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| 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 | ba6e32758d41f1117fc125b32008c2f411eec8b1 (patch) | |
| tree | 5eb85dcf427ef8a924fe45d4feb2a61c24ca156b /Main.hs | |
| parent | 2a59314ffa3997b6365bf2130ef8df0e0bc0185d (diff) | |
| download | xmonad-ba6e32758d41f1117fc125b32008c2f411eec8b1.tar.gz xmonad-ba6e32758d41f1117fc125b32008c2f411eec8b1.tar.xz xmonad-ba6e32758d41f1117fc125b32008c2f411eec8b1.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
darcs-hash:20070504081649-9c5c1-954b406e8c21c2ca4428960e4fc1f9ffb17fb296.gz
Diffstat (limited to 'Main.hs')
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