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Performance issues when using actions in expressions [message #560088]

Tue, 21 September 2010 07:41

Roland S.

Messages: 36
Registered: September 2009

Member

Hi there,

right now my grammar definition for expressions looks like this:



Expression:									
	
		firstoperator=Operator? firstvalue=BasicValue (moreexpressions+=BasicValueWithOperator)*;
 
BasicValueWithOperator:

		operator=Operator prefix=AddOp? value=BasicValue;

As you can see, expressions are just stored in a list.

When parsing this file:

https://svn.modelica.org/projects/Modelica/trunk/Modelica/Fl uid/Utilities.mo

the performance is acceptable (but far from good). The parser needs 2.1 seconds to parse the file.

Now I want to store the expressions in a tree-like way as explained by Sven Efftinge ( http://blog.efftinge.de/2010/08/parsing-expressions-with-xte xt.html).

My revised grammar then looks like this:


Expression:									
	
		BasicExpression ({Expression.left=current} operator=Operator prefix=AddOp? right=Expression)? ;
 

BasicExpression returns Expression:
 	
 		operator=Operator? value=BasicValue ;

The resulting AST is far better for post-processing (as checked with a smaller file). But the parser doesn't even stop parsing any more, when using the file from above.

I would be thankful for any hint solving this issue.

Regards,
Roland

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Re: Performance issues when using actions in expressions [message #560102 is a reply to message #560088]

Tue, 21 September 2010 08:37

Meinte Boersma

Messages: 434
Registered: July 2009
Location: Leiden, Netherlands

Senior Member

The pattern Sven described would like this in your case:

Expression:									
	
		BasicExpression ({Expression.left=current} operator=Operator prefix=AddOp? right=BasicExpression)* ;
 

BasicExpression returns Expression:
 	
 		operator=Operator? value=BasicValue ;

I.e., the assignment to the 'right' feature calls BasicExpression instead of Expression. This might explain both the performance issue as well as the non-termination thing, but I haven't tried because you didn't provide the rest of the grammar (specifically the AddOp, Operator, BasicValue rules).

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