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

[Mark Proctor]

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 <mailto: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
>     <mailto: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
>
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