The question is: what is BASIC? Just to take two examples, Atari BASIC and Atari Turbo-BASIC XL. They share some keywords but on the other side are totally diff

The question is: what is BASIC? Just to take two examples, Atari BASIC and Atari Turbo-BASIC XL. They share some keywords but on the other side are totally different languages, for instance Turbo BASIC has structured programming constructs like procedures. Part of the problem is that the OS API is kind of restricted to basic sounds and graphics drawing primitives. For everything else you need PEEK and POKE.