\subsection{Paper organisation}
\label{sec:intro:org}
In this paper we present different advantages of working with imperative code
in a functional style. We do this by means of a case study, an interpreter of
the language While~\citep{proganal}. This example language is briefly described
in \autoref{sec:intro:while}. Before discussing our interpreter, we discuss
basic definitions that will be helpful in \autoref{sec:predefs}.  Since
extensive research has already been done into lexing and parsing \citep[see
e.g.][]{monads,yard}, we skip these steps and assume we already have an
abstract syntax tree (AST). This AST is described in \autoref{sec:ast}. In
\autoref{sec:eval} we discuss different possibilities of evaluating
mathematical expressions. Finally, in \autoref{sec:interp} we propose a While
interpreter. We finish by articulating the advantages of functional
interpretation in \autoref{sec:concl}.

\autoref{sec:ftypes} lists the functions and types that the reader is supposed
to know. Affinity with monads is required.