T16902.hs:11:10: error:
    • Expected a type, but found something with kind ‘a’
      ‘a’ is a rigid type variable bound by
        the data constructor ‘MkF’
        at T16902.hs:11:3-12
    • In the type ‘F a’
      In the definition of data constructor ‘MkF’
      In the data declaration for ‘F’