[Tex/LaTex] Why do people use braces around the control sequence in \newcommand

macros

I've seen in every introductory material on LaTeX and in a lot of code of other people (event experts) that the \newcommand command is used by wrapping the first argument in braces, even if it seems unnecessary to me.

The braces are consistent with the usual way arguments are passed to LaTeX commands (since usually the braces are used even if the argument is made of a single token, for consistency and clarity), but in this single case they appear very ugly to me and in my opinion they lower readability.

But these are opinions, while the question is technical: is there any technical reason why one should write this:

\newcommand{\mycmd}[1]{Hello #1}

instead of this:

\newcommand\mycmd[1]{Hello #1}

Best Answer

The official latex syntax, as described by the LaTeX book only ever uses the braced form, and similarly always uses x^{2} rather than x^2.

However the unbraced form works fine and for arguments that are necessarily a single token such as the first argument of \newcommand. That is effectively also supported syntax and you will find many examples from the LaTeX Project team using that style.

Of course dropping braces technically also works even when the argument isn't necessarily a single token, people go \frac12 instead of \frac{1}{2} or even, x^\frac12 instead of x^{\frac{1}{2}} but really, they shouldn't....

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[Tex/LaTex] Why do people use unnecessary braces

With my LaTeX3 'hat' on, I'd like to give a slightly different perspective. This will overlap with the other answers, but hopefully will be useful. To follow this you need to understand 'tokens', I'm afraid. TeX turns input into tokens, and in particular control sequences such as \bar are single tokens.

When Leslie Lamport designed LaTeX, he decided that all LaTeX arguments should be wrapped in braces. This is in contrast to TeX, where many of the primitives require arguments without braces. However, when only a single token is begin passed you can omit the braces, hence the fact that

\newcommand{\bar}

and

\newcommand\bar

both work.

There are really two different cases where you can omit braces:

Cases where the argument is always a single token. This is the case for \newcommand, where you have to have a macro name as the argument. The braces will never be needed as the argument is always \<something>. I do not use braces for these.
Places where you are passing a single token to an argument that will accept more. The classic example would be a subscript, where a_i will work but you'd need a_{ii}. I would always use braces here, so favour a_{i}.

The LaTeX3 part to this answer is that we are trying to be much more rigourous about which arguments are single tokens and which are multiple tokens. At the moment this is only happening at a code level, but I'd anticipate a similar approach for users. So if the argument must be a single token, then make this clear by not using braces. On the other hand, it the argument can take multiple tokens then you must use braces even if only passing a single token.

[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.

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[Tex/LaTex] Why do people use unnecessary braces

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

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