Another golang port, this time a toy virtual machine.

Monday, 2 July 2018

I don't understand why my toy virtual machine has as much interest as it does. It is a simple project that compiles "assembly language" into a series of bytecodes, and then allows them to be executed.

Since I recently started messing around with interpreters more generally I figured I should revisit it. Initially I rewrote the part that interprets the bytecodes in golang, which was simple, but now I've rewritten the compiler too.

Much like the previous work with interpreters this uses a lexer and an evaluator to handle things properly - in the original implementation the compiler used a series of regular expressions to parse the input files. Oops.

Anyway the end result is that I can compile a source file to bytecodes, execute bytecodes, or do both at once:

I made a couple of minor tweaks in the port, because I wanted extra facilities. Rather than implement an opcode "STRING_LENGTH" I copied the idea of traps - so a program can call-back to the interpreter to run some operations:

int 0x00  -> Set register 0 with the length of the string in register 0.

int 0x01  -> Set register 0 with the contents of reading a string from the user


This notion of traps should allow complex operations to be implemented easily, in golang. I don't think I have the patience to do too much more, but it stands as a simple example of a "compiler" or an interpreter.

I think this program is the longest I've written. Remember how verbose assembly language is?

Otherwise: Helsinki Pride happened, Oiva learned to say his name (maybe?), and I finished reading all the James Bond novels (which were very different to the films, and have aged badly on the whole).

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