[Xmonad] darcs patch: fix potential hole in userCode.

[Stefan O'Rear]

On Fri, Oct 12, 2007 at 08:15:52PM -0700, Stefan O'Rear wrote:
> The main issue is:
> 
> modify (\x -> posionWithBottoms x)
> 
> That will not fail immediatly, but will cripple xmonad by causing all
> commands that read the state to fail, including mod-q.  Your only choice
> is to quit xmonad wholesale.
> 
> My proposal (shared, I believe, with sjanssen) is "fail early, fail
> often, and force the people who commit bugs to wear imaginary dunce
> caps".

Another option is to deepseq the state after every command.  (That bugs
like this exist in the first place is IMO a serious failing of lazy
languages; where's SML-with-qualified-types-and-good-syntax when you
need it? *grin*)

Stefan
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