Ylang-Type type use Display type class
Display Ylang-Unit-Type (`()`)
Refactoring
Refactoring
Refactoring (Reduce case nest)
Refactoring
Merge branch 'types'

* types:
  Refactoring
  Refactoring (Reduce case nest)
  Refactoring
  Refactoring
  Display Ylang-Unit-Type (`()`)
  Ylang-Type type use Display type class