G'day Marco.
Quoting Marco Righele <[EMAIL PROTECTED]>:
> How can I achieve the same effect (if it is ever possible)?
> I feel like it should be something almost trivial, but I really can't get it.
One approach is to use a monad which works like Maybe, but as a monad
transformer over IO.
You might want to try NegateT, which does pretty much precisely this:
http://cvs.sourceforge.net/viewcvs.py/hfl/hfl/mtl/Negate.hs?rev=1.2
Cheers,
Andrew Bromage
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