doing code with "with"

with.ex

defp validate_params(params) do
  with :ok <- validate?("frequency", params["frequency"]),
       :ok <- validate?("storage_duration", params["storage_duration"]),
       :ok <- validate?("status", params["status"]),
       do: :ok
end

def validate?("status", "on"),            do: :ok
def validate?("status", "off"),           do: :ok
def validate?("status", "on-scheduled"),  do: :ok
def validate?("status" = key, _invalid),  do: invalid(key)

def validate?(key, value) when is_integer(value),   do: :ok
def validate?(key, value) when value in [nil, ""],  do: invalid(key)
def validate?(key, value) when is_bitstring(value), do: validate?(key, to_integer(value))

def validate?(key, _invalid), do: invalid(key)

defp invalid(key), do: {:invalid, "The parameter '#{key}' isn't valid."}
defp to_integer(value) do
  case Integer.parse(value) do
    {number, _} -> number
    _ -> :error
  end
end