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Phase 2 control flow. (branch pred then else) selects then/else node by running pred on the threaded input; named 'branch' since 'cond' is a Scheme special form. Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
39 lines
1.9 KiB
Plaintext
39 lines
1.9 KiB
Plaintext
;; lib/flow/spec.sx — flow combinators as a Scheme prelude.
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;;
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;; A flow is a Scheme procedure of one argument: the upstream value.
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;; node : input -> output
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;; A leaf node ignoring its argument is effectively a thunk. Combinators
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;; build composite nodes out of child nodes. The whole flow runs INSIDE the
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;; Scheme interpreter so that Phase 3's `suspend` (call/cc) can capture the
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;; flow continuation directly.
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;;
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;; Phase 1 combinators (flow-combinators-src):
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;; (flow-node f) — wrap a 1-arg procedure as a node (identity)
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;; (flow-id input) — pass the upstream value through unchanged
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;; (flow-const v) — node that ignores input and yields v
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;; (sequence n ...) — thread input left-to-right through children
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;; (parallel n ...) — fan input to every child, join results into a list
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;; (SEQUENTIAL evaluation; true concurrency is Phase 3)
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;; (defflow name body)— bind a named flow
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;;
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;; Phase 2 combinators (flow-control-src):
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;; (branch pred then else) — pred on input selects then/else node
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;; (`cond` is a Scheme special form, so the combinator is named `branch`)
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(define
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flow-combinators-src
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"(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))))")
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(define
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flow-control-src
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"(define (branch pred then else)\n (lambda (input) (if (pred input) (then input) (else input))))")
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(define
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flow-load-combinators!
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(fn
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(env)
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(begin
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(scheme-eval-program (scheme-parse-all flow-combinators-src) env)
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(scheme-eval-program (scheme-parse-all flow-control-src) env)
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env)))
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