[Haskell] SOLVED Catching error / making library functions monadic (in failure)

[Philip K.F. Hölzenspies]

Dear all,

Thank you very much for your reactions. Neil told me I should have posted this 
in haskell-cafe, so sorry for the inconvenience. Since my problem has since 
been solved, I figured I would send this "thanks all, it's solve" e-mail to 
the list, to close the issue.

The magic answer turned out to be Control.Exception.evaluate as opposed to 
return. This was the problem:

catch (return $ [] !! 0) (error "foo")

(which I had oversimplified by omitting the return) gave

*** Exception: Prelude.(!!): index too large

while

catch (evaluate $ [] !! 0) (error "foo")

gave

*** Exception: bar

even when unsafePerformIO was applied to it.

Thank you all, but especially the people that suggested this: Martijn & Koen

Regards,
Philip