*Main> zip [1 .. 10] "abcde" 
[(1,'a'),(2,'b'),(3,'c'),(4,'d'),(5,'e')]
*Main> :t (:)
(:) :: a -> [a] -> [a]
*Main> 'a' : ['b', 'c', 'd']
"abcd"
*Main> :r
[1 of 1] Compiling Main             ( lec3.hs, interpreted )
Ok, one module loaded.
*Main> zip' [1 .. 10] "abcde" 
[(1,'a'),(2,'b'),(3,'c'),(4,'d'),(5,'e')]
*Main> zip' [] "abcde" 
[]
*Main> :t reverse
reverse :: [a] -> [a]
*Main> reverse "abcde"
"edcba"
*Main> reverse [1..10]
[10,9,8,7,6,5,4,3,2,1]
*Main> :r
[1 of 1] Compiling Main             ( lec3.hs, interpreted )
Ok, one module loaded.
*Main> reverse' [1 .. 10]
[10,9,8,7,6,5,4,3,2,1]
*Main> :r
[1 of 1] Compiling Main             ( lec3.hs, interpreted )
Ok, one module loaded.
*Main> reverse'' [1..10]
[10,9,8,7,6,5,4,3,2,1]
*Main> (\ x -> x + 1) 10
11
*Main> :t (\ x -> x + 1)
(\ x -> x + 1) :: Num a => a -> a
*Main> :t (\ x -> (\ y -> x + y))
(\ x -> (\ y -> x + y)) :: Num a => a -> a -> a
*Main> (\ x -> (\ y -> x + y)) 10 4
14
*Main> :t (\ x -> (\ y -> x + y)) 10
(\ x -> (\ y -> x + y)) 10 :: Num a => a -> a
*Main> (\ x -> (\ y -> x + y)) 10

<interactive>:19:1: error:
    • No instance for (Show (Integer -> Integer))
        arising from a use of ‘print’
        (maybe you haven't applied a function to enough arguments?)
    • In a stmt of an interactive GHCi command: print it
*Main> 
*Main> 
*Main> 
*Main> 
*Main> 
*Main> 
*Main> map (\ x -> x + 1) [1 .. 10]
[2,3,4,5,6,7,8,9,10,11]
*Main> :t map (\ x -> [x, ',']) "abc"
map (\ x -> [x, ',']) "abc" :: [[Char]]
*Main> map (\ x -> [x, ',']) "abc"
["a,","b,","c,"]
*Main> :t concat
concat :: Foldable t => t [a] -> [a]
*Main> concat (map (\ x -> [x, ',']) "abc")
"a,b,c,"
*Main> :r
[1 of 1] Compiling Main             ( lec3.hs, interpreted )
Ok, one module loaded.
*Main> map' (\ x -> x + 1) [1 .. 10]
[2,3,4,5,6,7,8,9,10,11]
*Main> :t filter
filter :: (a -> Bool) -> [a] -> [a]
*Main> filter even [1 .. 10]
[2,4,6,8,10]
*Main> filter (\ x -> x > 4) [1 .. 10]
[5,6,7,8,9,10]
*Main> filter (\ x -> x == 'r') "helloworld"
"r"
*Main> length (filter (\ x -> x == 'r') "helloworld")
1
*Main> length (filter (\ x -> x == 'l') "helloworld")
3
*Main> length (filter (\ x -> x == 'z') "helloworld")
0
*Main> :r
[1 of 1] Compiling Main             ( lec3.hs, interpreted )
Ok, one module loaded.
*Main> filter' (\ x -> x == 'l') "helloworld"
"lll"
*Main> :t zipWith
zipWith :: (a -> b -> c) -> [a] -> [b] -> [c]
*Main> zipWith (\ x y -> (x, y)) [1..10] "helloworld"
[(1,'h'),(2,'e'),(3,'l'),(4,'l'),(5,'o'),(6,'w'),(7,'o'),(8,'r'),(9,'l'),(10,'d')]
*Main> :t zipWith (\ x y -> (x, y)) 
zipWith (\ x y -> (x, y)) :: [a] -> [b] -> [(a, b)]
*Main> :t show 
show :: Show a => a -> String
*Main> show 1
"1"
*Main> zipWith (\ x y -> x + y) [1..10] [11 .. 21]
[12,14,16,18,20,22,24,26,28,30]
*Main> zipWith (\ x y -> x + y) [1..10] [11 .. 20]
[12,14,16,18,20,22,24,26,28,30]
*Main> :r
[1 of 1] Compiling Main             ( lec3.hs, interpreted )

lec3.hs:46:19: error:
    • Couldn't match type ‘b’ with ‘c’
      ‘b’ is a rigid type variable bound by
        the type signature for:
          zipWith' :: forall a b c. (a -> b -> c) -> [a] -> [b] -> [c]
        at lec3.hs:45:1-46
      ‘c’ is a rigid type variable bound by
        the type signature for:
          zipWith' :: forall a b c. (a -> b -> c) -> [a] -> [b] -> [c]
        at lec3.hs:45:1-46
      Expected type: [c]
        Actual type: [b]
    • In the expression: y
      In an equation for ‘zipWith'’: zipWith' f [] y = y
    • Relevant bindings include
        y :: [b] (bound at lec3.hs:46:15)
        f :: a -> b -> c (bound at lec3.hs:46:10)
        zipWith' :: (a -> b -> c) -> [a] -> [b] -> [c]
          (bound at lec3.hs:46:1)
   |
46 | zipWith' f [] y = y
   |                   ^
Failed, no modules loaded.
Prelude> :r
[1 of 1] Compiling Main             ( lec3.hs, interpreted )
Ok, one module loaded.
*Main> zipWith' (\ x y -> x + y) [1..10] [11 .. 20]
[12,14,16,18,20,22,24,26,28,30]