slides: changes to course 3 and 4

slides/course-03.md

@@ -279,11 +279,10 @@ show :: Show a => a -> String
 </br>
 
 ```bash
-:type (<)
-(<) :: Ord a => a -> a -> Bool
+map2 :: [a] -> (a -> b) -> [b]
 ```
 
-- What is the type of `(<) 3`?
+- What is `map2`? How would you explain it to a coworker?
 
 --
 
@@ -340,20 +339,22 @@ To solve problems functionally:
 - Recursion: divide a problem into smaller subproblems
 - Fold: iterate over data, accumulate a value along the way
 
-<!-- exdown-skip 6 7 -->
+<!-- exdown-skip 1 3 4 -->
 ```hs
-data Tree a = Node a [Tree a]
-
-find :: (a -> Bool) -> Tree a -> Maybe a
-find f t = undefined
+data Tree a = ...
 
 map :: (a -> b) -> Tree a -> Tree b
 map f t = undefined
+
+find :: (a -> Bool) -> Tree a -> Maybe a
+find f t = undefined
 ```
 
 ???
 
 ```hs
+data Tree a = Node a [Tree a]  -- Discuss alternatives
+
 treeFind :: (a -> Bool) -> Tree a -> Maybe a
 treeFind f (Node x children) =
   if f x then Just x

slides/course-04.md

@@ -92,23 +92,23 @@ Define:
 ```hs
 instance Eq Bool where
   (==) a b = undefined
-
-instance Eq a => Eq (Maybe a) where
-  (==) a b = undefined
 ```
 
-???
-
-- Discuss `equals` and `hashCode` in Java
+--
 
-<!-- exdown-skip  -->
+<!-- exdown-skip 4 5 -->
 ```hs
+instance Eq a => Eq (Maybe a) where
+  (==) _a _b = undefined
+
 instance Eq a => Eq [a] where
-  (==) = undefined
+  (==) _xs _ys = undefined
 ```
 
 ???
 
+- Discuss `equals` and `hashCode` in Java
+
 ```hs
 instance Eq a => Eq [a] where -- Build bigger instances from smaller ones
   (==) [] []                         = True
@@ -359,7 +359,6 @@ class Functor f where
 - What does `fmap` do?
 - Give instances:
   - `Maybe a`
-  - `Either a b`
   - `[a]`
 
 ---
@@ -407,6 +406,8 @@ Typeclasses:
 
 - Choose runtime behavior based on static types (/= dynamic dispatching)
 - Leverage the compiler's generation capabilities
+- Build APIs and features bottom up:
+  - from small values, to more structured values.
 
 ---