Beefed up `Scope`

01-scope.ts

import type { Stream, Task, Operation, Result } from "./types.ts";

export interface Scope extends Operation<void> {
  run<T>(operation: () => Operation<T>): Task<T>;
  close(): Operation<void>;
  created: Stream<Task<unknown>, void>;
  enqueued: Stream<Operation<unknown>, void>;
  dropped: Stream<Operation<unknown>, void>;
  results: Stream<{task: Task<unknown>, result: Result<unknown>}, void>;
}

// spawn is not an instruction, it is a context effect. Where
// a spawn happens, and where its errors are dependent on the "spawn context"

function* spawn<T>(operation: () => Operation<T>): Task<T> {
  let scope = yield* SpawnContext;
  return scope.run(operation);
}

/* possible spawn contexts */

//default spawn scope does not constrain tasks
//if an error happens, it crashes, but subsequent scopes can override.
createScope({
  maxConcurrency: Math.Infinity,
  *onResult(result: Result<unknown>, task: Task<unknown>) {
    if (!result.ok) {
      throw result.error;
    }
  }
});

//http handler
createScope({
  maxCurrency: 1000,
  maxQueue: 10_000,
  drop: "newest"
})

//click handler with AJAX request
createScope({
  maxConcurrency: 1,
  drop: "oldest",
});

// file uploader.
createScope({
  maxConcurrency: 10,
  maxQueue: 10,
  *onDrop() {
    window.alert('10 files are already waiting to upload');
  }
});