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

Nils Schweinsberg writes:

On Sun, 4 Jul 2010 15:47:21 +0200, Ertugrul Soeylemez 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?

I've been told that it's safe to use; enabling it just tells GHC that you're sure that the instance constraints are OK (as they might be too complicated for GHC's type checker; e.g. I have to use it when doing a whole bunch of associated type constraints as GHC doens't like having such a large set of constraints on the instance definition). -- Ivan Lazar Miljenovic Ivan.Miljenovic@gmail.com IvanMiljenovic.wordpress.com