Gdtyjr

I have a command that formats a single character, let's call it d. (In my case, d adds a dot under a Chinese character, as this is the custom to emphasize Chinese texts).

I want to define a new command ds such that it applies d over every letter of the string.

For example dsabc would be equivalent to dadbdc.

Thanks!

You can use @tfor. I provide also a better redefinition of the dot under according to your wish:

documentclassarticle
usepackagegraphicx

letdrelax
DeclareRobustCommandd[1]%
 oalign#1crhidewidthscalebox0.5textbullethidewidthcr%

makeatletter
newcommandds[1]%
 @tfornext:=#1dodnext%

makeatother

begindocument

xdddsdax

xdsdsax

enddocument

What does @tfor do? Its syntax is

@tfor<scratch macro>:=<tokens>do<code>

The scratch macro is traditionally next, but it can be anything. The <tokens> part is any (brace balanced) list of tokens. In the loop, LaTeX essentially does def<scratch macro><next token>, so

@tfornext:=dsadodnext

will perform

defnextddnextdefnextsdnextdefnextadnext

However, with @tfornext:=d sadodnext we will just obtain

defnextddnextdefnextsadnext

Explicit space tokens are ignored and braced groups of tokens are treated as one.

The expl3 analog is tl_map_inline:nn:

documentclassarticle
usepackagexparse
usepackagegraphicx

letdrelax
DeclareRobustCommandd[1]%
 oalign#1crhidewidthscalebox0.5textbullethidewidthcr%


ExplSyntaxOn
NewDocumentCommanddsm
 
 tl_map_inline:n #1 d ##1 
 
ExplSyntaxOff

begindocument

xdddsdax

xdsdsax

xdsd sabcx

enddocument

No scratch macro is used: the current item in the loop is denoted by #1 (which becomes ##1 in the body of a definition, as usual).

In this particular case where just a single command is applied with the current item as argument, one can use tl_map_function:nN:

NewDocumentCommanddsm
 
 tl_map_function:n #1 d
 

which has the same effect and is shorter. It can also appear in a full expansion context (not for this particular case, because of d).

This solution allows word wrap and handles spaces between words. In addition, the [w] option allows the task to be performed on each word, rather than each character.'

In the MWE, I demonstrate with variously defined tasks:

1. overstrike each character (2 different settings)




2. place a dot under each character




3. place a semicolon under each word




4. apply extra intercharacter space




5. apply extra interword space.

The task is defined in charop for characters and wordop for words, while the chariterate[] macro does the iteration. Here is the MWE:

% WHILE THIS EXAMPLE IS SET UP FOR BOLDING A CALLIGRAPHIC FONT
% ITS GENERAL USE IS TO DO SOMETHING ON EACH char OF ITS ARGUMENT, ALLOWING LINE WRAP
% THE [W] OPTION TO chariterate DOES SOMETHING TO EACH WORD.
documentclass[10pt,a4paper,BCOR10mm,DIV11,toc=listof,parskip=full, openany]scrbook
usepackagestackengine
newcommandchariterate[2][c]if w#1worditeratehelper#2 relaxrelaxelse
 chariteratehelpA#2 relaxrelaxfi
defchariteratehelpA#1 #2relax%
 chariteratehelpB#1relaxrelax%
 ifxrelax#2else chariteratehelpA#2relaxfi

defchariteratehelpB#1#2relax%
 charop#1%
 ifxrelax#2else
 chariteratehelpB#2relax%
 fi

defworditeratehelper#1 #2relax%
 wordop#1%
 ifxrelax#2else worditeratehelper#2relaxfi

defcharop#1#1
defwordop#1#1
% THIS EXAMPLE ARTIFICIALLY BOLDS EACH char WITH A SHIFTED OVERSTRIKE
defcharopA%
 %defuseanchorwidthT%
 defstacktypeL%
 defstackalignmentl%
 defcalup.2pt%
 defcalover.15pt%
 renewcommandcharop[1]stackon[calup]##1kerncalover##1%

% HERE'S AN EXAMPLE PLACING DOT UNDER EACH char
defcharopB%
 defuseanchorwidthT%
 defstacktypeL%
 defstackalignmentc%
 renewcommandcharop[1]stackunder[3pt]##1.%

% EXTRA INTER-CHARACTER SPACE
defcharopCrenewcommandcharop[1]##1,
% HERE'S AN EXAMPLE PLACING DOT UNDER EACH WORD
defwordopA%
 renewcommandwordop[1]defstackalignmentcstackunder[3pt]##1;

% EXTRA INTER-WORD SPACE
defwordopBrenewcommandwordop[1]##1 
%
newenvironmentcalligraphic%
fontencodingT1fontfamilypzcfontseriesmfontshapeitfontsize12pt12ptselectfont%
renewcommand*sectfontnormalcolorusefontT1pzcmit
begindocument
charopA
 begincalligraphic
 Test textbfthis is not boldpar
 Test chariteratethis is bold with .2pt up shift and .15pt right shiftpar
 defcalup.0pt
 defcalover.2pt
 Test chariteratethis is bold with .0pt up shift and .2pt right shiftpar
 chariteratecvxc This is a test. This is a test. This is a test. This is a test. 
 This is a test. This is a test. This is a test. This is a test. This is a 
 test. This is a test. This is a test. This fdsfsd is a test. This is a test. 
 This is a test. This is a test. This is adfsdf test. This is a test.par
 endcalligraphicpar
charopB
wordopA
 chariterateThis is doing something to each character.par
 chariterate[w]This is doing something to each word.par
 chariterateIch bin m"ude. 
 chariterate[w]Ich bin m"ude.par
charopC
wordopB
 chariterateThis is doing something to each character.par
 chariterate[w]This is doing something to each word.par
enddocument

In the most simple incarnation, to do merely underdots on characters alone, the code can be greatly reduced:

documentclassarticle
usepackagestackengine
newcommandchariterate[2][c]if w#1worditeratehelper#2 relaxrelaxelse
 chariteratehelpA#2 relaxrelaxfi
defchariteratehelpA#1 #2relax%
 chariteratehelpB#1relaxrelax%
 ifxrelax#2else chariteratehelpA#2relaxfi

defchariteratehelpB#1#2relax%
 charop#1%
 ifxrelax#2else
 chariteratehelpB#2relax%
 fi

defworditeratehelper#1 #2relax%
 wordop#1%
 ifxrelax#2else worditeratehelper#2relaxfi

 defuseanchorwidthT%
 defstacktypeL%
 defstackalignmentc%
 newcommandcharop[1]stackunder[3pt]#1.%
 defwordop#1#1
begindocument
chariterateThis is doing something to each character.
This is doing something to each character.
This is doing something to each character.par
enddocument