Org mode (La)TeX macros for HTML and LaTeX export

This is inspired by the if-latex-else macro under the `Advanced' heading here: https://github.com/fniessen/org-macros. Apparently, Org mode will evalute Emacs Lisp code in macros, although I have not yet found any documentation that explains why this works.

The when form is like if, except it only returns a string when the condition is true, returning nil instead when it is false. We use when because we want to perform an action for LaTeX and HTML formats, and we do not want to assume that the user wants the same behavior for all non-LaTeX or non-HTML formats.

#+MACRO: when-fmt (eval (when (org-export-derived-backend-p org-export-current-backend '$1) "$2"))

Since the parameter $2 is inside quotes, it will be necessary to double any (literal) backslashes, despite the fact that Org mode macros do not normally require this (except between parameters).

Using the 1.1 macro, we wrap HTML output in \(...\) so that the MathJax library will recognize that it should process them. So long as we only use this to define LaTeX macros, MathJax will not generate any spurious output. In LaTeX output, we use the #+LATEX_HEADER: Org mode syntax to ensure that it is put in the proper LaTeX preamble.

#+MACRO: preamble {{{when-fmt(html,\\($1\\))}}}{{{when-fmt(latex,\n#+LATEX_HEADER: $1\n)}}}

Note: the \n before #+LATEX_HEADER: and after the parameter $1 are an attempt to ensure that the command starts and ends with a new line, so that Org mode commands are recognized correctly. This is not bulletproof: if you put a newline inside the command, that may still foul things up.

The plain TeX command, which allows you to (re)define anything that (MathJax's implementation of) TeX can handle, including LaTeX. This flexibility comes at the price of no warnings when you attempt to define something new and it redefines something essential. The first argument is the control sequence to define, which may begin with a backslash (escaped: \\), but must not contain curly brackets ({...}); the second argument is what it should expand to, automatically enclosed in curly brackets.

#+MACRO: def {{{preamble(\\def$1{$2})}}}

The standard LaTeX command for defining a macro, which must not already exist. The first argument is the command name, which is automatically enclosed in brackets. The second argument is what it should expand to, which is also automatically enclosed in brackets. The third argument, if any, is inserted as is between the first and second argument; this lets you give a parameter count, or a parameter count and a default value for the first parameter, each in square brackets ([...]).

#+MACRO: newcommand {{{preamble(\\newcommand{$1}$3{$2})}}}

The LaTeX command for redefining an existing macro, which must already exist. The arguments are the same as for the 2.2 macro.

#+MACRO: renewcommand {{{preamble(\\renewcommand{$1}$3{$2})}}}

The LaTeX command for defining a new environment, which must not already exist. The first, second, and third arguments are enclosed in curly brackets in that order. The fourth argument, if any, is inserted (as is) between the first and second arguments, like the third argument for the 2.2 macro.

#+MACRO: newenvironment {{{preamble(\\newenvironment{$1}$4{$2}{$3})}}}

The LaTeX command for redefining an existing environment, which must already exist. The arguments are the same as for the 2.4 macro.

#+MACRO: renewenvironment {{{preamble(\\renewenvironment{$1}$4{$2}{$3})}}}

\(\newcommand{\myvqeqn}{y = 2(x-1)^2+1}\)

Say you are writing a book on Intermediate Algebra, and introducing the vertex form of quadratic equations. And you find yourself referring to the equation \[\myvqeqn\] a lot, so you would like to abbreviate it. Easy! Anywhere (almost) before your first usage — we do it right before this text, to help keep it consistent with the example text and explanation here — just type

{{{newcommand(\\myvqeqn,y = 2(x-1)^2+1)}}}

and use it like so:

The equation $\myvqeqn$ shows ...

It will look like "The equation \(\myvqeqn\) shows …", in both HTML and LaTeX, the latter thanks to the use of #+LATEX_HEADER: in the 1.2 macro.

\(\newcommand{\mat}[1]{\mathbf{#1}}\)

Say you are writing a book on Linear Algebra. You will certainly be writing a lot about the names of certain matrices, and you will probably want to abbreviate the names of (at least) the most common matrices you talk about. For two reasons, you will want to use a parameter for the matrix name:

1. you may be writing about several matrices, and it would be a waste of effort to write a separate command for each one;
2. you want to ensure that your typographical treatment of the various matrices is consistent, even if you change your mind later.

So, you might define a command like this:

{{{newcommand(\\mat,\\mathbf{#1},[1])}}}

and use it like this:

The matrices $\mat{A}$ and $\mat{B}$ represent ...

Now, the result looks like "The matrices \(\mat{A}\) and \(\mat{B}\) represent …", but if you want to change how it looks later, there is only one definition that needs to be changed.