[1 of 3] Processing p
  [1 of 2] Compiling H[sig]           ( p\H.hsig, nothing )
  [2 of 2] Compiling M                ( p\M.hs, nothing )
[2 of 3] Processing h
  Instantiating h
  [1 of 1] Compiling H                ( h\H.hs, bkpfail23.out\h\H.o )
[3 of 3] Processing r
  Instantiating r
  [1 of 1] Including p[H=h:H]
    Instantiating p[H=h:H]
    [1 of 2] Compiling H[sig]           ( p\H.hsig, bkpfail23.out\p\p-6KeuBvYi0jvLWqVbkSAZMq\H.o )

bkpfail23.bkp:15:9: error: [GHC-15843]
    • Type constructor ‘F’ has conflicting definitions in the module
      and its hsig file.
      Main module: type F :: * -> *
                   type F a = ()
        Hsig file: type role F phantom
                   type F :: * -> *
                   data F a
      Illegal parameterized type synonym in implementation of abstract data.
    • While checking that ‘h:H’ implements signature ‘H’ in ‘p[H=h:H]’.
    Suggested fix:
      If possible, eta-reduce the type synonym ‘F’ so that it is nullary.