completed Chapter 4

src/Chapter4.hs

@@ -115,22 +115,38 @@ the output in here:
 
 >>> :k Char
 
+Char :: *
+
 >>> :k Bool
 
+Bool :: *
+
 >>> :k [Int]
 
+[Int] :: *
+
 >>> :k []
 
+[] :: * -> *
+
 >>> :k (->)
 
+(->) :: * -> * -> *
+
 >>> :k Either
 
+Either :: * -> * -> *
+
 >>> data Trinity a b c = MkTrinity a b c
 >>> :k Trinity
 
+Trinity :: * -> * -> * -> *
+
 >>> data IntBox f = MkIntBox (f Int)
 >>> :k IntBox
 
+IntBox :: (* -> *) -> *
+
 -}
 
 {- |
@@ -293,7 +309,8 @@ values and apply them to the type level?
 -}
 instance Functor (Secret e) where
     fmap :: (a -> b) -> Secret e a -> Secret e b
-    fmap = error "fmap for Box: not implemented!"
+    fmap _ (Trap a) = Trap a 
+    fmap f (Reward a) = Reward(f a)
 
 {- |
 =⚔️= Task 3
@@ -307,6 +324,12 @@ data List a
     = Empty
     | Cons a (List a)
 
+instance Functor List where
+  fmap :: (a->b) -> List a -> List b
+  fmap _ Empty = Empty
+  fmap f (Cons x xs) = Cons (f x) (fmap f xs)
+
+
 {- |
 =🛡= Applicative
 
@@ -472,10 +495,12 @@ Implement the Applicative instance for our 'Secret' data type from before.
 -}
 instance Applicative (Secret e) where
     pure :: a -> Secret e a
-    pure = error "pure Secret: Not implemented!"
+    pure = Reward
 
     (<*>) :: Secret e (a -> b) -> Secret e a -> Secret e b
-    (<*>) = error "(<*>) Secret: Not implemented!"
+    Reward f <*> a = fmap f a 
+    Trap e <*> _ = Trap e
+
 
 {- |
 =⚔️= Task 5
@@ -488,6 +513,18 @@ Implement the 'Applicative' instance for our 'List' type.
   may also need to implement a few useful helper functions for our List
   type.
 -}
+join :: List a -> List a -> List a
+join Empty l = l 
+join (Cons x xs) l = Cons x (join xs l)
+
+instance Applicative List where
+  pure :: a -> List a 
+  pure x = Cons x Empty
+
+  (<*>) :: List (a->b) -> List a -> List b
+  Empty <*> _ =Empty
+  _ <*> Empty = Empty
+  Cons x xs <*> l = join (fmap x l) (xs <*> l)
 
 
 {- |
@@ -600,7 +637,8 @@ Implement the 'Monad' instance for our 'Secret' type.
 -}
 instance Monad (Secret e) where
     (>>=) :: Secret e a -> (a -> Secret e b) -> Secret e b
-    (>>=) = error "bind Secret: Not implemented!"
+    Trap e >>= _ = Trap e
+    Reward x >>= f = f x 
 
 {- |
 =⚔️= Task 7
@@ -609,8 +647,21 @@ Implement the 'Monad' instance for our lists.
 
 🕯 HINT: You probably will need to implement a helper function (or
   maybe a few) to flatten lists of lists to a single list.
+
+  data List a
+    = Empty
+    | Cons a (List a)
 -}
 
+flatten :: List(List a) -> List a 
+flatten Empty = Empty
+flatten (Cons x xs) = join x (flatten xs)
+
+instance Monad List where
+  (>>=) :: List a -> (a -> List b) -> List b
+  l >>= f = flatten (fmap f l)
+
+
 
 {- |
 =💣= Task 8*: Before the Final Boss
@@ -629,7 +680,7 @@ Can you implement a monad version of AND, polymorphic over any monad?
 🕯 HINT: Use "(>>=)", "pure" and anonymous function
 -}
 andM :: (Monad m) => m Bool -> m Bool -> m Bool
-andM = error "andM: Not implemented!"
+andM a b = a >>= \f -> if f then b else pure False 
 
 {- |
 =🐉= Task 9*: Final Dungeon Boss
@@ -673,6 +724,19 @@ Specifically,
  ❃ Implement the function to convert Tree to list
 -}
 
+data Tree a = Leaf | Node a (Tree a) (Tree a)
+instance Functor Tree where
+  fmap :: (a -> b) -> Tree a -> Tree b 
+  fmap _ Leaf = Leaf 
+  fmap f (Node a l r) = Node (f a) (fmap f l) (fmap f r)
+
+revTree :: Tree a -> Tree a
+revTree Leaf = Leaf
+revTree (Node a l r)  = Node a (revTree r) (revTree l)
+
+listTree :: Tree a -> List a 
+listTree Leaf= []
+listTree (Node a l r) = a : (listTree l) ++ (listTree r)
 
 {-
 You did it! Now it is time to open pull request with your changes