Bubblewrap implements two most common monadic data types:

• Bubblewrap.Result - container for a result of operation or error. Result can be created using a constructor macro: {:ok, value} or {:error, e}, where underlying structure is a tuple: {:ok, value} or {:error, e} respectively.

• Bubblewrap.Option - container for a value that might be present or missing. Simple wrapper around a value that could be nil.

• Bubblewrap - collection of utility functions to work with both of these types.

Result

Result type fits perfectly with idiomatic Erlang/Elixir return values. When some library function returns either {:ok, val} or {:error, err}, you can use functions provided by Bubblewrap right away. The most typical example, where Bubblewrap shines, is a pipeline, where each operation can fail. Normally this would be organized in a form of nested case expressions:

final = case op1(x) do
  {:ok, res1} ->
    case op2(res1) do
      {:ok, res2} -> op3(res2)
      {:error, e} -> {:error, e}
    end
  {:error, e} -> {:error, e}
end

With Bubblewrap you can do the same using flat_map operation:

final = op1(x) |> flat_map(&op2/1) |> flat_map(&op3/1)

Once any of the operations returns {:error, e}, following operations are skipped and the error is returned. You can either do something based on pattern matching or provide a fallback (can be a function or a default value).

case final do
  {:ok, value} -> IO.puts(value)
  {:error, e} -> IO.puts("Oh, no, the error occured!")
end

final |> fallback({:ok, "No problem, I got it"})

Option

Option type wraps the value. If value is present, it's value, if it's missing, nil is used instead. With Option type, you can use the same set of functions, such as map, flat_map, etc.

find_user(id)
|> map(&find_posts_by_user/1)

This will only request for posts if the user was found.

See docs per Result and Option modules for details.