[tex-eplain] \optionalarg delimitation

[Rodolfo Medina]

How can I delimit an \@optionalarg?  E.g., suppose I want a space after it.  In
the following example:

\input /home/rodolfo/macros/eplain-3.2

\catcode`@=\letter
\def\myhallo{%
  \@getoptionalarg\@myhallo}

\def\@myhallo{%
  \ifx\@optionalarg\empty Hallo!
  \else Hallo, \@optionalarg!
  \fi
}


\myhallo[Mary]
John

\bye

, if I don't delimit the \@optionalarg with a space after it, an extra
undesired horizontal glue is added between `Mary!' and `John'.

Help very welcome.

Thanks,
Rodolfo