\doc{Infix, prefix, and postfix operators}
\ref{infix-operators}
\ref{prefix-operators}
\ref{postfix-operators}

LP allows users to \clink{declare} symbols that can be used for infix, postfix,
and prefix notations.  Users can declare a simple operator (i.e., a
\slink{operator}{simpleOp}) for such use by decorating it with one or two
markers (\f{__}) to indicate the location(s) of its arguments.  For example,
the declarations
\begin{verbatim}
declare operators 
  __+__, __\mod__: Nat, Nat -> Nat   % infix operators
  -__:             Nat      -> Nat   % prefix operator
  __!:             Nat      -> Nat   % postfix operator
  ..
\end{verbatim}
allow the use of infix (e.g., \f{(x + 1) \mod n}), prefix (e.g., \f{~p} and
\f{-x}), and postfix (e.g., \f{3!}) notations.  Users can also declare a
\def{selection operator} for use in postfix notations.  For example, the
declaration 
\begin{verbatim}
declare operator __.first: Queue -> Element
\end{verbatim}
allows the use of postfix notations such as \fq{q.first}.  See
\dlink{operator}{operator}.