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> 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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