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

[Anton Shepelev <anton.txt-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>]

EBkysko:

> From the Lua filter page:
>
> > Lua  filters  are  tables  with element names as
> > keys and values consisting of  functions  acting
> > on those elements.
>
>
> `{Span  =  OnSpan}`  is a table in which `Span` is
> the key, `OnSpan` is the value, a function  acting
> on `Span` element.

OK.

> You  could  put  more key-values in the filter you
> send for a that walk_block:
>
> `{ Span = OnSpan, BulletList = MyBulletList, Para = HerPara }`
>
> which is a table of functions, each function being
> key-value  "indexed"  so  to say by a key which is
> necessarily one Pandoc element. This would  be  an
> example of a filter containing more than one func-
> tion.

Thank you for the explanation, I was wrong.

> Independently of pandoc, `{ Id1  =  Func1,  Id2  =
> Func2,  Id3 = Func3 }`, to take your last example,
> is a table of functions, each accessible by  their
> respective key.

No, it is not my example. My example was an array of
tables:
                { { Id1 = Func1 }
                  { Id2 = Func2 }
                  { Id3 = Func3 } }

A Lua filter is such an array of tables, whereas the
`filter' argument to the `walk_' functions is a sin-
gle table as in your examples above. They  are  dif-
ferent  and  incompatible stuctures. The entire .lua
script must return the one whereas the `walk_'  fun-
cions accept the other.

For examle, when a filter end with:

   return { Header=OnHeader }

it does not work. But when it ends with

   return { { Header=OnHeader } }

it  works.  This  is  the difference between the two
structures.