Allow pattern-matching on 'XMonad.Layout.Choose' by exporting constructors

[jumper149]

Export the constructor Choose to be able to construct and pattern-match Choose l r a. To do that it is also necessary to export LR with constructors.

Description

I just added the constructor Choose and LR with constructors to the exports of the module XMonad.Layout

Checklist

• I've read CONTRIBUTING.md

• I've confirmed these changes don't belong in xmonad-contrib instead

• I tested my changes with xmonad-testing (that seems to be a dead repository)

• I updated the CHANGES.md file

[jumper149]

Here in my dotfiles you can see an example of what can be done with this change:

I use everything that Choose provides but wrap it in a newtype and define a different instance of LayoutClass, so that I'm able to handle specific Messages differently.
I send the messages ModifyWindowBorderEnabled a and ModifyScreenBorderEnabled a to both sub-layouts instead of just the current one.

This way I can set the spacing for all sub-layouts on my workspaces with just using toggleGaps.

[liskin]

I have no opinion about whether exposing these constructors should be done or not, but I think there is an easier way to implement this.

If I understand your setup correctly, you have a global toggle for gaps that broadcasts a message to all workspaces and all sublayouts and this message toggles the inner state of all those layouts (or layout modifiers). So what you really want is a single global boolean toggle instead of a hundred local ones that you toggle, hoping they'll never come out of sync. How about this:

Store this global toggle in ExtensibleState and whenever the layout is switched, sync this state into it using something like

setGaps enabled :: X ()
setGaps enabled = do traverse_ broadcastMessage messages
                    refresh
   where messages = [ ModifyWindowBorderEnabled (const enabled)
                    , ModifyScreenBorderEnabled (const enabled)
                    ]

It's not the cleanest solution, I guess, but it's simpler than adding a LayoutClass that delivers messages to both active and inactive layouts (which is probably dangerous in general).

[liskin]

I am now in favor of merging this. In #242 and xmonad/xmonad-contrib#398 I started working on being able to query the current layout state. The next step is to add a InspectLayoutModifier type class to xmonad-contrib to allow inspecting the current state of some modifier. A wip version of that is sitting here: liskin/xmonad-contrib@77c1821. This class will need instances for many layout combinators, including Choose, so I also need the constructors to be exported.

Can you please rebase and fix the conflicts?
@psibi, @byorgey can you folks then merge it please?
Thanks!

[psibi]

@jumper149 Thanks for for the MR!

@liskin Done.

[liskin]

This ended up breaking compilation of xmonad-contrib as modules that define their own L/R data constructors (X.U.Types, X.L.GridVariants, X.L.ResizeScreen, X.L.TallMastersCombo, X.C.Types) cause ambiguity now.
As LR was never exported before, the best course of action is probably to rename it and its constructors so it doesn't conflict. Exporting L and R from XMonad is really nasty. :-/

And then maybe also reduce the duplication in xmonad-contrib: use the renamed/exported LR in TallMastersCombo.

Reported here: https://old.reddit.com/r/xmonad/comments/ka1qxg/fixing_fullscreen/