giles
4674620d7e
Some checks failed
Test, Build, and Deploy / test-build-deploy (push) Failing after 30s
(retry n node) re-runs up to n attempts on a raised exception; the last attempt's exception propagates. Explicit (fail ...) values are NOT retried — they pass through. Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
48 lines
3.1 KiB
Plaintext
48 lines
3.1 KiB
Plaintext
;; lib/flow/spec.sx — flow combinators as a Scheme prelude.
|
|
;;
|
|
;; A flow is a Scheme procedure of one argument: the upstream value.
|
|
;; node : input -> output
|
|
;; A leaf node ignoring its argument is effectively a thunk. Combinators
|
|
;; build composite nodes out of child nodes. The whole flow runs INSIDE the
|
|
;; Scheme interpreter so that Phase 3's `suspend` (call/cc) can capture the
|
|
;; flow continuation directly.
|
|
;;
|
|
;; Phase 1 combinators (flow-combinators-src):
|
|
;; (flow-node f) — wrap a 1-arg procedure as a node (identity)
|
|
;; (flow-id input) — pass the upstream value through unchanged
|
|
;; (flow-const v) — node that ignores input and yields v
|
|
;; (sequence n ...) — thread input left-to-right through children
|
|
;; (parallel n ...) — fan input to every child, join results into a list
|
|
;; (SEQUENTIAL evaluation; true concurrency is Phase 3)
|
|
;; (defflow name body)— bind a named flow
|
|
;;
|
|
;; Phase 2 combinators (flow-control-src):
|
|
;; (branch pred then else) — pred on input selects then/else node
|
|
;; (`cond` is a Scheme special form, so the combinator is named `branch`)
|
|
;; (fail reason) — make an explicit failure value (data, not an exception)
|
|
;; (failed? x) — is x a failure value?
|
|
;; (fail-reason x) — the reason carried by a failure value
|
|
;; (try-catch node handler) — run node; if it raises, call (handler error)
|
|
;; with the reified error and return the handler's value
|
|
;; (retry n node) — run node, re-running up to n attempts total on a raised
|
|
;; exception; the last attempt's exception propagates. Only RAISED exceptions
|
|
;; are retried — explicit (fail ...) values pass through unchanged. (Once a
|
|
;; node has suspended in Phase 3, retry does not re-run it; resume continues.)
|
|
|
|
(define
|
|
flow-combinators-src
|
|
"(define (flow-node f) f)\n (define (flow-id input) input)\n (define (flow-const v) (lambda (input) v))\n (define (flow-seq-step ns v)\n (if (null? ns) v (flow-seq-step (cdr ns) ((car ns) v))))\n (define sequence (lambda ns (lambda (input) (flow-seq-step ns input))))\n (define parallel (lambda ns (lambda (input) (map (lambda (n) (n input)) ns))))\n (define-syntax defflow\n (syntax-rules ()\n ((defflow nm body) (define nm body))))")
|
|
|
|
(define
|
|
flow-control-src
|
|
"(define (branch pred then else)\n (lambda (input) (if (pred input) (then input) (else input))))\n (define (fail reason) (list (quote flow-fail) reason))\n (define (failed? x) (and (pair? x) (eq? (car x) (quote flow-fail))))\n (define (fail-reason x) (car (cdr x)))\n (define (try-catch node handler)\n (lambda (input) (guard (e (#t (handler e))) (node input))))\n (define (flow-retry-step n node input)\n (guard (e (#t (if (<= n 1) (raise e) (flow-retry-step (- n 1) node input))))\n (node input)))\n (define (retry n node) (lambda (input) (flow-retry-step n node input)))")
|
|
|
|
(define
|
|
flow-load-combinators!
|
|
(fn
|
|
(env)
|
|
(begin
|
|
(scheme-eval-program (scheme-parse-all flow-combinators-src) env)
|
|
(scheme-eval-program (scheme-parse-all flow-control-src) env)
|
|
env)))
|