interface DSL
    {
        Task<bool> CheckSomething();
        Task RunTrue();
        Task RunFalse();
    }

    class Program
    {
        static async Task DoWork(DSL dsl)
        {
            // pure stuff (as static methods maybe)

            if (await dsl.CheckSomething())
            {
                // some pure stuff mb
                await dsl.RunTrue();
            }
            else
            {
                await dsl.RunFalse();
            }
        }
    }