list
  ident module
  ident main
list
  ident fn
  ident add
  list
    list
      ident a
      ident i32
    list
      ident b
      ident i32
  arrow ->
  ident i32
  list
    ident +
    ident a
    ident b
list
  ident fn
  ident main
  list
  arrow ->
  ident i32
  list
    ident print_i32
    list
      ident add
      int 20
      int 22
  int 0