provide a more concise and natural abstractions / API around journey's functionality

[markmark206]

for example, ReactiveStruct (https://github.com/chgeuer/reactive_struct/blob/main/test/reactive_struct_test.exs) has a nice, concise abstractions:

    defmodule KeywordTestStruct do
      use ReactiveStruct

      defstruct [:a, :b, :sum]

      computed(:sum, fn %{a: a, b: b} ->
        if a && b, do: a + b, else: nil
      end)
    end