This is a assembler for a "hack" machine language from a Nand2Tetris Coursera course.
I believe there is nothing to see here.
I had to write a fair top-down parser probably. But it's too easy specs and not too much time to set up a state machine and to do things right. It also the part of contract that there is NO invalid asm input. I'm ok with this, I don't even have a Invalid token type in enum