Re: Idea: Support for centred block-level elements, without necessarily needing to revise pandoc

[Gordon Steemson <gsteemso-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>]

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I actually tried that already. Since I have a custom writer, I just needed
to have Blockquote() emit <CENTER> instead of <BLOCKQUOTE> tags. Alas, in
addition to the crippled formats I described earlier, I also publish to
real HTML and actually do need real block quotes as well, so I think the
“-> markup <-” and filtering option is my best bet.

Thank you for explaining about the --filter option. I had somehow managed
to not see that despite repeatedly scanning through the documentation.

On Sunday, 1 February 2015, John MacFarlane <jgm-TVLZxgkOlNX2fBVCVOL8/A@public.gmane.org> wrote:

> I think for your purposes (if you don't need blockquotes for another
> purpose, which sounds like the case), you could just write a filter that
> converts blockquotes to HTML center elements.
>
> You can write the filter in Haskell or in python, perl, or a number of
> other languages with pandoc filter libraries.
>
> In Haskell it would look something like
>
> ``` haskell
> #!/usr/bin/env runhaskell
> import Text.Pandoc.JSON
>
> main = toJSONFilter bqToCenter
>  where bqToCenter (Just (Format "html")) (BlockQuote bs) =
>          RawBlock (Format "html") "<center>" :
>          bs ++ [RawBlock (Format "html") "</center>"
>        bqToCenter x = [x]
> ```
>
> (untested).  See the pandocfilters library in PyPI for many examples
> using the python library, if that's what you prefer.
>
> To invoke your filter (assuming it's executable and called bqToCenter.hs):
>
>    pandoc --filter ./bqToCenter.hs etc.
>
>
> +++ Gordon Steemson [Feb 01 15 00:14 ]:
>
>> Well, it still seems straightforward enough. These days Unicode is
>> available. If someone wants a literal arrow in those positions they can
>> use
>> a dash other than an ASCII hyphen-minus, or use an angle bracket other
>> than
>> an ASCII less-than / greater-than, or just break down and use a Unicode
>> arrow character directly (several exist to choose from).
>>
>> I agree with you that centred or right alignment are presentational things
>> (unless you’re trying to write Arabic or Hebrew, in which case left
>> alignment is), but I strongly believe that being able to centre something
>> on the page is nevertheless important to conveying meaning in certain
>> narrow use cases, in the same way as a hard line break is within a postal
>> address. I am attempting to use Pandoc to publish my mediocre attempts at
>> fiction to various online repositories, and in examining the results of my
>> past (pre-Pandoc) efforts, I have come to the conclusion that there is a
>> marked difference in effect when some important bit of information is
>> placed in the middle of the page, versus as just an unusually short
>> paragraph clustered at the left edge with all the others.
>>
>> I approve in principle of your proposed solution (“just use a ‹div›
>> element
>> and style it with CSS”); unfortunately, several of the submission formats
>> I
>> am forced to conform to are extremely crippled, and do not support either
>> of those features of HTML. Rephrasing them as some other feature is far
>> from simple from within the Lua custom writer.
>>
>> Short of outputting to a native Haskell representation file, piping that
>> to
>> a filter program, and piping that result back through a second invocation
>> of Pandoc, is there any way of invoking a transformational filter on the
>> native AST as it is being processed? I keep seeing various language
>> bindings (Perl, Python, PHP, etc.) that appear to be for doing just that,
>> but I can’t find any mention of how you actually invoke a filter written
>> to
>> use one of them when you start the Pandoc tool.
>>
>> On Saturday, 31 January 2015 22:45:48 UTC-8, John MacFarlane wrote:
>>
>>>
>>> +++ Gordon Steemson [Jan 31 15 18:25 ]:
>>> >1) If someone, just to be difficult, needs to have literal ASCII arrows
>>> at
>>> >the start and/or end of their actual output text block, can it be
>>> >accommodated in a simple way by backslash-escaping? At what stage does
>>> that
>>> >get stripped out — before the custom writer functions get called or
>>> after?
>>>
>>> Before.  The escaping is resolved in the parser.
>>>
>>>
>>
>>  2) What would be involved in modifying the Pandoc markdown parser to
>>> >recognize the obvious extension to this syntax, demonstrated below?
>>>
>>> Well, it would be quite involved.  We'd need to modify the Pandoc
>>> document model to add these alignment containers (though I suppose
>>> we could use Div elements with special classes), then modify the
>>> Markdown parser and all the writers.
>>>
>>> Centering has come up before on this list (you can search for earlier
>>> discussions).  My general feeling is that pandoc should focus on
>>> structural elements of documents, and things like centering and
>>> right-aligning are too presentational.
>>>
>>> Note you can always put things in divs with classes, and format them
>>> with CSS in HTML or with a simple filter in other formats.
>>>
>>>
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