CLIPS: asserting facts from within a function does not respect template constraints

0
votes

I have a single-slot deftemplate definition with a constraint on the allowed symbols. If I directly assert a fact from the top level, the constraints work as expected (i.e. I can only use one of the allowed symbols). However, if I do it from within a deffunction, the constraint is effectively non-existent (see code output below). How do I enforce the constraint from within my function?

CLIPS> (clear)
CLIPS> (deftemplate test-template (slot myslot (type SYMBOL) (allowed-symbols A B C)))
CLIPS> (deffunction test-function (?s) (assert (test-template (myslot ?s))))
CLIPS> (assert (test-template (myslot X)))

[CSTRNCHK1] A literal slot value found in the assert command
does not match the allowed values for slot myslot.
CLIPS> (test-function X)
<Fact-1>
CLIPS> (facts)
f-0     (initial-fact)
f-1     (test-template (myslot X))
For a total of 2 facts.
CLIPS>
1
constraintsassertclipsslot

1 Answers

0
votes

Static constraint checking (which occurs during parsing) is enabled by default. Dynamic constraint checking (which occurs during code execution) is not (see section 11 of the Basic Programming Guide). If you enable it you'll get a constraint violation in your example (although you need to assert a fact with a slot value other than X--duplicate facts are not allowed and during execution this check will occur before the constraint check).

CLIPS> (clear)
CLIPS> (deftemplate test-template (slot myslot (type SYMBOL) (allowed-symbols A B C)))
CLIPS> (deffunction test-function (?s) (assert (test-template (myslot ?s))))
CLIPS> (assert (test-template (myslot X)))

[CSTRNCHK1] A literal slot value found in the assert command
does not match the allowed values for slot myslot.
CLIPS> (test-function Y)
<Fact-1>
CLIPS> (set-dynamic-constraint-checking TRUE)
FALSE
CLIPS> (test-function Z)

[CSTRNCHK1] Slot value Z found in fact f-2     
does not match the allowed values for slot myslot.
[PRCCODE4] Execution halted during the actions of deffunction test-function.
<Fact-2>
CLIPS>