Set.lookup?

[Christian Maeder]

Serge D. Mechveliani wrote:
> How do you think, maybe,  Data.Set  also needs to provide
> `lookup' ?

Admittingly, using 'Set.filter (==e) s' to find the matching element may 
be a bit slower.

When trying to use 'Set.intersection s $ singleton e' I just noticed 
that intersection is not left-biased (see below)!

I'm not sure if Data.Set should be extended to better support elements 
with an equivalence relation and a corresponding order. I've such sets 
too, but never really cared about the additional component.

Do you also want functions 'insertWith', 'unionWith', 'splitLookup' (and 
what not)?

I'ld rather suggest to use Data.Map instead and use a proper total order 
for the keys (although that may also be awkward).

Christian

*Main> findMin $ union (singleton $ D 0 "3") $ singleton $ D 0 "2"
D 0 "3"

*Main> findMin $ intersection (singleton $ D 0 "3") $ singleton $ D 0 "2"
D 0 "2"