*Main> :info Monoid
class Semigroup a => Prelude.Monoid a where
  mempty :: a
  mappend :: a -> a -> a
  mconcat :: [a] -> a
  {-# MINIMAL mempty #-}
  	-- Defined in ‘GHC.Base’
instance Prelude.Monoid [a] -- Defined in ‘GHC.Base’
instance Prelude.Monoid Ordering -- Defined in ‘GHC.Base’
instance Semigroup a => Prelude.Monoid (Maybe a)
  -- Defined in ‘GHC.Base’
instance Prelude.Monoid a => Prelude.Monoid (IO a)
  -- Defined in ‘GHC.Base’
instance Prelude.Monoid b => Prelude.Monoid (a -> b)
  -- Defined in ‘GHC.Base’
instance (Prelude.Monoid a, Prelude.Monoid b, Prelude.Monoid c,
          Prelude.Monoid d, Prelude.Monoid e) =>
         Prelude.Monoid (a, b, c, d, e)
  -- Defined in ‘GHC.Base’
instance (Prelude.Monoid a, Prelude.Monoid b, Prelude.Monoid c,
          Prelude.Monoid d) =>
         Prelude.Monoid (a, b, c, d)
  -- Defined in ‘GHC.Base’
instance (Prelude.Monoid a, Prelude.Monoid b, Prelude.Monoid c) =>
         Prelude.Monoid (a, b, c)
  -- Defined in ‘GHC.Base’
instance (Prelude.Monoid a, Prelude.Monoid b) =>
         Prelude.Monoid (a, b)
  -- Defined in ‘GHC.Base’
instance Prelude.Monoid () -- Defined in ‘GHC.Base’

class Main.Monoid a 	-- Defined at lec7.hs:3:1
*Main> :r
[1 of 1] Compiling Main             ( lec7.hs, interpreted )

lec7.hs:8:14: error:
    • Illegal type signature in instance declaration: mempty' :: [a]
      (Use InstanceSigs to allow this)
    • In the instance declaration for ‘Monoid' [a]’
  |
8 |   mempty' :: [a]
  |              ^^^
Failed, no modules loaded.
Prelude> :r
[1 of 1] Compiling Main             ( lec7.hs, interpreted )

lec7.hs:7:10: warning: [-Wmissing-methods]
    • No explicit implementation for
        ‘mappend'’
    • In the instance declaration for ‘Monoid' [a]’
  |
7 | instance Monoid' [a] where
  |          ^^^^^^^^^^^
Ok, one module loaded.
*Main> :r
[1 of 1] Compiling Main             ( lec7.hs, interpreted )
Ok, one module loaded.
*Main> :t 'a'
'a' :: Char
*Main> :k Char
Char :: *
*Main> :t 1 :: Int
1 :: Int :: Int
*Main> :t True
True :: Bool
*Main> :k Bool 
Bool :: *
*Main> :t Nothing
Nothing :: Maybe a
*Main> :k Maybe
Maybe :: * -> *
*Main> :k []
[] :: * -> *
*Main> :r
[1 of 1] Compiling Main             ( lec7.hs, interpreted )

lec7.hs:15:21: error:
    Illegal kind signature: ‘* -> *’
      Perhaps you intended to use KindSignatures
    In the declaration for class ‘Functor’
   |
15 | class Functor (f :: * -> *) where
   |                     ^^^^^^
Failed, no modules loaded.
Prelude> :r
[1 of 1] Compiling Main             ( lec7.hs, interpreted )
Ok, one module loaded.
*Main> :r
[1 of 1] Compiling Main             ( lec7.hs, interpreted )
Ok, one module loaded.
*Main> :t (\ x -> x + 1)
(\ x -> x + 1) :: Num a => a -> a
*Main> :t (\ x -> x + 1 :: Int)
(\ x -> x + 1 :: Int) :: Int -> Int
*Main> :k (Int -> Int)
(Int -> Int) :: *
*Main> :k [Int]
[Int] :: *
*Main> :k []
[] :: * -> *
*Main> :k Maybe 
Maybe :: * -> *
*Main> :k Maybe Int
Maybe Int :: *
*Main> :k (\ x -> Maybe [x])

<interactive>:1:2: error: parse error on input ‘\’
*Main>