Am 16.12.2010 um 18:28 schrieb Vedran Miletić:

2010/12/16 Jonas Stein <news@jonasstein.de>
>>> \define[1]\myoneliner{#1 \par }
>>> raises an error.

>> \define[1]\myoneliner{#1 \endgraf}

works fine. Thank you!

> This is also nicely covered in TeXBook.
> Alternatively \long\def might work.

\long\define[1]\myoneliner{#1 \par } 
fails too

\long\def\myoneliner#1{#1 \par} should work.

You don’t need \long in this case, the problem is that
\define itself isn’t defined as \long while in mkiv
all commands are defined as \long.

Wolfgang