ourmaninamsterdam

import NetInfo, { NetInfoState, NetInfoSubscription } from '@react-native-community/netinfo';
import { useState, useRef, useEffect } from 'react';

const useDeviceOnlineStatus = () => {
  const [online, setOnline] = useState(false);
  const unsubscribeRef = useRef<NetInfoSubscription | undefined>();

  useEffect(() => {
    unsubscribeRef.current = NetInfo.addEventListener((state: NetInfoState) => {
      setOnline(state.isConnected);

ourmaninamsterdam

const wait = async (ms: number) =>
  new Promise((resolve) => {
    setTimeout(() => resolve(), ms);
  });


await wait(10000); // wait for 10 seconds
// Continue...

ourmaninamsterdam

import { getProviderStatusAsync, LocationProviderStatus } from 'expo-location';
import { useState } from 'react';
import { Platform } from 'react-native';
import useInterval from 'use-interval';

const useLocationProviderStatus = (delay: number = 2000) => {
  const [locationProviderAvailable, setLocationProviderAvailable] = useState<boolean | undefined>(undefined);

  const getLocationProviderStatus = ({
    gpsAvailable,

ourmaninamsterdam

type BST = {
  key: number;
  value: string;
  left: BST | false;
  right: BST | false;
} | false;

const BST0: BST = false;
const BST1: BST = {
  key: 1,

ourmaninamsterdam

(define-struct node (k v l r))
;; BinaryTree is one of:
;; - false
;; - (make-node Natural String BinaryTree BinaryTree)
(define BT0 false)
(define BT1 (make-node 1 "a" false false))
(define BT4 (make-node 4 "d"
                       (make-node 2 "b"
                                  (make-node 1 "a" false false)
                                  (make-node 3 "c" false false))

ourmaninamsterdam

(define (find name dir)
  (local [(define (c1 n rdirs rimgs)
            (or (string=? name n)
                rdirs
                rimgs))
          (define (c2 rdir rdirs)
            (or rdir rdirs))
          (define (c3 img rimgs)
            false)]
    (fold-dir c1 c2 c3 false false dir)))

ourmaninamsterdam

Natural -> (listof X) - build-list

(listof X) -> (listof X) - filter

(listof X) -> (listof Y) - map

(listof X) -> Boolean - andmap

(listof X) -> Boolean - ormap

ourmaninamsterdam

import { useState } from 'react';
import useAppState from 'react-native-appstate-hook';
import RNFS from 'react-native-fs';

async function copyDir(source: string, destination: string) {
  const fileChangeLog: string[] = [];

  await copyDirRecursive(source, destination, fileChangeLog);

  return fileChangeLog;

ourmaninamsterdam

// From https://stackoverflow.com/questions/44654291/is-it-good-practice-to-use-ordinal-of-enum

public enum Person {
  GRANDPARENT(null),
  PARENT(GRANDPARENT),
  CHILD(PARENT);

  private final Person parent;

  private Person(Person parent) {

ourmaninamsterdam

// Adapted from https://howtodoinjava.com/typescript/function-overloading

class MiddleEarthResident {
    name: string;
    constructor(name: string) {
        this.name = name;
    }
}

class ShireResident extends MiddleEarthResident {