darcs patch: add Data.Set.notMember and Data.Map.notMember

[Christian Maeder]

John Meacham wrote:
> On Thu, Mar 09, 2006 at 11:09:50PM +0100, Jean-Philippe Bernardy wrote:
[...]
>> Any evidence to add to the case ?
> 
> * symmetry with elem/notElem

I don't like notElem either

> * quite useful for cleaning up guards:
> 
> f x | not (x `Set.member` map) && foo = ...
> is hard to read.

You may swap quards (or the "then" and "else" branches of "if"), or 
avoid the infix notation (which is horrible in this case anyway).

I don't think we need negated versions of any boolean function, that's 
what "not" is for!

Christian