digit = "0" | "1" | "2" | "3" | "4" | "5" | "6" | "7" | "8" | "9" ;
integer = ['-' | '+'] "0" digit {digit} ;

hex_letters = "a" | "b" | "c" | "d" | "e" | "f"
hex_integer = "0x", {hex_letters | digit} ;

oct_digits = "0" | "1" | "2" | "3" | "4" | "5" | "6" | "7" ;
octal_integer = "0o", {oct_digits} ;

program =