As far as I know Elixir does not implements any helper function to work with pipes except Kernel.tap/2 and Kernel.then/2, but those works for all type of input - not only specific one

How about writing a simple macro based on then?

defmodule Example do
  defmacro ok_then(value, fun) do
    quote do
      case unquote(value) do
        {:ok, result} -> {:ok, unquote(fun).(result)}
        result -> result
      end
    end
  end

  def divide(_x, 0), do: {:error, :zero_divisor}
  def divide(x, y), do: {:ok, div(x, y)}
end

require Example

x
|> Example.divide(y)
|> Example.ok_then(&(&1 * 6))
|> Example.ok_then(&(&1 * 7))
|> then(fn
  {:ok, result} -> IO.inspect(result, label: "Transformed result")
  {:error, :zero_divisor} -> IO.warn("Zero divisor problem …")
  {:error, error} -> IO.warn("Unexpected error #{error}")
end)

Using this you can work only on data you are interested and optionally if something fails you can handle all errors in one place.

There is no strict requirement that :ok or :error will be:

• tuple
• with exactly 2 elements

There is plenty of examples where that do not apply:

• GenServer.start_link/3 can also return :ignore
• Code.fetch_docs/1 returns :docs_v1-tuple or :error tuple
• IO.binread/2 can return iodata() on success, unary :error-tuple on error or :eof

Examples like that can be written and written, especially when you add Erlang libraries to the mix. It is hard to have “one catch them all” solution.

I would like to know as well, as functions fits much better there.