Re: Type of the `filter' argument to traversal functions

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

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I wrote:

> why it is useful that a filter script can return an array of filters

That should obviously have been "must return"! Sorry for any confusion!

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Den ons 12 aug. 2020 10:19BPJ <melroch-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> skrev:

> I suppose that it might be worth pointing out that the reason why it is
> useful that a filter script can return an array of filters is explained
> here:
>
> https://pandoc.org/lua-filters.html#execution-order
>
> A note on terminology: Since "table" on its own is rather ambiguous in Lua may
> be a good idea to clarify what kind of data a it given table is supposed
> to contain by using the terms "array table" and "map table" and possibly
> "mixed table" for a table with both array and map data, which are sometimes
> convenient in Lua code, e.g. to tag an array.
>
> --
> Better --help|less than helpless
>
> Den ons 12 aug. 2020 02:27John MacFarlane <jgm-TVLZxgkOlNX2fBVCVOL8/A@public.gmane.org> skrev:
>
>> Anton Shepelev <anton.txt-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> writes:
>>
>> > John MacFarlane to Anton Shepelev:
>> >
>> >> > The  documentation to walk_block() and walk_fil-
>> >> > ter() states that the second parameter is "a Lua
>> >> > filter (table of functions) to be applied within
>> >> > the block element".
>> >> > [...]
>> >> > Is the documentation incorrect or do I misinter-
>> >> > pret  it?  For  aught I know, {Span = OnSpan} is
>> >> > not a "table of functions".
>> >>
>> >> { } makes a table.  OnSpan is a function.   So,  a
>> >> table of functions.
>> >
>> > Please,  bear with me. A table in Lua is the one-to-
>> > rule-them-all complex type, that can represent  many
>> > sturctures,  including  array, associative array, or
>> > structure.  On the other hand,  the  generally  used
>> > meaning of `table' in programming and mathematics is
>> > a two-dimensional sturcture  with  columns  and  any
>> > number of rows from zero up, which, too, can be rep-
>> > resented as a table in Lua, although it would  be  a
>> > compound one.
>>
>> I would have thought that in the context of documenting a Lua
>> function 'table' would be naturally interpreted as 'Lua table'.
>>
>> > But  since the parameter is described as "a Lua fil-
>> > ter" and "a table of functions", the only way to in-
>> > terpret it is as describing the structure of the Lua
>> > filter itself, which is a table of functions in both
>> > Lua and general terminology:
>> >
>> >                 { { Id1 = Func1 }
>> >                   { Id2 = Func2 }
>> >                   { Id3 = Func3 } }
>>
>> According to the docs, "Lua filters are tables with element names
>> as keys and values consisting of functions acting on those
>> elements." So yes, the parameter to walk_block is a Lua filter as
>> defined in the documentation.
>>
>> If you had
>>
>>   { { Id1 = Funct1,
>>       Id2 = Funct2 } }
>>
>> that would be an array of Lua filters. But now, I see where you
>> may be getting confused. Reading on in the docs: "Pandoc expects
>> each Lua file to return a list of filters. The filters in that
>> list are called sequentially, each on the result of the previous
>> filter." It may be confusing that one often uses the term
>> "lua filter" for the file itself. But the file can return
>> a list (technically an array, implemented as a Lua table) of
>> filters.  I suspect you are confusing an array of Lua filters --
>> which can be defined in a single Lua file -- with a Lua filter.
>>
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>> .
>>
>

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