[rules-dev] Backwards chaining: the difference between input and output variables
Michael Anstis
michael.anstis at gmail.com
Thu Apr 21 05:25:07 EDT 2011
@ge0ffrey,
*you* know "looc" is a typo, but "loc" could equally be an unused bound
variable and "looc" an unused output value.
I find it difficult to see there is sufficient "context" to give a suitable
error message - other than perhaps warning of unused bindings.
@wolfgang,
Your proposition works for slotted parameters; whereas the ";" allowed for
positional parameters too.
AFAIK the BC changes bring two discrete features: BC and positional
parameters.
@all
I've expressed my "simpleton" view on how, as a user, I would best
understand its operation.
It isn't based upon science or a wealth of experience with a multitude of
other programming languages; just a "feeling" of what I consider right.
Being just a "feeling" I am happy to watch this discussion evolve and learn
from others' experience.
With kind regards,
Mike
On 21 April 2011 07:50, Geoffrey De Smet <ge0ffrey.spam at gmail.com> wrote:
> and instead have the tooling inject what ever is necessary as a
> visulation.
>
> > Most questions we have to the user mailing list involve people writing
> DRL not using tooling.
>
> IntelliJ users and NetBeans users don't have any (up-to-date) DRL tooling.
> Some Eclipse users I know don't install extra plugins such as the drools
> plugin out of fear of Eclipse instability.
> The new Eclipse plugin wont do that visualization yet either?
>
>
> I like Laun's and Manstis and mine proposal,
> as long as there's something in the syntax that makes it clear whether that
> food is
> - an input variable => constrains the rule, potentially decreasing the
> number of activations
> - an output variable => frees the rule, potentially increasing the number
> of activations
>
> And a typo shouldn't change the behavior from one to the other, it should
> give a compilation error.
> rule typo2
> when
> Here( loc : location)
> ?editableThings(food, looc;) // looc is a typo of 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 kitchen // BUG: that food is in the
> living room!
> // Food chips at location kitchen // BUG: that food is in the living
> room!
> end
>
>
>
>
> Op 21-04-11 08:27, Wolfgang Laun schreef:
>
> Designing syntax well is not easy. With extensions, one should strive for
> as much
> conformity with the existing language, while trying to follow general
> principles.
>
> One might have discussed (for instance) the use of field names for
> referencing
> the query relations, taken from their parameter definition. And then one
> could write,
> as usual:
>
> ?editableThings(food: thing, location == loc )
>
> or
>
> ?editableThings(food: thing, loc: location )
>
> And the in/out is clear to all who know a little legacy DRL.
>
> And the ugly semicolon evaporates.
>
> And the maintainability/readability disadvantage of "positional" is gone.
>
> Cheers
> -W
>
>
> On 20 April 2011 22:52, Michael Anstis <michael.anstis at gmail.com> wrote:
> >
> > Simple yes, but consistent too should be a factor.
> >
> > Most questions we have to the user mailing list involve people writing
> DRL not using tooling.
> >
> > So DRL, IMO, has to be seen as the "tool" to author rules. Drop the
> proposed colon altogether or make it's use consistent.
> >
> > On 20 April 2011 17:42, Mark Proctor <mproctor at codehaus.org> wrote:
> >>
> >> My personally opinion is to keep the language simple and instead have
> the tooling inject what ever is necessary as a visulation. Be it different
> colouring, hover over or graphic symbol. It keeps the language simple and
> actually achieve the desired result better.
> >>
> >> Mark
> >> On 20/04/2011 14:00, Leonardo Gomes wrote:
> >>
> >> +1 for Michael's suggestion.
> >>
> >> It's a bit more verbose, but makes things clear.
> >>
> >> The semicolon here:
> >> ?editableThings(food : ?, loc;)
> >>
> >> Is a typo, right? You actually meant:
> >>
> >> ?editableThings(food : ?, loc);
> >>
> >> - Leo.
> >>
> >>
> >>
> >> On Wed, Apr 20, 2011 at 11:59 AM, Michael Anstis <
> michael.anstis at gmail.com> wrote:
> >>>
> >>> 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 at gmail.com>
> 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 at lists.jboss.org
> >>>> https://lists.jboss.org/mailman/listinfo/rules-dev
> >>>>
> >>>
> >>>
> >>> _______________________________________________
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> >>> https://lists.jboss.org/mailman/listinfo/rules-dev
> >>>
> >>
> >>
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> >>
> >>
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> >
> >
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>
> --
> With kind regards,
> Geoffrey De Smet
>
>
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