diff options
author | Don Stewart <dons@cse.unsw.edu.au> | 2007-05-04 10:16:49 +0200 |
---|---|---|
committer | Don Stewart <dons@cse.unsw.edu.au> | 2007-05-04 10:16:49 +0200 |
commit | d93284dd514485bdc06c1bb6b984608271804dcb (patch) | |
tree | 5eb85dcf427ef8a924fe45d4feb2a61c24ca156b /Config.hs | |
parent | 7d2c080540f57cfb4bca155cf27b792c7e5d2d8c (diff) | |
download | metatile-d93284dd514485bdc06c1bb6b984608271804dcb.tar metatile-d93284dd514485bdc06c1bb6b984608271804dcb.zip |
Constrain layout messages to be members of a Message class
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.
darcs-hash:20070504081649-9c5c1-954b406e8c21c2ca4428960e4fc1f9ffb17fb296
Diffstat (limited to 'Config.hs')
-rw-r--r-- | Config.hs | 4 |
1 files changed, 2 insertions, 2 deletions
@@ -154,8 +154,8 @@ keys = M.fromList $ , ((modMask, xK_j ), raise GT) , ((modMask, xK_k ), raise LT) - , ((modMask, xK_h ), layoutMsg Shrink) - , ((modMask, xK_l ), layoutMsg Expand) + , ((modMask, xK_h ), sendMessage Shrink) + , ((modMask, xK_l ), sendMessage Expand) , ((modMask .|. shiftMask, xK_c ), kill) |