Steps to repeat:
Jeremys-MBP:~ jeremy$ csharp
Mono C# Shell, type "help;" for help
Enter statements below.
csharp> int x = 5;
csharp> int y = 6;
csharp> x * y
(1,2): error CS0246: The type or namespace name `x' could not be found. Are you missing an assembly reference?
I also tried it on Linux with the same results.
I'm trying to use the REPL to teach students how to code in C# and this makes that difficult.