Action

An Action is something a program does. Actions are used in the then and but clauses of an example.

There are many kinds of Actions, described in the table below

Name	Description
Append	Add an item to a field that is a collection
Arbitrary	A textually described arbitrary action
Ask	Send a message to an entity, asynchronously process result
Become	Instructs an entity change to a new handler
Compound	Execute a group of nested actions
Error	Produce an error with a message
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 of the current state of an entity
Tell	Send a message to an entity, do not wait for result
Yield	Place a message on an entity’s event pipe

Applicability

Not all actions can be used in every situation. The table below show the exceptions. Examples occur in handlers and they in turn occur in contexts, entities, functions, projections, and states.

Name	Context	Entity	Function	Projection	State
Append	⚠	✓	⚠	✓	✓
Arbitrary	✓	✓	✓	✓	✓
Ask	✓	✓	✓	✓	✓
Become	⚠	✓	⚠	✓	✓
Compound	✓	✓	✓	✓	✓
Error	✓	✓	✓	✓	✓
FunctionCall	✓	✓	✓	✓	✓
Morph	⚠	✓	⚠	⚠	✓
Publish	✓	✓	✓	✓	✓
Reply	⚠	✓	⚠	✓	✓
Return	✓	⚠	✓	✓	⚠
Set	⚠	✓	⚠	✓	✓
Tell	✓	✓	✓	✓	✓
Yield	⚠	✓	✓	✓	✓