signature MLTON_VECTOR =
   sig
      val unfoldi: int * 'b * (int * 'b -> 'a * 'b) -> 'a vector
   end

• unfoldi (n, b, f)

constructs a vector v of a length n, whose elements v_i are determined by the equations b₀ = b and (v_i, b_i+1) = f (i, b_i).