How can I work with the type content in show rules to check for content and maybe even change it?

[Adrian_Weitkemper]

Hi there!
I have a pretty broad questions, so sry for that, but maybe someone can still help me
I am currently struggling a bit with the type content. When working with a show rule like

#show outline.entry: it => {
  if ("Adrian" in str(it.element.body)) {
    [This is my name]
  }
}

I would like to modify the content/body or at least work with it’s value.
Another example would be lists:

#show list: it => {
  it.children
}
- some

shows
. Also, the autocomplete shows all the array functions, so I think it is an array. But when I do

#show list: it => {
  it.children.at(0)
}

it throws the error “Missing argument: index”
Using .first() instead throws the error “Cannot access fields on type array”.
So at this point, I don’t even know how to get through to the content.
Something similar happened in
this post

description of the problem I am briefly describing in the post

#import "@preview/lilaq:0.1.0" as lq
#show lq.selector(lq.tick-label): it => {
  let str_it = to-string(it)
  if (str_it == "") {
    [#it.children.at(0)]
  }
}
#lq.diagram(
  lq.plot((-1,3),(-3,1))
)

shows the following plot:

When I comment out the line “[#it.children.at(0)]”, all the numbers disappear, so they have to be in that line. In this case it maybe doesn’t have the type context though, because when I write something like “it.children.at(0).felds()” in that line, it says " Element context has no method felds". On the other hand, all the auto-complete functions are the ones of content. Regardless, writing “it.children.at(0).fields()” in that line results in this:

So the fields are an empty dict and I have no idea where the content is hiding again…

So I found this github post which includes a function that tries to convert content into a string. This is definitely very helpful and seems to solve my first two examples, but in my last example, the string is just empty (because the field is empty I guess) and I would have no idea what to do.
So I guess the custom to-string function is the best solution I have for now, but I would like to understand how to go through these dicts and thought maybe there is a better alternative
PS: just to be clear: these are no concrete code problems I have, these are just some examples to be able to better describe my general problem with the type content/dics in show rules. Also, I’m open to changes to the title because I’m aware that it’s not really good…

[SillyFreak]

@Adrian_Weitkemper

But when I do

#show list: it => {
  it.children.at(0)
}

it throws the error “Missing argument: index”
Using .first() instead throws the error “Cannot access fields on type array”.

This gave me a different error: “Maximum grouping depth exceeded”. I understand this is because a single list item is treated as a list with one item, which again results in the show rule being applied, etc. Normally I’d expect “maximum show rule depth exceeded”, but I guess this results in both the show rule and grouping depth rising, and the maximum grouping depth is lower.

One way around this (since you presumably want to do more with the list item anyway) is to use repr(...):

#show list: it => {
  repr(it.children.at(0))
}

The next step would be to access the body:

#show list: it => {
  it.children.at(0).body
}

Neither leads to the same problem, since the problem was not with the access but with the specific intermediate element

---

I know that was pretty specific for this one problem, but maybe it already helps you. For more information, I would recommend these two topics:

How can I manipulate content values?

Content is not really meant to be manipulated, usually the better way is to only create content from data that has already been processed in any way necessary. This is often the right advice for e.g. tables – however, it is not really applicable to your use case because the data you have is fundamentally already formatted text. The next best way, though, is not manipulating the full hierarchy of the content value you’re dealing with, but applying a rule. Your specific case can be handled by thi…

Is there a way to convert content to bytes for use in plugins?

There is no built-in way, but it’s not too hard to build one yourself (with limitations). There’s been this post on handling content, which I think is at least somewhat relevant: A main takeaway here is that, whenever you can, you should strive to not have content as the basis of your computation. Use structured data as long as possible and then format it. In your case, you want to specifically create bytes to communicate arbitrary content to a plugin. The approach will be similar to what is…

Maybe these help you narrowing down your issues. Feel free to follow up here with a more concrete question

[Andrew]

@SillyFreak

This gave me a different error: “Maximum grouping depth exceeded”.

This is because the documents used in both cases are most certainly different. Which highlights the importance of MRE (minimal reproducible example) when asking a question about a specific thing. There is a great website about such stuff: https://sscce.org/.

[Adrian_Weitkemper]

Thank you for answering!
Could you maybe explain why the show rule calls itself in a little more detail?
The tip with the repr function might help in the future, so thank you for that. I think the post I read about manipulating content is the one you referenced, but it’s good that you found it again.
The be honest I don’t really have a specific issue at the moment, but I thought it would be good to know how to handle this things in case I need it later (when I don’t have as much time as now).
Wouldn’t it be better to open a new question for a concrete case? I mean I could still reference this question…

[SillyFreak]

@Adrian_Weitkemper

Could you maybe explain why the show rule calls itself in a little more detail?

Sure! a more common example would be something like

#show heading: it => {
  heading(upper(it.body))
}

= foo

this instructs Typst to replace each heading with a new heading, which is then replaced, which is then replaced… the error here is “maximum show rule depth exceeded”. In your case you get a different error, but I think the reason is the same.

you have a show rule for list, and the code you showed gives back a list.item. However, if Typst sees a list item on its own, it recognizes it as a list:

#show list: set text(red)

#list.item[a]
#list.item[b]

This is not a “full” list, but it’s still colored red. So extracting a list item from a list, and then inserting that in a document creates a new list, consisting of that single list item, which will re-trigger the list show rule.

---

@Adrian_Weitkemper

Wouldn’t it be better to open a new question for a concrete case? I mean I could still reference this question…

I thought that maybe I missed some issue you already faced (I misunderstood your PS as “this is not the only concrete problem, just an example and I want a general answer”) in which case following up here makes sense. Sometimes getting an answer that doesn’t fully address the issue helps getting a clearer picture of what you want to ask, so that’s what I was going for.

But yes, since there are no concrete issues yet, a new question is better.

[Adrian_Weitkemper]

Thank you for your long answer. I came across another example while trying to help others in the forum. My code is the following:

#show cite: it => [
  #repr(it)
]
This was stated by #cite(<doe2020>, form: "prose").
#bibliography("bibliography.bib", style: "ieee")

and the bib file bibliography.bib:

@article{doe2020,
  author = {John Doe},
  title = {An IEEE Example},
  journal = {Journal of Examples},
  year = {2020}
}

The code produces the following output:

So it basically displays the fields, but the content “J. Done [1]”, which is shown without the repr function, can’t be found. So is the content somewhere in there or is it just not part of the element at all and you have to access it differently using the key or something like that?
By the way: the to-string function from above also fails again (empty string)

[Andrew]

@Adrian_Weitkemper

#show cite: it => [
  #repr(it)
]

You can just write #show cite: repr.

---

@Adrian_Weitkemper

@article{doe2020,
  author = {John Doe},
  title = {An IEEE Example},
  journal = {Journal of Examples},
  year = {2020}
}

You can include this in the Typst file now:

#let bib-file-text = ```bib
@article{doe2020,
  author = {John Doe},
  title = {An IEEE Example},
  journal = {Journal of Examples},
  year = {2020}
}
```.text

#show cite: repr

This was stated by #cite(<doe2020>, form: "prose").

#bibliography(bytes(bib-file-text), style: "ieee")

---

@Adrian_Weitkemper

So it basically displays the fields, but the content “J. Done [1]”, which is shown without the repr function, can’t be found. So is the content somewhere in there or is it just not part of the element at all and you have to access it differently using the key or something like that?

Currently, you can’t retrieve bibliography data in any way other than reading directly from the file.

Bibliography customization from within Typst

---

@Adrian_Weitkemper

By the way: the to-string function from above also fails again (empty string)

I didn’t find the function you are referring to. A good function exists in t4t:

#import "@preview/t4t:0.4.2": get
#get.text[almost any content]

[SillyFreak]

@Adrian_Weitkemper

So is the content somewhere in there or is it just not part of the element at all and you have to access it differently using the key or something like that?

It’s not really in there; as Andrew wrote there’s an open issue, and the same problem is discussed here on the forum: How to access the elements of a bibliography?

Why is it not really in there? Because Typst first has to create the content from the bibliography, and that is not necessarily possible immediately. With IEEE for example (i.e. “[1]”), Typst has to collect all the citations to know what the correct numbering is and which reference gets a [1] and which gets [2] etc.

Effectively, cite() is therefore similar to context in that you can not inspect its content (see Why is the value I receive from context always content?); you can however inspect the input given to produce that content, which is what repr() shows you.