value depend on dialog window

I’m using Gtk and GtkReactive
I want to make the value of a Signal depend on input from a newly spawned window.
How do I make a Signal open a dialog-window (a new window with some widgets in it) and have said Signal’s value depend on the dialog’s input (from the user)?
I don’t know how to get the signal to update from the input from the dialog window. The newly opened window needs to return the value of the Signal that spawned it. But the value wouldn’t be composed before the user inputs all their choices (in the newly opened windows’ widgets). So the Signal needs to wait on the input from the window, or it needs to update to each of the changes made by the window, not sure…
Any minimal example would be very helpful, thanks!

Found it!
A widget updates a Signal that calls on a function that creates a window filled with other widgets. That window returns a Signal to the Signal that spawned the window. Then you just need to flatten that Signal, and you’re done!