Re: [ Q ] Lua-filter: "Dynamic linking not supported" error when loading certain lua module(s)

[BPJ <melroch-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>]

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Do you know that you can use Pandoc itself as a YAML parser?

https://pandoc.org/lua-filters.html#default-metadata-file

Some things to look out for:

-   Pandoc parses YAML scalar values (but not keys) as Pandoc markdown and
returns a tree of objects. To get a "plain" data structure out of that you
have to run the `meta` part of the Pandoc object through a function along
the lines of

    ````lua
    local function meta2data (x)
      if 'table' == type(x) then
        local t = x.t -- tag == element type
        if not t or 'MetaMap' == t or 'MetaList' == t then
          -- turn into a plain data table
          local d = {}
          for k,v in pairs(x) do
            d[k] = meta2data(v) -- call recursively
          end
          return d
        elseif t then
          -- probably text, so stringify it
          return pandoc.utils.stringify(x)
        end
      else
        -- something else, probably a string or boolean
        return x
      end
    end

    local data = meta2data(doc.meta)
    -- or less expensively:
    local some_data = meta2data(doc.meta.some_field)
    ````

    NOTE: I'm "quoting" the meta2data function from brain memory so some
detail covering some edge case may be missing, but it's the general idea.

-   The restringification of the MetaBlocks and MetaInlines elements (or
rather their contents) removes everything which Pandoc considers
formatting, so you, or your users, have to wrap any literal strings in the
YAML where whitespace and/or punctuation is important in Pandoc code
elements, and these need in turn to be wrapped in YAML quoted strings since
YAML reserves the backtick for future use as a metacharacter:

    ````````yaml
    foo: '`2**10`'
    bar: |
      ````
      No Markdown parsing here
      ````
    ````````

-   If you read in YAML from a file you have to make sure that it starts
and ends with appropriate YAML block delimiters so that Pandoc recognises
it as "metadata"

    ````lua
    if not yaml:match('^%-%-%-%f[^%-]') then
      yaml = "---\n" .. yaml
    end
    if not yaml:match('\n([%.%-])%1%1%s*$') then
      yaml = yaml .. "\n...\n"
    end
    ````

This looks complicated but the first two points are generally what you have
to do/observe anyway if you configure your filter through metadata, and
having Pandoc parse the YAML using Haskell is probably still more efficient
and robust than using a pure Lua YAML parser. (I've taken a stab at
reimplementing [YAML::Tiny](https://metacpan.org/pod/YAML::Tiny) in Lua and
it isn't easy!)

Den mån 8 juli 2019 20:41K4zuki <k.yamamoto.08136891-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> skrev:

> You seem to be totally right: C-based libraries are not supported by
> static-built pandoc binaries(e.g. deb file)
> I agree that setting LUA_PATH/LUA_CPATH is also preferred.
>
> I will use lua-yaml instead of lyaml package. lfs cannot be used in this
> case but as penlight package requires it, I will leave it installed(and
> unused).
>
> Thanks for the advice.
>
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