From db32368e34cb40fc1c3f0147f492cc58a5c20363 Mon Sep 17 00:00:00 2001
From: Lilly <lilly@lillycat.tech>
Date: Wed, 5 Oct 2022 14:48:03 +0100
Subject: [PATCH 1/9] Complete chapter 2

---
 src/Chapter2.hs | 62 +++++++++++++++++++++++++++++++++++--------------
 1 file changed, 45 insertions(+), 17 deletions(-)

diff --git a/src/Chapter2.hs b/src/Chapter2.hs
index f7c02ce2..92ecfd34 100644
--- a/src/Chapter2.hs
+++ b/src/Chapter2.hs
@@ -186,32 +186,43 @@ Evaluate the following expressions in GHCi and insert the answers. Try
 to guess first, what you will see.
 
 >>> [10, 2] ++ [3, 1, 5]
+[10, 2, 3, 1, 5]
 
 >>> [] ++ [1, 4]  -- [] is an empty list
+[1, 4]
 
 >>> 3 : [1, 2]
+[3, 1, 2]
 
 >>> 4 : 2 : [5, 10]  -- prepend multiple elements
+[4, 2, 5, 10]
 
 >>> [1 .. 10]  -- list ranges
+[1,2,3,4,5,6,7,8,9,10]
 
 >>> [10 .. 1]
+[]
 
 >>> [10, 9 .. 1]  -- backwards list with explicit step
+[10,9,8,7,6,5,4,3,2,1]
 
 >>> length [4, 10, 5]  -- list length
+3
 
 >>> replicate 5 True
+[True,True,True,True,True]
 
 >>> take 5 "Hello, World!"
+"Hello"
 
 >>> drop 5 "Hello, World!"
+", World!"
 
 >>> zip "abc" [1, 2, 3]  -- convert two lists to a single list of pairs
+[('a', 1), ('b', 2), ('c', 3)]
 
 >>> words "Hello   Haskell     World!"  -- split the string into the list of words
-
-
+["Hello","Haskell","World!"]
 
 👩‍🔬 Haskell has a lot of syntax sugar. In the case with lists, any
   list literal like "[3, 1, 2]" is syntax sugar for prepending elements
@@ -336,7 +347,7 @@ from it!
 ghci> :l src/Chapter2.hs
 -}
 subList :: Int -> Int -> [a] -> [a]
-subList = error "subList: Not implemented!"
+subList a b xs = drop a . take b $ xs 
 
 {- |
 =⚔️= Task 4
@@ -348,9 +359,10 @@ Implement a function that returns only the first half of a given list.
 >>> firstHalf "bca"
 "b"
 -}
--- PUT THE FUNCTION TYPE IN HERE
-firstHalf l = error "firstHalf: Not implemented!"
 
+firstHalf :: [a] -> [a]
+firstHalf l = take len l
+  where len = (length l) `div` 2
 
 {- |
 =🛡= Pattern matching
@@ -501,7 +513,10 @@ True
 >>> isThird42 [42, 42, 0, 42]
 False
 -}
-isThird42 = error "isThird42: Not implemented!"
+
+isThird42 :: Integral a => [a] -> Bool
+isThird42 (_ : x : _) = x == 42
+isThird42 _ = False
 
 
 {- |
@@ -605,9 +620,10 @@ Implement a function that duplicates each element of the list
 "aabbaacc"
 
 -}
-duplicate :: [a] -> [a]
-duplicate = error "duplicate: Not implemented!"
+-- Couldn't figure out how to do it with a pattern match? Not sure if this is right
 
+duplicate :: [a] -> [a]
+duplicate = concatMap (replicate 2)
 
 {- |
 =⚔️= Task 7
@@ -621,7 +637,11 @@ Write a function that takes elements of a list only in even positions.
 >>> takeEven [2, 1, 3, 5, 4]
 [2,3,4]
 -}
-takeEven = error "takeEven: Not implemented!"
+
+takeEven (x : y ) = x : go y
+   where go (y:x) = takeEven x
+         go []    = []
+takeEven    []    = []
 
 {- |
 =🛡= Higher-order functions
@@ -727,8 +747,9 @@ value of the element itself
 
 🕯 HINT: Use combination of 'map' and 'replicate'
 -}
+
 smartReplicate :: [Int] -> [Int]
-smartReplicate l = error "smartReplicate: Not implemented!"
+smartReplicate l = map (\x -> replicate x x) l
 
 {- |
 =⚔️= Task 9
@@ -741,7 +762,8 @@ the list with only those lists that contain a passed element.
 
 🕯 HINT: Use the 'elem' function to check whether an element belongs to a list
 -}
-contains = error "contains: Not implemented!"
+contains :: Integral a => a -> [[a]] -> [[a]]
+contains n xs = filter (\ys -> n `elem` ys) xs
 
 
 {- |
@@ -780,14 +802,16 @@ nextInt = add 1
 Let's now try to eta-reduce some of the functions and ensure that we
 mastered the skill of eta-reducing.
 -}
+
 divideTenBy :: Int -> Int
-divideTenBy x = div 10 x
+divideTenBy = div 10
 
--- TODO: type ;)
-listElementsLessThan x l = filter (< x) l
+listElementsLessThan :: (Num a, Ord a) => a -> [a] -> [a]
+listElementsLessThan x = filter (< x)
 
 -- Can you eta-reduce this one???
-pairMul xs ys = zipWith (*) xs ys
+pairMul :: Num a => [a] -> [a] -> [a]
+pairMul xs = (zipWith (*) xs)
 
 {- |
 =🛡= Lazy evaluation
@@ -842,7 +866,9 @@ list.
 
 🕯 HINT: Use the 'cycle' function
 -}
-rotate = error "rotate: Not implemented!"
+rotate n xs = if (n /= (abs n)) then
+  [] 
+  else take (length xs) $ drop n $ (cycle xs)
 
 {- |
 =💣= Task 12*
@@ -858,8 +884,10 @@ and reverses it.
   function, but in this task, you need to implement it manually. No
   cheating!
 -}
-rewind = error "rewind: Not Implemented!"
 
+rewind :: [a] -> [a]
+rewind (x:xs) = rewind xs ++ [x]
+rewind [] = []
 
 {-
 You did it! Now it is time to open pull request with your changes

From 92f21a2009a1b6ff1ab14acbd2a3962bd1a6c5cc Mon Sep 17 00:00:00 2001
From: Lilly <lilly@lillycat.tech>
Date: Wed, 5 Oct 2022 14:55:27 +0100
Subject: [PATCH 2/9] Update Chapter2.hs

---
 src/Chapter2.hs | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/Chapter2.hs b/src/Chapter2.hs
index 92ecfd34..bf0de427 100644
--- a/src/Chapter2.hs
+++ b/src/Chapter2.hs
@@ -749,7 +749,7 @@ value of the element itself
 -}
 
 smartReplicate :: [Int] -> [Int]
-smartReplicate l = map (\x -> replicate x x) l
+smartReplicate l = concatMap (\x -> replicate x x) l
 
 {- |
 =⚔️= Task 9

From f49ac11f749ea7420788f522c8913c20e5caf3f0 Mon Sep 17 00:00:00 2001
From: Lilly <lilly@lillycat.tech>
Date: Wed, 5 Oct 2022 15:01:13 +0100
Subject: [PATCH 3/9] Update Chapter2.hs

---
 src/Chapter2.hs | 22 +++++++++++-----------
 1 file changed, 11 insertions(+), 11 deletions(-)

diff --git a/src/Chapter2.hs b/src/Chapter2.hs
index bf0de427..e3cee315 100644
--- a/src/Chapter2.hs
+++ b/src/Chapter2.hs
@@ -136,43 +136,43 @@ functions in GHCi and insert the corresponding resulting output below:
 
 List of booleans:
 >>> :t [True, False]
-
+[True, False] :: [Bool]
 
 String is a list of characters:
 >>> :t "some string"
-
+"c" :: String
 
 Empty list:
 >>> :t []
-
+[] :: [a]
 
 Append two lists:
 >>> :t (++)
-
+(++) :: [a] -> [a] -> [a]
 
 Prepend an element at the beginning of a list:
 >>> :t (:)
-
+(:) :: a -> [a] -> [a]
 
 Reverse a list:
 >>> :t reverse
-
+reverse :: [a] -> [a]
 
 Take first N elements of a list:
 >>> :t take
-
+ake :: Int -> [a] -> [a]
 
 Create a list from N same elements:
 >>> :t replicate
-
+replicate :: Int -> a -> [a]
 
 Split a string by line breaks:
 >>> :t lines
-
+lines :: String -> [String]
 
 Join a list of strings with line breaks:
 >>> :t unlines
-
+unlines :: [String] -> String
 
 -}
 
@@ -186,7 +186,7 @@ Evaluate the following expressions in GHCi and insert the answers. Try
 to guess first, what you will see.
 
 >>> [10, 2] ++ [3, 1, 5]
-[10, 2, 3, 1, 5]
+[10,2,3,1,5]
 
 >>> [] ++ [1, 4]  -- [] is an empty list
 [1, 4]

From a6a9a653b911b1c60afce517d5bd73f55556861e Mon Sep 17 00:00:00 2001
From: Lilly <lilly@lillycat.tech>
Date: Wed, 5 Oct 2022 15:07:01 +0100
Subject: [PATCH 4/9] fix doctests

---
 src/Chapter2.hs | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/src/Chapter2.hs b/src/Chapter2.hs
index e3cee315..b55926ac 100644
--- a/src/Chapter2.hs
+++ b/src/Chapter2.hs
@@ -140,7 +140,7 @@ List of booleans:
 
 String is a list of characters:
 >>> :t "some string"
-"c" :: String
+"some string" :: String
 
 Empty list:
 >>> :t []
@@ -189,13 +189,13 @@ to guess first, what you will see.
 [10,2,3,1,5]
 
 >>> [] ++ [1, 4]  -- [] is an empty list
-[1, 4]
+[1,4]
 
 >>> 3 : [1, 2]
-[3, 1, 2]
+[3,1,2]
 
 >>> 4 : 2 : [5, 10]  -- prepend multiple elements
-[4, 2, 5, 10]
+[4,2,5,10]
 
 >>> [1 .. 10]  -- list ranges
 [1,2,3,4,5,6,7,8,9,10]
@@ -219,7 +219,7 @@ to guess first, what you will see.
 ", World!"
 
 >>> zip "abc" [1, 2, 3]  -- convert two lists to a single list of pairs
-[('a', 1), ('b', 2), ('c', 3)]
+[('a',1),('b',2),('c',3)]
 
 >>> words "Hello   Haskell     World!"  -- split the string into the list of words
 ["Hello","Haskell","World!"]

From 4f71b401359c43e01ffd023cf18cddc621156953 Mon Sep 17 00:00:00 2001
From: Lilly <lilly@lillycat.tech>
Date: Wed, 5 Oct 2022 15:19:51 +0100
Subject: [PATCH 5/9] Update Chapter2.hs

---
 src/Chapter2.hs | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/src/Chapter2.hs b/src/Chapter2.hs
index b55926ac..18f01ded 100644
--- a/src/Chapter2.hs
+++ b/src/Chapter2.hs
@@ -347,7 +347,7 @@ from it!
 ghci> :l src/Chapter2.hs
 -}
 subList :: Int -> Int -> [a] -> [a]
-subList a b xs = drop a . take b $ xs 
+subList a b xs = drop a . take (b + 1) $ xs 
 
 {- |
 =⚔️= Task 4
@@ -515,7 +515,7 @@ False
 -}
 
 isThird42 :: Integral a => [a] -> Bool
-isThird42 (_ : x : _) = x == 42
+isThird42 (_ : _ : x : _) = x == 42
 isThird42 _ = False
 
 

From ce8d66bc6249150a4fd953a3e6007fd6001fbb9b Mon Sep 17 00:00:00 2001
From: Lilly <lilly@lillycat.tech>
Date: Wed, 5 Oct 2022 15:27:12 +0100
Subject: [PATCH 6/9] Update Chapter2.hs

---
 src/Chapter2.hs | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/Chapter2.hs b/src/Chapter2.hs
index 18f01ded..0f26088c 100644
--- a/src/Chapter2.hs
+++ b/src/Chapter2.hs
@@ -140,7 +140,7 @@ List of booleans:
 
 String is a list of characters:
 >>> :t "some string"
-"some string" :: String
+"some string" :: [Char]
 
 Empty list:
 >>> :t []

From 1bd50057bc72c7ffebd4f0a9a09f393e2058ffdd Mon Sep 17 00:00:00 2001
From: Lilly <lilly@lillycat.tech>
Date: Wed, 5 Oct 2022 15:35:05 +0100
Subject: [PATCH 7/9] Update Chapter2.hs

---
 src/Chapter2.hs | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/Chapter2.hs b/src/Chapter2.hs
index 0f26088c..ab3497d7 100644
--- a/src/Chapter2.hs
+++ b/src/Chapter2.hs
@@ -160,7 +160,7 @@ reverse :: [a] -> [a]
 
 Take first N elements of a list:
 >>> :t take
-ake :: Int -> [a] -> [a]
+take :: Int -> [a] -> [a]
 
 Create a list from N same elements:
 >>> :t replicate

From cd371655faaba32c766e108ceb7d2d5a7ad86e63 Mon Sep 17 00:00:00 2001
From: Lilly <lilly@lillycat.tech>
Date: Wed, 5 Oct 2022 17:40:05 +0100
Subject: [PATCH 8/9] Update Chapter2.hs

---
 src/Chapter2.hs | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/src/Chapter2.hs b/src/Chapter2.hs
index ab3497d7..fded3c7b 100644
--- a/src/Chapter2.hs
+++ b/src/Chapter2.hs
@@ -347,7 +347,8 @@ from it!
 ghci> :l src/Chapter2.hs
 -}
 subList :: Int -> Int -> [a] -> [a]
-subList a b xs = drop a . take (b + 1) $ xs 
+subList a b xs = if a < b then [] else
+ drop a . take (b + 1) $ xs 
 
 {- |
 =⚔️= Task 4

From 878e071e7ada1309f3e172468f7147eba6939697 Mon Sep 17 00:00:00 2001
From: Lilly <lilly@lillycat.tech>
Date: Wed, 5 Oct 2022 17:48:05 +0100
Subject: [PATCH 9/9] Update Chapter2.hs

---
 src/Chapter2.hs | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/src/Chapter2.hs b/src/Chapter2.hs
index fded3c7b..bc4b2f21 100644
--- a/src/Chapter2.hs
+++ b/src/Chapter2.hs
@@ -347,8 +347,8 @@ from it!
 ghci> :l src/Chapter2.hs
 -}
 subList :: Int -> Int -> [a] -> [a]
-subList a b xs = if a < b then [] else
- drop a . take (b + 1) $ xs 
+subList a b xs = if a > b then [] else
+  drop a . take (b + 1) $ xs 
 
 {- |
 =⚔️= Task 4