1 sig pixel screen: (addr screen), x: int, y: int, color: int
2 sig read-key kbd: (addr keyboard) -> _/eax: byte
3 sig draw-grapheme screen: (addr screen), g: grapheme, x: int, y: int, color: int
4 
5 sig write f: (addr stream byte), s: (addr array byte)
6 sig append-byte f: (addr stream byte), n: int
7 sig read-byte s: (addr stream byte) -> _/eax: byte
8 sig stream-empty? s: (addr stream _) -> _/eax: boolean