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|
% language=uk
\environment math-layout
\startbuffer[oldcolor]
\disableexperiments[simplegroups]%
% when we no longer have it as experiment
\unprotect \pushoverloadmode
\permanent\protected\def\color[#1]%
{\bgroup % \beginsimplegroup
\edef\currentcolorname{#1}%
\ifempty\currentcolorprefix
\colo_helpers_activate_nop
\else
\colo_helpers_activate_yes
\fi
\let\nexttoken}%
\popoverloadmode \protect
\stopbuffer
\startbuffer[newcolor]
\enableexperiments[simplegroups]%
\stopbuffer
\startcomponent math-grouping
\startchapter[title=Grouping]
\startsection[title=Some details]
In \TEX\ there are all kind of groups. When you start with a curly brace, you
often enter a group but when you start a box or table cell you also do that. When
you enter math a math group is started. Assignments are, unless explicitly done
global, nearly always local to the group. Here we discuss the following two
cases:
\starttyping
{ .... }
\bgroup .... \egroup
\begingroup .... \endgroup
\stoptyping
We say two cases, not three, because the first two are equivalent: the two macros
in the second line are not primitives but aliases to the curly braces. There is
however one fundamental difference between them. The verbose \type {\begingroup}
starts a so called simple group so let's call the other complex. A complex group
is bounded by equivalents to the two characters (braces) that have catcodes that
begin and end these groups. So, the following is valid.
\starttyping
{ .... }
{ .... \egroup
\bgroup .... }
\bgroup .... \egroup
\stoptyping
This means that a macro like this is okay:
\starttyping
\def\foo{\bgroup\bf\let\next} \foo{text}
\stoptyping
The \type {\foo} will start a complex group, switch font and then pick up the
brace. The group will be closed by the matching right brace or an equivalent.
The following two cases are invalid:
\starttyping
\bgroup .... \endgroup
\begingroup .... \egroup
\stoptyping
which means that:
\starttyping
\def\foo{\begingroup\bf\let\next} \foo{text}
\stoptyping
will trigger an error message. This is rather unfortunate because using braces
to wrap an argument in curly braces is rather convenient. The way out is this:
\starttyping
\def\foo#1{\begingroup\bf#1\endgroup} \foo{text}
\stoptyping
which is perfectly valid apart from the fact that the argument is first picked up
and then fed back into the input. Apart from a small performance hit and using
more memory it also adds noise to tracing.
\stopsection
\startsection[title=Side effects]
In math mode matters are complicates by the fact that complex groups (the ones
started with the curly brace) start a math list. And that has side effects because
the spacing between math elements depends on what we deal with: math symbol, lists,
fenced material. The following example shows a whole lot of this:
\startbuffer[example]
\starttabulate[|j1|j1||]
\NC $\sin{\left(xxx\right)}$
\NC $f {\left(xxx\right)}$
\NC $x {\left(xxx\right)}$
\NR
\NC $\sin\begingroup\left(xxx\right)\endgroup$
\NC $f \begingroup\left(xxx\right)\endgroup$
\NC $x \begingroup\left(xxx\right)\endgroup$
\NR
\NC $\sin\left(xxx\right)$\par
\NC $f \left(xxx\right)$\par
\NC $x \left(xxx\right)$\par
\NR
\NC $\sin\color[darkgreen]{(xxx)}$\par
\NC $f \color[darkgreen]{(xxx)}$\par
\NC $x \color[darkgreen]{(xxx)}$\par
\NR
\NC $\sin\startcolor[darkblue](xxx)\stopcolor$\par
\NC $f \startcolor[darkblue](xxx)\stopcolor$\par
\NC $x \startcolor[darkblue](xxx)\stopcolor$\par
\NR
\NC $\sin(xxx)$\par
\NC $f (xxx)$\par
\NC $x (xxx)$\par
\NR
\NC $\sin{\color[darkyellow]{(xxx)}}$\par
\NC $f {\color[darkyellow]{(xxx)}}$\par
\NC $x {\color[darkyellow]{(xxx)}}$\par
\NR
\NC $\sin\begingroup\color[darkred]{(xxx)}\endgroup$\par
\NC $f \begingroup\color[darkred]{(xxx)}\endgroup$\par
\NC $x \begingroup\color[darkred]{(xxx)}\endgroup$\par
\NR
\stoptabulate
\stopbuffer
\typebuffer[example]
A valid question is why we would want to add curly braces. One reason is that we
we want to apply something to a few characters, in this case color the argument
to the sinus. Now, when a color command is defined as the \type {\foo} before, we
start a complex group and that influences spacing! This is demonstrated in the
left part of \in {figure} [fig:grouping:sin] (you can zoom in on the table to
see the details; we also report the kind of spacing applied).
\startplacefigure[reference=fig:grouping:sin,title=Grouping influencing math spacing (list).]
\startcombination[nx=2,ny=1,distance=2em,style=bold]
\startcontent
\showmakeup[math,fontkern,italic]% laps into the margin hence the -2em
\getbuffer[oldcolor]%
\scale[width=\dimexpr\measure{combination}-2em\relax]{\getbuffer[example]}%
\stopcontent
\startcaption
pseudo grouping
\stopcaption
\startcontent
\showmakeup[math,fontkern,italic]% laps into the margin hence the -2em
\getbuffer[newcolor]%
\scale[width=\dimexpr\measure{combination}-1em\relax]{\getbuffer[example]}%
\stopcontent
\startcaption
grouping
\stopcaption
\stopcombination
\stopplacefigure
The right variant in that figure uses a different way of grouping, one that is
equivalent to:
\starttyping
\def\foo{\beginsimplegroup\bf\let\next}
\stoptyping
This time we effectively do \type {\begingroup} but permits both \type
{\endgroup} or a curly brace (or \type {\egroup} to wrap up the group. That means
that we don't get the side effect of starting a math list.
\startbuffer[example]
$ x = y \quad x \color[red]{=} y$
\stopbuffer
This example shows the effect of coloring a single character (the result is shown
in \in {figure} [fig:grouping:char]):
\typebuffer[example]
\startplacefigure[reference=fig:grouping:char,title=Grouping influencing math spacing (symbol).]
\vkern4ex
\startcombination[nx=2,ny=1,distance=4em,style=bold]
\startcontent
\showmakeup[math,fontkern,italic]% laps into the margin hence the -2em
\getbuffer[oldcolor]%
\scale[width=\dimexpr\measure{combination}-2em\relax]{\getbuffer[example]}%
\stopcontent
\startcaption
pseudo grouping
\stopcaption
\startcontent
\showmakeup[math,fontkern,italic]% laps into the margin hence the -2em
\getbuffer[newcolor]%
\scale[width=\dimexpr\measure{combination}-2em\relax]{\getbuffer[example]}%
\stopcontent
\startcaption
grouping
\stopcaption
\stopcombination
\vkern2ex
\stopplacefigure
\stopsection
\stopchapter
\stopcomponent
|
