tcfail201.hs:17:56: error:
• Couldn't match type ‘a’ with ‘HsDoc t0’
‘a’ is a rigid type variable bound by
the type signature for:
gfoldl' :: forall (c :: * -> *) a.
(forall a1 b. c (a1 -> b) -> a1 -> c b)
-> (forall g. g -> c g) -> a -> c a
at tcfail201.hs:15:12
Expected type: c a
Actual type: c (HsDoc t0)
• In the expression: z DocEmpty
In a case alternative: DocEmpty -> z DocEmpty
In the expression: case hsDoc of { DocEmpty -> z DocEmpty }
• Relevant bindings include
hsDoc :: a (bound at tcfail201.hs:16:13)
gfoldl' :: (forall a1 b. c (a1 -> b) -> a1 -> c b)
-> (forall g. g -> c g) -> a -> c a
(bound at tcfail201.hs:16:1)