NotEmptyArray definition

NotEmptyArray.ts

export interface NonEmptyArray<A> extends ReadonlyArray<A> {
  // tslint:disable-next-line: readonly-keyword
  0: A;
}
type ReadOnlyNotEmptyArray<T> = Readonly<NotEmptyArray<T>>;

function isNotEmptyArray<T>(as: T[]): as is NotEmptyArray<T> {
  return as.length > 0;
}

function freeze(as: NotEmptyArray<T>): ReadOnlyNotEmptyArray<T> {
  return Object.freeze(as);
}

const head = <T>(as: NotEmptyArray<T>): T => as[0];
const tail = <T>([, ...rest]: NotEmptyArray<T>): T[] => rest;