foo.hack

```
use namespace HH\Lib\Vec;

function process(
  vec<(string, string, string, string)> $input
): dict<string, dict<string, dict<string, vec<string>>> {
  $result = dict[];
  foreach($input as $tuple) {
    $result[$tuple[0]][$tuple[1]][$tuple[2]] = Vec\concat(
      $result[$tuple[0]][$tuple[1]][$tuple[2]] ?? vec[],
      vec[$tuple[3]],
    );
  }

  return $result;
}

<<__EntryPoint>>
async function main(): Awaitable<void> {
  $data = vec[
    tuple('sam', 'john', 'tim', 'tom'),
    tuple('sam', 'john', 'tim', 'dom'),
    tuple('sam', 'john', 'jim', 'ryan'),
    tuple('sam', 'john', 'jim', 'bryan'),
    tuple('sam', 'oscar', 'kim', 'mike'),
    tuple('sam', 'oscar', 'kim', 'ike'),
    tuple('sam', 'oscar', 'liz', 'jared'),
    tuple('sam', 'oscar', 'liz', 'jay'),
    tuple('will', 'ann', 'ray', 'jill'),
    tuple('will', 'ann', 'ray', 'phil'),
    tuple('will', 'ann', 'abe', 'henry'),
    tuple('will', 'ann', 'abe', 'jackie'),
    tuple('will', 'don', 'clive', 'katie'),
    tuple('will', 'don', 'clive', 'bill'),
    tuple('will', 'don', 'hank', 'sherlock'),
    tuple('will', 'don', 'hank', 'bruce'),
  ]
  |> process($$)
  |> \json_encode($$);

  \var_dump($data);
}
```