Building a BASIC interpreter in Ruby

I've been working on a side project: Build a BASIC interpreter in Ruby. The purpose is to help me learn the Ruby language, and to that end the project has worked well.

Learning a new programming language can be difficult. It's easy enough to write a simple "Hello, world!" program, but that simply confirms that the compiler (or interpreter) is installed correctly. What does one do next?

I picked the BASIC interpreter as a task with some complexity, but not too much. The BASIC language gives me a challenge but not one that is insurmountable. Also, I have an early text on programming in BASIC that provides example programs with their expected outputs.

As a bonus, programming a BASIC interpreter is a stroll down memory lane. BASIC was the first programming language that I learned. It is an old friend, one I have not seen in quite some time.

So as a project, the BASIC interpreter is challenging, supported, and fun.

I spell BASIC in all capitals because of the variant I am implementing. The BASIC language had a number of variants over time, from the early Dartmouth implementation in the 1960s to the DEC versions of the 1970s and 1980s, culminating in Visual Basic 6 from Microsoft. (Or perhaps VB.NET, but that seems less BASIC than any of the variants.)

My project is to implement an early version, one that is close to Dartmouth BASIC. It has a simplicity about it, yet it also has its intricacies. Dartmouth BASIC allows one to specify user-defined functions, but only on one line and only with a very limited set of names ('FNA' through 'FNZ'). It supports some elements of structured programming but still allows GOTO statements, and one can 'GOTO' from the inside of a loop to the outside, do some work, and 'GOTO' back into the loop. (One can also 'GOTO' out of a loop and not return into the loop.)

Early version or late, my experience has been a good one. I have been forced to learn the Ruby language. While I am not an expert, I am at least comfortable with the major constructs and classes of the language. And that was the point.