u16

u16 -- returns value of unit type u16s

This is a convenience feature that allows using, e.g., 'u16.sum' to
get the the monoid of (u16, infix +) instead of 'u16s.sum'.

since this u16 with no arguments is a routine and not a constructor, it
does not define a type (which would cause a name clash with u16 with one
argument).