[Tex/LaTex] Remove extra curly braces

argumentsbraces

In this MWE, I demonstrate my problem:

\documentclass{article}
\usepackage{seqsplit}
\newcommand{\dosomething}[1]{\uppercase{#1}}
\newcommand{\dosomethingelse}[1]{\seqsplit{#1}}
\begin{document}
    \dosomething{looooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooong}

    % works with extra {...}
    \dosomething{{looooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooong}}

    \dosomethingelse{looooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooong}

    % does not work with extra {...}
    \dosomethingelse{{looooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooooong}}
\end{document}

Some commands work with extra curly braces, some don't. Why is that, and how can I make them work by preprocessing my arguments when they do have extra curly braces?

Best Answer

If the argument is not empty and starting spaces can be removed, then the following trick helps:

\makeatletter
\newcommand{\dosomethingelse}[1]{%
  \expandafter\seqsplit\expandafter{\@firstofone#1}%
}
\makeatother

\@firstofone is defined in the LaTeX kernel as:

\long\def\@firstofone#1{#1}

It grabs the first token as argument and outputs it again, thus it does "nothing". But if the argument is not a single token, but a token group in braces, then one level of braces are removed.

Related Solutions

[Tex/LaTex] Why does TeX remove braces around delimited arguments

One thing to note is that TeX's only means of nesting arguments are braces. You can define a macro \def\whatever[#1]{...} but when you call it as \whatever[oh[well]], things go down the drain awfully. Calling it as \whatever[{oh[well]}] however works swimmingly, and \whatever never notices it has been taken for a ride by slipping a ] into its argument. So the braces can be used as a means of hiding occurences of the closing delimiter from TeX without actually affecting the intended argument.

It also means that whenever you call a macro using delimited arguments with a non-literal argument (more exactly, an argument not completely under your own control, as it often happens when you write a macro package to be used by others), you should always add a layer of braces around each delimited argument, like \whatever[{#1}] or similar. There is no other way to ensure that arguments will not get chopped up into something different because they themselves may contain a closing bracket.

[Tex/LaTex] Splitting a command syntax across a \newenvironment definition

As noted in comments the standard minipage and lrbox environments are designed for this use, or for the particular case of framing a box, mdframed package.

To note why the definition shown does not work, you can not delimit macro arguments with \begingroup.

 \fbox \begingroup

is the same as

 \fbox{\begingroup}

and passes the \begingroup token as the content of the box. After that things are bound to go wrong.

Similarly

\parbox{10cm} \begingroup

\parbox{10cm}{\begingroup}

with \begingroup being passed as the argument to \parbox.

Best Answer

Related Solutions

[Tex/LaTex] Why does TeX remove braces around delimited arguments

[Tex/LaTex] Splitting a command syntax across a \newenvironment definition

Related Question