The backend/frontend separation sounds right but the "sub" split of the frontend sounds odd. You dont care if in the AST some functions are doing too much. In

The backend/frontend separation sounds right but the "sub" split of the frontend sounds odd. You dont care if in the AST some functions are doing too much. In my opinion the most important is the ability to _drive the compilation_, for example stop after lexical, stop after semantics. Then if too much code got compiled into the *.a that's unfortunate but not dramatic. BTW there's is also the split between the driver and the frontend, but I think this is done.