These are primitive abstractions for insurance that will be
improved upon over time.
Some notable TODOs:
\begin{enumerate}
\item Enforce naming convention;
\item Support scalar results;
\item Fail on zero premium unless explicitly stated;
\item Fail on negative premium (use a credit template);
\item Rounding direction (currently only nearest); and
\item Credit, surcharge, and factor templates.
\end{enumerate}
\todo{Template to abstract these {\tt rate-each} generation
templates.}