I've been following along with the "Learn to program using Lazarus" book. I'm working on the Polymorphic drawing example, and it seems to compile fine. But when the program is run, I get an EClassNotFound exception, saying that the TRadioGroup class is not found.
As far as I can see, I am including the correct Unit, but the exception trace seems to go deep into the LCL. I've tried the same code on mac OS, mac OS X PPC, and Windows 10.
Is there something simple I'm missing? I've attached the relevant code.