type InferDone<R> =
  InferErr<R> extends infer Errors
    ? Errors extends Done<infer D>
      ? D
      : never
    : never;

import {
  assertType,
  type InferDone,
  type NextResult,
  type Typed,
} from "@evolu/common";

type ReadResult = NextResult<string, ReadFailedError, number>;

interface ReadFailedError extends Typed<"ReadFailed"> {}

assertType<number, InferDone<ReadResult>>();