This module implements the set data structure, given a total ordering function over the set elements. All operations over sets are purely applicative (no side-effects). The implementation uses balanced binary trees, and is therefore reasonably efficient: insertion and membership take time logarithmic in the size of the set, for instance.

The Make functor constructs implementations for any type, given a compare function. For instance:

     module IntPairs =
       struct
         type t = int * int
         let compare (x0,y0) (x1,y1) =
           match Pervasives.compare x0 x1 with
               0 -> Pervasives.compare y0 y1
             | c -> c
       end

     module PairsSet = Set.Make(IntPairs)

     let m = PairsSet.(empty |> add (2,3) |> add (5,7) |> add (11,13))
   

This creates a new module PairsSet, with a new type PairsSet.t of sets of int * int.