Can't use document() inside a function

[Andrew15-5]

Description

This code doesn't do anything:

#let set-title(title) = {
  set document(title: title)
}
#set-title("custom title")

But it should've changed the title metadata/entry in the PDF file. Same way, I can't change the author of the document.

Reproduction URL

No response

Operating system

Linux

Typst version

• I am using the latest version of Typst

---

Idea discussion: #2153.

[Myriad-Dreamin]

If I understand correctly, it works as expected, since the set rules only affect its belonging scope.

#let set-title(title) = { // scope inner
  set document(title: title)
}

// scope outer

#set-title("custom title")

[LuxxxLucy]

Relevant #1913

Setting a variable inside the scope of the function does not change the outer variable. And this is what is expected. Maybe you should follow conventional way of using #set_title or #show doc => template(title: "custom title", doc) in the beginning of the document instead of a function.

[Andrew15-5]

I know about the scope and everything like that, but aren't there any other way besides using #show: template.with(title: "title")?

Maybe it's just functional programming got a hold of me.

[Andrew15-5]

My main problem is that I have a template and a separate function for a title page with a dictionary of values:

#import "@local/package:0.0.1": template, title-page
#show: template
#title-page((
  title: "title",
  a: 1,
  b: "c",
  d: (3, 4, 5),
))

Right now, I have to set document between show and title-page, because it's a global scope. Setting document inside title-page isn't working. I can do this in template. But this means, that I have to do:

#let title = "title"
#show: template.with(title: title)
#title-page((
  title: title,
))

Which I fill is a bit too verbose than just passing the title one to title-page and setting the document there.
To fix this, I would have to convert title-page function to a template that is used in the show rule, which also doesn't feel right.

I don't know, I just want the code to be elegant and minimalistic.

[Andrew15-5]

Maybe I want to compose a title from some values that are passed to the title-page. This would be so simple: just combine values inside title-page and set the title also there. Instead, I have to compose the title in the main file (unwanted mess at the beginning of the main file!). It seems that then I just have to pass all the needed arguments to the template and compose the title there, instead of in the title-page.

In other words, if making the title makes sense in a function (and therefore setting the title there), because it has all the needed information (and there is literally "title" in title-page), you can't. You have to tear off the logic from the function and put it inside the template (main template or a separate one).

[LuxxxLucy]

Have you consider passing doc as a argument?

#let template(title: none, doc) = {
set document(title: title)
// do something
doc
}

#let title-page(title: none, doc) = {
// do something else. Modify title here
set document(title: title)
// do something else
doc
}

#show doc => template(title: “first title”, doc)

#show doc => title-page(title: “second title”, doc)

I did some quick test and this seems to be working.

[Andrew15-5]

#show doc => template(title: “first title”, doc)

#show doc => title-page(title: “second title”, doc)

I already mentioned this:

To fix this, I would have to convert title-page function to a template that is used in the show rule, which also doesn't feel right.

And the title is the same, so I would have to add another line with a variable, which I also already mentioned:

#let title = "title"
#show: template.with(title: title)
#title-page((
  title: title,
))

[LuxxxLucy]

Sorry I cannot comprehend.

Perhaps make a wrapper to get the template and title-page into another (bigger) template and then calling it?

[Andrew15-5]

It can be another workaround, but template and title-page live in different files, because they have nothing (or almost nothing) in common. Your approach will require either making another file that will have the bigger wrapper, or join the code from both files. Either way, it will only complicate the code itself.

Since title-page will set the title/first page, it does make sense that it could also set the title of the document itself. But this is unfortunately not possible (yet) in Typst.

[LuxxxLucy]

From my understanding, you are correct.

Because what you want is a function call with side effects. It would not be compatible with the general design of typst, where memorization of function call is a core feature; side effects will break it.

So it is not something that is not supported yet. It is a deliberate design for not supporting it.

[Andrew15-5]

I've opened a related discussion here: #2153.