T7861: T7861.hs:10:5: error:
    • Couldn't match type ‘a’ with ‘[a]’
      Expected: (forall b. a) -> a
        Actual: (forall b. a) -> [a]
      ‘a’ is a rigid type variable bound by
        the type signature for:
          f :: forall a. (forall b. a) -> a
        at T7861.hs:9:1-23
    • In the expression: doA
      In an equation for ‘f’: f = doA
    • Relevant bindings include
        f :: (forall b. a) -> a (bound at T7861.hs:10:1)
(deferred type error)