darcs patch: Add proximal lookup functions in Map (and 2 more)

[Ross Paterson]

On Tue, May 22, 2007 at 10:28:24AM -0700, Adam Langley wrote:
> Please see attached 2 patches (and 1 misc patch) to Data.Map which add
> the ability to lookup entries by proximity. For example, if I have a
> Map which relates times to the state of a system at that time:
>  let m = Map.fromList [(1, x), (10, y), (15, z)]
> Then, if I want to find out the state at time 5:
>  Map.nearestLesserOrEqual 5 m
>  -> (1, x)
> 
> In a similar fashion, nearestGreaterOrEqual and nearest are also provided.

nearest needs Num, but the other two shouldn't.