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

Ertugrul Soeylemez es at ertes.de
Sun Jul 4 21:07:41 EDT 2010

Nils Schweinsberg <ml at n-sch.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?

Essentially UndecidableInstances turns the type system into a
Turing-complete programming language.  One direct consequence is that
type checking may not terminate and, because of the halting problem, the
type system is unable to tell when that happens.


nightmare = unsafePerformIO (getWrongWife >>= sex)

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