That makes perfect sense.
Thank you.
- Original Message -
From: Friedman-Hill, Ernest
To: jess-users
Sent: Thursday, November 10, 2011 2:15 PM
Subject: RE: JESS: Scoping Question
Since control structures are functions in Jess, the ability for a function to
peek from one stack frame to another is important. I could have implemented
this using some kind of special form or keyword -- like the Tcl uplevel
function -- but in the first go-round, I think I just took the easy way out,
and this behavior has stuck ever since. Note that it's read-only by default:
binding a value to a variable in a deffunction creates a new variable in the
local scope. That's why recursive functions are possible.
--
From: owner-jess-us...@sandia.gov [mailto:owner-jess-us...@sandia.gov] On
Behalf Of David Scuse
Sent: Wednesday, November 09, 2011 11:43 AM
To: jess-users
Subject: JESS: Scoping Question
Hi Ernest:
I came across a strange feature of Jess as a result of a typing error.
It appears as though Jess uses dynamic scoping -- any variables defined in
a rule
are visible in any functions called by the RHS of the rule.
I looked for references to this in the book and the manual but couldn't
find anything.
Is this the expected behaviour? (This is just a curiosity question.)
Thanks
David
(deftemplate person (slot name) (slot age))
(deffacts initialFacts
(person (name bill) (age 20))
(person (name will) (age 25))
(person (name dill) (age 25))
(person (name jill) (age 22)) )
(defrule findOldest
?f - (person (age ?max))
(not (person (age ?less:( ?less ?max
=
(my-function) )
(deffunction my-function ()
(printout t crlf Processing fact (?f toString) crlf)
(printout t crlf Max age is ?max crlf)
(printout t crlf Max age is ?f.age crlf crlf) )
(reset)
(run)
(facts)
