Thomas Gentsch mentioned that a Userfunction equivalent to Java's
"instanceof" operator would be useful. I wrote a quick one that makes
use of the existing facilities offered by the Jess "import" function,
and I thought I'd share it. If you've got the Jess source, just tack
this onto the end of jess/ReflectFunction.java (it needs to be defined
in the jess package since it uses the package-protected findClass
method) and in the add() method at the top, insert
addFunction(new InstanceOf(), table);
at the end of the list of addFunction() calls. Then you can use it
like this:
Jess> (import jess.*)
TRUE
Jess> (instanceof (engine) Rete)
TRUE
Jess> (instanceof (engine) String)
FALSE
Jess> (instanceof "asdf" String)
TRUE
Jess>
Enjoy! This will be in the next Jess release.
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class InstanceOf implements Userfunction, Serializable {
public String getName() { return "instanceof"; }
public Value call(ValueVector vv, Context context)
throws JessException {
Object o = vv.get(1).externalAddressValue(context);
String className = vv.get(2).stringValue(context);
try {
Class clazz = context.getEngine().findClass(className);
return clazz.isInstance(o) ? Funcall.TRUE : Funcall.FALSE;
} catch (ClassNotFoundException cnfe) {
throw new JessException("instanceof",
"Class not found: " + className,
cnfe);
}
}
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Ernest Friedman-Hill
Distributed Systems Research Phone: (925) 294-2154
Sandia National Labs FAX: (925) 294-2234
Org. 8920, MS 9012 [EMAIL PROTECTED]
PO Box 969 http://herzberg.ca.sandia.gov
Livermore, CA 94550
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