define grammar:
- declarations
  - var decl
    - ptr/array
  - fn decl
  - struct/enum/union
- statements
  - if/while/for/switch
  - expr
  - assignment
  - return
- expressions
  - fn call
  - unary/binary/(ternary) operator
  - variable "call"
  - literal
  - parenthesis
  - array access
  - .
  - cast

- complete grammar
- semantic checks when visiting
- type modifier
- operator precedence
- ...