Core extensionsThe Expressions extension

Parent topic: The Expressions extension

Expressions usage patterns

This section introduces various patterns such as operations that send and receive only flag fields, operations that use constants or services that have states.

Codec Operations pattern
A codec operation uses minimal markup to send reply sets comprising flag fields.
Constant Operations pattern
A constant operation outputs constant values for a particular request- or consume-reply operation.
Function Operations pattern
A function operation contains a function mapping the input values, if any, to output values, possibly in alternate output sets.
Metadata pattern
You can extract and use metadata, such as the owner of a mix or a mix component, or the name of a user or a mix component.
Static Bindings in Services pattern
An Erlang function defined as a service property can be referenced by any operation on that service. This way a function can be used by multiple operations. You can also bind functions to variables declared on the operation level.
Stateful Services pattern
State variable bindings allow the svc_expr service to act as a stateful service, where values are persisted in the service instance.
Services as Databases pattern
svc_expr services can function as databases, which can be updated or queried by operations on them.
Notify triggers
The Expressions extension can be used to trigger notify operations if certain conditions are met. The triggers can be bound to state changes or specific patterns, such as periodically triggered events. You can also specify conditions for a triggered notify to be fired or not.

Parent topic: The Expressions extension