JSS continuation prompt when eval=FALSE

[cderv]

Following #254 comment, the continuation prompt should be + for code chunk, evaluated or not.
That means

```{r}
f <- function(a, b) mean(c(a,b))
f(a = 1,
  b = 2)
```
or 

```{r, eval = FALSE}
f <- function(a, b) mean(c(a,b))
f(a = 1,
  b = 2)
```

shoult be rendered as this in both case

R> f <- function(a, b) mean(c(a,b))
R> f(a = 1,
+   b = 2)

Currently, it is not the case. #294 fixed part of the issue in rticles by changing R+ to + but this works only for evaluated chunks.

In fact, the transformation is based on a hook

rticles/R/jss_article.R

Lines 46 to 53 in ec5e82b

	hook_input <- function(x, options) {
	if (options$prompt && length(x)) {
	x <- gsub("\\n", paste0("\n", "+ "), x)
	x <- paste0("R> ", x)
	}
	paste0(c('\n\\begin{CodeInput}', x, '\\end{CodeInput}', ''),
	collapse = '\n')
	}

but for eval=FALSE , chunk input is not parsed the same as when eval=TRUE so the hook does not apply the same.
It could be a bug elsewhere than rticles...

[yihui]

Originally I thought it was a knitr bug. With the example below, however, I guess it is a problem specific to jss_article():

---
title: "Prompts"
---

```{r}
knitr::opts_chunk$set(prompt = TRUE)
```


```{r}
f <- function(a, b) mean(c(a,b))
f(a = 1,
  b = 2)
```

```{r, eval = FALSE}
f <- function(a, b) mean(c(a,b))
f(a = 1,
  b = 2)
```

I'll leave it to you to investigate.

[yihui]

When eval=FALSE, you'll need to split the code into complete expressions, and add prompts to each expression. Here is what I did in knitr: https://github.com/yihui/knitr/blob/cb796995ffac0a1fc1a81648151b6fde2e0bcdf8/R/highlight.R#L19-L23

It used an internal function in highr, and I'll try to move and export it in xfun so you can call it.

[cderv]

Yes this fixes it. It is odd that we must rewrite this prompt stuff in the jss_article format and not be able to use knitr stuff or highr stuff. I would have expect we could manage this by setting options(prompt = "R> ") and use default getOption('continue') which is +

I am not enough familiar with this jss_article function and why we need for example out_format = sweave. it is working so we'll just make the fix for now.

Note: We may need also to export the one_string function currently in rmarkdown or knitr. I could easily add it in utils.R but it seems that having it in one place it better.

[yihui]

I am not enough familiar with this jss_article function and why we need for example out_format = sweave

The code was mainly copied from https://github.com/yihui/knitr/blob/cb796995ffac0a1fc1a81648151b6fde2e0bcdf8/R/hooks-latex.R#L300-L319

It is odd that we must rewrite this prompt stuff in the jss_article format and not be able to use knitr stuff or highr stuff. I would have expect we could manage this by setting options(prompt = "R> ") and use default getOption('continue') which is +

Yes, I agree with you. We should reuse knitr output hooks instead of providing new hook functions in this package. Currently there is a small problem that makes it inconvenient to reuse the hooks, though. I've opened yihui/knitr#1885 and it can be a good first issue for you when you start working on knitr.

[github-actions]

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