Hello it's me again!
I have another problem i need some help with.
I have the following facts in my database:
(deffacts initial-data
(on (x a) (y b))
(on (x b) (y c))
(on (x c) (y table))
)
I have the following rule:
(defrule put_on
"rule to put x on y"
(goal {x != y} (y ?goal_y) (x ?goal_x))
(goal {x != table})
?on <-(on (x ?goal_x) (y ?myy))
?goal <- (goal (x ?goal_x) (y ?goal_y))
(test (strips_clear ?goal_x))
(test (strips_clear ?goal_y))
=>
(retract ?goal)
(retract ?on)
(assert (on (x ?goal_x) (y ?goal_y)))
(assert (move (x ?x) (y ?myy) (z ?y)))
)
And i have the following function and query:
(defquery qry_clear
"comment"
(declare (variables ?x))
(on (y ?x) (x ?myx))
)
(deffunction strips_clear (?x)
"check if x is clear. means that nothing is ontop of x"
(if (eq ?x table) then
(return TRUE)
else
(bind ?result (count-query-results qry_clear (sym-cat ?x)))
(if (= ?result 0) then
(return TRUE)
else
(bind ?result (run-query* qry_clear ?x))
(?result next)
(bind ?resultx (?result getSymbol myx))
(?result close)
(bind ?tmp (str-cat "(on (x " ?resultx ") (y " ?x "))"))
(printout t ?tmp crlf)
;(return FALSE)
(strips_clear ?resultx)
(retract-string ?tmp)
(assert-string (str-cat "(on (x " ?resultx ") (y table))"))
(assert-string (str-cat "(move (x " ?resultx ") (y " ?x ") (z
table))"))
)
)
)
What the function should do is, check if there is something "ontop" of the
given parameter and if there is actually something ontop, it should get
removed and put on the table (yep it's the famous blocks world ;) ). That is
indicated with a fact in the db. E.g. (on (x a) (y b)) means that a is ontop
of b. If something is ontop of the parameter the function is called
recursively to check if something is ontop of that particular parameter.
The problem i'm facing now is when i actually have a recursive call of the
function (bind ?resultx (?result getSymbol myx)) fails with the message: The
cursor is before the first row; you must call next() before accessing query
result . It works fine if i don't have a recursive call. Isn't it possible
to achieve this bahaviour?
Regards and thanks in advance,
Christoph
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