Module type Binary_searchable_intf.Indexable

module type Indexable = sig .. end
An Indexable type is a finite sequence of elements indexed by consecutive integers 0 ... length t - 1. get and length must be O(1) for the resulting binary_search to be lg(n).

type elt 
type t 
val get : t ->
int -> elt
val length : t -> int
module For_test: sig .. end
To implement the test provided by Binary_searchable, we need to be able to construct t with two different values small < big.