T15139.hs:11:1: warning: [-Wincomplete-patterns (in -Wextra)]
    Pattern match(es) are non-exhaustive
    In an equation for ‘f1’:
        Patterns of type  ‘Bool’ not matched: False
   |
11 | f1 True = case can'tHappen of {}
   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

T15139.hs:12:1: warning: [-Wincomplete-patterns (in -Wextra)]
    Pattern match(es) are non-exhaustive
    In an equation for ‘f2’:
        Patterns of type  ‘Bool’ not matched: False
   |
12 | f2 True = case can'tHappen of
   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

T15139.hs:13:1: warning: [-Wincomplete-patterns (in -Wextra)]
    Pattern match(es) are non-exhaustive
    In an equation for ‘g’: Patterns of type  ‘Bool’ not matched: False
   |
13 | g  True = case () of () -> True
   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^