5.4.1.1 Literal Constraints

The most basic constraint which can be used in a pattern CE is one which precisely defines the exact value that will match a field. This is called a literal constraint. A literal pattern CE consists entirely of constants such as floats, integers, symbols, strings, and instance names. It does not contain any variables or wildcards. All constraints in a literal pattern must be matched exactly by all fields of a pattern entity.

Syntax

An ordered pattern conditional element containing only literals has the following basic syntax:

(<constant-1> ... <constant-n>)

A deftemplate pattern conditional element containing only literals has the following basic syntax:

(<deftemplate-name> (<slot-name-1> <constant-1>)
                                        ï
                                        ï
                                        ï
                    (<slot-name-n> <constant-n>))

Example 1

This example utilizes the datafacts deffacts shown in section 5.4.1.

CLIPS> (clear)
CLIPS> (defrule find-data (data 1 blue red) =>)
CLIPS> (reset)
CLIPS> (agenda)
0      find-data: f-3
For a total of 1 activation.
CLIPS> (facts)
f-0     (initial-fact)
f-1     (data 1.0 blue "red")
f-2     (data 1 blue)
f-3     (data 1 blue red)
f-4     (data 1 blue RED)
f-5     (data 1 blue red 6.9)
For a total of 6 facts.
CLIPS>

Example 2

This example utilizes the person deftemplate and people deffacts shown in section 5.4.1.

CLIPS> (clear)
CLIPS>
(defrule Find-Bob
  (person (name Bob) (age 20))
  =>)
CLIPS>
(defrule Find-Sue
  (person (age 34) (name Sue))
  =>)
CLIPS> (reset)
CLIPS> (agenda)
0      Find-Sue: f-4
0      Find-Bob: f-2
For a total of 2 activations.
CLIPS> (facts)
f-0     (initial-fact)
f-1     (person (name Joe) (age 20) (friends))
f-2     (person (name Bob) (age 20) (friends))
f-3     (person (name Joe) (age 34) (friends))
f-4     (person (name Sue) (age 34) (friends))
f-5     (person (name Sue) (age 20) (friends))
For a total of 6 facts.
CLIPS>