How can I write a function for custom heading numbering?

Questions
,
1

I am dabbling with Typst… one seemingly simple thing I wanted to do was to define a custom alternative to:

#set heading( numbering: "1." )

I wanted a different intermediate and final separator - and I wanted to fix the width of the numbered part of the headings - so the fist letter of the textual headings align horizontally throughout the document.

I supposed that I wanted to implement a function, to put in place of “1.” - and that it would need to iterate over the counters for the heading - and decorate those with the separators I choose using conditionals. I assumed I’d want to use a for loop to iterate over the hierarchical heading numbers. I found I could extract the current hierarchical heading numbers using:

#let labels= context(counter(heading).get()) 
#labels // Outputs an array - e.g. "(1,2,7)"

However, when I tried to iterate over the heading numbers in labels:

#for label in labels { /* Deal with each level separately */ }

I get the typst error: “cannot loop over content” I also note that while labels renders as an array of integers, typst does not let me call len on it to get its length… a hurdle to iterating over the heading numbers by index.

I assume there is something I’m overlooking? Is the sort of customisation I envisage supported by Typst?

I’ve read the numbering documentation - but this has left me with more questions than answers. Is one restricted to a unary function to provide custom hierarchical heading numbers?

2

The first thing to realize that comes to mind is Why is the value I receive from context always content? - #2 by laurmaedje

Also, you will find many example of numbering functions on this forum such as How to Create Independent Numbering Levels Inside a Custom Function or How to produce a heading numbering 1.0.0 as first level? .

If you give us an example of exactly what you are trying to achieve as a result, perhaps we can help.

3

For the code you posted (which is not using the correct formatting by the way. See here) you can see why you get a complaint about content and why len() didn’t work:

#let labels= context(counter(heading).get()) 
#labels\
#type(labels)\
#repr(labels)

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The reason for this is as vmartel08 pointed out in their first link: everything returned by context is of type content.

If you instead check the type inside the context scope:

#context {
  let labels = counter(heading).get()
  [#labels]
  linebreak()
  [#type(labels)]
  linebreak()
  [#repr(labels)]
}

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1 Like
4

For different numbering separators you would modify the set rule, similar to: How can I change the heading numbering for headings of different levels differently?

About the heading numbering width, I think the easiest would be to rebuild the headings in a custom show rule, and maybe use a grid with a fixed size column for the number. The following answer shows the general approach on how to modify headings: How can I show the heading number after the heading itself? - #2 by janekfleper

5

Thanks for the reply vmartel08, I think I’ve mostly overcome the headings counter issue like this:

#let hierarchical-dot-fixed-heading-numbers = (label-width: 50pt) => {
  return (..labels) => {
    box(width: label-width, labels.pos().map(str).join("."))
  }
}
#set heading(
  numbering: hierarchical-dot-fixed-heading-numbers(label_width: 40pt)
)

I’m able to access the raw array when I accept it as an argument to my numbering formatting function. It’s not absolutely perfect… as I’d prefer the width of the box to be determined dynamically - for example as 12pt wider than the widest box content (numeric labelling) in the document. I’m not sure how that could be tackled.

Thanks to gezepi’s answer - I’ve now grasped that I need to use values like counter(heading).get() - c.f. the function calls themselves - inside the scope of a *context"… and I can now see how to do that in a variety of ways in which I want to dynamically create layout depending upon counters. I’ll play with it some more. :slight_smile:

I’m not sure I follow flokl’s answer. If the grid had a fixed size column for the numeric part of headings… then I’d still need to pick that width by hand. If I want the width to be dynamically set, from document content, then I’d need a way to calculate the length of the longest numeric-part of any heading. Can this be done using context() - or am I barking up the wrong tree?

6

Whether you create a box or use a grid, you’ll need a fixed width. You can query for the final heading number and measure its width like this:

#set heading(numbering: "1")

#context {
  let max-heading = counter(heading).final().first()
  let max-heading-width = measure([#max-heading]).width

  [The last heading is number #max-heading which has a width of #max-heading-width]
}
#pagebreak()

#for i in range(100) {heading([Heading #str(i)])}

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1 Like
7

I misinterpreted your level of knowledge and wanted to give you general pointers on where to start :smiley: