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Chapter 16. Patterns
16.1. Patterns
A pattern element is the most important Conditional Element. It can potentially match on each fact that is inserted in the working memory. A pattern contains constraints and has an optional pattern binding.
16.2. Pattern Example
This is what a pattern looks like:
rule "2 unconnected patterns" when Pattern1() Pattern2() then ... // actions end // The above rule is internally rewritten as: rule "2 and connected patterns" when Pattern1() and Pattern2() then ... // actions end
Note
An
and
cannot have a leading declaration binding. This is because a declaration can only reference a single fact at a time, and when the and
is satisfied it matches both facts.
16.3. Pattern Matching
A pattern matches against a fact of the given type. The type need not be the actual class of some fact object. Patterns may refer to superclasses or even interfaces, thereby potentially matching facts from many different classes. The constraints are defined inside parentheses.
16.4. Pattern Binding
Patterns can be bound to a matching object. This is accomplished using a pattern binding variable such as
$p
.
16.5. Pattern Binding with Variable Example
This is what pattern binding using a variable looks like:
rule ... when $p : Person() then System.out.println( "Person " + $p ); end
Note
The prefixed dollar symbol (
$
) is not mandatory.
16.6. Constraints
A constraint is an expression that returns
true
or false
. For example, you can have a constraint that states five is smaller than six.