Yes, but there are a bunch of tradeoffs. do you try to lex the floating point format, or push that back to the parser? Do in introduce an extra pass for constant folding or do you try to shoehorn it into AST generation in the parser?

The nice thing about compilers, it requires a ton of code.

It's the kind of thing that any programmer can do (well good ones), and there are organizational tradeoffs to be made. There is no "right" answer, it's an opportunity to talk about organization. There are blind alleys that seem like a good idea, but turn out not to be. There are opportunities to merge and split passes. Some layers might want information from other layers, some layers might look very similar to other layers.