Statement
A Statement is an action that can be taken in response to a message. Statements form the body of an on clause which is what [handlers]({{relref “handlers.md”>}}] are composed of. There are many kinds of statements, described in the table below.
| Name | Description |
|---|---|
| Arbitrary | A textually described arbitrary statement |
| Ask | Send a message to an entity, asynchronously process result |
| Become | Instructs an entity change to a new handler |
| Error | Produce an error with a message |
| ForEach | Invoke statements on each item of a multi-valued field |
| IfThenElse | Evaluate a condition and choose execute a statement set |
| FunctionCall | Call a function to get a result |
| Morph | Morph the state of an entity to a new state |
| Publish | Publish a message to a pipe |
| Reply | Provide the reply message to the entity that invoked a query |
| Return | Return a value from a function |
| Set | Set a field value |
| Tell | Send a message to an entity directly, do not wait for result |
Statements are aimed at writing pseudocode in a structured but abstract way. RIDDL does not intend the system model to contain the code that will be used in its implementation. It also expects the reader to be intelligent and fill in the (obvious) gaps that are left missing. This leads to these objectives for writing an onclause’s:
- Converting the specification to executable code should be done by a human or a sufficiently capable AI/ML
- The statements are designed to capture interactions between the definitions of the model, and are specifically not Turing complete.
- Statements should capture significant references to data and
- There is no need to model computational expresses exhaustively when a simple natural language statement will do.
Not all statements may be used in every On Clause. It depends on the kind of
definition the statement is attached to. Statements occur in the
onclause of the
handlers of all the
vital definitions.
Note that the Become and Morph statements are only applicable to
statements in an Entity. The others are generally applicable.
Some statements contain conditionals, values and path identifiers to reference things in the system models. None of these are definitions.