Displaying a function and a script in knitr

Define engines

These engines are made of two ingredients: the function formatR::tidy_source to format the code, and the function highr::hi_html to highlight the code.

• Engine to show a script

engine_showscript <- function(options){
  tidycode <- formatR::tidy_source(
    source = options$script,
    indent = 2L
  )$text.tidy
  out <- c("<pre class='hl'>", highr::hi_html(tidycode), "</pre>")
  options$results <- "asis"
  options$echo <- FALSE
  knitr::engine_output(options, "", out)
}
knitr::knit_engines$set(showscript = engine_showscript)

• Engine to show a function

engine_showfun <- function(options){
  body <- capture.output(eval(parse(text=options$fun)))
  if(substr(tail(body,1), 1, 4) == "<env"){
    body <- head(body,-1)
  }
  body[1] <- sprintf("%s <- %s", options$fun, body[1])
  tidycode <- formatR::tidy_source(text=body,
                                   indent=2)$text.tidy
  out <- c("<pre class='hl'>", highr::hi_html(tidycode), "</pre>")
  options$results <- "asis"
  options$echo <- FALSE
  knitr::engine_output(options, "", out)
}
knitr::knit_engines$set(showfun = engine_showfun)

• For both engines, you have to include a css by adding this line at the beginning of the document (otherwise highr::hi_html has no effect):

<link rel='stylesheet' href='hl.css'/>

The content of this file is given at the end of this document. Of course you are free to modify the styles.

Demo showscript

Make an empty chunk with the option engine="showscript" and the option script set to the path of your script:

```{r, engine="showscript", script="path/to/script.R"}
```

• Example:

# a function
f <- function(x) {
  return(x + 1)
}

# another function
g <- function(y) {
  z <- sqrt(y)
  return(z)
}

Demo showfun

For example:

```{r, engine="fun", fun="engine_showscript"}
```

Result:

engine_showscript <- function(options) {
  tidycode <- formatR::tidy_source(source = options$script, indent = 2L)$text.tidy
  out <- c("<pre class='hl'>", highr::hi_html(tidycode), "</pre>")
  options$results <- "asis"
  options$echo <- FALSE
  knitr::engine_output(options, "", out)
}

The css file

This is the content of the file hl.css:

body.hl { background-color:#e0eaee; }
pre.hl  { color:#000000; background-color:seaShell; font-size:10pt; font-family:'Courier New';}
.hl.num { color:#b07e00; }
.hl.esc { color:#ff00ff; }
.hl.str { color:#AB0000; }
.hl.pps { color:#818100; }
.hl.slc { color:#838183; font-style:italic; }
.hl.com { color:#514F51; font-style:italic; }
.hl.ppc { color:#008200; }
.hl.opt { color:#B95F0A; }
.hl.lin { color:#555555; }
.hl.kwa { color:#3A003A; font-weight:bold; }
.hl.kwb { color:#008000; }
.hl.kwc { color:#6F4827; font-weight:bold; }
.hl.kwd { color:#010181; font-weight:bold;}