conditionals
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
For simple integer comparisons, TeX provides \ifcase:
\ifcase<integer>
% Case 0
\or
% Case 1
\or
...
\else
% Optional
\fi
So you can define a wrapper such as
\newcommand\myswitch[1]{%
\ifcase#1\relax
\ValueWasZero
\or
\ValueWasOne
\or
\ValueWasTwo
...
\else
\OtherCases
\fi
}
Here, you start from the 0 case and work upward: often you'll see \ifcase#1\relax\or with no 0 case at all. You can use as many \or statements as you like, depending on how many numbers you need. The \else is optional, and is used if you want 'otherwise do this' functionality.
By the way, don't define \if: this is a TeX primitive which you should not change!
You could \unskip and/or \ignorespaces as part of your condition. However, version control is easier when you combine the possible outputs in a single macro:
\documentclass{article}
% Display the argument if \cond is True/False
\newcommand{\IfCond}[2]{%
\ifnum\pdfstrcmp{\cond}{True}=0
\ifnum\pdfstrcmp{}{#1}=0\unskip\else#1\fi%
\else
\ifnum\pdfstrcmp{}{#2}=0\unskip\else#2\fi%
\fi\ignorespaces}
% Display the argument if \cond is False
\newcommand{\IfCondFalse}[1]{%
\ifnum\pdfstrcmp{\cond}{True}=0 \unskip\else #1\fi\ignorespaces}
\begin{document}
\def\cond{True}% Version control
This is fake \IfCond{text}{hooplah}. \par
This is fake \IfCond{}{hooplah}.
\def\cond{False}% Version control
This is fake \IfCond{text}{hooplah}. \par
This is fake \IfCond{text}{}.
\end{document}
String comparison is done using pdfTeX's \pdfstrcmp.
Best Answer
If arguments 2 and/or 3 are blank, they are omitted, along with the space that follows.