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% F W L W . S T Y ( First Word, Last Word )
%
% Donald Arseneau (1993, 1995)
%
% The fwlw package provides a mechanism to determine the first and
% last words on the current page, plus the first word on the *next*
% page. These can be used in head-lines or foot-lines. The `words'
% you see may not be real words, but any unbreakable object.
%
% Two pagestyles are defined to print these words: \pagestyle{NextWordFoot}
% which helps you read ahead to the word on the next page; and \pagestyle
% {fwlwhead} which is like the headers in a lexicon. Or you can use the
% words in your own page-style. The words are made available in the box
% registers:
% \FirstWordBox - first word on this page
% \NextWordBox - first word on next page
% \LastWordBox - last word on this page
% Use them in your header lines like: \usebox\LastWordBox.
%
% Such labelling does not make much sense when \chapter generates a page
% break, so the last page before a \chapter (or any \clearpage) gets
% a blank "next word", and the first page of the chapter gets a blank
% "first word".
%
% Note that `words' may unfortunately be things like:
% - two~words
% - [ ]Word ( [ ] represents a parindent box)
% - a whole displayed equation
% - the first column of an aligned equation
% - anomalously blank, if there are \writes or split footnotes etc.
% - partial words like par- or -tial due to hyphenation.
%
% (Major digression...)
% An entirely different approach is possible using \mark and \obeyspaces,
% and would have different problems. The problems with catcode changes
% may be more or less serious for your particular application. (You are
% invited to write a package using that method!) The best solution would
% involve \mark and an input filter program to
% `\w{tag} \w{each} \w{word}, \w{in} \w{some} \w{way}.'
% TeX has no \everyword hook to insert such tagging.
%
% Copyright (C) 1993,1995 by Donald Arseneau
% Vancouver, Canada, email asnd@triumf.ca
% This software package may be freely used, transmitted, reproduced,
% or modified provided that this notice is left intact.
%
% Declare a "unique" penalty value as flag
\mathchardef\LW@pen 12345
% allocate box registers
\newbox\FirstWordBox \global\setbox\FirstWordBox\hbox{}
\newbox\NextWordBox \global\setbox\NextWordBox\hbox{}
\newbox\LastWordBox \global\setbox\LastWordBox\hbox{}
\newbox\LW@box \global\setbox\LW@box\hbox{}
\newbox\LW@saved
% pagestyle fwlwhead: header line hsa first word and last word
\def\ps@fwlwhead{\let\@mkboth\@gobbletwo
\def\@oddhead{\if@fcolmade\else % no word-heads on float pages.
\usebox\FirstWordBox\hfil\usebox\LastWordBox\fi}%
\let\@evenhead\@oddhead
\let\@oddfoot\@empty\let\@evenfoot\@oddfoot
\let\chaptermark\@gobble\let\sectionmark\@gobble\let\subsectionmark\@gobble
}
% pagestyle NextWordFoot: foot line has page number and next-page first word,
% but only on odd pages
\def\ps@NextWordFoot{\let\@mkboth\@gobbletwo
\let\@oddhead\@empty\let\@evenhead\@oddhead
\def\@oddfoot{\hfil\thepage\hfil\llap{\usebox\NextWordBox}}%
\let\@evenfoot\@empty
\let\chaptermark\@gobble\let\sectionmark\@gobble\let\subsectionmark\@gobble
}
% Shell around old output routine. Gets first word from next page by
% letting TeX continue with \vsize=0 to get a look at the next line.
% Values of \outputpenalty for \specialoutput ( -10001 to -19999 ) are
% simply run through the output routine.
% \supereject and \clearpage give a blank "next word".
% When called after making a stub-page the stub is returned to the
% vertical list, the previous page is restored and shipped out normally,
% but knowing what the next word will be.
\edef\FWLWnorm@L@output{\the\output}
\output{\@tempswafalse
\ifnum \outputpenalty>-\@MM \ifnum\outputpenalty<-\@M \@tempswatrue\fi\fi
\if@tempswa % special (float) output
% \message{Float handler: penalty=\the\outputpenalty}%
\FWLWnorm@L@output
\else
\ifvoid\LW@saved % end of real page
% \message{End of real page}%
\global\setbox\LW@saved\copy\@cclv % save page
\setbox\@tempboxa\vbox{\unvbox\@cclv \unskip\unkern\unpenalty
\unskip\unkern\unpenalty \unskip\unkern\unpenalty
\setbox\@tempboxa\lastbox
\LW@getlast@word\@tempboxa\LastWordBox
}\ifnum\outputpenalty>-\@MM % not \supereject
\xdef\LW@vsize{\global\vsize\the\vsize
\global\holdinginserts\the\holdinginserts}%
\global\vsize\z@ \global\holdinginserts\@ne
\else % \supereject, just output, don't look for word on next page
% \message{caused by super-eject.}
\global\setbox\@cclv\box\LW@saved
\global\setbox\NextWordBox\hbox{}%
\FWLWnorm@L@output
\global\setbox\FirstWordBox\box\NextWordBox
\fi
\else % saved page => just did tiny page to get next word
% \message{Just got next line:}{\tracingall\showboxdepth2 \showbox\@cclv}%
\setbox\@tempboxa\vbox{\penalty\LW@pen\unvcopy\@cclv \LW@getall@boxes
\ifvbox\LW@box \penalty\LW@pen\unvbox\LW@box \LW@getall@boxes\fi
\ifvbox\LW@box \global\setbox\NextWordBox\hbox{}\else
\LW@getfirst@word\LW@box\NextWordBox
\fi}% Return tiny page to page list:
\unvbox\@cclv \ifnum\outputpenalty<\@M \penalty\outputpenalty\fi
\LW@vsize\relax
\global\setbox\@cclv\box\LW@saved
\FWLWnorm@L@output
\global\setbox\FirstWordBox\box\NextWordBox
\fi\fi}
% globally get last "word" from a box (#1) into another box (#2)
\def\LW@getlast@word#1#2{\setbox\@tempboxa\vbox{\hsize\maxdimen \@parboxrestore
\hyphenpenalty\@M \exhyphenpenalty\@M
\rightskip\fill \looseness\@M \linepenalty\z@
\noindent\unhbox#1\endgraf
\unskip\unkern\unpenalty \global\setbox\LW@box\lastbox
}\LW@repack{#2}}
% globally get first "word" from a box (#1) into another box (#2)
\def\LW@getfirst@word#1#2{\setbox\@tempboxa\vbox{\@parboxrestore
\parshape\thr@@ \z@\z@ \z@\z@ \z@\maxdimen \parfillskip\fill
\hyphenpenalty\@M \exhyphenpenalty\@M
\hbadness\@MM \overfullrule\z@ \hfuzz\maxdimen
\ifhbox#1\noindent
\vadjust{\penalty\LW@pen}\penalty-\@M\unhbox#1% eliminate previous \leftskip
\else\ifvbox#1\penalty\LW@pen\unvbox#1\fi\fi
\endgraf
\@tempcnta\z@ \LW@getall@boxes}\LW@repack{#2}}
% Go through a vertical list that starts with special penalty
\def\LW@getall@boxes{\global\setbox\LW@box\lastbox \unskip\unkern \unskip\unkern
\let\@tempa\relax
\ifvoid \LW@box \advance\@tempcnta\@ne \else \@tempcnta\z@ \fi
\ifnum\lastpenalty=\LW@pen \else \unpenalty\fi
\ifnum\lastpenalty=\LW@pen \else \unpenalty\fi
\ifnum\lastpenalty=\LW@pen \else \ifnum\@tempcnta<5
\let\@tempa\LW@getall@boxes \fi \fi \unpenalty \@tempa}
% Put contents of \LW@box into hbox #1
\def\LW@repack#1{\global\setbox#1\hbox{\ifhbox\LW@box
\unhbox\LW@box\unskip\unskip\unpenalty\unskip
\else\ifvbox\LW@box\box\LW@box\fi\fi}}
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