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From: Peter Kelly <pmkelly@apache.org>
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Subject: Re: lenses
Date: Tue, 16 Jun 2015 00:00:39 +0700
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> On 15 Jun 2015, at 7:59 pm, Ian C <ian@amham.net> wrote:
>=20
> Hi Peter,
>=20
> I see in the word processing you use a series of structures with get =
and
> put function pointers (lenses ) to drill down - focus on  - particular
> parts of the document.
>=20
> Do you think we should replicate this for odf processing?
>=20
> I was thinking just of a series of functions to drill down but hadn't =
seen
> the funky lenses idea. I kind of like it but wonder as to whether it =
helps
> or obscures?

The design of the Word filter (and what I=E2=80=99d had in mind for =
other filters but had not gotten round to implementing) is based on the =
idea of bidirectional transformation, which is actually a whole field of =
research within the domain of programming languages. The best overview =
I=E2=80=99ve seen is this:

http://www.cis.upenn.edu/~bcpierce/papers/icmt-2009-slides.pdf =
<http://www.cis.upenn.edu/~bcpierce/papers/icmt-2009-slides.pdf>

There=E2=80=99s a lot of underlying theory here (and in other papers), =
which I=E2=80=99ve yet to fully explore myself, but currently the parts =
of the theory I=E2=80=99ve used are the notion of get/put/update =
operations. When I started out with the original version of the code (in =
Objective C), each lens was a class.

A key aspect of lenses (at least in other work that=E2=80=99s been done, =
not fully realised in the current DocFormats implementation) is their =
composability. That is, the notion of building up larger/more complex =
lenses out of smaller ones, combining them using different relations.

I=E2=80=99ve got a lot more to say on this topic, and I=E2=80=99ll =
outline this in a separate email as it=E2=80=99s a pretty long =
discussion.

=E2=80=94
Dr Peter M. Kelly
pmkelly@apache.org

PGP key: http://www.kellypmk.net/pgp-key =
<http://www.kellypmk.net/pgp-key>
(fingerprint 5435 6718 59F0 DD1F BFA0 5E46 2523 BAA1 44AE 2966)


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