Map(3) OCaml library Map(3)

# [NAME](#NAME)

Map - Association tables over ordered types.

# [Module](#Module)

Module Map

# [Documentation](#Documentation)

Module **Map**  
: **sig end**

Association tables over ordered types.

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 Stdlib.compare x0 x1 with


               0 -> Stdlib.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** .

*module type OrderedType =* **sig end**

Input signature of the functor **Map.Make** .

*module type S =* **sig end**

Output signature of the functor **Map.Make** .

*module Make :* **functor (Ord : OrderedType) -> sig end**

Functor building an implementation of the map structure given a totally ordered type.

2026-09-15 OCamldoc

---

Document: Map(3o) from ocaml-4 4.14.4-r3 (Chainguard OS)
Source: https://github.com/ocaml/ocaml