BareBones Interpreter

This is a humble BareBones interpreter written in Java and here's how it works.

How It Works

To understand exactly how the interpreter is implemented, one has to first build up some theoretical basin to stand on. To allow computer to exectute the BareBones code, we have to first separate code -- a stream of characters -- into some structures that make sense to the machine.

Loking at the code, we can see that there can be found three types of syntactic "beasts":

1. Code itself, defined as collection of the "beasts" listed below;
2. Statement -- a single line command like incr X; or clear X; -- there are tree statements in total;
3. While loop that consists of three sub-parts (which we shall discuss later).

Statement has two parts: operator and varname. While loop has three parts: header, inner code, and a terminating end. While loop's header can also be split up into the constant part and varname.

while X not 0 do;
    ... code ...
end;

In the example above, while ... not 0 do; is a constant part, and X is varname -- it will be different from case to case.

Now, using only the three "beasts", we can split any BareBones file into recursive sections:

┏━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━┓
┃ ┌─────────────┐                            ┃
┃ │ clear X;  statement                      ┃    
┃ └─────────────┘                         ┏━━┻━━━┓
┃   incr X;                                 code  
┃   incr X;                               ┗━━┳━━━┛
┃   incr X;                                  ┃    
┃ ╔═══════════════════════╣ while ╠═══╗      ┃
┃ ║ while X not 0 do;                 ║      ┃
┃ ║   ┏━━━━━━━━━━━━━━━━━━━━━━━━┓      ║      ┃
┃ ║   ┃┌───────────┐        ┏━━┻━━━┓  ║      ┃
┃ ║   ┃│decr X;  statement    code    ║      ┃
┃ ║   ┃└───────────┘        ┗━━┳━━━┛  ║      ┃
┃ ║   ┗━━━━━━━━━━━━━━━━━━━━━━━━┛      ║      ┃
┃ ║ end;                              ║      ┃
┃ ╚═══════════════════════════════════╝      ┃
┗━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━┛