Re: [xmonad] Strange workspace switching bug in my config

13 May 2012


      On Sun, May 13, 2012 at 8:45 AM, Norbert Zeh  wrote:
...
Leo Alekseyev [2012.05.13 0127 -0400]:
...
Hi all,
A couple of years back I made the following addition to my xmonad.hs:
instead of 10 workspaces, it admits 20 workspaces, logically arranged
in two rows of 10.  I think of it as having a "scratch" workspace for
every main workspace, and I use up/down arrows to switch between the
main and the scratch workspace.  For instance, if you are on workspace
4, Mod4-<down> will move to workspace 4SCR and Mod4-<up> will move
back to workspace 4.
Recently this config started misbehaving (without any changes to
xmonad.hs, but with possible changes in xmonad/GHC version to 0.10 and
7.4.1 as my system was upgraded).  In particular, in the example
above, now Mod4-<down> moves from workspace 4 to workspace 3SCR and
Mod4-<up> then moves from 3SCR to 2.  To fix it, I have to log in and
out of X, but the problem always reoccurs, possibly after sleep/resume
cycle(?).
The embarrassing thing here is that I haven't touched Haskell in a
while, and barely grok my config anymore, so I don't know where to
start troubleshooting.  The code I described seems straightforward
enough, so it's my hope that maybe someone here can tell me what is
going on without too much effort...
The relevant parts of my config are below, and the full file in its
horrifying glory is at http://hpaste.org/68453.  If someone seems
something obviously amiss, please shout...
--leo
myWorkspaces = ["1:terminals", "2:emacs", "3:web", "4", "5", "6",
"7","8","9","0"] ++ map (\x -> show x ++ "SCR") ([1..9]++[0])
.....
zeroSub 0 = 10
zeroSub x = x
jumpToMain = gets windowset >>= \W.StackSet { W.current = W.Screen {
W.workspace = w } } -> withNthWorkspace W.greedyView (-1+(zeroSub $
read [head(W.tag w)]))
jumpToScratch = gets windowset >>= \W.StackSet { W.current = W.Screen
{ W.workspace = w } } -> withNthWorkspace W.greedyView (9+(zeroSub $
read [head(W.tag w)]))
The math here looks all wrong, and I'm surprised that it worked at all before.
What you want, I think, is the following:
jumpToMain = gets (W.tag . W.workspace . W.current . windowset)
        >>= W.greedyView . toMain
 where
   toMain ws = [head ws]
jumpToScratch = gets (W.tag . W.workspace . W.current . windowset)
           >>= W.greedyView . toScratch
 where
   toScratch ws | length ws == 1 = ws ++ "SCR"
                | otherwise      = ws
The idea here is that you simply want to add or take away the "SCR" suffix in
the workspace tag or, in the latter case, do nothing if it's already present.
Hi Norbert,
Yes, my original math was kind of dodgy...  Your solution seems
better, but it doesn't compile for me...  any ideas?

xmonad.hs:452:14:
    No instance for (MonadState
                       XState ((->) (W.StackSet [Char] l3 a3 s3 sd3)))
      arising from a use of `gets'
    Possible fix:
      add an instance declaration for
      (MonadState XState ((->) (W.StackSet [Char] l3 a3 s3 sd3)))
    In the first argument of `(>>=)', namely
      `gets (tag . W.workspace . W.current . windowset)'
    In the expression:
      gets (tag . W.workspace . W.current . windowset)
      >>= W.greedyView . toMain
    In an equation for `jumpToMain':
        jumpToMain
          = gets (tag . W.workspace . W.current . windowset)
            >>= W.greedyView . toMain
          where
              toMain ws = [head ws]


xmonad.hs:456:17:
    No instance for (MonadState
                       XState ((->) (W.StackSet [Char] l1 a1 s1 sd1)))
      arising from a use of `gets'
    Possible fix:
      add an instance declaration for
      (MonadState XState ((->) (W.StackSet [Char] l1 a1 s1 sd1)))
    In the first argument of `(>>=)', namely
      `gets (tag . W.workspace . W.current . windowset)'
    In the expression:
      gets (tag . W.workspace . W.current . windowset)
      >>= W.greedyView . toScratch
    In an equation for `jumpToScratch':
        jumpToScratch
          = gets (tag . W.workspace . W.current . windowset)
            >>= W.greedyView . toScratch
          where
              toScratch ws
                | length ws == 1 = ws ++ "SCR"
                | otherwise = ws