\newcommand{\abc}{joy, oh #1!}
or (using TeX primitive definitions):
\def\abc{joy, oh #1!}
In either of the above, the definition uses an argument, but the
programmer did not tell (La)TeX, in advance, that she was going to.
The fix is simple — \
newcommand{
, in the
LaTeX case, \
abc
}[1]\def\abc#1
in the basic TeX case.
\newcommand{\abc}{joy, oh joy!% \newcommand{\ghi}[1]{gloom, oh #1!}% }
will also produce this error, as will its TeX primitive equivalent:
\def\abc{joy, oh joy!% \def\ghi#1{gloom, oh #1!}% }
This is because special care is needed when defining one macro within the code of another macro. This is explained elsewhere, separately for LaTeX definitions and for TeX primitive definitions
This question on the Web: http://www.tex.ac.uk/cgi-bin/texfaq2html?label=errparnum