chain_example.rb

      validation :email do
        key(:email).required
      end

      validation :after_email, if: lambda { |results| results[:email]==true } do # extends the above.
        key(:username).required
      end

      # block gets evaled in form instance context.
      validation :password, if: lambda { |results| email == "john@trb.org" } do
        key(:password).required
      end

dry.rb

rule(:user_inactive, user_active?: [:email])
rule(:password_invalid, password_valid?: [:email, :password])

rule(:password_invalid) do
  value(:email).user_active? & value(:email).password_valid?(value(:password))
end # It doesn't work as expected since if user is inactive, then it returns false and also puts :password_invalid into errors