This module implements applicative association tables, also known as finite maps or dictionaries, given a total ordering function over the keys. All operations over maps are purely applicative (no side-effects). The implementation uses balanced binary trees, and therefore searching and insertion take time logarithmic in the size of the map.

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 PairsMap = Map.Make(IntPairs)

     let m = PairsMap.(empty |> add (0,1) "hello" |> add (1,0) "world")
   

This creates a new module PairsMap, with a new type 'a PairsMap.t of maps from int * int to 'a. In this example, m contains string values so its type is string PairsMap.t.