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0928bb484a
Using Typeables as the only constraint on layout messages is a bit
scary, as a user can send arbitrary values to layoutMsg, whether they
make sense or not: there's basically no type feedback on the values you
supply to layoutMsg.
Folloing Simon Marlow's dynamically extensible exceptions paper, we use
an existential type, and a Message type class, to constrain valid
arguments to layoutMsg to be valid members of Message.
That is, a user writes some data type for messages their layout
algorithm accepts:
data MyLayoutEvent = Zoom
| Explode
| Flaming3DGlassEffect
deriving (Typeable)
and they then add this to the set of valid message types:
instance Message MyLayoutEvent
Done. We also reimplement the dynamic type check while we're here, to
just directly use 'cast', rather than expose a raw fromDynamic/toDyn.
With this, I'm much happier about out dynamically extensible layout
event subsystem.
xmonad : a lightweight X11 window manager.
http://xmonad.org
About:
Xmonad is a minimalist tiling window manager for X, written in Haskell. Windows
are managed using automatic layout algorithms, which can be dynamically
reconfigured. At any time windows are arranged so as to maximise the use of
screen real estate. All features of the window manager are accessible purely
from the keyboard: a mouse is entirely optional. Xmonad is configured in
Haskell, and custom layout algorithms may be implemented by the user in config
files. A principle of Xmonad is predictability: the user should know in advance
precisely the window arrangement that will result from any action.
By default xmonad provides three layout algorithms: tall, wide and fullscreen.
In tall or wide mode, windows are tiled and arranged to prevent overlap and
maximise screen use. Sets of windows are grouped together on virtual screens,
and each screen retains its own layout, which may be reconfigured dynamically.
Multiple physical monitors are supported via Xinerama, allowing simultaneous
display of a number of screens.
By utilising the expressivity of a modern functional language with a rich
static type system, Xmonad provides a complete, featureful window manager in
less than 500 lines of code, with an emphasis on correctness and robustness.
Internal properties of the window manager are checked using a combination of
static guarantees provided by the type system, and type-based automated
testing. A benefit of this is that the code is simple to understand, and easy
to modify.
Building:
Get the dependencies
mtl http://hackage.haskell.org/cgi-bin/hackage-scripts/package/mtl-1.0
X11 http://hackage.haskell.org/cgi-bin/hackage-scripts/package/X11-1.2
(Unfortunately X11-1.2 does not work correctly on AMD64. The latest
darcs version from http://darcs.haskell.org/packages/X11 does.)
X11-extras: http://hackage.haskell.org/cgi-bin/hackage-scripts/package/X11-extras-0.1
unix http://hackage.haskell.org/cgi-bin/hackage-scripts/package/unix-2.0
(included with ghc)
dmenu 2.* http://www.suckless.org/download/dmenu-2.7.tar.gz
(optional)
And then build with Cabal:
runhaskell Setup.lhs configure --prefix=/home/dons
runhaskell Setup.lhs build
runhaskell Setup.lhs install
Finally, add:
exec /home/dons/bin/xmonad
to the last line of your .xsession file
Authors:
Spencer Janssen
Don Stewart
Jason Creighton