Sets and home-made ordered types

[Matthias Puech <puech@cs.unibo.it>]

Dear Camlists,

This is my first post on this list, so please excuse me if it is too 
vague/off-topic/already discussed... I've been asking myself this 
question about the standard library's Set for quite a while.

The ability of the module Set to take an order (compare) as input, 
possibly larger than Pervasive's one, allows for some valuable tricks, 
i.e. assure that a set contains at most one element of each equivalence 
class. This element is actually stored in the structure, but then it 
seems not possible to retreive it (efficiently): the only interaction is 
to test if some element of the same equivalence class is present, with 
mem : elt -> t -> bool.

My question is : why isn't there a function find : elt -> t -> elt, 
where find e s would return the stored element  e' s.t compare e e' = 1 
? These two elements can be interestingly distinct though...

Thanks in advance for all enlightenment.

    --Matthias

PS: Of course I don't want to fold, filter or such, for efficiency 
reasons...