LaTeX `or` statements

Question

I need to test if one of multiple is defined. I know this command:

\ifIsDefined{\MYVAR}{
    % Do sometyhing
}

But, I need to test for two conditions like

if A or B is defined, then do this

How can you do this?

.

Answer 1

Use the package ifthen which is small to test if something is defined.

\ifthenelse{\(\NOT \isundefined{\MYVAR} \OR \NOT \isundefined{\MYSECONDVAR}\)}
{
    %True case
}
{
    % False case
}

See more examples here: https://riptutorial.com/latex/example/28656/if-statements

Answer 2

Essentially no additional package, because expl3 is now loaded in the LaTeX kernel. You could even dispense with xparse by doing

\ExplSyntaxOn
\newcommand{\xifthenelse}[3]
 {
  \bool_if:nTF { #1 } { #2 } { #3 }
 }

in the first few lines, but I'd avoid it and prefer xparse for consistency. The code is drawn from another answer of mine.

What's the difference with \ifthenelse from ifthen? That this new implementation has fully expandable tests. In the first argument of \xifthen you can use any of the defined tests linked together with ! (for “not”), && (for “and”) or || (for “or”) and normal parentheses.

\documentclass{article}
\usepackage{xparse}

\ExplSyntaxOn
\NewExpandableDocumentCommand{\xifthenelse}{mmm}
 {
  \bool_if:nTF { #1 } { #2 } { #3 }
 }

\cs_new_eq:NN \numtest     \int_compare_p:n
\cs_new_eq:NN \oddtest     \int_if_odd_p:n
\cs_new_eq:NN \fptest      \fp_compare_p:n
\cs_new_eq:NN \dimtest     \dim_compare_p:n
\cs_new_eq:NN \deftest     \cs_if_exist_p:N
\cs_new_eq:NN \namedeftest \cs_if_exist_p:c
\cs_new_eq:NN \eqdeftest   \token_if_eq_meaning_p:NN
\cs_new_eq:NN \streqtest   \str_if_eq_p:ee
\cs_new_eq:NN \emptytest   \tl_if_blank_p:n
\prg_new_conditional:Nnn \xxifthen_legacy_conditional:n { p,T,F,TF }
 {
  \use:c { if#1 } \prg_return_true: \else: \prg_return_false: \fi:
 }
\cs_new_eq:NN \boolean \xxifthen_legacy_conditional_p:n
\ExplSyntaxOff

\begin{document}

\xifthenelse{ \deftest\MYVAR || \deftest\MYSECONDVAR }{%
  One of them is defined%
}{
  Neither is defined%
}

\newcommand\MYVAR{x}

\xifthenelse{ \deftest\MYVAR || \deftest\MYSECONDVAR }{%
  One of them is defined%
}{
  Neither is defined%
}

\end{document}