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% tabto.sty
%
% version 1.4 (Dec 2018)
%
% Tabbing to fixed positions in a paragraph.
%
% Copyright 2006,2009,2012,2013,2018 by
% Donald Arseneau, Vancouver, Canada (asnd@triumf.ca)
% Permission to use, distribute and modify this software is granted
% under the conditions of the LaTeX Project Public License, either
% version 1.3 or (at your option) any later version. The license is
% found at http://www.latex-project.org/lppl.txt, and is part of all
% recent distributions of LaTeX.
%
% This work has the LPPL maintenance status `maintained' (by author).
%
% Two new text positioning commands are defined: \tabto and \tab.
%
% \tabto{<length>}
% Tab to a position relative to the left margin in a paragraph (any
% indentation due to a list or \leftskip is part of the `margin' in
% this context). If the text on the line already goes past the desired
% position, the tab starts a new line and moves to the requested
% horizontal position.
%
% \tabto*{<length>}
% Similar to \tabto, except it will perform backspacing, and over-
% print previous text on the line whenever that text is already
% longer than the specified length (i.e., no linebreak is produced).
% Line-breaks are suppressed immediately after \tabto or \tabto*.
%
% The length register "\CurrentLineWidth" will report the width
% of the existing text on the line, and it may be used in the
% <length> argument (using calc.sty, for example). Also, there
% is "\TabPrevPos" which gives the "\CurrentLineWidth" from the
% previous tab command (the position where the tab command occurred,
% not where it went to), and can be used to return to that position
% if no line breaks have occurred in between, or directly below it,
% if there were line breaks.
%
% \tab
% Tab to the next tab-stop chosen from a list of tab positions, in
% the traditional style of typewriters. A \tab will always move
% to the next tab stop (or the next line), even if it is already
% exactly at a tab stop. Thus, "\tab" at the beginning of a line,
% or "\tab\tab" elsewhere skips a position. A linebreak is permitted
% immediately following a \tab, in case the ensuing text does not
% fit well in the remaining space.
%
% If you do not want to skip positions, use "\tabto{\NextTabStop}"
% instead of "\tab". This is particularly useful when you want to
% use \tab in some other command, but do not want to skip a column
% for the first item.
%
% The tab-stop positions are declared using either \TabPositions
% or \NumTabs:
%
% \TabPositions{<length>, <length>,...<length>}
% Declares the tab stops as a comma-separated list of positions
% relative to the left margin. A tab-stop at 0pt is implicit, and
% need not be listed.
%
% \NumTabs{<number>}
% Declares a list of <number> equally-spaced tabs, starting at the
% left margin and spanning \linewidth. For example \NumTabs{2}
% declares tab-stops at 0pt and 0.5\linewidth, the same as
% \TabPositions{0pt, 0.5\linewidth} or \TabPositions{0.5\linewidth}
%
% After these declarations, the list of tab positions is saved in
% \TabStopList, and the next tab position, relative to the current
% position, is given by \NextTabStop. You do not normally need
% to access them, but they are available.
%
% Problems:
%
% Tall objects after a tab stop may overlap the line above, rather
% than forcing a greater separation between lines.
\ProvidesPackage{tabto}[2018/12/28 \space v 1.4 \space
Another tabbing mechanism]\relax
\newdimen\CurrentLineWidth
\newdimen\TabPrevPos
\newcommand\tabto[1]{%
\leavevmode
\begingroup
\def\@tempa{*}\def\@tempb{#1}%
\ifx\@tempa\@tempb % \tab*
\endgroup
\TTo@overlaptrue % ... set a flag and re-issue \tabto to get argument
\expandafter\tabto
\else
\ifinner % in a \hbox, so ignore
\else % unrestricted horizontal mode
\null% \predisplaysize will tell the position of this box (must be box)
\parfillskip\fill
\everydisplay{}\everymath{}%
\predisplaypenalty\@M \postdisplaypenalty\@M
$$% math display so we can test \predisplaysize
\lineskiplimit=-999pt % so we get pure \baselineskip
\abovedisplayskip=-\baselineskip \abovedisplayshortskip=-\baselineskip
\belowdisplayskip\z@skip \belowdisplayshortskip\z@skip
\halign{##\cr\noalign{%
% get the width of the line above
\ifdim\predisplaysize=\maxdimen %\message{Mixed R and L, so say the line is full. }%
\CurrentLineWidth\linewidth
\else
\ifdim\predisplaysize=-\maxdimen
% \message{Not in a paragraph, so call the line empty. }%
\CurrentLineWidth\z@
\else
\ifnum\TTo@Direction<\z@
\CurrentLineWidth\linewidth \advance\CurrentLineWidth\predisplaysize
\else
\CurrentLineWidth\predisplaysize
\fi
% Correct the 2em offset
\advance\CurrentLineWidth -2em
\advance\CurrentLineWidth -\displayindent
\advance\CurrentLineWidth -\leftskip
\fi\fi
\ifdim\CurrentLineWidth<\z@ \CurrentLineWidth\z@\fi
% Enshrine the tab-to position; #1 might reference \CurrentLineWidth
\setlength\@tempdimb{#1}% allow calc.sty
%\message{*** Tab to \the\@tempdimb, previous width is \the\CurrentLineWidth. ***}%
% Save width for possible return use
\global\TabPrevPos\CurrentLineWidth
% Build the action to perform
\protected@xdef\TTo@action{%
\vrule\@width\z@\@depth\the\prevdepth
\ifdim\CurrentLineWidth>\@tempdimb
\ifTTo@overlap\else
\protect\newline \protect\null
\fi\fi
\protect\nobreak
\protect\hskip\the\@tempdimb\relax
}%
%\message{\string\TTo@action: \meaning \TTo@action. }%
% get back to the baseline, regardless of its depth.
\vskip-\prevdepth
\prevdepth-99\p@
\vskip\prevdepth
}}%
$$
% Don't count the display as lines in the paragraph
\count@\prevgraf \advance\count@-4 \prevgraf\count@
\TTo@action
%% \penalty\@m % to allow a penalized line break
\fi
\endgroup
\TTo@overlapfalse
\ignorespaces
\fi
}
% \tab -- to the next position
% \hskip so \tab\tab moves two positions
% Allow a (penalized but flexible) line-break right after the tab.
%
\newcommand\tab{\leavevmode\hskip2sp\tabto{\NextTabStop}%
\nobreak\hskip\z@\@plus 30\p@\penalty4000\hskip\z@\@plus-30\p@\relax}
% Expandable macro to select the next tab position from the list
\newcommand\NextTabStop{%
\expandafter \TTo@nexttabstop \TabStopList,\maxdimen,>%
}
\def\TTo@nexttabstop #1,{%
\ifdim#1<\CurrentLineWidth
\expandafter\TTo@nexttabstop
\else
\ifdim#1<0.9999\linewidth#1\else\z@\fi
\expandafter\strip@prefix
\fi
}
\def\TTo@foundtabstop#1>{}
\newcommand\TabPositions[1]{\def\TabStopList{\z@,#1}}
\newcommand\NumTabs[1]{%
\def\TabStopList{}%
\@tempdimb\linewidth
\divide\@tempdimb by#1\relax
\advance\@tempdimb 1sp % counteract rounding-down by \divide
\CurrentLineWidth\z@
\@whiledim\CurrentLineWidth<\linewidth\do {%
\edef\TabStopList{\TabStopList\the\CurrentLineWidth,}%
\advance\CurrentLineWidth\@tempdimb
}%
\edef\TabStopList{\TabStopList\linewidth}%
}
% default setting of tab positions:
\TabPositions{\parindent,.5\linewidth}
\newif\ifTTo@overlap \TTo@overlapfalse
\@ifundefined{predisplaydirection}{
\let\TTo@Direction\predisplaysize
\let\predisplaydirection\@undefined
}{
\let\TTo@Direction\predisplaydirection
}
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