UpdatePointer in XMonad Contrib v0.12

The time came to replace an ailing macbook air with a new machine, and I’ve chosen a Lenovo. Now that I have something that uses an Intel WiFi chip, I’m much happier to take a shot at running Arch Linux, and I thought while I was undergoing this change I would switch from i3wm to xmonad.

However, as part of the setup I wanted the mouse to follow the window focus, which is provided by the XMonad-Contrib. At the time of writing, the version in the ArchLinux repository is 0.12, but the documentation is for the 0.11 release. This means that the advice on the XMonad.Actions.UpdatePointer page is invalid, since there was a breaking change to the API the PointerPosition data constructor uses to position the cursor.

This lead to me getting a very confusing error: Not in scope: data constructor ‘Relative’, the fix for which is outlined in the source code, and reproduced below for convenience.

-- nearest point of window
logHook = updatePointer (0.5, 0.5) (1, 1)
-- exact centre of window
logHook = updatePointer (0.5, 0.5) (0, 0)
-- near the top-left
logHook = updatePointer (0.25, 0.25) (0.25, 0.25)
-- within 110% of the edge
logHook = updatePointer (0.5, 0.5) (1.1, 1.1)

This syntax replaces the previous use of the data constructors (Nearest, Relative and TowardsCentre);