[Haskell-cafe] Re: Is my code too complicated?

[Nils Schweinsberg]

On Sun, 4 Jul 2010 15:47:21 +0200, Ertugrul Soeylemez <es at ertes.de> wrote:
> This requires a bunch of type system extensions, though, most notably
> the UndecidableInstances extension.  But it's safe to use here.

Probably a bit off topic, but whats wrong with UndecidableInstances? Where
is it safe to use, when would you avoid it and what can go wrong here?