Node

A Node is a vertex in a Computation Graph. It is coupled to its graph — a node has no meaning outside one; the graph’s topology defines what each node receives and where its output goes.

The three roles

• Entry node — reads one or more named sources from the cache. In Rust it takes Option<&T> per source (the Option is None until that source is populated); in Python it receives the owned value.
• Processing node — takes its upstream node’s output (&T in Rust, owned in Python) and returns a new value.
• Terminal node — the node with no downstream; its return value is the graph’s result.

Interfaces

Rust

// entry node: reads the "orderbook" source
pub async fn ingest(orderbook: Option<&OrderBookSnapshot>) -> SpreadSignal { /* ... */ }

// processing/terminal node: takes its upstream's output
pub async fn format_output(input: &SpreadSignal) -> FormattedOutput { /* ... */ }

Python

@cloaca.node
def ingest(orderbook):          # entry: receives the owned source value
    return spread_signal(orderbook)

@cloaca.node
def format_output(ingest):      # processing: parameter name = upstream node
    return formatted(ingest)

Routing nodes return a (variant_name, value) tuple; the variant selects the downstream route.

See also

• Computation Graph — nodes only exist inside one.
• Boundary event — what populates an entry node’s source.