*Main> head [1 .. 5]
1
*Main> tail [1 .. 5]
[2,3,4,5]
*Main> :t head
head :: [a] -> a
*Main> :t tail 
tail :: [a] -> [a]
*Main> :t head []
head [] :: a
*Main> head []
*** Exception: Prelude.head: empty list
*Main> :t tail [] 
tail [] :: [a]
*Main> tail []
*** Exception: Prelude.tail: empty list
*Main> [1, 2, 3] ++ [4, 5] 
[1,2,3,4,5]
*Main> :t (++)
(++) :: [a] -> [a] -> [a]
*Main> "hello" ++ "world" 
"helloworld"
*Main> [] ++ [1,2]
[1,2]
*Main> :t length 
length :: Foldable t => t a -> Int
*Main> length "helloworld" 
10
*Main> :t zip 
zip :: [a] -> [b] -> [(a, b)]
*Main> zip [1 .. 5] "hello"
[(1,'h'),(2,'e'),(3,'l'),(4,'l'),(5,'o')]
*Main> zip [1 .. 3] "hello"
[(1,'h'),(2,'e'),(3,'l')]
*Main> :t zip
zip :: [a] -> [b] -> [(a, b)] == [a] -> ([b] -> [(a, b)])
*Main> :t zip [1 .. 3]
zip [1 .. 3] :: (Num a, Enum a) => [b] -> [(a, b)]
*Main> :t zip [1 .. 3] "abc"
zip [1 .. 3] "abc" :: (Num a, Enum a) => [(a, Char)]
*Main> :t zip [1 .. 3] :: [b] -> [(Int, b)]
zip [1 .. 3] :: [b] -> [(Int, b)] :: [b] -> [(Int, b)]
*Main> :t zip [True, False] 
zip [True, False] :: [b] -> [(Bool, b)]
*Main> zip [True, False] "abc"
[(True,'a'),(False,'b')]
*Main> :t zip [True, False] "abc"
zip [True, False] "abc" :: [(Bool, Char)]
*Main> :t (++)
(++) :: [a] -> [a] -> [a]
*Main> :t (++) [True, False]
(++) [True, False] :: [Bool] -> [Bool]
*Main> (++) [True, False] [False, False]
[True,False,False,False]
*Main> [True, False] ++ [False, False]
[True,False,False,False]
*Main> :r
[1 of 1] Compiling Main             ( lec2.hs, interpreted )
Ok, one module loaded.
*Main> :t add
add :: Int -> Int -> Int
*Main> add 1 2
3
*Main> :t add 1
add 1 :: Int -> Int
*Main> add 1 5
6
*Main> :r
[1 of 1] Compiling Main             ( lec2.hs, interpreted )
Ok, one module loaded.
*Main> appendLength "hello" "world"
10
*Main> :t appendLength "hello" [True, False]

<interactive>:1:23: error:
    • Couldn't match expected type ‘Char’ with actual type ‘Bool’
    • In the expression: True
      In the second argument of ‘appendLength’, namely ‘[True, False]’
      In the expression: appendLength "hello" [True, False]

<interactive>:1:29: error:
    • Couldn't match expected type ‘Char’ with actual type ‘Bool’
    • In the expression: False
      In the second argument of ‘appendLength’, namely ‘[True, False]’
      In the expression: appendLength "hello" [True, False]
*Main> appendLength "hello" [True, False]

<interactive>:37:23: error:
    • Couldn't match expected type ‘Char’ with actual type ‘Bool’
    • In the expression: True
      In the second argument of ‘appendLength’, namely ‘[True, False]’
      In the expression: appendLength "hello" [True, False]

<interactive>:37:29: error:
    • Couldn't match expected type ‘Char’ with actual type ‘Bool’
    • In the expression: False
      In the second argument of ‘appendLength’, namely ‘[True, False]’
      In the expression: appendLength "hello" [True, False]
*Main> :r
[1 of 1] Compiling Main             ( lec2.hs, interpreted )
Ok, one module loaded.
*Main> factorial 4
24
*Main> :t error
error :: [Char] -> a
*Main> :r
[1 of 1] Compiling Main             ( lec2.hs, interpreted )
Ok, one module loaded.
*Main> factorial -1

<interactive>:42:1: error:
    • No instance for (Num (Int -> Int)) arising from a use of ‘-’
        (maybe you haven't applied a function to enough arguments?)
    • In the expression: factorial - 1
      In an equation for ‘it’: it = factorial - 1
*Main> factorial (-1)
*** Exception: n is negative
CallStack (from HasCallStack):
  error, called at lec2.hs:35:13 in main:Main
*Main> :r
[1 of 1] Compiling Main             ( lec2.hs, interpreted )
Ok, one module loaded.
*Main> factorial' 4
24
*Main> :r
[1 of 1] Compiling Main             ( lec2.hs, interpreted )
Ok, one module loaded.
*Main> factorial' 4
24
*Main> factorial' (-4)
*** Exception: n is negative
CallStack (from HasCallStack):
  error, called at lec2.hs:41:16 in main:Main
*Main> :r
[1 of 1] Compiling Main             ( lec2.hs, interpreted )
Ok, one module loaded.
*Main> first (True, "abc")
True
*Main> :r
[1 of 1] Compiling Main             ( lec2.hs, interpreted )
Ok, one module loaded.
*Main> second (True, "abc")
"abc"
*Main> :r
[1 of 1] Compiling Main             ( lec2.hs, interpreted )
Ok, one module loaded.
*Main> length' "abc"
3
*Main> :r
[1 of 1] Compiling Main             ( lec2.hs, interpreted )

lec2.hs:66:19: error: Variable not in scope: x
   |
66 | length'' l | l == x:xs = 1 + length'' xs
   |                   ^

lec2.hs:66:21: error: Variable not in scope: xs :: [a]
   |
66 | length'' l | l == x:xs = 1 + length'' xs
   |                     ^^

lec2.hs:66:39: error: Variable not in scope: xs :: [a0]
   |
66 | length'' l | l == x:xs = 1 + length'' xs
   |                                       ^^
Failed, no modules loaded.
Prelude> :r
[1 of 1] Compiling Main             ( lec2.hs, interpreted )
Ok, one module loaded.
*Main> append [1 .. 3] [4 .. 10]
[1,2,3,4,5,6,7,8,9,10]
*Main> append [1,2] []
[1,2]