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+%November 1994, Aug 1995, March 1996
+%Paradigm: Headache?
+%C.G. van der Laan, cgl@rc.service.rug.nl
+\input blue.tex  \loadtocmacros
+\tolerance500\hbadness=499\hfuzz=5pt
+\parindent=1pc
+\everyverbatim{\emc}
+ 
+\bluetitle Paradigms: Headache?
+                            
+\blueissue \maps{94}2 (revision March\on1996)
+
+\beginscript
+
+\bluehead BLUe's Design II
+
+Hi folks. When using \LaTeX{} 
+I was plagued in the past by the little glob of white space
+on the first line after a head.
+It made me clear that `spaces are harmful,' to paraphrase Dijkstra.
+When designing \bluetex{} I had to look at the problem again 
+among other things, and to 
+\bitem provide a simple suite, with hardly no knowledge of the user
+       assumed about parameter separators  
+\bitem gobble redundant spaces as much as possible
+\bitem allow also processing on the fly of the title
+\bitem choose a coding style, and
+\bitem choose a `markup language.'
+\smallbreak
+
+My starting point was \cs{beginsection}  \TB~\on355.
+I chose |head|  as root name conform to TUGboat.
+
+\bluesubhead The revision
+
+is about the superfluousness of the \#
+as last element of a parameter specification,
+from a functional point of view.
+
+The treatment of \cs{chapterhead} from BLUe's Reports
+has been appended of August \on1995. 
+
+A quick and dirty LP functionality to exhibit a ToC
+has been added of August \on1995. 
+This ToC is not meant to be published but just 
+   to assist developing notes, 
+   to keep track of the structure, the setup,
+which\Dash as reality taught me\Dash
+develops too while writing.
+
+Really handy, believe me\winksmiley. 
+
+\bluehead Headers
+
+I will design \cs{beginhead}  and \cs{endhead},
+next to the minimal markup variant |\head{ ...}|.\ftn
+{The subhead variants are similar but different in detail.
+ Especially in undoing  glue when heads follow-up
+ each other without intervening text. Beware!}
+
+\bluesubhead Design goals
+
+From a typography point of view I would like to
+\bitem discourage to  set the title alone at the end of a page
+\bitem typeset (flexible) vertical space (big) before and after (med) the title
+\bitem gobble spaces at the beginning of the title
+\bitem set the title in bold face (and the current size) unindented
+\bitem don't indent the first line of the text after.
+\smallbreak
+
+\bluesubhead What are the problems?
+
+The markup language constructs have to be chosen. 
+In macro expansion the two-part macro 
+\TeX nique should be the basis. In blue's format I adopted 
+the pairs |\begin<tag>| and |\end<tag>|.
+
+In order to set the title loose from the context
+we have to determine values for the glue,
+and be sure that it disappears at the top of a page.
+The coding solution below has different values for the 
+parameters as supplied in \cs{beginsection}.
+From experiments it turned out that the values supplied by Knuth 
+don't give nice results with blue.fmt. 
+Too much glue was inserted for my taste.
+
+Another problem is to prevent the head title 
+to be printed at the bottom of a page on its own. 
+The latter is related to the `widow-orphan' phenomenon. 
+
+The coding of the minimal markup variant without parsing
+but with processing of the fly of
+`the argument' has to be resolved in some elegant way.
+
+The idea of a |\pre<tag>| and |\post<tag>| is  general.
+It parameterizes the placement of a document element
+within context. Important! Whether you talk about titles,
+displays, tables, graphs, or you name it. Perhaps
+this should be generalized in something like
+|\pasteup<tag>|.
+ 
+\beginverbatim
+\def\beginhead{\the\prehead\bgroup\headfont}
+\def\endhead{\egroup\the\posthead}
+%with auxiliaries
+\prehead{\vskip0pt plus2ex
+   \penalty-250\vskip0pt plus1ex
+   \bigskip\noindent}
+\posthead{\medskip\nobreak
+   \noindent\ignorewhitespace}%Mod Nov 94
+!endverbatim
+
+\bluesubhead Take a deep breath
+
+The minimal markup form, {\em with the same functionality}, reads
+
+\beginverbatim
+\def\head{\beginhead\bgroup
+   \aftergroup\endhead
+   \afterassignment\ignorespaces
+   \let\dummy=}
+!endverbatim
+
+Explanation.
+The replacement text starts \cs{beginhead} and a group.
+Immediately after the opening of the group \cs{aftergroup}
+takes care that the second part of the two-part macro will be invoked
+at the right place. 
+The opening brace after the invocation of \cs{head}
+is read away by assigning it to \cs{dummy}.
+Spaces after the opening brace are ignored, due to
+\cs{afterassignment}\cs{ignorespaces}. 
+The \TeX nique---moving the group opening---has been 
+borrowed from plain's \cs{footnote}, \TB~\on363. 
+There it is used at the end of the replacement text of \cs{fo@t}.
+\beginquote
+What is the difference with the macro with a \# as last element of the 
+parameter specification?\ftn
+{The \# as last character of the parameter text makes that
+ the opening brace and what follows
+ is placed after the replacement text of \cs{head}, \TB~\on204.}
+\endquote
+At first sight it looks identical. However, the difference is twofold.
+The situation with the \# at the end of the parameter text differs 
+because
+\bitem an opening brace after the invocation of \cs{head} is syntactically required 
+\bitem no braces are needed for the last argument, because $\{$ is
+       a parameter separator.\ftn{The example, \TB~\on204, 
+ used the invocation
+ |\a3pt{x}|, while without \# as last element of the parameter list
+ the markup would have read |\a{3pt}{x}|.} 
+\smallbreak
+
+Because of these extra safeguards, 
+I stayed with the \# as end of the parameter list,
+for building one-part macros on top of two-part macros.
+Quite something isn't it?
+
+\bluesubhead Paradigm
+
+We should build upon two-part macros.
+In order to add the short variant to {\em similar\/} two-part
+macros the following template can be used.
+
+\beginverbatim
+\def\<tag>#{\begin<tag>\bgroup
+   \aftergroup\end<tag>
+   \afterassignment\ignorespaces
+   \let\dummy=}
+!endverbatim
+
+\bluesubhead Take a deeper breath
+
+When using the above template in practice, 
+it occurred to me that \TeX{} could handle that too.
+For \cs{head} the desired functionality is that
+
+\beginverbatim 
+\onepartmacro{head}
+!endverbatim
+
+will build the macro \cs{head} based upon 
+the two-part macros \cs{beginhead} and \cs{endhead}.
+
+The naive coding\Dash which does not work, but makes 
+the purpose quite clear\Dash reads
+
+\beginverbatim
+\def\onepartmacro#1{\def\#1##{\begin#1
+   \bgroup\aftergroup\end#1
+   \afterassignment\ignorespaces
+   \let\dummy=}}
+!endverbatim
+
+Several desired functionalities have to be coded 
+in \TeX's peculiar way, with as result
+
+\beginverbatim
+\def\onepartmacro#1{{
+\ea\let\csname begin#1\endcsname=\relax
+\ea\let\csname end#1\endcsname=\relax
+\toks0={\bgroup\aftergroup}
+\toks1={\afterassignment\ignorespaces
+        \let\dummy=}
+\ea\xdef\csname#1\endcsname##{%
+  \csname begin#1\endcsname
+  \the\toks0 \csname end#1\endcsname
+  \the\toks1 }}}
+!endverbatim
+
+Explanation. 
+A lot of the trickery about partial expansion, \TB~\on216, has been applied.
+
+First a \cs{csname} is used to compose the names from the root name. 
+
+Second the one-part macro is defined via an \cs{xdef}
+with suppression of  the expansion of the 
+|\begin<name>|, |\end<name>|, and the other tags.
+It is an \cs{xdef}  to keep the auxiliaries used local.
+The first is handled via the property that a control sequence
+equal to a character, and in general to an unexpandable token, is not expanded.
+The second is handled by the property that a \cs{the}
+on a token list is a one-step expansion.
+
+\bluesubhead Some remarks
+
+Note that I did not gobble spaces at the end of the title argument. 
+In the headtitle they won't harm because
+the title is set on a line of its own.\ftn
+{In the other heads the space at the end of the argument can be there on purpose.
+  Watch out!}
+
+Processing a title on the fly is needed for verbatims
+and in general when we don't like the `eyes' of \TeX{}
+to set catcodes differently from those the script expects
+when digested in the `stomach.' 
+
+\bluesubsubhead The bad news
+
+Minimal markup for \cs{head} and the like can be
+felt as an anachronism.
+With \AllTeX{} intelligent editors we don't need minimal markup anymore.
+
+\bluesubsubhead Disclaimer
+
+The above template does not work for all two-part macros,
+for example not for my btable (or any \cs{halign}).\ftn
+{See however, `Paradigms: Two-part macros.'}
+ 
+\bluesubsubhead The good news
+
+Via this mechanism we can abstract
+at the {\em user level\/} from token variables and definitions. 
+The user can supply the information as if it was a token variable. 
+The using of the long form or the minimal form has been reduced
+to a matter of taste. And that is a good thing.
+
+\def\head{\beginhead\bgroup
+   \aftergroup\endhead
+   \let\dummy=}
+
+\bluehead Tests?
+
+This note itself contains examples of use in its original form.
+
+\thisverbatim{\catcode`\|=12 }
+\beginverbatim 
+\beginhead|Head text 
+           in verbatim|\endhead
+   Text after\\next line
+
+\head{Head text, with |this| 
+      in verbatim}
+   Text after\\next line
+!endverbatim
+
+ with results
+\medskip
+\beginlines
+\kern-\medskipamount
+
+\beginhead|Head text in verbatim|\endhead
+%\head{{\tt Head text in verbatim}}
+   Text after\\next line
+
+\head{Head text, with |this| in verbatim}
+   Text after\\next line
+\medskip
+\endlines
+\medbreak
+Run it,\ftn{blue.tex is available form the CTAN,
+   as is the accompanying article BLUe's Format.}
+and have fun. All the best.
+
+\bluehead Note added in proof
+
+In order to allow blank lines after the heading in the script, 
+I replaced \cs{ignorespaces} in \cs{endhead} by  
+\cs{ignorewhitespace}.\ftn{Due to Phil Taylor. 
+  TUG's \cs{ignorespacesandpars} would probably do too.}
+
+A blank line after a heading is natural for a text without explicit markup.
+Knuth started from natural markup and stayed close to that, IMHO. 
+His markup tags to format the chapter (titles and contents) in \TB{}
+file are
+
+\beginverbatim
+\beginchapter
+\endchapter
+!endverbatim
+
+Imagine ASCII text with visual layout, and in order to markup
+the title {\em and text\/} insert the above commands, with the natural
+blank line already there to end the arguments of \cs{beginchapter}.
+Knuth's \cs{beginchapter} not only takes care of the title but also
+handles the chapter contents {\em on the fly\/} until \cs{endchapter}
+is encountered. 
+Really much different from \LaTeX's approach, to name but
+one general set of markup tags.
+
+\bluesubhead Knuth and natural markup
+
+Imagine that the ASCII text of a section reads
+\beginverbatim
+Section 1. Title
+
+Now starts the section text 
+proper...
+And this is the last line of it.
+!endverbatim
+
+What is the simplest and most natural markup for this?
+First the requirements
+\bitem section should be flexible towards language variation
+\bitem title should be processed on the fly.
+\smallbreak
+
+A solution is the following extension heavily inspired by
+\cs{beginchapter} of manmac.
+
+\beginverbatim
+\def\beginsection#1 #2#3. {\bgroup
+   \def\par{\egroup\endhead}%
+   \beginhead#1 #2#3. }
+\posthead{\nobreak\medskip
+   \noindent\ignorewhitespace}
+%
+\let\endsection\relax%or forget about it
+%
+\def\ignorewhitespace{\begingroup
+%Due to Phil Taylor EuroTeX 94
+\catcode`\ =9
+\catcode`\^^I=9
+\catcode`\^^L=9
+\catcode`\^^M=9
+\futurelet\dummy\endgroup}
+!endverbatim
+
+The marked up script is obtained by only inserting \cs{beginsection}!
+
+\beginverbatim
+\beginsection Section 1. Title
+
+Now starts the section text 
+proper...
+And this is the last line of it.
+!endverbatim
+
+The beauty of the above approach, Knuth's IMHO, is that the total section 
+is handled, the title as well as the contents part, with the title
+proper part processed on the fly. 
+Moreover, it is as close to natural markup as I can think of.
+(trivial) Language problems are absent. 
+One can abstract from `Section' via a toks variable \cs{sectionname}.
+Automatic numbering can be inserted too, but the question is
+whether it is really handy, especially in view of subsections and the
+like.
+
+\bluehead Copied from BLUe's Report
+
+In BLUe's Report I have dealt with more complicate header matters, 
+which show up when we like to reuse the title for inclusion in
+the ToC, ToE and ilks. It turns out that `\cs{bluechapter}'
+is much more complicated than `\cs{bluehead}.' 
+Below the storing of titles and their reuse is dealt with among other things.
+Because of storing\Dash which fixes the catcodes\Dash
+the titles are not processed on the fly.
+
+\bluesubhead Chapter head matters
+
+The required functionalities\Dash the specs so to say\Dash are to
+\bitem start a new page
+\bitem store the title for reuse (running head, table of contents)
+\bitem maintain and store the chapter counter (for use with the exercises,
+        table of contents, and the like)
+\bitem write the title and title counter value to the contents file
+\bitem typeset the title on a new page with some white space after
+\bitem reset counters which start anew per chapter (headings, exercise number,
+       and the like)
+\bitem provide the right \cs{headline} and \cs{footline} with the title,
+       chapter title, and page number
+\bitem suppress the headline on the first page of a chapter (or supply for
+       an otherwise special headline)
+\bitem process the title on the fily to allow for example verbatim
+\bitem condition the writing of the title and title counter value 
+       to the examples file.
+\smallbreak
+
+Quite something, isn't? 
+That is why title matters are not trivial.
+The conditioning of writing the title to the examples file is there,
+because we don't like the title etc. to appear in that file if the chapter
+lacks examples.
+
+\beginverbatim
+\def\beginchapterhead{\the\prechapterhead
+  \storechaptertitle}
+%
+\def\storechaptertitle#1\endchapterhead{%
+   \global\chaptertitle={#1}\endchapterhead}
+%
+\def\endchapterhead{\centerline{\chapterfont
+   \the\chapternumbering\the\chaptertitle}
+   \the\postchapterhead\ignorewhitespace}
+!endverbatim
+
+This approach looks promising.
+What has to be done before is the concern of \cs{prechapterhead}.
+\cs{storechaptertitle} does what its name suggests.
+The formatting of the number of the chapter is the concern 
+of \cs{chapternumbering}.
+\cs{postchapterhead} takes care of leftovers.
+Default \cs{chapternumbering} is empty, that is, no number will be typeset.
+
+Undoubtedly, the careful reader would object that the title is stored
+and that the catcodes are set  before processing.
+That is right, of course, but via \cs{everychapterhead}\Dash in 
+\cs{prechapterhead}\Dash 
+we can guarantee that symbols will have the right catcodes.
+\cs{storechaptertitle} is there to allow the short variant
+|\chapterhead{...}|.
+The combination of storing and in-line verbatim does not work. Beware.\ftn
+{For me this does not hinder because I don't like these kinds of font changes
+ in a chapter header.}
+
+\beginverbatim
+\prechapterhead{\newpage\null\vskip4pc
+   \bgroup\catcode`\^=7 
+   \the\everychapterhead\the\thischapterhead 
+   \global\advance\chaptercnt1 }
+%
+\postchapterhead{\egroup
+   \headcnt0 \exercisecnt0 \examplecnt0 
+   \write\toc{\nx\separator
+      {\alfanum\the\chaptercnt}
+      {\the\chaptertitle}}
+   %suppress headline first page chapter
+   \headline{\global\headline
+    {\hbox to\pagewd
+     {\sl\the\chaptertitle\hfill
+                    \the\title}}}%
+   \footline{\hbox to\pagewd{\small
+     \rlap{Draft \today}\hfill\dash
+    {\oldstyle\the\pagenumber}\dash
+     \hfill\llap{\copyright
+                 \the\crowner}}}%
+%Example is redefined here such that on 
+%first use if ever in the chapter, it 
+%redefines itself into the regular macro, 
+%while writing the chapter titles to the 
+%table-of-examples, ToE, file.
+%In this way chapter titles of chapters 
+%without examples will not be written to
+%the ToE. 
+   \def\example{\write\toe{\nx\separator
+       {\alfanum\the\chaptercnt}
+       {\the\chaptertitle}}
+      \let\example\regularexample
+      \example}
+   \thischapterhead{}\vskip3pc}
+!endverbatim
+
+The material is enclosed within a group to keep the effect
+of \cs{thischapter} local.
+
+\cs{example} is defined such that only when it is used
+the title and number of the chapter will be written to the file
+associated with \cs{toe}. \cs{regularexample} writes the example title
+and number to the file associated with \cs{toe}.
+
+Intriguing is \cs{alfanum}. The purpose is to control whether a number
+or a letter should appear. This is particularly useful with appendices.
+\beginverbatim
+\def\setupappendices{\thischapterhead=
+   {\chaptercnt64 \gdef\alfanum{\char}%
+    \global\chapternumbering=
+    {\alfanum\the\chaptercnt: }}}
+!endverbatim
+
+And what about the one-part macro on top?
+The above was already complicated. 
+What is the problem for a one-part macro?
+For most of the cases we can do with a simple variant. 
+However, when we like to process math, especially the circumflex,
+as part of the title more work has to be done. The mechanism has been 
+explained in `Paradigm: Two-part macros.'
+
+\beginverbatim
+\def\chapterhead{\bgroup
+   \def\storechaptertitle##1{\egroup
+     \global\chaptertitle{##1}%
+     \endchapterhead}\beginchapterhead}
+!endverbatim
+
+As a tribute to manmac I also defined the following limited variant.\ftn
+{The circumflex in math in the title will hiccup. Most of the time we
+ don't need that.}
+
+\beginverbatim
+\def\bluechapter#1\par{\beginchapterhead
+   #1\unskip\endchapterhead}
+!endverbatim
+
+A trivial user interface on top which counteracts the curly braces mania
+at the expense of processing on the fly.\ftn
+{What does on-the-fly mean anyway, when we have to store the title for multiple use?
+ The answer is that we would like to allow for math too. No verbatims however.}
+
+\bluehead A little LP functionality
+
+Of late with notes I needed to generate automatically a small rudimentary
+ToC to assist my writing and developing notes. Just quick and dirty.
+For that purpose I provided the following for the |\blue(sub(sub))head|-s.\ftn
+{Be aware that these head titles are not processed on the fly.
+ In March \on1996 I replaced writing to a file by maintaing the toc in a toks variable,
+ because in general it is not a mouth-only process the writing can go astray.
+ It did with |$\longrightarrow$|. Actually, for this toc assitant I did not need 
+ the output functionality of adding page numbers.}
+
+\beginverbatim
+\newtoks\tocvar
+\let\bh\bluehead
+\long\def\bluehead#1\par{\bh#1\par
+\tocvar\ea{\the\tocvar\par#1}}
+\let\bsh\bluesubhead
+\long\def\bluesubhead#1\par{\bsh#1\par
+\tocvar\ea{\the\tocvar\par\quad#1}}
+\let\bssh\bluesubsubhead
+\long\def\bluesubsubhead#1\par{\bssh#1\par
+\tocvar\ea{\the\tocvar\par\qquad#1}}
+\let\be\blueexample
+\long\def\blueexample#1\par{\be#1\par
+\tocvar\ea{\the\tocvar\par\qquad ex: #1}}
+!endverbatim
+
+For pasting up the ToC I supplied.
+\beginverbatim
+\long\def\pasteuptoc{\newcol
+   \bluehead Contents\par
+   \the\tocvar
+   \let\makesignature\relax}
+!endverbatim
+
+Finally, I merged the above into BLUe's format system. 
+The toks storage allocation for \cs{tocvar}
+and \cs{loadtocmacros} in blue.tex, and 
+the rest in tools.dat.
+
+The user can supply 
+\cs{loadtocmacros} at the beginning after |\input blue.tex|, and
+\cs{pasteuptoc} just before \cs{endscript}.
+
+In this way these macros don't conflict, just an extra
+to support your notes with a ToC at the end, to maintain 
+the overview.\ftn{Note that \cs{report} already provides for a ToC.}
+
+\bluehead Acknowledgements
+
+Phil Taylor is kindly acknowledged for his \cs{ignorewhitespace}
+as generalization of \cs{ignorespaces}, and his suggestion to assign 
+\cs{relax} to tokens to inhibit expansion instead of a number.
+The latter is done on \TB~\on216.
+
+Have fun, and all the best.
+\makesignature
+\pasteuptoc
+\endscript
\ No newline at end of file