Re: [rules-dev] Backwards chaining: the difference between input and output variables

Hmmmmm.... Personally, I don't like the use of ":" i isolation as it's what we currently use to bind variables and I feel "cheese:" as an output definition could just make people question whether they've missed something. Perhaps "cheese : ?" would be a viable alternative. This would be in keeping with (a) current variable declaration, (b) the use of "?" to identify a call to a query. Geoffrey's examples would then become:- rule outputinput when Here( loc : location) ?editableThings(food : ?, loc;) then System.out.println("Food " + food + " at location " + loc); // Output: // Food crackers at location kitchen // Food apple at location kitchen end rule outputOutput when ?editableThings(food : ?, loc : ?;) then System.out.println("Food " + food + " at location " + loc); // Output: // Food crackers at location kitchen // Food apple at location kitchen // Food chocolate at location living room // Food chips at location living room end rule typo when Here( looc : location) ?editableThings(food : ?, loc : ?;) then System.out.println("Food " + food + " at location " + loc); // Output: // Food crackers at location kitchen // Food apple at location kitchen // Food chocolate at location living room // Food chips at location living room // looc is just an unused bound variable end On 20 April 2011 10:16, Geoffrey De Smet <ge0ffrey.spam(a)gmail.com&gt; wrote: > Mark and I were discussing backwards chaining > http://blog.athico.com/2011/04/backward-chaining-emerges-in-drools.html > on IRC and we 'd like your opinion on a design issue. > > The example > ======== > > Let's say you have this data: > Location("crackers", "kitchen") > Location("apple", "kitchen") > Location("chocolate", "living room") > Location("chips", "living room") > > Let's say you have this code: > > query editableThings( String thing, String location ) > Location(thing, location) > end > > And then these 3 rules: > > rule outputinput > when > Here( loc : location) > ?editableThings(food, loc;) > then > System.out.println("Food " + f + " at location " + loc); > // Output: > // Food crackers at location kitchen > // Food apple at location kitchen > end > > rule outputOutput > when > ?editableThings(food, loc;) > then > System.out.println("Food " + f + " at location " + loc); > // Output: > // Food crackers at location kitchen > // Food apple at location kitchen > // Food chocolate at location living room > // Food chips at location living room > end > > rule typo > when > Here( looc : location) > ?editableThings(food, loc;) > then > System.out.println("Food " + f + " at location " + loc); > // Output: > // Food crackers at location kitchen > // Food apple at location kitchen > // Food chocolate at location living room > // Food chips at location living room > end > > > The discussion > ========= > > Both rules have the same statement: > ?editableThings(food, loc;) > > In the outputInput rule, "loc" is an input variable. > In the outputOutput rule, "loc" is an output variable. > > I am wondering if we don't need a visual demarcation that a variable is an > output variable, > to make it stand out of an input variable? > > Proposition 1: Suffix output variables with ":" > > rule outputinput > when > Here( loc : location) > ?editableThings(food:, loc;) > then ... end > > rule outputOutput > when > ?editableThings(food:, loc:;) > then ... end > > rule typo > when > Here( looc : location) > ?editableThings(food:, loc;) // compiler error because input variable > loc is not declared > then ... end > > > -- > With kind regards, > Geoffrey De Smet > > _______________________________________________ > rules-dev mailing list > rules-dev(a)lists.jboss.org > https://lists.jboss.org/mailman/listinfo/rules-dev > > _______________________________________________ rules-dev mailing list rules-dev(a)lists.jboss.org https://lists.jboss.org/mailman/listinfo/rules-dev