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Completes the host ABI from work-queue to driver loop: the host supplies only a (kind payload) -> answer dispatch fn; flow-drive-host services one tick of pending requests, flow-run-host ticks until quiescent (bounded). Tested via the art-dag render -> human-review -> publish pipeline driven entirely by flow-run-host. The art-dag integration is now: define dispatch, call flow-run-host. 166/166, 11 suites. Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
43 lines
3.6 KiB
Plaintext
43 lines
3.6 KiB
Plaintext
;; lib/flow/host.sx — the host integration ABI (Phase 8).
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;;
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;; `suspend` is flow's seam to the outside world, but a bare (suspend tag) is just a
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;; signal — every author would invent their own tag shape. This layer defines a
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;; stable request/response contract so a host (e.g. an art-dag driver, or a human
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;; review UI) can hook in WITHOUT reverse-engineering ad-hoc tags.
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;;
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;; A flow asks the host to do something and waits for the answer:
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;; (request kind payload) — suspend with a typed envelope (flow-request kind
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;; payload); evaluates to the host's resume value.
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;; (await-human prompt) — request kind=human (a decision point)
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;; (await-render recipe) — request kind=render (e.g. an art-dag job)
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;; (await-effect kind p) — request of an arbitrary kind
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;;
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;; The host drives flows by polling its work queue and resuming:
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;; (flow-host-requests) — ((id kind payload) ...) for every SUSPENDED flow whose
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;; waiting tag is a host request. The host dispatches by kind (render -> submit a
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;; Celery job; human -> show UI), then calls (flow/resume id answer).
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;; (request? tag) / (request-kind tag) / (request-payload tag) — parse one tag.
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;;
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;; Reference driver — the host only supplies `dispatch`, a (kind payload) -> answer:
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;; (flow-drive-host dispatch) — one tick: service every CURRENTLY pending
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;; request (snapshot), resuming each with (dispatch kind payload); returns the
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;; count serviced. Resumes may create new requests — serviced on the next tick.
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;; (flow-run-host dispatch maxticks) — tick until quiescent (no pending requests)
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;; or maxticks reached; returns total requests serviced. Bounded for determinism.
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;;
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;; Contract: the host owns IO and persistence. flow stays deterministic — a flow
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;; never performs IO itself, it only `request`s; the host performs the effect and
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;; feeds the result back via resume (which the replay log records, so the effect is
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;; not re-run on recovery). Persist with flow-store-export after each transition and
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;; flow-store-import! on boot.
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(define
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flow-host-src
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"(define (request kind payload) (suspend (list (quote flow-request) kind payload)))\n (define (request? tag) (and (pair? tag) (eq? (car tag) (quote flow-request))))\n (define (request-kind tag) (car (cdr tag)))\n (define (request-payload tag) (car (cdr (cdr tag))))\n (define (await-human prompt) (request (quote human) prompt))\n (define (await-render recipe) (request (quote render) recipe))\n (define (await-effect kind payload) (request kind payload))\n (define (flow-host-req-step pend)\n (if (null? pend)\n (list)\n (let ((id (car (car pend))) (tag (car (cdr (car pend)))))\n (if (request? tag)\n (cons (list id (request-kind tag) (request-payload tag))\n (flow-host-req-step (cdr pend)))\n (flow-host-req-step (cdr pend))))))\n (define (flow-host-requests) (flow-host-req-step (flow/pending)))\n (define (flow-drive-host-step reqs dispatch)\n (if (null? reqs)\n 0\n (begin\n (flow/resume (car (car reqs)) (dispatch (car (cdr (car reqs))) (car (cdr (cdr (car reqs))))))\n (+ 1 (flow-drive-host-step (cdr reqs) dispatch)))))\n (define (flow-drive-host dispatch) (flow-drive-host-step (flow-host-requests) dispatch))\n (define (flow-run-host dispatch maxticks)\n (if (<= maxticks 0)\n 0\n (let ((n (flow-drive-host dispatch)))\n (if (= n 0) 0 (+ n (flow-run-host dispatch (- maxticks 1)))))))")
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(define
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flow-load-host!
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(fn
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(env)
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(begin (scheme-eval-program (scheme-parse-all flow-host-src) env) env)))
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