47 lines
2.0 KiB
JavaScript
47 lines
2.0 KiB
JavaScript
import { todo } from './todo.js'
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/**
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* An event stream as a pure automaton (a Mealy machine).
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* `Stream<A> = { step: input => [outputs, nextStream] }`: feed one input, get the (possibly empty) array
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* of outputs it produced and the stream to use for the next input. Nothing is mutated, so a stream value
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* can be run any number of times with the same results.
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* Inputs: `{tag:'Time', t}`, `{tag:'KeyDown', key}`, `{tag:'KeyUp', key}`.
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*/
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/** Emits the `key` of every KeyDown input; ignores everything else. */
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export const keyDowns = { step: () => todo('m08') }
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/** Emits the `key` of every KeyUp input; ignores everything else. */
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export const keyUps = { step: () => todo('m08') }
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/**
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* On `Time t`, emits every multiple `k*ms` with `last < k*ms <= t`, ascending, where `last` starts at 0
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* and becomes `t` afterwards. A big time jump can emit several values. Ignores key inputs.
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* Hint: write a private helper that carries `last`.
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*/
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export const interval = (ms) => todo('m08')
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/** Apply `f` to every output of `s`. */
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export const map = (s, f) => todo('m08')
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/** Keep only the outputs of `s` for which `p` is true. */
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export const filter = (s, p) => todo('m08')
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/** Apply `f` to every output of `s`; `f` returns a value or `null`, and nulls are dropped. */
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export const filterMap = (s, f) => todo('m08')
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/** Both streams step on every input; the outputs of `a` come before the outputs of `b`. */
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export const merge = (a, b) => todo('m08')
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/** Fold the outputs of `s` into an accumulator, starting from `z`; emits each new accumulator (not `z` itself). */
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export const scan = (s, f, z) => todo('m08')
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/**
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* Emit `v` once, before the outputs of the first step; later steps are unaffected.
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* Note: streams only act when an input arrives, so if no input ever arrives, `v` is never emitted.
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*/
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export const startWith = (s, v) => todo('m08')
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/** Feed all inputs through the stream and collect every output, in order. A pure fold (reduce). */
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export const run = (s, inputs) => todo('m08')
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