Use of parameters in chunk options

[Dobrokhotov1989]

Hi there!

I'm trying to migrate from RMarkdown to quarto. I'm lucky because I've heard about quatro just a few days after I began a new project.
In RMarkdown, I used params to conditionally execute some chunks of code (setting params in yaml and then passing them into chunk option 'eval'). I've tried to do this trick in quarto, but the chunk option is not recognized as a parameter, but just as a character string and thus just ignored. Is it possible to achieve such behavior in quarto?

Example:
In RMarkdown (works):

```{r eval=params$ChunkNumberOne}
SomeCode <- That + ShouldNotBe + Evaluated
```

In quarto (doesn't work:

```{r}
#| eval: params$ChunkNumberOne

SomeCode <- That + ShouldNotBe + Evaluated
```

[mcanouil]

you have to use the keyword/command !expr as noted in https://quarto.org/docs/computations/r.html#chunk-options

#| eval: !expr params$ChunkNumberOne

SomeCode <- That + ShouldNotBe + Evaluated

[hebertodelrio]

Don’t you think that this can be treated similarly like the inline code case (#1520 (reply in thread))?

extract the top comments (#|) create a fake code cell with them and execute it therefore every occurrence of {{ code }} will be replaced with the appropriate result, and replace the top comments with the result.

I can tinkle with the idea and see how far I can get. One issue I have is to understand the definition of options (#|) do they must be at the very top of the code cell and no empty newlines in between them, first empty newline determines the end of the options? Or there is something different?

Again if this work will be as a Notebook filter

[mcanouil]

Parameters are already handled in Quarto especially using an external yaml file passed as parameter in Quarto CLI (at least according to documentation), thus the issue here seems to be a syntax error which we can't see without the actual code.

[hebertodelrio]

What I meant is that the use of !expr is only valid if you are using knitr, so people that uses Python or Julia (like me) are in a bit of disadvantage

Mote than parameters I was referring to chunk options with pseudo dynamic content

[mcanouil]

For Jupyter engine hence Python: https://quarto.org/docs/computations/parameters.html#jupyter
So you could get the same behaviour in python cells by adding if else statement rather than using the eval yaml cell option.

[Dobrokhotov1989]

@mcanouil, thank you for your help.

I have three files in the same project folder:

File test.qmd

## Test

```{r}
#| eval: !expr params$chunkeval
1 + 1
```

File _quarto.yml

project:
  title: "Test"

editor: visual

File params.yml

params:
  chunkeval: false

When I use command quarto render test.qmd --execute-params params.yml in terminal I got the following error:

processing file: test.qmd
Error: object 'params' not found
Error in yaml::yaml.load(yaml, eval.expr = TRUE) :
  Could not evaluate expression: params$chunkeval
Calls: .main ... parse_block -> partition_yaml_options -> <Anonymous>
Execution halted