declare const builtIn: (option: BuiltInOptions) => CommandDirective<never>

declare const userDefined: <A>(leftover: ReadonlyArray<string>, value: A) => CommandDirective<A>

declare const map: {
  <A, B>(f: (a: A) => B): (self: CommandDirective<A>) => CommandDirective<B>
  <A, B>(self: CommandDirective<A>, f: (a: A) => B): CommandDirective<B>
}

export interface BuiltIn {
  readonly _tag: "BuiltIn"
  readonly option: BuiltInOptions
}

type CommandDirective<A> = BuiltIn | UserDefined<A>

export interface UserDefined<A> {
  readonly _tag: "UserDefined"
  readonly leftover: ReadonlyArray<string>
  readonly value: A
}

declare const isBuiltIn: <A>(self: CommandDirective<A>) => self is BuiltIn

declare const isUserDefined: <A>(self: CommandDirective<A>) => self is UserDefined<A>