# std.agent_loop > Reflected API reference for the Sema standard-library module std.agent_loop. > Generated by `sema doc` from `stdlib/sema/agent_loop.sema`. Import with `from std.agent_loop import …`. For a narrative introduction see [std.agent_loop](/stdlib/agent_loop/). # `agent_loop` std.agent_loop — the agentic loop as a reusable combinator (design ④). `loop_until(init, max_iters, step, done)` runs `step` (a pure state -> state function) until `done(state)` or `max_iters`. Replaces the ~300-line hand-rolled `_run_deep` while loop; the termination policy is data. `step`/`done` are pure lambdas over an immutable state (Sema forbids a lambda mutating captured state, which keeps the loop parallel-safe). # `loop_until` ```sema def loop_until(init: any, max_iters: int, step: fn, done: fn) -> any !{} ``` **Parameters** | name | type | |---|---| | `init` | `any` | | `max_iters` | `int` | | `step` | `fn` | | `done` | `fn` | **Returns** `any` **Effects** `!{}`