stdin

instancesOfFunc> configure (lib)
Configuring instancesOfFunc-0.1.0.0...
instancesOfFunc> build (lib)
Preprocessing library for instancesOfFunc-0.1.0.0..
Building library for instancesOfFunc-0.1.0.0..
[1 of 1] Compiling InstancesOfFunc

/data/info/programming/haskell/haskellbook/exercises/Ch16/src/InstancesOfFunc.hs:28:31: error:
    • Couldn't match expected type ‘a’ with actual type ‘b’
      ‘b’ is a rigid type variable bound by
        the type signature for:
          fmap :: forall a b. (a -> b) -> Pair a -> Pair b
        at src/InstancesOfFunc.hs:28:3-6
      ‘a’ is a rigid type variable bound by
        the type signature for:
          fmap :: forall a b. (a -> b) -> Pair a -> Pair b
        at src/InstancesOfFunc.hs:28:3-6
    • In the second argument of ‘Pair’, namely ‘(f b)’
      In the expression: Pair a (f b)
      In an equation for ‘fmap’: fmap f (Pair a b) = Pair a (f b)
    • Relevant bindings include
        b :: a (bound at src/InstancesOfFunc.hs:28:18)
        a :: a (bound at src/InstancesOfFunc.hs:28:16)
        f :: a -> b (bound at src/InstancesOfFunc.hs:28:8)
        fmap :: (a -> b) -> Pair a -> Pair b
          (bound at src/InstancesOfFunc.hs:28:3)
   |
28 |   fmap f (Pair a b) = Pair a (f b)
   |                               ^^^

/data/info/programming/haskell/haskellbook/exercises/Ch16/src/InstancesOfFunc.hs:31:15: error:
    • Couldn't match type ‘a0 -> Pair a0’ with ‘Pair a’
      Expected type: Gen (Pair a)
        Actual type: Gen (a0 -> Pair a0)
    • In the expression: Pair <$> arbitrary
      In an equation for ‘arbitrary’: arbitrary = Pair <$> arbitrary
      In the instance declaration for ‘Arbitrary (Pair a)’
    • Relevant bindings include
        arbitrary :: Gen (Pair a) (bound at src/InstancesOfFunc.hs:31:3)
   |
31 |   arbitrary = Pair <$> arbitrary
   |               ^^^^^^^^^^^^^^^^^^

--  While building package instancesOfFunc-0.1.0.0 (scroll up to its section to see the error) using:
      /home/gbell2/.stack/setup-exe-cache/x86_64-linux/Cabal-simple_mPHDZzAJ_3.0.1.0_ghc-8.8.4 --builddir=.stack-work/dist/x86_64-linux/Cabal-3.0.1.0 build lib:instancesOfFunc --ghc-options ""
    Process exited with code: ExitFailure 1