string a(double b,double c=0)=>c<.9?(b<0|b>c?"🔵":"⚪")+a(b,c+.1):"";

​

System.Console.WriteLine(a(0.0));

System.Console.WriteLine(a(0.0001));

System.Console.WriteLine(a(0.1337));

System.Console.WriteLine(a(0.269));

System.Console.WriteLine(a(0.333));

System.Console.WriteLine("...");

System.Console.WriteLine(a(-1));

​

​