Tiny BASIC interpreter implemented in Rust

What is this project for?

Science isn't about why - it's about why not. Why is so much of our science dangerous? Why not marry safe science if you love it so much? In fact, why not invent a special safety door that won't hit you in the butt on the way out, because you are fired! -- Cave Johnson, Portal 2

There is not much practical value in it, I just wanted to build an interpreter for a simple language to learn how programming languages are implemented. I have chosen Rust because I like it, event when it annoys me.

Short description

The implementation is based upon this design note. The interpreter runs in an interactive mode in which user inputs code. The program is not translated into some intermediate representation, i.e. there is no abstract syntax tree involved. Each line is interpreted as is according to this scheme:

Line of code -> CharStream -> Interpreter

The CharStream provides methods to consume keywords, numbers, etc., while the interpreter executes the code line using the grammar from the aforementioned design note.

Some caveats of the current implementation

1. All input is required to be ASCII-only. UTF-8 support might be added later.
2. Line numbers are in range [0; 32767];
3. Numbers are 16-bit signed integers;
4. If the condition in IF statement is evaluated to false, the statement following THEN is ignored, so any syntax errors which might be present in it will not be detected.