∀ {α : Type u} {r : Std.Rio α} [inst : LT α] [inst_1 : DecidableLT α] [inst_2 : Std.PRange.Least? α]
  [inst_3 : Std.PRange.UpwardEnumerable α] [inst_4 : Std.PRange.LawfulUpwardEnumerableLT α]
  [inst_5 : Std.PRange.LawfulUpwardEnumerableLeast? α] [inst_6 : Std.Rxo.IsAlwaysFinite α]
  [inst_7 : Std.PRange.LawfulUpwardEnumerable α] {γ : Type u} {init : γ} {m : Type u → Type w} [inst_8 : Monad m]
  [LawfulMonad m] {f : (a : α) → a ∈ r → γ → m (ForInStep γ)},
  forIn' r init f = forIn' r.toArray init fun a ha acc => f a ⋯ acc