Checking the type of an AST value?

Checking the type of an AST value?

[Axel Rauschmayer]

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My use case is similar to the following code (taken from pagebreak.lua in 
the example repository):

-- Turning paragraphs which contain nothing but a form feed
-- characters into line breaks.
function Para (el)
  if #el.content == 1 and el.content[1].text == '\f' then
    return newpage(FORMAT)
  end
end

Question: How do I check the type of an AST value? Here, it is done by 
checking whether the value has the field .text (implying an instance of 
pandoc.Str), but that doesn’t always work. A work-around would be to walk 
the value and set a flag to true if a handler is invoked. But I was hoping 
there is something simpler.

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Re: Checking the type of an AST value?

[BPJ]

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You can check `element.t` (tag) like `if 'Str' == element.t`. It contains a
string equal to the element type name. It is also the best way to check
whether a table is an asset element: if it isn't `table.t` is most likely
`nil`.

Den mån 13 maj 2019 06:50Axel Rauschmayer <rauschma-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> skrev:

> My use case is similar to the following code (taken from pagebreak.lua in
> the example repository):
>
> -- Turning paragraphs which contain nothing but a form feed
> -- characters into line breaks.
> function Para (el)
>   if #el.content == 1 and el.content[1].text == '\f' then
>     return newpage(FORMAT)
>   end
> end
>
> Question: How do I check the type of an AST value? Here, it is done by
> checking whether the value has the field .text (implying an instance of
> pandoc.Str), but that doesn’t always work. A work-around would be to walk
> the value and set a flag to true if a handler is invoked. But I was hoping
> there is something simpler.
>
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> .
> For more options, visit https://groups.google.com/d/optout.
>

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Re: Checking the type of an AST value?

[Axel Rauschmayer]

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Thanks! Works perfectly.

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