From the blog post "Error Handling with Either Monads in Ruby"

either_example.rb

class UserUpdater
  include Dry::Monads[:result]
  
  attr_reader :user_model, :mailer

  def initialize(user_model, mailer)
    @user_model = user_model
    @mailer = mailer
  end

  # The main method in this class. Ignore the "Pyramid of Doom" for now.
  def call(fields)
    validate_fields(fields).bind do |fields|
      validate_email(fields['email']).bind do |email|
        find_user(fields['id']).bind do |user|
          update_user(user, {name: fields['name'], email: fields['email']}).bind do |user|
            send_email(user, :profile_updated).bind do |sent|
              Success(user)
            end
          end
        end
      end
    end
  end

  private
  # Keeping validations and other methods here simple for the purpose of this example

  def validate_fields(fields)
    if fields['name'] && fields['email']
      Success(fields)
    else
      Failure(:missing_fields)
    end
  end
  
  def validate_email(email)
    if email =~ URI::MailTo::EMAIL_REGEXP 
      Success(email)
    else
      Failure(:invalid_email)
    end
  end
  
  def find_user(id)
    user = user_model.find_by(id: id)
  
    if user
      Success(user)
    else
      Failure(:user_not_found)
    end
  end
  
  def update_user(user, data)
    user.update(data)
  
    if user.save
      Success(user)
    else
      Failure(:user_update_failed)
    end
  end
  
  def send_email(email, reason)
    result = mailer.deliver!(email, template: reason)

    if result
      Success()
    else
      Failure(:send_email_failed)
    end
  end
end

I think the user.update(data) should be in place of the user.save, since update already saves the object and returns a boolean.