ResultChain

Result-aware chaining operator for Elixir workflows.

What It Does

ResultChain helps you compose workflows where some steps return plain values and other steps may fail with :error or {:error, reason}.

Plain |> always passes its left-hand value into the next call. ResultChain adds ~>, which continues on successful values and short-circuits on errors. When you use ResultChain, you can mix |> and ~> in the same chain.

Installation

Add result_chain to your list of dependencies in mix.exs:

def deps do
  [
    {:result_chain, "~> 0.1.0"}
  ]
end

Usage with use ResultChain

Use ResultChain when you want to mix ordinary pipe steps with result-aware steps in the same chain. use ResultChain locally replaces Kernel.|>/2 in that module and imports ResultChain.

defmodule MyWorkflow do
  use ResultChain

  def parse(value) do
    case Integer.parse(value) do
      {integer, _} -> integer
      _ -> :error
    end
  end

  def reciprocal(0), do: {:error, :division_by_zero}
  def reciprocal(value), do: {:ok, 1 / value}

  def run(value) do
    value
    |> parse()
    ~> reciprocal()
  end
end

Usage with import ResultChain

Import ResultChain when you only need ~> and want to keep the standard Kernel.|>/2 out of the picture.

defmodule MyWorkflow do
  import ResultChain

  def parse(value) do
    case Integer.parse(value) do
      {integer, _} -> {:ok, integer}
      _ -> {:error, :not_an_integer}
    end
  end

  def reciprocal(0), do: {:error, :division_by_zero}
  def reciprocal(value), do: {:ok, 1 / value}

  def run(value) do
    value
    ~> parse()
    ~> reciprocal()
  end
end

Do not mix ~> and |> in the same chain when you only import ResultChain.

Result Semantics

~> treats values as follows:

• {:ok, value} unwraps to value before the next call
• :ok continues as the value :ok
• :error stops the chain and returns :error
• {:error, reason} stops the chain and returns {:error, reason}
• nil is treated as a successful value
• any other non-error value is treated as a successful value

License

Apache License 2.0. See LICENSE.