% pandoc -f markdown+latex_macros -t markdown \newcommand{\my}{\phi} $\my+\my$ ^D $\phi+\phi$
% pandoc -f markdown-latex_macros -t markdown \newcommand{\my}{\phi} $\my+\my$ ^D \newcommand{\my}{\phi} $\my+\my$
\let
macros should be expanded at point of
definition, while \newcommand
macros should be
expanded at point of use:
% pandoc -f latex -t latex \let\a\b \newcommand{\b}{\emph{ouk}} \a ^D \b
% pandoc -f latex -t latex \newcommand{\a}{\b} \newcommand{\b}{\emph{ouk}} \a ^D \emph{ouk}
% pandoc -f latex -t latex \def\BDpos{} \def\BDneg{-} \def\beq{\begin{align}} \def\eeq{\end{align}} \def\e#1{\emph{#1}} \def\f#1#2{\emph{#1--#2}} $5\BDneg 6\BDpos 7$ \beq x &= y\\ \eeq \e{hi} \f{hi}{ok} ^D \(5-67\) \[\begin{aligned} x &= y\\\end{aligned}\] \emph{hi} \emph{hi--ok}
% pandoc -f markdown+latex_macros -t markdown \newcommand{\my}{\phi} \begin{equation} \my+\my \end{equation} ^D \begin{equation} \phi+\phi \end{equation}
% pandoc -f markdown-latex_macros -t markdown \newcommand{\my}{\phi} \begin{equation} \my+\my \end{equation} ^D \newcommand{\my}{\phi} \begin{equation} \my+\my \end{equation}
% pandoc -f markdown+latex_macros -t markdown \newcommand{\my}{\emph{a}} \my ^D \emph{a}