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Using XPath for AST querying [message #1722085]

Tue, 02 February 2016 16:46

Alexandr Petrov

Messages: 1
Registered: February 2016

Junior Member

Hello,

I'm trying to implement code generator for DSL. I write grammar in XText and now write generator with Xtend.

I think, it would be useful to have ability to find some AST nodes in declarative style, e.g. by XPath query. Now I have to write some recursive functions to traverse within AST..

Sample code, that I want to simplify with XPath:

 @Inject
 private IQualifiedNameProvider nameProvider;
 
 private boolean flagObjectParent = false;
 private QualifiedName origQualName;
 private EObject origObject;
 private String qualNameString = "";
 /**
  * Получить строку fullQualifiedName с разделителем "_".
  * @param obj узел direct_declarator для переменной или функции в AST-дереве
  * @return Строка fullQualifiedName (разделитель "_") для переданного direct_declarator
  */ 
 def public String getQualifiedName(EObject obj) {
  if (!flagObjectParent) {
   qualNameString = "";
   origObject = obj;
   origQualName = nameProvider.getFullyQualifiedName(obj);
   flagObjectParent = true;
  }
  if ((obj != null) && ((origObject.eContainer).eContainer instanceof init_declarator)) {
   if (obj instanceof function_definition) {
    for (segmIterator: origQualName.segments) {
     if (segmIterator == origQualName.getSegment(origQualName.segmentCount-1))
      qualNameString = qualNameString.concat("_" + obj.decl.dir_decl.get_var_decl.name);
     qualNameString = qualNameString.concat("_" + segmIterator); 
    }
    flagObjectParent = false;
    return qualNameString.substring(1);
   }
   else {
    getQualifiedName(obj.eContainer);
   }
  } else {
   flagObjectParent = false;
   return origQualName.toString("_");
  }
 }

I couldn't find any sample of using XPath for such task. Might be somebody know it?

Thanks,
Alexander

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Re: Using XPath for AST querying [message #1725612 is a reply to message #1722085]

Fri, 04 March 2016 23:10

Harald Weiner

Messages: 23
Registered: January 2015
Location: Linz, Austria

Junior Member

I am not sure if this is possible, but I think it would require some work-arounds. Xtext is parsing a text file using the ANTLR tool to read in the file and returns EMF EObjects and EMF resources. They are more Java-like. Only the serialization (saving the EMF objects on the hard disk) might use the XMI (XML intermediate) file format. Also the meta-models of these models themselves are stored as XMI files. So you might parse text files with Xtext and save the resulting EMF objects as XMI files. And then you can query the XMI files with XPath. There is also a dedicated query language for EMF, called EMFIncquery, maybe you would like to take a look on it at http://wiki.eclipse.org/VIATRA/Query

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Re: Using XPath for AST querying [message #1725677 is a reply to message #1725612]

Sun, 06 March 2016 17:16

Harald Weiner

Messages: 23
Registered: January 2015
Location: Linz, Austria

Junior Member

Yeah, just found it in the Emf eclipse modeling framework book (steinberg et al.) at page 487/488 in the sub-chapter DOM conversion: persist (save the resulting xtext model to a xml-resource and then invoke the getDOMHelper function of the XMLResource. Do something like:

ResourceSet rs = new ResourceSetImpl (); 
XmlResource res = (XmlResource) rs.createResouce (uri); 
res.getContents ().add (myModel); 
Map options = new HashMap (); 
options.put (XMLResource.OPTIONS_KEEP_DEFAULT_CONTENT, Boolean.TRUE); 
Document doc = res.save (null, options, null); 
DOMHelper helper = res.getDOMHelper (); 
String query = "//foo [@bar > 50]"; 
NodeList nodes = XPathAPI.selectNodeList (doc, query); 
...

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