#define BUFFER_HEIGHT 23
#define BUFFER_WIDTH 80
#define N BUFFER_HEIGHT * BUFFER_WIDTH

datatype color =
  | Black 
  | Blue 
  | Green 
  | Cyan 
  | Red 
  | Magenta 
  | Brown 
  | LightGray 
  | DarkGray 
  | LightBlue 
  | LightGreen 
  | LightCyan 
  | LightRed 
  | Pink 
  | Yellow 
  | White 

typedef screenChar = @{ ascii_character = char, color_code = uint8}

fn put_string (str : string) :<!wrt> void
fn clear_screen() : void