r - Custom language engine on Knitr

Question

I have added a custom language engine on Knitr according the documentation.

require(knitr)
knit_engines$set(upper = function(options) {
  code <- paste(options$code, collapse = "
")
  if (options$eval) 
    toupper(code) else code
})

And when I add text a following command to Rmd-file I can run a current chunk in RStudio.

```{upper}
Hello, **knitr** engines!
```.

HELLO, KNITR ENGINES!

But If I try to Knit a whole file to a html-page I can't see the result of chunked code. And I will get the following warning message on R Markdown tab.

Warning message:
In get_engine(options$engine) :
  Unknown language engine 'upper' (must be registered via knit_engines$set()).

So how can I register the engine so that the program will see it later on?

question from:https://stackoverflow.com/questions/66048267/custom-language-engine-on-knitr

Answer 1

---
title: "Untitled"
output: html_document
---

```{r setup, include=FALSE}
knitr::opts_chunk$set(echo = TRUE)

knitr::knit_engines$set(upper = function(options) {
  code <- paste(options$code, collapse = "
")
  if (options$eval) 
    toupper(code) else code
})
```

```{upper}
Hello, **knitr** engines!
```