"Created by" plugin

The @model macro is capable of saving arbitrary extra metadata information for individual factor nodes upon creation. This feature is used by various plugins, one of which is GraphPPL.NodeCreatedByPlugin.

NodeCreatedByPlugin

This plugin saves the expression that has been used to create a particular factor node, which can later be queried, for example, for debugging purposes. Here's how it works:

@model function probabilistic_model()
    x ~ Beta(1, 1)
    for i in 1:10
        y[i] ~ Normal(x, 1)
    end
end

model = GraphPPL.create_model(
    GraphPPL.with_plugins(
        probabilistic_model(),
        GraphPPL.PluginsCollection(GraphPPL.NodeCreatedByPlugin())
    )
)

We can now read the :created_by extra field for each individual node to see the expression that has created it. To do that we need to call the GraphPPL.getextra on GraphPPL.NodeData object with the :created_by as the key.

GraphPPL.factor_nodes(model) do label, nodedata
    println("Node ", label, " has been created by ", GraphPPL.getextra(nodedata, :created_by))
end

Node Distributions.Beta_4 has been created by x ~ Beta(1, 1)
Node Distributions.Normal_7 has been created by y[i] ~ Normal(x, 1)
Node Distributions.Normal_10 has been created by y[i] ~ Normal(x, 1)
Node Distributions.Normal_13 has been created by y[i] ~ Normal(x, 1)
Node Distributions.Normal_16 has been created by y[i] ~ Normal(x, 1)
Node Distributions.Normal_19 has been created by y[i] ~ Normal(x, 1)
Node Distributions.Normal_22 has been created by y[i] ~ Normal(x, 1)
Node Distributions.Normal_25 has been created by y[i] ~ Normal(x, 1)
Node Distributions.Normal_28 has been created by y[i] ~ Normal(x, 1)
Node Distributions.Normal_31 has been created by y[i] ~ Normal(x, 1)
Node Distributions.Normal_34 has been created by y[i] ~ Normal(x, 1)

The nodes correctly identify the expressions, which have created them.