[xmonad] Help with ManageHook

[Daniel Schoepe]

Mike Sampson wrote:
> Hi,
> I'm trying to write my own ManageHook however as I am still trying to
> learn Haskell and don't have a 100% clear view of the internals of
> XMonad I'm having some trouble.
> 
> My goal is to set the transparency of certain windows, matched via class
> name, as they are created. FadeInactive.hs has a setOpacity function
> which does this no problem. FadeInactive is driven from a LogHook
> whereas I want to drive it from a ManageHook. What is the *magic glue*
> needed to do something like:
> 
> [ className =? "URxvt" --> setOpacity window 0x99999999]
> 
> in my manage hooks. I know that setOpacity is not a ManageHook and that
> i need to wrap it in something however looking at other ManageHooks,
> such as doFloat, has not made things clear to me. Can anyone help with
> this or provide a better way of doing it?
> 
> Regards,
> 
> Mike

If you want to get the window in question, you need to use `ask':

.. --> (ask >>= \w -> liftX (setOpacity w 0x99999999) >> idHook)

One also needs liftX to lift a normal X action into a Query(The type
expected by the `-->' operator). idHook ensures the proper return
type(ManageHooks have to return transformations of the window set, but
since we don't want to change the window set itself, we use idHook).