T7869.hs:3:12: error:
    • Couldn't match type ‘a1’ with ‘a’
      Expected: [a1] -> b1
        Actual: [a] -> b
      ‘a1’ is a rigid type variable bound by
        an expression type signature:
          forall a1 b1. [a1] -> b1
        at T7869.hs:3:20-27
      ‘a’ is a rigid type variable bound by
        the inferred type of f :: [a] -> b
        at T7869.hs:3:1-27
    • In the expression: f x
      In the expression: (\ x -> f x) :: [a] -> b
      In an equation for ‘f’: f = (\ x -> f x) :: [a] -> b
    • Relevant bindings include
        x :: [a1] (bound at T7869.hs:3:7)
        f :: [a] -> b (bound at T7869.hs:3:1)