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>Design and Implementation of a validating XML parser in Haskell: Master's thesis; 
			University of Applied Sciences Wedel
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>Chapter 4. Package hvalidator</TD
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>4.2. Creating a validating XML parser</H1
><P
>&#13;		The only public module for validating XML documents is the module <TT
CLASS="classname"
>Validation</TT
>. It exports several functions for validating XML documents, parts of XML documents and transforming them.
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><TT
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>validateAndTransform :: XmlSFilter</TT
></DT
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>&#13;					Combines validation and transformation of a document. If errors or fatal errors occurred during validation, a list of errors is returned. Otherwise the transformed document is returned.
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></DD
><DT
><TT
CLASS="function"
>validate :: XmlSFilter</TT
></DT
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>&#13;					Checks if the DTD and the document are valid.
					</P
></DD
><DT
><TT
CLASS="function"
>validateDTD :: XmlSFilter</TT
></DT
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>&#13;					Checks if the DTD is valid.
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><TT
CLASS="function"
>validateDoc :: XmlSFilter</TT
></DT
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>&#13;					Checks if the document corresponds to the given DTD.
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><TT
CLASS="function"
>transform :: XmlSFilter</TT
></DT
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>&#13;					Transforms the document with respect to the given DTD. Validating parsers are expected to  normalize attribute values and add default values. This function should be called after a successful validation.
					</P
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>&#13;		The following example shows how the functions <TT
CLASS="function"
>validate</TT
> and <TT
CLASS="function"
>transform</TT
> can be used in an XML processing application. The document is valid, if <TT
CLASS="function"
>validate</TT
> returns an empty list or a list containing only errors of type <SPAN
CLASS="emphasis"
><I
CLASS="emphasis"
>warning</I
></SPAN
>. If the list contains errors of type <SPAN
CLASS="emphasis"
><I
CLASS="emphasis"
>error</I
></SPAN
> or <SPAN
CLASS="emphasis"
><I
CLASS="emphasis"
>fatal error</I
></SPAN
>, the document is not valid. If the document is valid the document is transformed and displayed to the user.
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>&#13;
printMsg :: XmlTrees -&#62; XmlTrees -&#62; IO()
printMsg errors doc
    = if null ((isError +++ isFatalError) $$ errors)
        then do
             if null errors
               then
                  putStrLn "The document is valid."
                  putStrLn (xmlTreesToString $ transform doc)
             else do
                  putStrLn "The document is valid, but there were warnings:"
                  putStrLn (xmlTreesToString $ transform doc)
                  putStrLn (showXErrors errors)
        else do
             putStrLn "The document is not valid. List of errors:"
             putStrLn (showXErrors errors)



main :: IO()
main
    = do
      doc &#60;- parseDoc "invalid.xml"
      printMsg (validate doc) doc
      return ()

		</PRE
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>&#13;		Calling the module <TT
CLASS="classname"
>ValidateExample</TT
> from the directory <SPAN
CLASS="emphasis"
><I
CLASS="emphasis"
>example</I
></SPAN
> of the Haskell XML Toolbox with the invalid document <SPAN
CLASS="emphasis"
><I
CLASS="emphasis"
>invalid.xml</I
></SPAN
> produces the following error messages.
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>Example 4-1. Validating a document with errors</B
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>&#13;&#60;?xml version="1.0" encoding="UTF-8" standalone="yes" ?&#62;

&#60;!DOCTYPE a [
&#60;!ATTLIST a  att1  CDATA  #IMPLIED&#62;
&#60;!ELEMENT a  (z, c?)&#62;
&#60;!ELEMENT b  EMPTY&#62;
&#60;!ELEMENT c  (#PCDATA)&#62;
]&#62;

&#60;a att2="test"&#62;
    &#60;y/&#62;
    &#60;c&#62;hello world&#60;/c&#62;
&#60;/a&#62;

The document is not valid. List of errors:
Warning: The element type "z", used in content model of element "a", is not declared.
Error: The content of element "a" must match ( "z" , "c"? ). Element "z" expected,
       but Element "y" found.
Error: Attribute "att2" of element "a" is not declared in DTD.
Error: Element "y" not declared in DTD.
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