include "sys.m";
sys:= load Sys Sys->PATH;
byte2char: fn(buf: array of byte, n: int): (int, int, int);
char2byte: fn(c: int, buf: array of byte, n: int): int;

If the input sequence is not long enough to determine its validity, byte2char consumes zero bytes. If the input sequence is otherwise invalid, byte2char consumes one input byte and generates an error character (16r80, Sys->UTFerror), which prints (in most fonts) as a boxed question mark.

Notes