Partial construction of variants

[mlhaufe]

Partial construction of variants:

const Disk = Data(['position', 'velocity', 'radius', 'item'])

const PartialDisk = Disk([12, 15], [87, 14], 7, _)

const diskItem = PartialDisk('foo')

TODO: Need a real use case to justify this enhancement

Open question: How can this work with pattern matching in traits?