[rules-users] How to use the value of a function in both theLHSand RHS side of the rule ?

[Anstis, Michael (M.)]

Hi Mithun,
 
Assert(), assertLogical(), modify() and retract() in DRL are implicit
functions to do the exact same as WorkingMemory's related members (much
like request and response in a JSP).
 
What's more there is an implicit "drools" global too that can be used to
access an instance of DefaultKnowledgeHelper.
 
I don't know whether there are any other implicit objects.
 
With kind regards,
 
Mike


________________________________

	From: rules-users-bounces at lists.jboss.org
[mailto:rules-users-bounces at lists.jboss.org] On Behalf Of Mithun Gooty
	Sent: 31 May 2007 08:01
	To: Rules Users List
	Subject: RE: [rules-users] How to use the value of a function in
both theLHSand RHS side of the rule ?
	
	
	Hi All,
	 
	        Can anybody tell as to wat does the assert() method do
in a DRL file, like the way it is used in the below example. I am aware
of assertObject() method but not assert() method. 
	 
	Thank you,
	Mithun

		-----Original Message-----
		From: rules-users-bounces at lists.jboss.org
[mailto:rules-users-bounces at lists.jboss.org] On Behalf Of Edson Tirelli
		Sent: Thursday, May 17, 2007 7:28 PM
		To: Rules Users List
		Subject: Re: [rules-users] How to use the value of a
function in both the LHSand RHS side of the rule ?
		
		
		   Krishnan,
		
		   I always prefer to use specific tools for specific
jobs. So, if I were implementing that, I would not put the I/O code
inside the DRL.
		   If you want your rules to drive the parsing, I would
model it like that: 
		
		1) Create a class to "represent" your file... that would
be your File interface. It would have a method: readLine() that returns
a Line object, as well as an "eof" property (true when EOF was reached).

		
		2) Create a rule to drive your parsing:
		
		
		rule "R1: Read one more line"
		    when 
		        $f : File( eof == false )
		    then 
		        System.out.println("Generate new line");
		        assert( $f.readLine() ); 
		        modify( $f ); // as readLine "modifies" the
state of the File 
		end
		
		3) Create the rules to effectivelly "analyze" your
lines. If you want to read all lines first and then analyze them, just
make rule R1 to have a greater salience. Otherwise, if you want each
line analyzed as it is parsed, make your other rules have a greater
salience as showed bellow: 
		
		rule "Rx: analyze line"
		   salience 10
		when
		    Line( content matches "xxx" ) 
		then
		    // do something
		end
		
		4. Create the rule to close your file when EOF is
reached:
		
		rule "close file'
		when
		    $f: File( eof == true )
		then
		    $f.closeFile();
		end
		
		   Keeping the procedural code in your java classes
instead of DRL functions makes all your rules more clear, makes easy to
unit test each part, and reduces the overall complexity. 
		
		   That is how I would do it.
		
		   Hope it helps.
		    Edson
		
		
		2007/5/17, Krishnan <krishiyer at gmail.com>: 

			
			Hi, 
			
			I want to parse a file and match the file for
several regular expressions. Based on what I match, I write more 
			rules so that based on all the rules, I can set
my results. 
			
			Brute force method : Parse the entire file and
add all the lines into the working memory. Write rules that 
			check each line for some regular expression.
This works great. 
			
			I want to optimize the above, as we are checking
each line, if we got we are looking for, then I want to get out. 
			
			
			
			So, I wrote a function inside the rule file like
the below 
			
			function String getLine(BufferedReader
fileReader) {
			    String line;
			    try {
			        if ((line = fileReader.readLine()) !=
null) {
			            return line.toLowerCase();
			        } else {
			            System.out.println("This is an empty
line.");
			        }
			    } catch (Exception ex) {      
			    }
			    return line;
			}
			
			Now, I need to write the rules that will use
this. 
			
			rule "Generate New Line"
			
			    when 
			        eval (getLine(fileReader) != null)
			    then 
			        System.out.println("Generate new line");
			        //assert(getLine(fileReader)); // need
to somehow assert the line specified in the eval condition 
			
			end
			
			Also, I am confused, how to specify file end. 
			
			rule "File End"
			
			    when 
			        eval (getLine(fileReader) == null)
			    then 
			        System.out.println("Reached end of
file"); // I am assuming this is not needed since if all rules are
executed, then it will get out of fireRules() anyways ?
			
			end
			
			Any help is appreciated. 
			
			TIA, 
			Krishnan (newbie)
			
			
			- 
			Sivaramakrishna Iyer Krishnan (Anand) 
			
			Never assume the obvious is true. 
			- William Safire 
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		-- 
		  Edson Tirelli
		  Software Engineer - JBoss Rules Core Developer
		  Office: +55 11 3529-6000
		  Mobile: +55 11 9287-5646 
		  JBoss, a division of Red Hat @ www.jboss.com 

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