Dry::Monads::Do::All is broken for singleton classes

example.rb

require 'bundler/inline'

gemfile do
  source 'https://rubygems.org'

  gem 'dry-monads'
  gem 'rspec'
end

module ConvertToUpperCase
  class SingletonDoAllShortcut
    class << self
      include Dry::Monads[:do, :try]

      def call(string)
        yield to_upper(string)
      end

      private

      def to_upper(s)
        Try { String(s).upcase }
      end
    end
  end

  class SingletonDoFor
    class << self
      include Dry::Monads[:try]
      include Dry::Monads::Do.for(:call)

      def call(string)
        yield to_upper(string)
      end

      private

      def to_upper(s)
        Try { String(s).upcase }
      end
    end
  end

  class SingletonDoAllExplicit
    class << self
      include Dry::Monads[:try]
      include Dry::Monads::Do::All

      def call(string)
        yield to_upper(string)
      end

      private

      def to_upper(s)
        Try { String(s).upcase }
      end
    end
  end

  class NonSingleton
    include Dry::Monads[:try]
    include Dry::Monads::Do::All

    def self.call(string)
      new.call(string)
    end
    
    def call(string)
      yield to_upper(string)
    end
    
    private
    
    def to_upper(s)
      Try { String(s).upcase }
    end
  end      
end

require 'rspec'
require 'rspec/core'

module ConvertToUpperCase
  RSpec.describe 'Do::All is broken for singleton_classes' do
    shared_examples_for 'an upcasing object' do
      let(:input) { 'pow!' }
      let(:result) { described_class.call(input) }

      it 'does not raise an error' do
        expect { result }.not_to raise_error
      end

      it 'upcases the string' do
        expect(result).to eq('POW!')
      end
    end

    [SingletonDoAllShortcut, SingletonDoAllExplicit, SingletonDoFor, NonSingleton].each do |example|
      describe example do
        it_behaves_like 'an upcasing object'
      end
    end
  end
end

RSpec::Core::Runner.invoke