Various utility functions concerning event handlers.
A value of type
AddHandler a is just a facility for registering
callback functions, also known as event handlers.
The type is a bit mysterious, it works like this:
do unregisterMyHandler <- addHandler myHandler
The argument is an event handler that will be registered. The return value is an action that unregisters this very event handler again.
Build a facility to register and unregister event handlers.
Apply a function with side effects to an