[tex-eplain] \definexref problem

[Adam Fenn]

I made a slight modification to Oleg's suggestion:

\def\book#1#2#3{%
    \definexref{#3:long}{#1}{}%
    \definexref{#3:short}{#2}{}%
    \definexref{#3full}{#1}{}%
    }

  \def\bookref#1{%
    \readauxfile % make sure the xrefs are loaded
    \expandafter \ifx\csname\xrlabel{#1}\endcsname\relax % no marker defined
      \global\expandafter\let\csname\xrlabel{#1}\endcsname\empty % define it
      \csname\xrlabel{#1:long}\endcsname % produce the long ref
    \else % the marker already defined
      \csname\xrlabel{#1:short}\endcsname % produce the short ref
    \fi
  }


\book
{first book (long reference)}
{first book (short ref)}
{firstbook}

\book
{article in \xrefn{firstbookfull}}
{article (short ref)}
{article}

\bookref{firstbook} % a long first reference

\bookref{firstbook} % a short second reference

\bookref{article} % a long reference to article in first book

\bookref{article} % a short reference


This worked, but when I changed over to eplain 3.0 (from 2.8.4) I get

! Undefined control sequence.
\@optionaltemp ...ingroup \def \extension
                                          {#1}\immediate \openin 0 = ...
\@getoptionalarg #1->\let \@optionaltemp =
                                           #1\let \@optionalnext = \r...
<argument> article in \xrefn
                             {firstbookfull}
\definexref ...g \@definelabel {\temp }{#2
                                          }{#3}}}\@wr \ignorespaces
\book #1#2#3->\definexref {#3:long}{#1}{}
                                         \definexref {#3:short}{#2}{}...
l.31 {article}

Is this a bug? and if not why does it work with the earlier version and not 
the latest?

Adam Fenn.