Crate takeln 

takeln

Typed Rust runtime for durable DAG-based agent workflows.

takeln is a lightweight, production-grade execution engine for Directed Acyclic Graphs (DAGs) in Rust. It provides built-in wave-based parallel scheduling, robust state checkpointing, retry policies, budget enforcement, and LLM metadata instrumentation.

Feature Flags

Flag	Default	Description
postgres	No	Enables PostgresCheckpointer backed by PostgreSQL via sqlx
sqlite	No	Enables SqliteCheckpointer backed by SQLite via rusqlite

Quick Start

use async_trait::async_trait;
use takeln::{Graph, Node, NodeContext, NodeOutput, GraphError, InMemoryCheckpointer};

#[derive(Clone, serde::Serialize, serde::Deserialize, Default)]
struct MyState { value: String }

struct AppendNode { suffix: String }

#[async_trait]
impl Node<MyState> for AppendNode {
    async fn call(&self, _ctx: NodeContext, mut state: MyState) -> Result<NodeOutput<MyState>, GraphError> {
        state.value.push_str(&self.suffix);
        Ok(NodeOutput::bare(state))
    }
}

#[tokio::main]
async fn main() {
    let mut graph = Graph::new();
    graph.add_node("A", AppendNode { suffix: "Hello".to_string() });
    graph.add_node("B", AppendNode { suffix: " World".to_string() });
    graph.add_edge("A", "B");
    graph.add_edge("B", "__END__");

    let checkpointer = InMemoryCheckpointer::new();
    let state = graph.run("thread_1", MyState::default(), "A", &checkpointer, None).await.unwrap();
    assert_eq!(state.value, "Hello World");
}

Re-exports

pub use checkpoint::Checkpointer;

pub use checkpoint_meta::CheckpointMeta;

pub use checkpoint_meta::CheckpointStatus;

pub use checkpoint_meta::CrashRecoveryPolicy;

pub use checkpoint_meta::RetentionPolicy;

pub use context::NodeContext;

pub use dag::DAGBuilder;

pub use dag::DAGNode;

pub use dag::NodeStatus;

pub use dag::DAG;

pub use dynamic::ChildRunner;

pub use dynamic::DynamicFnNode;

pub use dynamic::DynamicNode;

pub use emitter::NoopEmitter;

pub use emitter::SpanContext;

pub use emitter::SpanEmitter;

pub use emitter::SpanStatus;

pub use emitter::TracingEmitter;

pub use error::GraphError;

pub use error::TakelnError;

pub use graph::Edge;

pub use graph::FnNode;

pub use graph::Graph;

pub use graph::GraphBuilder;

pub use graph::GraphEvent;

pub use graph::Node;

pub use graph::NodeConfig;

pub use graph::NodeMeta;

pub use graph::NodeOutput;

pub use graph::RetryPolicy;

pub use graph::State;

pub use graph::WaveFailurePolicy;

pub use history::ExecutionRecord;

pub use hitl::ResumeContext;

pub use hitl::ResumeMode;

pub use hitl::ResumeRecord;

pub use hitl::YieldRequest;

pub use merge::Merge;

pub use metrics::MetricsHook;

pub use metrics::NoopMetricsHook;

pub use resource_limits::ResourceLimits;

pub use store::memory::InMemoryCheckpointer;

pub use store::postgres::PgPool;

pub use store::postgres::PostgresCheckpointer;

pub use store::sqlite::SqliteCheckpointer;

Modules

checkpoint

checkpoint_meta

context

Execution context passed to every node invocation.

dag

dynamic

Dynamic node execution primitives.

emitter

error

graph

history

hitl

Structured Human-in-the-Loop (HITL) yield requests.

merge

metrics

resource_limits

Resource limits for graph execution.

store