distributed programming</A>.</P>



<?php section("exttype", "extensible types") ?>

<P>Extensible types are a generalization of SML's exception type. In effect,
the programmer can arbitrarily introduce new sum types similar to <TT>exn</TT>,
which have a potentially unlimited set of constructors.</P>

<P>An extensible type is declared as follows:</P>

<PRE class=code>
exttype 'a message</PRE>

<P>Fresh constructors are introduced as follows:</P>

<PRE class=code>
constructor DoThis of int : 'a message
const