# Trampoline


fx.experimental.desc-interp.trampoline: qApp/run/handle interpreters trampolining FreeFx Desc values via genericClosure for O(1) stack depth on long chains.

## `handle`

_handle Eff Resp A { return?; handler; dispatch; state } prog — thin wrapper over `run` with a custom `return` clause folding the final (value, state) pair._

```
handle : Hoas U -> Hoas (U -> U) -> Hoas U -> { return?, handler, dispatch, state } -> Hoas (μ freeFxApp Eff Resp A) -> b
```

## `qApp`

_qApp Eff Resp q x — apply queue `q` to value `x : Hoas q._index.X`; trampolines Pure-returning leaves via genericClosure; on Impure splices the inner queue with the remaining tail. The queue's `_index` sidecar carries the (X, A) indexing that the kernel's μI U² slot witnesses._

```
qApp : Hoas U -> Hoas (U -> U) -> Hoas (μI U² kontQueueApp …) -> Hoas X -> Hoas (μ freeFxApp Eff Resp A)
```

## `qAppend`

_qAppend Eff Resp l r — concatenate two queues. Identity short-circuits on either side mirror `queue.nix:append`; otherwise builds `qNode l r` with the seam M = `l._index.A` (= `r._index.X`, asserted host-level by qNode). The composite queue inhabits μI U² kontQueueApp (l._index.X, r._index.A)._

```
qAppend : Hoas U -> Hoas (U -> U) -> Hoas (μI U² kontQueueApp …) -> Hoas (μI U² kontQueueApp …) -> Hoas (μI U² kontQueueApp …)
```

## `run`

_run Eff Resp A { handler; dispatch } prog initialState — drive `prog : μ(freeFxApp Eff Resp A)` to completion via a `genericClosure` worklist; per Impure node, the kernel-resident `handler` term is applied to the op + threaded state via `vApp`, and the Nix-side `dispatch` interpreter reads the kernel-eval'd result to produce a step decision._

```
run : Hoas U -> Hoas (U -> U) -> Hoas U -> { handler; dispatch } -> Hoas (μ freeFxApp Eff Resp A) -> Hoas State -> { value; state }
```