[r2005-06-25 12:54:15 by beppe] added dynamic type check

Original author: beppe
Date: 2005-06-25 12:54:15+00:00

web/tutorial/getting_started.xml

@@ -272,19 +272,28 @@ type <code>ParentBook</code>) then it performs the assignment (the variable
 <code>x&amp;ParentBook</code>) otherwise it raises an exception.
 </p>
 <p>
-Of course an exception such as "parents.xml is not a document of type ParentBook" it is not
-very informative about why the document failed the match an where the error might be. In CDuce it is 
-possible to ask the program to perform this check and raise an informative exception (a string
-that describes and localize the problem) by using the dynamic type check construction <code>(%%e%%:?%%t%%)</code> which 
-checks whether the expression  <code>%%exp%%</code> has type  <code>%%t%%</code> and it either returns the result of
- <code>%%exp%%</code> or raise an informative exception. The dynamic type check can be also used in a let construction as follows
+Of course an exception such as "parents.xml is not a document of type
+ParentBook" it is not very informative about why the document failed the match
+an where the error might be. In CDuce it is possible to ask the program to
+perform this check and raise an informative exception (a string that describes
+and localize the problem) by using the dynamic type check construction
+<code>(%%e%%:?%%t%%)</code> which checks whether the expression
+<code>%%exp%%</code> has type <code>%%t%%</code> and it either returns the
+result of <code>%%exp%%</code> or raise an informative exception. 
 </p>
 <sample><![CDATA[
-let parents :? ParentBook = load_xml "parents.xml"
+let parents  = load_xml "parents.xml" :? ParentBook
 ]]></sample>
 <p>
-which does the same test as the previous program but in case of failure give
+which perform the same test as the previous program but in case of failure give
 information to the programmer on the reasons why the type check failed.
+The dynamic type check can be also used in a let construction as follows
+</p>
+<sample><![CDATA[
+let parents :? ParentBook = load_xml "parents.xml"
+]]></sample>
+<p>
+which is completely equivalent to the previous one.
 </p>
 <p>
 The command <code>load_xml "parents.xml"</code> is just an abbreviated form for