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I'm using the following from a dictionary template:
\newcommand{\entry}[4]{\framebox(7,7){}\hspace{.75em}\markboth{#1}{#1}\textbf{#1}\ {(#2)}\ \textit{#3}\ $\bullet$\ {#4}}
\entry{Purfling}{pur-fling}{Guitar Part}{Definition}
\entry{Neck}{}{}{Definition}
Produces
Purfling (pur-fling) Guitar Part * Definition
Neck () * Definition
I'd like the second element (the parenthesis) to appear only if there is text inside it:
Purfling (pur-fling) Guitar Part * Definition
Neck * Definition
If arguments 2 and/or 3 are blank, they are omitted, along with the space that follows.
\documentclass{article}
\newcommand{\entry}[4]{\framebox(7,7){}\hspace{.75em}\markboth{#1}{#1}\textbf{#1}\ %
\ifx\relax#2\relax\else{(#2)}\ \fi%
\ifx\relax#3\relax\else\textit{#3}\ \fi%
$\bullet$\ {#4}}
\begin{document}
\entry{Purfling}{pur-fling}{Guitar Part}{Definition}
\entry{Neck}{}{}{Definition}
\end{document}
\if is quite risky, as it triggers expansion of the first token in #2, if not empty. Not really a big deal, but if the expansion starts with \relax, as some macros do…
– egreg
May 19 '16 at 18:06
\ifx would be "safer"? Then, you'd have to purposefully aim at your foot with a \relax in order to shoot it.
– Steven B. Segletes
May 19 '16 at 18:15
\tl_if_blank:VF approach also allows { } (that is, spaces sneaking in).
– egreg
May 19 '16 at 19:38
You have also to gobble the spaces, when the argument is void:
\documentclass{article}
\newcommand{\IfNotBlank}[2]{%
\if\relax\detokenize{#1}\relax\else#2\fi
}
\newcommand{\entry}[4]{%
\framebox(7,7){}%
\hspace{.75em}%
\markboth{#1}{#1}%
\textbf{#1}\ %
\IfNotBlank{#2}{(#2)\ }%
\IfNotBlank{#3}{\textit{#3}\ }%
$\bullet$\ {#4}%
}
\begin{document}
\entry{Purfling}{pur-fling}{Guitar Part}{Definition}
\entry{Neck}{}{}{Definition}
\end{document}
You may want to look at a key-value interface:
\documentclass{article}
\usepackage{xparse}
\ExplSyntaxOn
\NewDocumentCommand{\entry}{mm}
{
\group_begin:
\keys_set:nn { kale/dict } { #1 }
\framebox(7,7){} \hspace{.75em}
\markboth{\l_kale_dict_main_tl}{\l_kale_dict_main_tl}
\textbf{\l_kale_dict_main_tl}~
\tl_if_blank:VF \l_kale_dict_hyphen_tl
{
(\l_kale_dict_hyphen_tl)~
}
\tl_if_blank:VF \l_kale_dict_note_tl
{
\textit{\l_kale_dict_note_tl}~
}
\textbullet{}~
#2
\group_end:
}
\keys_define:nn { kale/dict }
{
main .tl_set:N = \l_kale_dict_main_tl,
hyphen .tl_set:N = \l_kale_dict_hyphen_tl,
note .tl_set:N = \l_kale_dict_note_tl,
}
\ExplSyntaxOff
\begin{document}
\entry{
main=Purfling,
hyphen=pur-fling,
note=Guitar Part,
}{Definition}
\entry{
main=Neck,
}{Definition}
\end{document}
\detokenize buy you?
– Steven B. Segletes
May 19 '16 at 17:54
\relax as an argument, that would produce different results, but that is not really a usage case here.
– Steven B. Segletes
May 19 '16 at 17:59
Here comes some sort of safety-belt with(out eTeX) bloatware:
\documentclass{article}
\makeatletter
%%----------------------------------------------------------------------
%% Check whether argument is empty:
%%......................................................................
%% \@CheckWhetherNull{<Argument which is to be checked>}%
%% {<Tokens to be delivered in case that argument
%% which is to be checked is empty>}%
%% {<Tokens to be delivered in case that argument
%% which is to be checked is not empty>}%
%%
%% The gist of this macro comes from Robert R. Schneck's \ifempty-macro:
%% <https://groups.google.com/forum/#!original/comp.text.tex/kuOEIQIrElc/lUg37FmhA74J>
%%
%% A concern in his posting is that the argument is hit with \string
%% after some expansions which in edge cases might result in unbalancing
%% surrounding \if..\fi-constructs if the macro is used inside of such
%% \if..\fi-constructs.
%%
%% That challenging concern sickened me. ;-)
%%
%% Therefore I decided to implerment a variant where this cannot happen
%% as expansion is forced by \romannumeral:
%%
%% After the first expansion-step, \string is not applied yet.
%% After the second expansion-step, any possibly disturbing remainders
%% are already removed due to \romannumeral-expansion.
%%
%% No eTeX- or whatsoever extensions. No \if.. .Only \romannumeral,
%% digit 0, space token for terminating \romannumeral-expansion,
%% \string, \expandafter, \@firstoftwo, \@secondoftwo, {, }.
%%
%% May 20, 2016
%%
%% Ulrich Diez (e-mail: ud.usenetcorrespondence@web.de)
%%
\newcommand\@CheckWhetherNull[1]{%
\romannumeral0\expandafter\@secondoftwo\string{\expandafter
\@secondoftwo\expandafter{\expandafter{\string#1}\expandafter
\@secondoftwo\string}\expandafter\@firstoftwo\expandafter{\expandafter
\@secondoftwo\string}\expandafter\expandafter\@firstoftwo{ }{}%
\@secondoftwo}{\expandafter\expandafter\@firstoftwo{ }{}\@firstoftwo}%
}%
%%
%%----------------------------------------------------------------------
%% Check whether argument is blank (empty or only spaces):
%%......................................................................
%% -- Take advantage of the fact that TeX discards space tokens when
%% "fetching" _un_delimited arguments: --
%% \@CheckWhetherBlank{<Argument which is to be checked>}%
%% {<Tokens to be delivered in case that
%% argument which is to be checked is blank>}%
%% {<Tokens to be delivered in case that argument
%% which is to be checked is not blank}%
\newcommand\@CheckWhetherBlank[1]{%
\romannumeral\expandafter\expandafter\expandafter\@secondoftwo
\expandafter\@CheckWhetherNull\expandafter{\@firstoftwo#1{}.}%
}%
%%----------------------------------------------------------------------
%%
\newcommand{\entry}[4]{%
\framebox(7,7){}\hspace{.75em}\markboth{#1}{#1}\textbf{#1}\ %
\@CheckWhetherBlank{#2}{}{(#2)\ }%
\@CheckWhetherBlank{#3}{}{\textit{#3}\ }%
$\bullet$\ {#4}%
}%
\makeatother
\begin{document}
\entry{Purfling}{pur-fling}{Guitar Part}{Definition}
\entry{Neck}{}{ }{Definition}
\end{document}
The crucial point is:
It is tested whether arguments do consist only of space tokens or no tokens at all. It is not tested whether expanding arguments yields visible material and not just glue or "voidness".
In other words: Things like \entry{Neck}{\empty}{\empty}{Definition}
might require another "safety-belt".
