xfun (version 0.50)

protect_math: Protect math expressions in pairs of backticks in Markdown

Description

For Markdown renderers that do not support LaTeX math, we need to protect math expressions as verbatim code (in a pair of backticks), because some characters in the math expressions may be interpreted as Markdown syntax (e.g., a pair of underscores may make text italic). This function detects math expressions in Markdown (by heuristics), and wrap them in backticks.

Usage

protect_math(x, token = "", use_block = FALSE)

Value

A character vector with math expressions in backticks.

Arguments

x

A character vector of text in Markdown.

token

A character string to wrap math expressions at both ends. This can be a unique token so that math expressions can be reliably identified and restored after the Markdown text is converted.

use_block

Whether to use code blocks (```md-math) to protect $$ $$ expressions that span across multiple lines. This is necessary when a certain line in the math expression starts with a special character that can accidentally start a new element (e.g., a leading + may start a bullet list). Only code blocks can prevent this case.

Details

Expressions in pairs of dollar signs or double dollar signs are treated as math, if there are no spaces after the starting dollar sign, or before the ending dollar sign. There should be a space or ( before the starting dollar sign, unless the math expression starts from the very beginning of a line. For a pair of single dollar signs, the ending dollar sign should not be followed by a number, and the inner math expression should not be wrapped in backticks. With these assumptions, there should not be too many false positives when detecing math expressions.

Besides, LaTeX environments (\begin{*} and \end{*}) are also protected in backticks.

Examples

library(xfun)
protect_math(c("hi $a+b$", "hello $$\\alpha$$", "no math here: $x is $10 dollars"))
protect_math(c("hi $$", "\\begin{equation}", "x + y = z", "\\end{equation}"))
protect_math("$a+b$", "===")