Lua: print an AST value?

Lua: print an AST value?

[Axel Rauschmayer]

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As an error message in a Lua filter, I’d like to print an AST value in some 
manner:

   - I found plans for outputting AST values to Markdown etc. That would be 
   the best solution, but it’s not ready yet. 
   https://groups.google.com/d/topic/pandoc-discuss/LM1l4z8xEhQ/discussion
   - Alternatively, printing the AST would also do. E.g., it could look 
   like here: https://pandoc.org/try/

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Re: Lua: print an AST value?

[BPJ]

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Have you tried `pandoc.utils.stringify()`?

It doesn't include formatting but it's better than nothing. You could even
write a small `pandoc.walk_*()` filter which inserts some basic
"formatting" as literal strings like `*` around Emph and run it on an AST
value before stringifying:

````lua
local para = pandoc.Para({emph})
local insert_formatting = {
  Emph = function (elem)
    return {
      pandoc.Str('*'),
      elem,
      pandoc.Str('*'),
    }
  end
}
para = pandoc.walk_block(para, insert_formatting)
local str = pandoc.stringify(para)
````

I agree that it would be good to have an API function to convert an AST
element to markup, sort of `pandoc.read()` in reverse.

Den sön 26 maj 2019 13:21Axel Rauschmayer <rauschma-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> skrev:

> As an error message in a Lua filter, I’d like to print an AST value in
> some manner:
>
>    - I found plans for outputting AST values to Markdown etc. That would
>    be the best solution, but it’s not ready yet.
>    https://groups.google.com/d/topic/pandoc-discuss/LM1l4z8xEhQ/discussion
>    - Alternatively, printing the AST would also do. E.g., it could look
>    like here: https://pandoc.org/try/
>
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Re: Lua: print an AST value?

[Albert Krewinkel]

Axel Rauschmayer writes:

> As an error message in a Lua filter, I’d like to print an AST value in
> some manner:

This is not really supported yet. The closest you can get right now is
by monkey-patching Lua types, similar to what I proposed here:
https://github.com/jgm/pandoc/issues/5092#issuecomment-444526879

Just printing the native Haskell AST representation would be easy[1],
but I wonder if a more Lua-oriented output would be more appropriate.

[1]: https://github.com/tarleb/pandoc/commit/b66ae48913b3440c65d5cc3252d76d9b18a0ed9a

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Re: Lua: print an AST value?

[John MacFarlane]

Can't you use a generic lua table printer, like

https://github.com/kikito/inspect.lua

Re: Lua: print an AST value?

[BPJ]

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@Axel I misunderstood what you wanted to do. I use the `pl.pretty`[^1]
library from penlight[^2] to dump AST structures, however `element.t` isn't
automatically included since it is defined only in the metatable, and
sometimes `pl.pretty` will get into an infinite loop because of the
metatables. To work around these issues I use a function which copies the
element table structure to an ordinary table structure without a metatable,
including copying `element.t` to `copy._t` as needed — prepending more
underscores until a unique key is obtained —, and pass the output of that
function to `pl.pretty.dump()`:

````lua
local function copy_elem (elem)
  if 'table' ~= type(elem) then return elem end
  local copy = {}
  for k,v in pairs(elem) do
    copy[k] = copy_elem(v) -- yes call recursively!
  end
  if nil ~= elem.t and rawget(elem, 't') ~= elem.t then
    local k = '_t'
    while nil ~= elem[k] do
      k = '_' .. k
    end
    copy[k] = elem.t
  end
  return copy
end

-- elsewhere:

pretty_dump = require"pl.pretty".dump

pretty_dump(copy_elem(elem))
````

[^1]: <http://stevedonovan.github.io/Penlight/api/libraries/pl.pretty.html>


[^2]: <https://github.com/stevedonovan/Penlight>


Den sön 26 maj 2019 13:21Axel Rauschmayer <rauschma-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> skrev:

> As an error message in a Lua filter, I’d like to print an AST value in
> some manner:
>
>    - I found plans for outputting AST values to Markdown etc. That would
>    be the best solution, but it’s not ready yet.
>    https://groups.google.com/d/topic/pandoc-discuss/LM1l4z8xEhQ/discussion
>    - Alternatively, printing the AST would also do. E.g., it could look
>    like here: https://pandoc.org/try/
>
> --
> You received this message because you are subscribed to the Google Groups
> "pandoc-discuss" group.
> To unsubscribe from this group and stop receiving emails from it, send an
> email to pandoc-discuss+unsubscribe-/JYPxA39Uh5TLH3MbocFF+G/Ez6ZCGd0@public.gmane.org
> To post to this group, send email to pandoc-discuss-/JYPxA39Uh5TLH3MbocFF+G/Ez6ZCGd0@public.gmane.org
> To view this discussion on the web visit
> https://groups.google.com/d/msgid/pandoc-discuss/29f97153-8af9-442b-8458-6bd5d219a4f8%40googlegroups.com
> <https://groups.google.com/d/msgid/pandoc-discuss/29f97153-8af9-442b-8458-6bd5d219a4f8%40googlegroups.com?utm_medium=email&utm_source=footer>
> .
> For more options, visit https://groups.google.com/d/optout.
>

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