Re: I made gnuchess freak out

[Tim Mann]

xboard doesn't check move legality in all cases.  The engine is
supposed to report an "Illegal move" error on illegal moves (see the
protocol spec for details), but GNU Chess 5 tends to just ignore any
input it doesn't understand, including illegal moves.

If it's painful to tell the difference between "illegal move" and
"unimplemented command that we want to ignore without bothering to
write code to recognize it", you could set feature usermove=1.  Then
(if talking to a GUI that implements protocol version 2), moves from
the user will look like "usermove e2e4" instead of just "e2e4".  That
should make it easier to generate an error message when the move is
illegal, since you always know whether it's meant to be a move or not.

Alternatively, you could make sure that all the standard commands in
the protocol are recognized (even if GNU Chess does nothing with some
of them) and print a proper error message for all unrecognized commands.