Max Goldstein | July 30, 2015 | Elm 0.15.1
In Elm, signals always have a data source associated with them.
Window.dimensions is exactly what you think it is, and you can't send your own events on it. You can derive your own signals from these primitives using
merge, but the timing of events is beyond your control.
This becomes a problem when you try to add UI elements. We want to be able to add checkboxes and dropdown menus, and to receive the current state of these elements as a signal. So how do we do that?