T12957a.hs:25:35: warning: [GHC-40564] [-Winaccessible-code (in -Wdefault)]
    • Inaccessible code in
        a pattern with constructor: BFields :: [()] -> Fields B,
        in a case alternative
      Couldn't match type ‘A’ with ‘B’
    • In a record update at field ‘list’,
      with type constructor ‘Fields’
      and data constructor ‘BFields’.
      In the expression: emptyA {list = [a]}
      In a record update at field ‘sFields’,
      with type constructor ‘S’
      and data constructor ‘S’.

T12957a.hs:25:35: warning: [GHC-83865] [-Wdeferred-type-errors (in -Wdefault)]
    • Couldn't match type ‘B’ with ‘A’
      Expected: Fields A
        Actual: Fields B
    • In a record update at field ‘list’,
      with type constructor ‘Fields’
      and data constructor ‘BFields’.
      In the expression: emptyA {list = [a]}
      In a record update at field ‘sFields’,
      with type constructor ‘S’
      and data constructor ‘S’.