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Explicit events are raised in the rule postlude with a raise statement. You can raise events from a postlude like so:

raise <domain> event <expr> [for <expr>] [with <modifier_clause> | attributes <expr>] 

The event name is given by the <expr>. The expression is evaluated and the resulting string is used as the event name.

Because the event name is an expression, you must use a string rather than using a bare word.


Attributes for the event can be given using either the modifier clause denoted by the keyword with or the attributes clause denoted by the keyword attributes. You can use a modifier clause or an attributes clause, but not both. 

Modifier Clause

The modifier clause allows the developer to add event parameters to the event. The right side of the individual bindings in the with clause can be any KRL expression. The modifier clause takes the following form:

with <var> = <expr> [[and] <var> = <expr>]* 

Any variable in a modifier clause is used (with its associated value) as an event parameter.  

The following example illustrates this

raise explicit event "foo"
  with a = "hello"
       b = 4 + x;

Attributes Clause

The attributes clause also allows the developer to add event attributes to the event. The expression that follows the attributes key word must evaluate to a map. The keys and values in the map will be used as event attributes. This is particularly useful when you want to pass through all, or most, of the attributes that the current rule received:

raise explicit event "foo"
  attributes event:attrs()

This raises the event explicit:foo with all of the attributes that were passed into the enclosing rule.

What Rulesets See an Explicit Event?

You can control which rulesets see an explicit event using the optional for clause. 

The for clause is followed by an expression that is evaluated to determine which rule sets should see the event. The result must be a string, giving the target ruleset ID or an array of target rulesets. A target ruleset ID has the form <rid[.<ver>]> where the optional version may be the keyword "prod" for the production ruleset or a version number for the explicit version. If the version is unspecified, the system will match the target version to the version of the current ruleset.

In the Sky Event API, explicit events will be raised to any ruleset that an entity has installed unless a for clause is present. You can specify the current ruleset using the meta:rid() functions from the meta library.  Normally the API is determined by what API was used to raise the event that caused processing to commence. You can ensure that the behavior of explicit events will follow the Sky API behavior by specifying that the Sky API be used as follows:

raise explicit event "foo"
  with a = "hello"
       b = 4 + x
       _api = "sky";

Like any other postlude statement, explicit events can be guarded:

raise explicit event "foo"
  with a = "hello"
       b = 4 + x
 if (flipper == "two");

The event in the preceding example will only be raised if the variable flipper has the value "two".

Explicit events allow KRL programmers to chain rules together. Rule chaining is good for modularization, error handling, preprocessing, and abstraction.