let jz : OpcodeRoutine = fun (i, proc) ->
  i.Operands.Length |> Is.EqualTo 1
  i.HasBranchOffset |> Is.True

  let x = i.Operands.[0] |> proc.GetOperandValue
  let res = x = 0us
  if i.BranchOffset.Condition = res then
    proc.Branch i.BranchOffset

exception ContractFailureException of string

[<RequiredModuleAccess>]
module Is =

  let inline private fail message =
    raise <| ContractFailureException(message)

  let inline private failf fmt =
    Printf.ksprintf fail fmt

  let inline True condition =
    if condition <> true then
      fail "condition should be true."

  let inline False condition =
    if condition = true then
      fail "condition should be false."

  let inline Null obj =
    if obj <> null then
      fail "obj should be null."

  let inline Some obj =
    match obj with
    | Some(_) -> ()
    | None -> fail "obj should be Some."

  let inline None obj =
    match obj with
    | Some(_) -> fail "obj should be None."
    | None -> ()

  let inline NotNull obj =
    if obj = null then
      fail "obj should not be null."

  let inline EqualTo expected value =
    if value <> expected then
      failf "value should be equal to %A." expected

  let inline NotEqualTo expected value =
    if value = expected then
      failf "value should not be equal to %A." expected

  let inline LessThan high value =
    if value >= high then
      failf "value should be less than %A." high

  let inline LessThanOrEqualTo high value =
    if value > high then
      failf "value should be less than or equal to %A." high

  let inline GreaterThan low value =
    if value <= low then
      failf "value should be greater than %A." low

  let inline GreaterThanOrEqualTo low value =
    if value < low then
      failf "value should be greater than or equal to %A." low

  let inline InRange low high value =
    if value < low || value > high then
      failf "value should be in range %A to %A." low high

  let inline NotInRange low high value =
    if value >= low && value <= high then
      failf "value should not be in range %A to %A." low high

  let inline Empty (value : seq<_>) =
    if not (value |> Seq.isEmpty) then
      fail "value should be empty."

  let inline NotEmpty (value : seq<_>) =
    if value |> Seq.isEmpty then
      fail "value should not be empty."

  let inline OfType<'a> (value : obj) =
    match value with
    | :? 'a -> ()
    | _ -> failf "value should be of type %s." typeof<'a>.FullName

  let inline NotOfType<'a> (value : obj) =
    match value with
    | :? 'a -> failf "value should not be of type %s." typeof<'a>.FullName
    | _ -> ()