Re: Lua filter to automatically tag keywords for TeX indexing

[Bastien DUMONT <bastien.dumont-VwIFZPTo/vqsTnJN9+BGXg@public.gmane.org>]

Iterating over all possible values at every string can be expensive. You can speed up the process by rewriting Includes like this:

```
local bool_tables = {}

function Includes(tab, val)
  -- strip trailing punctuation before matching
  local bare = string.gsub(val,"[%.|,|;|:]", "")
  -- The first time a given value of tab is tested in Includes,
  -- a table is added in bool_tables which contains
  -- a boolean key-value entry for each element in tab.
  if not bool_tables[tab] then
    bool_tables[tab] = {}
    for _, elem in ipairs(tab) do
      bool_tables[tab][elem] = true
    end
  end
  -- So we only have to test once for the key-value entry
  -- instead of iterating over all elements in tab
  -- every time Inclues is called.
  return bool_tables[tab][val]
end
```


Le Wednesday 02 November 2022 à 06:20:37PM, bapt a a écrit :
> 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)
> 
> - 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)
> 
> Best regards,
> 
> baptiste
> 
> Lua filter:
> -----
> 
> local text = require 'text'
> local pandoc = require 'pandoc'
> 
> -- keywords to look for in the document
> local langs = {"Matlab", "R", "Julia", "C++"}
> 
> function Includes(tab, val)
> -- strip trailing punctuation before matching
> local bare = string.gsub(val,"[%.|,|;|:]", "")
> 
> for index, value in ipairs(tab) do
> if value == bare then
> return true
> end
> end
> 
> return false
> end
> 
> function Replace_langname(elem)
> if Includes(langs, elem.text) then
> return pandoc.SmallCaps(text.lower(elem.text))
> else
> return elem
> end
> end
> 
> return {{Str = Replace_langname}}
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
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