result.rb

def Ok(value)
  Okay.new(value)
end

def Err(value)
  Error.new(value)
end

class Result
  attr_reader :value

  def initialize(value)
    @value = value
  end

  def ok?
    raise "Not implemented"
  end

  def error?
    raise "Not implemented"
  end

  def and_then(&block)
    raise "Not implemented"
  end

  def or_else(&block)
    raise "Not implemented"
  end

  def to_s
    "#{self.class}(#{value})"
  end
end

class Okay < Result
  def ok?
    true
  end

  def error?
    false
  end

  def and_then
    result = yield(value)
    raise TypeError, "block did not return Result instance" unless result.is_a?(Result)
    result
  rescue StandardError => error
    Err(error)
  end

  def or_else
   self
  end
end

class Error < Result 
  def ok?
    false
  end

  def error?
    true 
  end

  def and_then
    self 
  rescue StandardError => error
    Err(error)
  end

  def or_else
    result = yield(value)
    raise TypeError, "block did not return Result instance" unless result.is_a?(Result)
    result
  rescue StandardError => error
    Err(error)
  end
end



# Usage

result = UserRepository.find(1)

result
  .and_then { |user| DocumentRepository.find_by(user.id) }
  .or_else { |error| # do something with error }
    
    
# Usage 2

def do_something
  # do something here and return a value to result
  Ok(result)
rescue StandardError => error
  Err(error)
end