%! TEX program = pdflatex
%\documentclass[12pt]{article}
\documentclass{standalone}
%\usepackage[paper=a4paper,margin=0.6cm]{geometry}
\usepackage{unravel}
\begin{document}
\errorcontextlines=10000
\def\othermacro{\let\a=bx}
\def\main{2^\othermacro}
$\main$
\end{document}