"Fragmenting" code block output in presentations

[agerlach]

Is there a convenient means for pausing or fragmenting the output of a code block for a presentation? I am envisioning something like

```{julia}
#| echo: true
#| fragment: default
rand(10,10) 
```

This would echo the code but only show the result after a pause. All current options I see available require the user to replicate the code-block which can become cumbersome.

Things I've tried w/ revealjs:

1. Use a ". . ." pause. This does not work and requires replicating code. There is no resulting pause

   ## Pause Try
   ```julia
   using Plots
   plot(sin)
   ```
   . . .
   
   ```{julia}
   using Plots
   plot(sin)
   ```

2. Use a fragment block. This does not work and requires replicating code. There is no resulting transition

   ## Fragment Try
   ```julia
   using Plots
   plot(sin)
   ```
   
   ::: {.fragment}
   ```{julia}
   using Plots
   plot(sin)
   ```
   :::

3. Use two slides. This does work but requires replicating code and has limited options vs fragment

   ## 2 Slides (1/2)
   ```julia
   using Plots
   plot(sin)
   ```
   
   ## 2 Slides (2/2)
   ```{julia}
   #| echo: true
   using Plots
   plot(sin)
   ```

[jjallaire]

I agree that this should be a feature! (and we'll make it one soon). In the meantime here is a workaround based on this Lua filter (fragment.lua):

function Div(el)
  if el.attr.attributes['fragment'] == 'true' then
    return pandoc.walk_block(el, {
      Div = function(el)
        el.attr.classes:insert("fragment")
        return el
      end
    })
  end
end

Use the Lua filter by adding it to the filters in the document options then adding fragment: true to the cell options:

---
title: "Fragment Demo"
format:
  revealjs:
     filters: [fragment.lua]
---

## Use Fragment

```{julia}
#| echo: true
#| fragment: true
rand(10,10) 
```

[agerlach]

That works great. Thank you

[jjallaire]

We've now implemented this as feature so the filter is no longer required: https://quarto.org/docs/presentations/revealjs/#executable-code. Revised code would look like this:

```{julia}
#| echo: true
#| output-location: fragment
rand(10,10) 
```

[agerlach]

Fantastic! Thanks for the quick turn-around

[jjallaire]

Hi there @agerlach, posting back here because I'm giving a talk on Quarto at JuliaCon next month and was hoping to find some good examples of using Julia w/ Quarto. If you are able to share any of your own (or are aware of others) please LMK over on this discussion thread: #1261. Thanks!

[agerlach]

Thanks for reaching out. Unfortunately, I cannot share the slides I have publicly. I very much look forward to your talk.