Comment by c0nfused

I rather like your syntax compared to the proposed version. It is less concise but must more consistent and parsable:

  return match(user, [
          [{first: $, middle: $, last: $}, (f, m, l) => f + ' ' + m + ' ' + l],
          [{first: $, last: $}           , (f, l) => f + ' ' + l],
          [_, 'unknown']
      ]);