1  export function intersperse<A>(as: A[], separator: (index: number) => A): A[] {
 2    return as.flatMap((a, i) => (i ? [separator(i), a] : [a]))
 3  }
 4  
 5  export function count<T>(arr: readonly T[], pred: (x: T) => unknown): number {
 6    let n = 0
 7    for (const x of arr) n += +!!pred(x)
 8    return n
 9  }
10  
11  export function uniq<T>(xs: Iterable<T>): T[] {
12    return [...new Set(xs)]
13  }