Re: Towards (better) Python filters for Pandoc with fluent queries

[Mark Szepieniec <mszepien-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>]

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Just from a first glance, wouldn't it be handy to be able to do

m = Matcher()
    ...

and then

if m.matches(block):
    ...

This way you could reuse Matchers easily?

More generally, this does seem like a significant improvement relative to
the current python workflow.

On Fri, Jan 2, 2015 at 7:58 AM, Elliott Slaughter <
elliottslaughter-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> wrote:

> I like being able to script Pandoc via filters in Python, but one of the
> major drawbacks of the approach as it currently stands is that Python has
> no pattern matching to speak of. As a result, code that needs to run
> queries of the structure of Pandoc documents quickly turns into a
> nightmare, especially if that code needs to check nested structures.
>
> Consider the following partial function in Haskell, which matches against
> a BlockQuote containing a Para where the first word is "Chapter" in small
> caps:
>
>     filter :: Block -> Block
>     filter (BlockQuote [Para (SmallCaps [Str "Chapter"]):_]) = ...
>
> Without pattern matching, the equivalent code in Python is painful to
> write, opaque, and quite brittle. Unfortunately, without support for
> pattern matching, there is no possibility of a direct analogue in Python.
> Instead, I propose a fluent interface
> <https://en.wikipedia.org/wiki/Fluent_interface> as a way to provide a
> query language of sorts for Python. So for example, the same query might
> look like:
>
>     m = Matcher(block).
>             BlockQuote(length = 1)[0].
>             Para(length = -1)[0].
>             SmallCaps(length = 1)[0].
>             Str(content = 'Chapter')
>     if m.matches():
>         ...
>
> The code is not quite as dense because I've split it out for legibility,
> but can be condensed better to fit on a single line if desired. It is at
> any rate a massive improvement over hand-written queries over the JSON
> structure of the document.
>
> A proof of concept library is available today, and has been demonstrated
> with the query above as well as other queries I have needed in my own
> projects. Current coverage of the Pandoc API is at around 50%. The code is
> made available under an MIT license:
>
> https://bitbucket.org/elliottslaughter/pandocpatterns
>
> I would greatly appreciate any thoughts or feedback on the concept,
> design, or implementation. Please feel free to take the code out for a test
> drive and kick the tires. If there is interest, I would be willing to
> invest the effort to improve the library and make it more robust and useful.
>
> Thank you for your time.
>
>
> --
> Elliott Slaughter
>
> "Don't worry about what anybody else is going to do. The best way to
> predict the future is to invent it." - Alan Kay
>
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