funmacros
I try do define a macro \onoff, which alternatively prints "on" and "off" each time it's used. For example the sequence \onoff \onoff \onoff would print on off on
My first guess would be to use the following code:
\def\a{on}
\def\b{off}
\newcommand\onoff{\a\def\c{\a}\def\a{\b}\def\b{\c}}
However this code doesn't work. Is there an elegant way to code this?
Here's a expl3 version with seq variables.
The command \NewListCommand declares the command list macro named like the first argument and uses a global seq variable with some prefix, see \g_cryingshadow_mynewlist_seq etc.
This is filled by the \mynewlist command and the content displayed depending on the content of the other parameters from #3 to #6. The 7th. parameter is used as a delimiter
Some notes: The empty parameter could be an optional one.
\documentclass{article}
\usepackage{xparse}
\ExplSyntaxOn
\NewDocumentCommand{\NewListCommand}{mmmmmmm}{%
\seq_new:c {g_cryingshadow_#1_seq} % Make a new sequence
\expandafter\NewDocumentCommand\csname #1\endcsname{m}{%
\seq_gclear:c {g_cryingshadow_#1_seq}% Clear the sequence
\seq_gclear:N \l_tmpa_seq % Clear a temporary `\l_tmpa_seq
\seq_set_split:Nnn \l_tmpa_seq {} {##1} % Split the sequence into tokens.
\seq_set_eq:cN {g_cryingshadow_#1_seq} \l_tmpa_seq % copy the temporary sequence to the real one → this would not be necessary if the sequence is not be used outside
\seq_if_empty:cTF {g_cryingshadow_#1_seq} {%
#2% Checked --> is empty
}{%
% Display the various styles
\int_case:nn { \seq_count:c {g_cryingshadow_#1_seq} }
{%
{1} {#3 \seq_use:cnnn {g_cryingshadow_#1_seq} {,} {#7} {#7} #4}
}%
\int_compare:nNnT { \seq_count:c {g_cryingshadow_#1_seq}} > 1 {%
#5 \seq_use:cnnn {g_cryingshadow_#1_seq} {#7} {#7} {#7} #6
}
}
}
}
\ExplSyntaxOff
\NewListCommand{mynewlist}{empty}{[}{]}{(}{)}{,}
\begin{document}
\mynewlist{{A}{B}{C}}
\mynewlist{{A}{B}}
\mynewlist{{a}}
\mynewlist{}
\mynewlist{{A}{B}{C}{D}{E}{F}}
Astronomer's alphabet:
\mynewlist{{Oh}{be}{a}{fine}{girl}{kiss}{me}}
\end{document}
Edit: Here's the working version for usual LaTeX:
\documentclass{article}
\usepackage{etoolbox}
\makeatletter
\def\definelistcommand#1#2#3#4#5#6#7{%
\expandafter\def\csname @firstinlist#1\endcsname##1{%
\@ifnextchar\@stoplist{%
#3##1#4\@endlist%
}{%
#5##1\csname @nextlist#1\endcsname%
}%
}
\expandafter\def\csname @nextlist#1\endcsname##1{%
\@ifnextchar\@stoplist{%
#7##1#6\@endlist%
}{%
#7##1\csname @nextlist#1\endcsname%
}%
}
\expandafter\def\csname @startlist#1\endcsname##1{%
\@ifnextchar\@stoplist{%
#3##1#4\@endlist%
}{%
\csname @firstinlist#1\endcsname##1%
}%
}
\expandafter\def\csname #1\endcsname##1{%
\ifblank{##1}{%
#2%
}{%
\csname @startlist#1\endcsname##1\@stoplist%
}%
}
}
\def\@endlist#1{}
\definelistcommand{mycmd}{empty}{[}{]}{(}{)}{,}
\definelistcommand{othercmd}{empty}{\textbraceleft}{\textbraceright}{(}{)}{+}
\begin{document}
\makeatother
\mycmd{{A}{B}{C}}
\mycmd{A}
\mycmd{{A}{B}}
\mycmd{}
\othercmd{{O}{B}}
\othercmd{{O}}
\end{document}
Here's a fully working package which does what you want. It uses expl3 and related packages and you have three ways of using your commands: you can specify a package option globally, use a setup command locally or pass an optional argument to one of the macros.
Note that the second A in the example is produced by passing an optional macro parameter.
\documentclass{article}
\usepackage{filecontents}
\begin{filecontents}{mypackage.sty}
\RequirePackage{xparse} % enable LaTeX3 interfaces
\ProvidesExplPackage{mypackage}{2018-09-05}{0.1.0}{Data processing}
\RequirePackage{l3keys2e}
\keys_define:nn { jan } % define keys for module `jan`
{
skiprepetitions .bool_set:N = \l__jan_skiprep_bool, % define a boolean switch which is saved into a local variable
skiprepetitions .initial:n = true, % set the value that is used when nothing is defined
skiprepetitions .default:n = true, % set the value to use if you only pass `skiprepetitions` and no `=…`
keeprepetitions .bool_set_inverse:N = \l__jan_skiprep_bool,
keeprepetitions .default:n = true
}
\ProcessKeysOptions { jan } % make sure package options are processed
\NewDocumentCommand { \datasetup } { m } % define a command that locally sets the keys (as underscores are not allowed in normal LaTeX commands)
{
\keys_set:nn { jan } { #1 }
}
\tl_new:N \g_jan_storedval_tl % create a new auxiliary variable to hold the last value
\prg_generate_conditional_variant:Nnn \tl_if_eq:nn { nV } { T, F, TF } % make \tl_if_eq semantically (and expansion-wise) better for our use-case
\NewDocumentCommand { \mycommand } { O{} m } % this is the main command with the first optional argument being empty if omitted and the second argument being mandatory
{
\group_begin: % start a group to make key changes local
\keys_set:nn { jan } { #1 } % locally set keys
\tl_if_empty:nTF { #2 } { \\ } % test if mandatory argument empty
{
\tl_if_eq:nVTF { #2 } \g_jan_storedval_tl % test if the mandatory argument equals the last value
{
\bool_if:NF \l__jan_skiprep_bool { #2 } % only output the mandatory argument if we are not in skip-mode
} { #2 }
\\
\tl_gset:Nn \g_jan_storedval_tl { #2 }
}
\group_end:
}
\end{filecontents}
\usepackage{mypackage}
\begin{document}
Testing:\\
\mycommand{A}
\mycommand[keeprepetitions]{A}
\mycommand{A}
\mycommand{}
\mycommand{B}
\mycommand{C}
\mycommand{C}
\mycommand{A}
\mycommand{A}
\end{document}
Best Answer
One way
Another way (was a now deleted separate answer)
A third way