Set more than one font feature in gb4e

Question

I'm trying to get in gb4e glosses the first line to be in bold roman font but I can only set roman or bold, not both. How can I set both?

The document is a beamer presentation with a sans serif font as default font. I tried these, but they don't work:

\let\eachwordone=\textbf{\rmfamily}

and

\let\eachwordone=\rmfamily\bf

What I get is just \bf with the first code and just roman with the second.

Answer 1

The two letter font commands are deprecated, and have been replaced. Your second attempt was on the right track but you needed to use \bfseries instead of \bf. But also the syntax of TeX \let only allows a single token after the =; to do what you want you should use the LaTeX \renewcommand instead.

Furthermore, if you want to change the font of the translation line also, you will need to use a different method, since gb4e provides no built-in hook for that. In the example below I've used the \pretocmd from the etoolbox package to modify the \glt macro (whose synonym is \trans).

\documentclass{beamer}
\usepackage{gb4e}
\usepackage{etoolbox}
\renewcommand{\eachwordone}{\rmfamily\bfseries}
\pretocmd{\glt}{\rmfamily}{}{}
\begin{document}
\begin{frame}
\begin{exe}
\ex{
\gll This is the first line\\
     This is the second line\\
\glt This is the translation
}
\label{ex}
\end{exe}
\end{frame}
\end{document}

Personally, however, I would not mix serif and sans serif fonts in a beamer presentation, so a simpler way would be just to use \usefonttheme{serif} and then define just \eachwordone to be \bfseries:

\documentclass{beamer}
\usefonttheme{serif}
\usepackage{gb4e}
\renewcommand{\eachwordone}{\bfseries}
\begin{document}
\begin{frame}
\begin{exe}
\ex{
\gll This is the first line\\
     This is the second line\\
\glt This is the translation
}
\label{ex}
\end{exe}
\end{frame}
\end{document}

If you would prefer all the text to be in the sans serif font to match the default beamer fonts, you will need to change each of the macros that determine the font for the gloss lines. These are \eachwordone, \eachwordtwo and \eachwordthree. So to get all gloss lines in sans serif you add

\renewcommand{\eachwordone}{\sffamily}
\renewcommand{\eachwordtwo}{\sffamily}
\renewcommand{\eachwordthree}{\sffamily}