T5380.hs:7:27:
    Couldn't match expected type ‘Bool’ with actual type ‘not_bool’
      ‘not_bool’ is a rigid type variable bound by
                 the type signature for:
                 testB :: not_bool -> (() -> ()) -> () -> not_unit
                 at T5380.hs:6:10
    Relevant bindings include
      b :: not_bool (bound at T5380.hs:7:7)
      testB :: not_bool -> (() -> ()) -> () -> not_unit
        (bound at T5380.hs:7:1)
    In the expression: b
    In the expression: proc () -> if b then f -< () else f -< ()

T5380.hs:7:34:
    Couldn't match type ‘not_unit’ with ‘()’
      ‘not_unit’ is a rigid type variable bound by
                 the type signature for:
                 testB :: not_bool -> (() -> ()) -> () -> not_unit
                 at T5380.hs:6:10
    Expected type: () -> not_unit
      Actual type: () -> ()
    Relevant bindings include
      testB :: not_bool -> (() -> ()) -> () -> not_unit
        (bound at T5380.hs:7:1)
    In the expression: f
    In the command: f -< ()