TD3: improvements found while delivering

Author: smelc

slides/course-03.md

@@ -178,7 +178,7 @@ lastv v1 v2 =
     (Beta, SemVer _ _ _) -> v2
     (SemVer x1 _ _, SemVer x2 _ _)   | x1 < x2             -> v2
     (SemVer x1 y1 _, SemVer x2 y2 _) | x1 == x2 && y1 < y2 -> v2
-    _ -> error "I'm too lazy"
+    _ -> error "TODO"
 ```
 
 ???
@@ -292,10 +292,9 @@ foldr :: Foldable t => (a -> b -> b) -> b -> t a -> b
 wordCount :: [[String]] -> Int
 wordCount files = undefined
 
--- | 'Word16' is a zero or positive number
-data Operation = Debit Word16 | Credit Word16
+data Operation = Debit Int | Credit Int
 
-balance :: [Operation] -> Word16
+balance :: [Operation] -> Int
 balance = undefined
 ```
 
@@ -305,7 +304,7 @@ balance = undefined
 wordCount :: [[String]] -> Int
 wordCount files = foldr (\words soFar -> (length words) + soFar) 0 files
 
-balance' :: [Operation] -> Word16
+balance' :: [Operation] -> Int
 balance' = foldr (\op soFar -> toInt op + soFar) 0
   where
     toInt = \case Debit x -> -x; Credit x -> x
@@ -315,8 +314,6 @@ balance' = foldr (\op soFar -> toInt op + soFar) 0
 
 ---
 
----
-
 # Composition
 
 Because functions are so central in functional programming, it is crucial
@@ -404,6 +401,8 @@ dubious accounts =
   `dubious`?
   - Would you rather have 3 loops or one loop?
 
+---
+
 # Composition on steroids
 
 <!-- exdown-skip -->