The lexer folder consumes and outputs tokens.
The parser folder consumes tokens and builds an abstract syntax tree (AST).
The ast folder lays out the structure for the abstract syntax tree.
The hir folder takes the AST and transforms it into high-level representation,
to be passed into the MIR
The mir folder takes the HIR input and transforms into a control-flow graph
(CFG).
The codegen folder takes the MIR and converts it into LLVM-IR.