Implementation of a Result monad for Ruby

result.rb

# frozen_string_literal: true

# Represents an immutable Result object that can contain either a successful value
# or an error message. This implements the Result pattern for handling success/failure
# scenarios in a functional way.
Result = Data.define(:value, :error_message, :creation_location) do
  def self.ok(value)
    new(value: value, error_message: nil, creation_location: caller_locations(1, 1).first)
  end

  def self.error(message)
    new(value: nil, error_message: message, creation_location: caller_locations(1, 1).first)
  end

  def ok?
    !value.nil?
  end

  def error?
    !error_message.nil?
  end

  def ok
    raise "Cannot get value from error result: #{error_message}" if error?

    value
  end

  def ok_or(default_value)
    value || default_value
  end

  def error
    raise "Cannot get error from ok result" if ok?

    error_message
  end

  def map
    return self if error?

    Result.ok(yield(ok))
  rescue StandardError => e
    Result.error(e.message)
  end

  def and_then
    return self if error?

    yield(ok)
  end

  def where
    creation_location
  end

  private

  def initialize(value:, error_message:, creation_location:)
    raise ArgumentError, "Cannot have both value and error" if value && error_message
    raise ArgumentError, "Must provide either value or error" if value.nil? && error_message.nil?

    super
  end
end