In his message of Tue March 7, 2000, Markus Mottl writes: 
> it sometimes happens that I need functions on abstract data types in the
> standard library which are not available there, but could be considered as
> "usual" operations on such data. Also some other very commonly useful
> functions could be added.

I agree. 

One may think  that the functions you suggest  can actually be defined
outside  the  standard library  using  iterators  like  fold (not  for
Stack.top, however). For instance, one can define set_exists as

======================================================================
# module Myset = Set.Make(struct type t = ... let compare = ... end);;
...
# let set_exists p s =                                             
    try Myset.fold (fun x _ -> if p x then failwith "t") s (); false
    with Failure "t" -> true;;                                     
val set_exists : (Myset.elt -> bool) -> Myset.t -> bool = <fun>
======================================================================

But  when  using functorial  interfaces  like  Set.Make,  you have  to
redefine these  functions for each  application of the  functor. Thus,
you  really need these  functions to  be defined  in the  functor i.e.
together with the datatype (and, by the way, you can then define these
functions a bit more efficiently---without using exceptions).

-- 
Jean-Christophe Filliatre    
  Computer Science Laboratory   Phone (650) 859-5173
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