declare const NoUpstream: (activeDownstreamCount: number) => UpstreamPullRequest<never>

declare const Pulled: <A>(value: A) => UpstreamPullRequest<A>

declare const match: {
  <A, Z>(options: {
    readonly onPulled: (value: A) => Z
    readonly onNoUpstream: (activeDownstreamCount: number) => Z
  }): (self: UpstreamPullRequest<A>) => Z
  <A, Z>(
    self: UpstreamPullRequest<A>,
    options: { readonly onPulled: (value: A) => Z; readonly onNoUpstream: (activeDownstreamCount: number) => Z }
  ): Z
}

export interface NoUpstream extends UpstreamPullRequest.Variance<never> {
  readonly _tag: "NoUpstream"
  readonly activeDownstreamCount: number
}

export interface Pulled<out A> extends UpstreamPullRequest.Variance<A> {
  readonly _tag: "Pulled"
  readonly value: A
}

type UpstreamPullRequest<A> = Pulled<A> | NoUpstream

declare const isNoUpstream: <A>(self: UpstreamPullRequest<A>) => self is NoUpstream

declare const isPulled: <A>(self: UpstreamPullRequest<A>) => self is Pulled<A>

declare const isUpstreamPullRequest: (u: unknown) => u is UpstreamPullRequest<unknown>

declare const UpstreamPullRequestTypeId: unique symbol

type UpstreamPullRequestTypeId = typeof UpstreamPullRequestTypeId

export interface Variance<out A> {
  readonly [UpstreamPullRequestTypeId]: {
    readonly _A: Types.Covariant<A>
  }
}