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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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>2.6. Access functions</H1
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>&#13;		Besides filters and combinators there exist some access functions for processing the attribute list <TT
CLASS="literal"
>TagAttrl</TT
> of nodes.
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>Functions for processing the attribute list</B
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>getAttrValue :: Eq a =&#62; a -&#62; [(a,b)] -&#62; Maybe b</TT
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>&#13;					Looks up the value for a certain attribute. If the attribute does not exist, the data type <TT
CLASS="literal"
>Nothing</TT
> is returned.
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>getAttrValue1 :: Eq a =&#62; a -&#62; [(a, String)] -&#62; String</TT
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>&#13;					Looks up the value for a certain attribute. If the attribute does not exist, an empty string is returned.
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>hasAttrValue :: Eq a =&#62; a -&#62; [(a,b)] -&#62; Bool</TT
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>&#13;					Returns true if there is an attribute with the searched name in the attribute list.
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>addAttrValue :: Eq a =&#62; a -&#62; b -&#62; [(a,b)] -&#62; [(a,b)]</TT
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>&#13;					Adds an attribute, the name and value, to the list.
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>addAttrValues :: Eq a =&#62; [(a,b)] -&#62; [(a,b)] -&#62; [(a,b)]</TT
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>&#13;					Adds a list of name-value pairs to the attribute list.
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>changeAttrValue :: Eq a =&#62; a -&#62; b -&#62; [(a,b)] -&#62; [(a,b)]</TT
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>&#13;					Changes the value of a certain attribute.
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>delAttrValue :: Eq a =&#62; a -&#62; [(a,b)] -&#62; [(a,b)]</TT
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>&#13;					Deletes an attribute from the list.
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>delAttrValues :: Eq a =&#62; [a] -&#62; [(a,b)] -&#62; [(a,b)]</TT
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>&#13;					Deletes a list of attributes from the attribute list.
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>&#13;		The following example shows the use of access functions for adding a new attribute with the name "<SPAN
CLASS="emphasis"
><I
CLASS="emphasis"
>att2</I
></SPAN
>" and the value "<SPAN
CLASS="emphasis"
><I
CLASS="emphasis"
>val2</I
></SPAN
>" to the attribute list of an <TT
CLASS="literal"
>XTag</TT
> node. The type of the node is detected by pattern-matching. If the node is of another type, it is simply returned.
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>Example 2-4. Adding a new attribute to an XTag node.</B
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>&#13;addAttribute :: XmlFilter
addAttribute n@(NTree (XTag name al) cs)
    = replaceAttrl newAttList n
      where
      newAttList = addAttrValue "att2" "val2" al

addAttribute n = [n]
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