[tex-eplain] \definexref problem

[Adam Fenn]

I have a small macro which prints a reference in full when first called and 
a short version on all subsequent calls.

\newif \iflongref \longreftrue
\def\myref{\iflongref a long reference \longreffalse\else a short 
reference\fi}

I would like to use this with the eplain cross-reference macro but

\definexref{mynewref}{\iflongref a long reference \longreffalse\else a short 
reference\fi}{}

fails with the error \end occurred when \iftrue.

How can I get this to work?

Adam Fenn.