why is Data.Set not a Monad?y

[Neil Mitchell]

Hi

> You could just have used {-# OPTIONS_GHC -fno-implicit-prelude #-} and
> rebound do.
>
> > {-# OPTIONS -fglasgow-exts -fallow-undecidable-instances #-}
>
> OPTIONS is obsolescent - new code should use OPTIONS_GHC, etc.  (since
> options are by there nature compiler dependant)

New code should ideally use LANGUAGE:

{-# LANGUAGE AllowUndecidableInstances #-}

It also means you can't throw in everything (all extensions), but have
to be more selective.

In some cases you still need to use OPTIONS_GHC though, particularly
for # in id's - although hopefully someone will be adding MagicHash
soon :-)

Thanks

Neil