bracesgroupingmacros
An example is a bit artificial, but the point is that I do not understand why
{} influence the outcome of \newcommand in the way described below.
Consider the following definition:
\newcommand\printit[1]{#1}
whose outcome is obvious. However, a small alteration:
\newcommand{\printit[1]}{#1}
and e.g. \printit{2} yields:
I have no idea why. Could you please shed some light on what is going on here?
If the intention is to start a new group then you can use
\newcommand{\openbrace}{\begingroup}
or, more simply, just
\begingroup
To close the group, the corresponding macro is \endgroup
Surrounding text with braces, i.e., {text} doesn't result in a error as it is perfectly valid syntax.
The braces define a group, which means that changes will be local to that group. In this case there aren't any settings in the group to keep local, but it is still valid syntax. For instance,
xxx {\bfseries abc} yyy
results in
Note that only the abc is in bold - the yyy is in normal font. The braces keep the \bfseries local to within the { and }.
Besides grouping there are some other uses of curly braces:
In text mode, curly braces can be used to control the spacing after a control word. So
\TeX code {\TeX} code
yields:
where the space following the control word is removed without the use of {}.
In the math mode, adding curly braces controls has additional effects. For instance, braces can affect the spacing around "math atoms". (Upshot: Don't add curly braces unnecessarily when in math mode.)
\documentclass{article}
\usepackage{amsmath}
\usepackage{xcolor}
\usepackage{showexpl}
\lstset{
language={[LaTeX]TeX},
backgroundcolor=\color{yellow!40},
basicstyle=\small\ttfamily,
}
\begin{document}
xxx {\bfseries abc} yyy \quad \TeX code {\TeX} code
\begin{LTXexample}[pos=r]
\par $a=b$
\par $a{=b}$
\par ${a=}b$
\par $a{=}b$
\end{LTXexample}
\end{document}
Best Answer
If LaTeX was being written now,
would give an error message that
\printit[1]was not a single token.The correct syntax is
or
LaTeX does nothing special to allow both forms, it is just on the general TeX macro syntax rules that braces can be omitted if a macro argument is a single token.
If you pass two (or in this case, four) tokens to
\newcommandthen anything that happens is essentially just accidental behaviour, as the system could not really afford the space or time required to catch "unlikely" errors.As to what happens,
produces the terminal log
The command defines
\printitto have an optional first argument, although the default value of 0 being supplied was intended as the default value for\newcommanditself. it is what makes\newcommand\foothe same as\newcommand\foo[0]and define a command with no arguments.The inner part of the command handling the optional argument is
\\printitwhich just drops the square brackets.So
is
which is
which typesets as 02