RIDDL Documentation
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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.

ArbitraryA textually described arbitrary statement
AskSend a message to an entity, asynchronously process result
BecomeInstructs an entity change to a new handler
ErrorProduce an error with a message
ForEachInvoke statements on each item of a multi-valued field
IfThenElseEvaluate a condition and choose execute a statement set
FunctionCallCall a function to get a result
MorphMorph the state of an entity to a new state
PublishPublish a message to a pipe
ReplyProvide the reply message to the entity that invoked a query
ReturnReturn a value from a function
SetSet a field value
TellSend a message to an entity directly, do not wait for result

Level of Detail

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.

Occurs In


Some statements contain conditionals, values and path identifiers to reference things in the system models. None of these are definitions.