Yeap am doing that at the moment
Have a requirement for a real cut down version of basic as a teaching add, (where users get their ideas amazes me).Basically doing it in "C" with a couple of other guys. You need to ascertain what commands/modifiers/etc are allowed, then determine an exceptable syntax, design an IDE for it, and on the compile option translate the code into...in our case it's "C" but you may want vb or whatever...then run the compiler. Also you need to incorporate a linker to ensure all libraries that are needed by the exe are included.
Phantomd is currently working on a language for bar-code printers which is extremely complex, but will by-pass any number of problems we are currently facing....
So yes have a go
As to number of incidents of a character in a string...which version of vb are you using?