LISTSERV mailing list manager LISTSERV 16.0

Help for LATEX-L Archives


LATEX-L Archives

LATEX-L Archives


LATEX-L@LISTSERV.UNI-HEIDELBERG.DE


View:

Message:

[

First

|

Previous

|

Next

|

Last

]

By Topic:

[

First

|

Previous

|

Next

|

Last

]

By Author:

[

First

|

Previous

|

Next

|

Last

]

Font:

Monospaced Font

LISTSERV Archives

LISTSERV Archives

LATEX-L Home

LATEX-L Home

LATEX-L  January 2000

LATEX-L January 2000

Subject:

template interfaces and what they mean

From:

Frank Mittelbach <[log in to unmask]>

Reply-To:

Mailing list for the LaTeX3 project <[log in to unmask]>

Date:

Tue, 25 Jan 2000 14:42:38 +0100

Content-Type:

text/plain

Parts/Attachments:

Parts/Attachments

text/plain (163 lines)

part of Achim's reply to "templates for galley" tempted me to think about this
once more and offer some thoughts for discussion.

main point is i would like you to think about is, what are the invariants of
that interface, ie what can be assumed to be the same from one template to the
next (within a type) and what can differ.


Here is the extract from Achim's mail that triggered this:

 > o pshape template. Perhaps it would be a good idea to add two arguments
 > to the pshape template for the horizontal and vertical dimension
 > (where the exact meaning depends on the template). Say, a template
 > for a rectangular cutout could interpret the horizontal dimension
 > as width of the cotout and the vertical dimension as number of lines
 > to be indented.
 >
 > o justification template. I'm not quiet sure how the galley templates
 > are intented to be used -- the package only defines the templates
 > themselve no commands to use them. But I think that the justification
 > templates shouldn't be able to choose whether they affect all
 > paragraphs or only the next one. Instead the user should be able to
 > tell the system which case is desired everywhere such a template is
 > used.


to formulate those a bit more abstractly:

 1) how much freedom has a template to interpret its arguments (ie data passed
    to it from the document)?

 2) what is the scope a template instance apply itself? is it well-defined?

let's tackle 1) first. Achim suggests that the pshape type should get two
arguments those meaning should depend on the template. in my opinion this is
likely to result in chaos.

the main idea behind the template types is that logical structure of the
document, i.e., the commands and environments therein, are transformed into
instance calls of templates of certain types. this is defined via, say, an
xpare interface and does define the document class (no formatting yet)
structure.

now the task of the designer is to declare such instances (whose names are
fixed by the structural part above). He/she does that by declaring instances
using \DeclareInstance{<type>}{<name>}{<template>}... and specifying values
for the keys that belong to <template>.

and that should be enough to design a layout (just a lot of \DeclareInstance)
nothing more (we leave out the case that there isn't a suitable template for a
design looking like ... and just assume that such templates are all written)

so to make this work templates of the same type need to interpret data coming
from the document (ie via arguments) in the same way. At best I see that they
might be allowed to ignore it.

to give an example: in xhj i defined two templates of type measure which
change the measure of the galley. One of the templates does this relative to
the current measure in the template and another one does this by specify
absolute values in its keys. This type accepts an argument to overwrite the
left margin width. Now if one template would interpret a value coming from the
document as "add this to the left margin" and the other as "this is the left
margin width" then guess how exchangable those templates get!

as for allowing a template to ignore such values, again an example: suppose we
have a list template type which as one of its arguments gets the left
indentation of the list matter (or \NoValue if nothing was specified by the
user in the document). The intention is to allow a document syntax like:

  \begin{description}[foobar]

where the string "foobar" defines the width of the indentation (eg could be
the widest label), in latex2e thebibliography is in fact an environment that
is more or less of this type (except that the argument is not optional)

Now suppose you have a design where nested lists at a certain level are
formatted in a paragraph instead of making each item a separate paragraph. In
that case a notion of "left margin" is no longer appropriate. Now one could
argue that those two type of lists should not have the same list type, but I
think they should since otherwise how do I switch from one such layout to the
other for the same "document class" (ie document level syntax)

So allowing to ignore argument values is a weak form of acceptance which (in
most cases) allows to format a document in different layouts even if the
document does contain some elements with "formatting like" data.

Of course, another way to avoid this problem would be to disallow arguments to
templates which do carry "formatting related" information. But that one the
other hand would render the interface much less flexible and if it is too
clumsy for the user to guide the layout in certain comon cases that i think
something was done wrong.

To return to the pshape template: so I don't think it should get arguments
that are interpreted differently by different templates. In fact for that
particular template type I don't think it should get arguments at all.

I see this template as something (again) to be used only as part of other
templates to define very specialised shapes in certain layouts --- but shapes
which are independent of of document data but exist in their own right.

For example, I came recently across a very nicely formatted book whose Capter
openings have all be done by having the first paragraph with a triangle like
cutout that was part of the design for the chapter head. That's the kind of
area where I see applications for pshape.

In contrast, if one wants to provide commands that allow the user to directly
manipulate the paragraph shape somehow (one example in a restricted sense
being Initials) then this should not be done via the templates provided in xhj
but by making use of the lower-level interface that comes with galley2.dtx

the module xinitials will do something like that

===================================================================

do you remember what the second abstract question was? No? Here is another
rephrase:

  to what elements should templates apply that do set parameters of underlying
  algorithms (in some way or other)

for example the "std" template of type justification sets the justification
for all upcoming paragraphs of the galley (potentially at least) while the
"single" template sets it only for the next. Achim suggested that not the
template but the user should decide on the scope.

Now I agree with him but who is the "user"? The user is the designer of the
document class layout and if this "user" says that the first paragraph of a
caption should have the first line centered and any following paragraphs
should be justified without indentation then he can do this now by setting a

 justification-setup =i

key to the appropriate value. by making the (i agree) somewhat different
feeling templates one and the same type I allowed for flexibility in
design. In an earlier implementation I had two types but that resulted in
either strange templates (making use of both) or in a lot of repitition, ie
the need to have nearly identical templates differing only in one key since
that key was of a different type.

another way to look at it is to say that the "single" one is actually also
setting all paragraphs in the galley (it sets the first to X and the rest to
whatever was before X).

yet another way is to get rid of "single" and implement what i called
"complex" differently since what in practise will be needed are the instances
from "std" and from "complex"

does this make some sense?

------------------------------

a related question is whether it is permissable for templates to do inheriting
of values while other templates of the same type do set all values. I think i
should be permissable for the sake of flexibility, however, it is a fact that
this makes looking at a design implementation (ie at a list of
\DeclareInstance commands) a bit diffcult if not used with care.
After all you may have difficulties to guess what is actually gonna be used if
such template instances then follow each other.

comments?


frank

Top of Message | Previous Page | Permalink

Advanced Options


Options

Log In

Log In

Get Password

Get Password


Search Archives

Search Archives


Subscribe or Unsubscribe

Subscribe or Unsubscribe


Archives

September 2019
July 2019
April 2019
March 2019
February 2019
January 2019
December 2018
November 2018
October 2018
September 2018
August 2018
June 2018
May 2018
April 2018
February 2018
January 2018
December 2017
September 2017
August 2017
July 2017
June 2017
May 2017
April 2017
March 2017
February 2017
January 2017
December 2016
July 2016
April 2016
March 2016
February 2016
January 2016
October 2015
September 2015
August 2015
July 2015
June 2015
May 2015
April 2015
March 2015
February 2015
January 2015
December 2014
November 2014
October 2014
September 2014
August 2014
July 2014
June 2014
May 2014
April 2014
March 2014
February 2014
January 2014
December 2013
November 2013
October 2013
August 2013
July 2013
June 2013
May 2013
April 2013
March 2013
February 2013
January 2013
December 2012
November 2012
September 2012
August 2012
July 2012
June 2012
May 2012
March 2012
February 2012
January 2012
December 2011
November 2011
October 2011
September 2011
August 2011
July 2011
June 2011
May 2011
April 2011
March 2011
February 2011
January 2011
December 2010
November 2010
October 2010
September 2010
August 2010
July 2010
June 2010
May 2010
March 2010
February 2010
January 2010
December 2009
November 2009
October 2009
September 2009
August 2009
July 2009
June 2009
May 2009
April 2009
March 2009
February 2009
January 2009
December 2008
November 2008
October 2008
September 2008
May 2008
April 2008
March 2008
February 2008
January 2008
December 2007
November 2007
September 2007
August 2007
June 2007
May 2007
March 2007
December 2006
November 2006
October 2006
August 2006
July 2006
June 2006
May 2006
April 2006
March 2006
February 2006
November 2005
October 2005
September 2005
August 2005
May 2005
April 2005
March 2005
November 2004
October 2004
August 2004
July 2004
May 2004
April 2004
March 2004
February 2004
January 2004
December 2003
October 2003
August 2003
July 2003
June 2003
May 2003
April 2003
March 2003
February 2003
January 2003
December 2002
October 2002
September 2002
August 2002
July 2002
June 2002
March 2002
December 2001
October 2001
September 2001
August 2001
July 2001
June 2001
May 2001
April 2001
March 2001
February 2001
January 2001
December 2000
November 2000
October 2000
September 2000
August 2000
July 2000
May 2000
April 2000
March 2000
February 2000
January 2000
December 1999
November 1999
October 1999
September 1999
August 1999
May 1999
April 1999
March 1999
February 1999
January 1999
December 1998
November 1998
October 1998
September 1998
August 1998
July 1998
June 1998
May 1998
April 1998
March 1998
February 1998
January 1998
December 1997
November 1997
October 1997
September 1997
August 1997
July 1997
June 1997
May 1997
April 1997
March 1997
February 1997
January 1997
December 1996

ATOM RSS1 RSS2



LISTSERV.UNI-HEIDELBERG.DE

Universität Heidelberg | Impressum | Datenschutzerklärung

CataList Email List Search Powered by the LISTSERV Email List Manager