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@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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