(* Binary search

   A classical example. Searches a sorted array for a given value v.
   Consult <https://gitlab.inria.fr/why3/why3/-/blob/master/examples/binary_search.mlw>.
 *)

module BinarySearch

  use int.Int
  use int.ComputerDivision
  use ref.Ref
  use array.Array

  let binary_search (a : array int) (v : int) : int
    requires { forall i1 i2 : int. 0 <= i1 < i2 < length a -> a[i1] <= a[i2] }
    ensures  { 0 <= result <= length a }
    ensures  { forall i: int. 0 <= i < result -> a[i] < v }
    ensures  { forall i: int. result <= i < length a -> v <= a[i] }
  =
    (* IMPORTANT: DON'T MODIFY THE ABOVE LINES *)
    0 (* TODO *)
end