Thank you both for the helpful replies; I don't fully understand how these 
boolean tables are used in Lua (clearly it works, I just don't fully get 
it), but it seems to be an important concept so I'll read up on it.

Thanks,

baptiste

On Friday, 4 November 2022 at 08:39:29 UTC+13 fiddlosopher wrote:

>
>
> > On Nov 2, 2022, at 6:20 PM, bapt a <augu...-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> wrote:
> > 
> > Hi all,
> > 
> > I've started writing a technical book using Quarto markdown, which uses 
> pandoc with Lua filters under the hood to produce a website as well as the 
> publisher's pdf format (via LaTeX). 
> > I quite like to keep the source document as plain as possible, and I'm 
> wondering if I could avoid the use of [concept]{.index}, which gets turned 
> into \index{concept}, and instead write a Lua filter with my custom list of 
> keywords, and have pandoc automatically match them as they appear in the 
> text. 
> > As a proof of principle I wrote the following code (see below), which 
> matches specific keywords, and reformats them as small-caps. I quickly 
> realised that trailing punctuation, such as "concept, ..." will fail to 
> match, so I'm using gsub to strip such punctuation before matching. It 
> works, but I'm a bit worried:
> > 
> > - what's the overhead of such a filter, in practice? From what I 
> understand, every single string element in the AST will be processed by 
> gsub then tested for a match. Are Lua filters walking down the AST fast 
> enough that I shouldn't worry about it? (as far as I can tell on small 
> examples, it seems fine)
>
> The AST walking is very fast. See the benchmarks at the beginning of 
> https://pandoc.org/lua-filters.html for one example.
>
> > - assuming this idea is reasonable, I might want to do a few similar 
> operations, e.g. reformatting program languages (as in this example code), 
> wrapping keywords in \index{}, etc., and the exact format will often depend 
> on the output target (html vs TeX etc.). Is there a better construct for 
> this than successive if/else statements to look for matches? (I don't know 
> much Lua)
>
> In lua you can do
>
> string.gusb(val, [“(%l*)”], function (word)
> if indexable[word] then
> .. whatever ..
> end
> end)
>
> This will run the function on every group of letters in the matched string.
> Here I’m assuming you have a lua table indexable that maps words to true, 
> e.g.
>
> { cow: true, horse: true }
>
> That will be much faster than iterating through an array as you’re doing 
> here.
>
>

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