<sect2 id="gadt-style">
<title>Declaring data types with explicit constructor signatures</title>
-<para>GHC allows you to declare an algebraic data type by
+<para>When the <literal>GADTSyntax</literal> extension is enabled,
+GHC allows you to declare an algebraic data type by
giving the type signatures of constructors explicitly. For example:
<programlisting>
data Maybe a where