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Membrane

Schema

A Membrane program’s graph is defined by its schema, autogenerated in <your-program>/memconfig.json based on the schema you configure in the Navigator panel.

The schema is a set of types that represent nodes in the program’s graph. Nodes can be fields, actions, or events.

  • Fields: queryable nodes and values
  • Actions: invocable functions on a node
  • Events: subscribable notifications

Root Type

Schemas must include a Root type which defines the type of the program’s root node. This node serves as the entry point into the program—all references are relative to the root node.

Nodes are referred to by the program’s name followed by a colon and then a path to the node from the Root type. For example:

  • github: refers to the root node of the github driver
  • twitter: refers to the root node of the twitter driver
  • github:users.one(name:"membrane-io") refers to a Github User
  • github:users.one(name:"membrane-io").repos.one(name:"directory") refers to a Repository

Fields

Fields are queryable nodes that hold values you can read. From the github driver:

  • github:status is a field of type String via the status field on the Root type
  • github:users is a field of type UserCollection via the users field on the Root type
  • github:users.one(name:"membrane-io") refers to a node of type User
  • github:users.one(name:"juancampa") refers to another node of type User

The two last examples show that parameters can be passed to fields where each combination of parameters represent a different node in the graph.

We call these references handles or grefs (short for graph reference).

Actions

Actions are functions that can be invoked in the context of a graph node. Note that since actions are graph nodes too, they can be passed around and referenced just like fields.

Events

Events are members on a type which can be “emitted” by programs when something of interest happens on one of its nodes. Other programs can subscribe to get notified.

Programs can subscribe an action to handle an event. When an event is emitted, the action will be invoked with an additional parameter called event.