Interface Description

Ruleby provides a pure Ruby Domain Specific Language (DSL) for defining rules, and asserting facts to the system. This interface takes advantage of the language features in Ruby that make it a good base for creating DSLs.

The following figure is an example of a Ruleby rule.

rule [Message, :m, m.status == :HELLO] do |v|

  puts v[:m].message

end

In this example, the left hand side of the production (the ‘when’) is represented by the Array parameter. The right hand side (the ‘then’) is represented by the block.

This rule asserts that an object with a status of :HELLO must exist in the collection of facts. If such an object has been added to the working memory, then the ‘action’ specified in the right-hand of this production rule will be fired.

Now let us demonstrate how this rule is used:

engine :hello_engine do |e|

  HelloWorldRulebook.new(e).rules

  assert e, Message.new(:HELLO, ‘Hello World’)

  e.match     

end

The ‘HelloWorld’ rule is contained in the HelloWorldRulebook class (this is shown in the source code). To use it we create a new inference engine, a new rule set, and a new fact. The ‘assert’ method adds the fact to working memory.

When the match method is invoked, the action in the ‘HelloWorld’ rule will be fired. And the system will output the following to the console:

Hello World

Now let us add some more actions to our rule and introduce a second rule to our rulebook:

rule [Message, :m, m.status == :HELLO] do |v|

  puts v[:m].message

  v[:m].message = “Goodbye world”

  v[:m].status = :GOODBYE

  modify v[:m]

end
rule [Message, :m, m.status == :GOODBYE] do |v| 

  puts v[:m].message 

end    

When the match method is called now, the output will be:

Hello World

Goodbye world

Because the fact in working memory was modified by the action in the first rule, the ‘Goodbye’ rule became satisfied.

There is a lot more that can be done in the Ruleby interface. Read The Ruleby DSL for more information.