Strange ghci :def failure

[Simon Marlow]

> This is an embarrassing bug in 6.0.  Alas.  We need more regression
> tests for ghci.
> 
> Workaround: do not write expressions in ghci with pattern matches that
> may fail.

There's a slightly less intrusive workaround:

Prelude> :t GHC.Err.error
GHC.Err.error :: forall a. [Char] -> a
Prelude> let [x] = []
Prelude> Leaving GHCi.

Cheers,
	Simon