Basically for the same reason that you can't say something like this
in Java:
String theMethodName = "toString";
String myString = myObject.(theMethodName)();
but instead you have to use reflection to find the method "toString"
and call it using the Method object. The compiler needs to know the
correct template to use to compile the code, and it can't do that if
the name of the template is in a variable.
Now, you may ask *could* it work the way you want? Indeed, it could --
but it doesn't at this time. We've talked in the past about allowing
this kind of thing, and it has its pros and cons.
On Aug 13, 2010, at 11:05 AM, Donald Winston wrote:
Can anyone explain to me why this does not work? Why can't I use
(deffacts initial-facts
"Facts to trigger a few appropriate salient initialization rules."
(assert-request-parameters))
(defrule assert-request-parameters-rule
"Assert stored data one time."
(declare (salience 100))
?x <- (assert-request-parameters)
=>
(foreach ?key (((fetch request-parameter-map) keySet) iterator)
(build str-cat "(assert (" ?key " " ((fetch request-
parameter-map) get ?key) "))"))
; why not (assert (?key ((fetch request-parameter-map)
get ?key))))
(retract ?x))
(bind ?map (new java.util.HashMap))
(?map put one 1)
(?map put two 2)
(?map put three 3)
(store request-parameter-map ?map)
(reset)
(facts)
(run)
(facts)
Jess, the Rule Engine for the Java Platform
Copyright (C) 2008 Sandia Corporation
Jess Version 7.1p2 11/5/2008
This copy of Jess will expire in 207 day(s).
f-0 (MAIN::initial-fact)
f-1 (MAIN::assert-request-parameters)
For a total of 2 facts in module MAIN.
f-0 (MAIN::initial-fact)
For a total of 1 facts in module MAIN.
---------------------------------------------------------
Ernest Friedman-Hill
Informatics & Decision Sciences, Sandia National Laboratories
PO Box 969, MS 9012, Livermore, CA 94550
http://www.jessrules.com
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