declare const empty: RequestBlock

declare const mapRequestResolvers: <A>(
  self: RequestBlock,
  f: (dataSource: RequestResolver.RequestResolver<A>) => RequestResolver.RequestResolver<A>
) => RequestBlock

declare const parallel: (self: RequestBlock, that: RequestBlock) => RequestBlock

declare const reduce: <Z>(self: RequestBlock, reducer: RequestBlock.Reducer<Z>) => Z

declare const sequential: (self: RequestBlock, that: RequestBlock) => RequestBlock

declare const single: <A>(
  dataSource: RequestResolver.RequestResolver<A>,
  blockedRequest: Request.Entry<A>
) => RequestBlock

export interface Empty {
  readonly _tag: "Empty"
}

export interface Par {
  readonly _tag: "Par"
  readonly left: RequestBlock
  readonly right: RequestBlock
}

type RequestBlock = Empty | Par | Seq | Single

export interface Reducer<in out Z> {
  emptyCase(): Z
  parCase(left: Z, right: Z): Z
  singleCase(dataSource: RequestResolver.RequestResolver<unknown>, blockedRequest: Request.Entry<unknown>): Z
  seqCase(left: Z, right: Z): Z
}

export interface Seq {
  readonly _tag: "Seq"
  readonly left: RequestBlock
  readonly right: RequestBlock
}

export interface Single {
  readonly _tag: "Single"
  readonly dataSource: RequestResolver.RequestResolver<unknown>
  readonly blockedRequest: Request.Entry<unknown>
}