Package soul underline problem with macro text

Question

I have been slowly learning LaTeX over the past few years. I have been mostly successful in these efforts.

Recently, I stumbled across a problem, I know is probably quite simple to fix, but it has me stumped. I figure, it has to do with macro expansion. These macro expansion issues are undoubtedly one of my big remaining hangups.

Looking for any input on the problem below. I tried doing various combinations of \expandafter, \edef, etc., but I was obviously just randomly stumbling around.

I have seen some related questions, but they each appear to be trying to do something slightly different and the suggestions do not appear to help me in my situation.

MWE provided:

\documentclass[10pt]{article}

\usepackage{soul}

\def\qwerty{happy new year}

\begin{document}

\ul{happy new year}
\ul{\qwerty}

\end{document}

And the error:

! Package soul Error: Reconstruction failed.

See the soul package documentation for explanation.
Type H <return> for immediate help.
 ...

l.10 \ul{\qwerty}

I know the solution is simple. Anything to point me in the direction, which will contribute to my understanding of the problem and solution, would be greatly appreciated.

@PhelypeOleinik which effectively disables the only advantage soul has compared to \underline or similar: disabling hyphenation and line breaks. Instead, if you know that the macro you're using is fully expandable, you can use the following (if you have an up to date LaTeX installation): \expandafter\ul\expandafter{\expanded{<macro>}} (which is the case for the shown definition of \qwerty). — Skillmon, Jun 21 '19 at 18:39
@PhelypeOleinik Thank you for your suggestion; that may work well for me in situations where I don't need line-breaking and etc. — mkd, Jun 21 '19 at 18:48
@Skillmon Thanks for your help! I'd like to figure out how to get that solution working. I don't appear to have the \expanded macro -- how recent a version of LaTeX do I need? I thought I was fairly up to date. — mkd, Jun 21 '19 at 18:49
I know there should be a way to just make LaTeX expand \qwerty into its definition, and only then to handle the \ul macro. — mkd, Jun 21 '19 at 19:12
Since soul has its own tag, I've added it. That does two things: adds more "suitable" entries in the "Linked" and "Related" columns on the right of this page, and alerts folks who are watching this tag. — barbara beeton, Jun 21 '19 at 19:24

score 3 · Answer 1 · answered Jun 21 '19 at 19:41

3

\documentclass[10pt]{article}

\usepackage{soul}

\def\qwerty{happy new year}

\begin{document}

\ul{happy new year}
\expandafter\ul\expandafter{\qwerty}

\end{document}

answered Jun 21 '19 at 19:41

David Carlisle

757,742

Terrific, this is close to what I expected would be a solution; now to work on understanding why it works ;). Thank you so much! – mkd Jun 22 '19 at 17:21
@mkd the first expandafter expands the second expandafter which expands \qwerty so the argument to \ul is happy new year – David Carlisle Jun 22 '19 at 17:22
@mkd note this is a generic answer that would apply to any macro, Ulrike's is much simpler (you should probably accept that) but is specific to the workings of \ul – David Carlisle Jun 22 '19 at 17:25

score 3 · Answer 2 · answered Jun 21 '19 at 20:04

3

You can let soul expand by removing the braces:

\documentclass[10pt]{article}

\usepackage{soul}

\def\qwerty{happy new year}

\begin{document}

\ul{happy new year}
\ul\qwerty

\end{document}

answered Jun 21 '19 at 20:04

Ulrike Fischer

327,261

Wow that just blew my mind; to this point I wouldn't have even suspected that would make any difference whatsoever.. Just when I think I have at least the basics understood... This language never stops surprising me.
Could you explain why this is the case? Or refer me to material elsewhere? I have been gradually reading TUGboat articles, I have started reading a few different books on LaTeX but I don't think anything I've read suggested the difference of omitting those brackets as above.

Thank you!
– mkd Jun 22 '19 at 17:26
Well I simply checked the documentation of soul ... – Ulrike Fischer Jun 22 '19 at 17:28
@mkd this wouldn't the case normally, it is only expanded because soul implemented this behaviour (with checking what the next token is). Ordinary macros defined with \newcommand\foo[1]{#1} won't expand their argument if it isn't contained in braces. – Skillmon Jun 22 '19 at 17:32
@Skillmon Thank you so much for explaining that; I thought this represented something about the language I wasn't aware of. I didn't realize it was related to soul itself; I thought this was going to apply generally. Thanks for your help! – mkd Jun 26 '19 at 03:21

score 0 · Answer 3 · answered Jun 21 '19 at 23:23

If you don't have the \expanded primitive and the argument is fully expandable (but you don't know how many expansions it would take), you can use \edef with a temporary macro:

\documentclass[]{article}

\usepackage{soul}

\makeatletter
\newcommand\edefexp[2]
  {%
    \begingroup
      \edef\edefexp@tmp{#2}%
      \expandafter
    \endgroup
    \expandafter\edefexp@aux\expandafter{\edefexp@tmp}{#1}%
  }
\newcommand\edefexp@aux[2]
  {%
    #2{#1}%
  }
\makeatother

\newcommand\qwerty{happy new \qwertz}
\newcommand\qwertz{year}

\begin{document}
\edefexp\ul{\qwerty}
\end{document}

I will probably upgrade my distribution as you suggested before. Thank you very much for posting this! — mkd, Jun 22 '19 at 17:29

Package soul underline problem with macro text

3 Answers3