Batteries user guide : BatInterfaces.Mappable

# Module type BatInterfaces.Mappable

    module type Mappable = sig .. end

A signature for data structures which have a `map : ('a -> 'b) -> ('a t -> 'b t)` operation.

If you create a new data structure, you should make it compatible with `Mappable`.

    type 'a mappable

The data structure, e.g. `'a List.t`

    val map : ('a -> 'b) ->
           'a mappable -> 'b mappable

`map f e` applies `f` to every element of `e` and returns the corresponding data structure