\documentclass{article}
\usepackage{stex}
\begin{document}

\begin{module}[id=source]
\symdef{compose}[2]{\infix\circ{#1}{#2}} 
\symdef{composeFN}{\circ}
\end{module}

\begin{view}[from=source,to=source,title=dummy view]
  $\vassign{\composeFN}{\lambda{x,y}.\compose{y}{x}}$
\end{view}

\end{document}