Customization of the highr package

If you are not satisfied with the default syntax highlighting commands in the highr package, you can just use your own tags/commands. In this vignette, we show a brief example.

The default highlighting commands are stored in two internal data frames cmd_latex and cmd_html:

library(highr)
highr:::cmd_latex

##                          cmd1 cmd2
## COMMENT              \\hlcom{    }
## DEFAULT              \\hldef{    }
## FUNCTION             \\hlkwa{    }
## IF                   \\hlkwa{    }
## ELSE                 \\hlkwa{    }
## WHILE                \\hlkwa{    }
## FOR                  \\hlkwa{    }
## IN                   \\hlkwa{    }
## BREAK                \\hlkwa{    }
## REPEAT               \\hlkwa{    }
## NEXT                 \\hlkwa{    }
## NULL_CONST           \\hlkwa{    }
## LEFT_ASSIGN          \\hlkwb{    }
## EQ_ASSIGN            \\hlkwb{    }
## RIGHT_ASSIGN         \\hlkwb{    }
## SYMBOL_FORMALS       \\hlkwc{    }
## SYMBOL_SUB           \\hlkwc{    }
## SLOT                 \\hlkwc{    }
## SYMBOL_FUNCTION_CALL \\hlkwd{    }
## NUM_CONST            \\hlnum{    }
## '+'                  \\hlopt{    }
## '-'                  \\hlopt{    }
## '*'                  \\hlopt{    }
## '/'                  \\hlopt{    }
## '^'                  \\hlopt{    }
## '$'                  \\hlopt{    }
## '@'                  \\hlopt{    }
## ':'                  \\hlopt{    }
## '?'                  \\hlopt{    }
## '~'                  \\hlopt{    }
## '!'                  \\hlopt{    }
## SPECIAL              \\hlopt{    }
## GT                   \\hlopt{    }
## GE                   \\hlopt{    }
## LT                   \\hlopt{    }
## LE                   \\hlopt{    }
## EQ                   \\hlopt{    }
## NE                   \\hlopt{    }
## AND                  \\hlopt{    }
## AND2                 \\hlopt{    }
## OR                   \\hlopt{    }
## OR2                  \\hlopt{    }
## NS_GET               \\hlopt{    }
## NS_GET_INT           \\hlopt{    }
## STR_CONST            \\hlsng{    }

This data frame is passed to the markup argument in hilight(), so we are free to pass a modified version there. Suppose I want to use the command \my<*> instead of \hl<*>:

m = highr:::cmd_latex
m[, 1] = sub('\\hl', '\\my', m[, 1], fixed = TRUE)
head(m)

##              cmd1 cmd2
## COMMENT  \\mycom{    }
## DEFAULT  \\mydef{    }
## FUNCTION \\mykwa{    }
## IF       \\mykwa{    }
## ELSE     \\mykwa{    }
## WHILE    \\mykwa{    }

Then

hilight("x = 1+1  # a comment")  # default markup

## \hldef{x} \hlkwb{=} \hlnum{1}\hlopt{+}\hlnum{1}  \hlcom{# a comment}

hilight("x = 1+1  # a comment", markup = m)  # custom markup

## \mydef{x} \mykwb{=} \mynum{1}\myopt{+}\mynum{1}  \mycom{# a comment}

This allows one to use arbitrary commands around the text symbols in the R code. See https://github.com/yihui/highr/blob/master/R/highlight.R for how cmd_latex and cmd_html were generated in highr.