LLNode.ts

type LLNode<T = any> = {
  prev: null | LLNode<T>
  value: T
  next: null | LLNode<T>
}

const LLAdd = <T>(prev: LLNode<T>, value: T, next = prev.next) => {
  prev.next = { prev, value, next }
  if (next !== null) next.prev = prev.next
}

const LLDel = ({ prev, next }: LLNode) => {
  if (prev !== null) prev.next = next
  if (next !== null) next.prev = prev
}

const LLFor = <T>(node: null | LLNode<T>, cb: Fn<[T]>) => {
  while (node !== null) {
    cb(node.value)
    node = node.next
  }
}