Function intersperse

src/utils/array.ts:1–3

(as: A[], separator: (index: number) => A)

export function intersperse<A>(as: A[], separator: (index: number) => A): A[] {
  return as.flatMap((a, i) => (i ? [separator(i), a] : [a]))
}

export function count<T>(arr: readonly T[], pred: (x: T) => unknown): number {
  let n = 0