Hi,
How exactly is the compare(Activation a1, Activation a2) method of the
Strategy interface to be written? The documentation is a little vague.
It says it should behave like Comparable.compare(). I assume this is a
typo for Comparator.compare(). (There is no Comparable.compare().
There's a Comparable.compareTo(), but it takes a single argument.)
Is compare(Activation a1, Activation a2) supposed to return a negative
int, 0, or a positive int if a1 is ordered less than a2, equal to a2, or
greater than a2 in the agenda?
Below is a Strategy class I wrote, but doesn't work. Perhaps Dr.
Friedman-Hill or other knowledgeable person could point out my mistake:
--------------------------------------------------------------
public class RecencyThenSalience implements Strategy
{
private static final String name = "RecencyThenSalience";
public RecencyThenSalience()
{
}
public int compare(Activation act1, Activation act2)
{
int result = 0;
Token token1 = act1.getToken();
Token token2 = act2.getToken();
if(token1.size() < token2.size())
{
result = -1;
}
else if(token1.size() > token2.size())
{
result = 1;
}
else
{
ArrayList<Integer> act1_times = new ArrayList<Integer>();
ArrayList<Integer> act2_times = new ArrayList<Integer>();
for(int i = 0; i < token1.size(); i++)
{
act1_times.add(new Integer(token1.fact(i).getTime()));
}
for(int i = 0; i < token2.size(); i++)
{
act2_times.add(new Integer(token2.fact(i).getTime()));
}
// sort the pseudo-times in descending order
Collections.sort(act1_times, Collections.reverseOrder());
Collections.sort(act2_times, Collections.reverseOrder());
Iterator<Integer> i = act1_times.iterator();
Iterator<Integer> j = act2_times.iterator();
while(i.hasNext())
{
int time1 = i.next().intValue();
int time2 = j.next().intValue();
if(time1 < time2)
{
result = -1;
break;
}
else if(time1 > time2)
{
result = 1;
break;
}
}
if(result == 0) result = (act1.getSalience() <
act2.getSalience())? -1 : 1;
}
return result;
}
public String getName()
{
return name;
}
}
-----------------------------------------------------------
Here is a sample Jess file that uses the Strategy:
(set-strategy elect.jess.support.RecencyThenSalience)
(deftemplate task (slot goal) (multislot args))
(deffacts init
(stapler ritchie)
(stapler big-guy)
(stapler ralphy)
(stapler tony-b)
(stapler jackie-jr)
(hole-punch livia)
(hole-punch artie)
(hole-punch ritchie)
(hole-punch tony-b)
(task (goal start)))
(defrule start
(task (goal start))
=>
(assert (task (goal stapler-owners)))
(assert (task (goal hole-punch-owners))))
(defrule hole-punch-and-stapler-owners
(task (goal hole-punch-owners))
(task (goal stapler-owners))
(stapler ?name)
(hole-punch ?name)
=>
(printout t ?name " owns both a hole-punch and a stapler." crlf))
(defrule hole-punch-owners
(task (goal hole-punch-owners))
(hole-punch ?name)
(not (stapler ?name))
=>
(printout t ?name " owns just a hole-punch." crlf))
(defrule stapler-owners
(task (goal stapler-owners))
(stapler ?name)
(not (hole-punch ?name))
=>
(printout t ?name " owns just a stapler." crlf))
(defrule gc-task
?t <- (task)
=>
(retract ?t))
-------------------------------------------------------------
Here is the error I get from the console:
Jess> (clear)
TRUE
Jess> (batch "C:/steve/jess/stapler.clp")
TRUE
Jess> (reset)
Jess reported an error in routine reset
while executing (reset).
Message: Error during execution.
Program text: ( reset ) at line 75.
Nested exception is:
null
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