Small updates

slides/Course02.hs

@@ -61,8 +61,8 @@ instance Collection Maybe where
   size = \case Nothing -> 0; Just _ -> 1
   toList = \case Nothing -> []; Just x -> [x]
 
-instance Mappable [] where
-  map f = \case [] -> []; (x : xs) -> f x : Course02.map f xs
+instance Mappable Maybe where
+  map _f = undefined
 
 data Either a b =
     -- | The left case, commonly used as the error case
@@ -76,14 +76,6 @@ readEither :: Read a => String -> Either String a
 
 readEither _ = undefined
 
-instance Collection (Either a) where
-  size _ = 1
-  isEmpty _ = False
-  toList = \case Left _ -> []; Right b -> [b]
-
-instance Mappable (Either a) where
-  map f = \case Left a -> Left a; Right b -> Right (f b)
-
 data Account = Account {
     balance :: Int,
     email :: String,
@@ -105,6 +97,19 @@ mkAccount2 email = Account { .. } -- Take fields from enclosing scope
 setBalance :: Int -> Account -> Account
 setBalance n account = account { balance = n } -- functional update
 
+data Interval a = Interval {
+  start :: a,
+  end :: a
+}
+
+instance Collection Interval where
+  size _ = undefined
+  isEmpty _ = undefined
+  toList _ = undefined
+
+instance Mappable Interval where
+  map _f _ = undefined
+
 class Semigroup a where
   -- | Associative binary operation
   (<>) :: a -> a -> a

slides/Course03.hs

@@ -82,9 +82,9 @@ data Account = Account {
 dubious :: [Account] -> [String]
 dubious accounts =
   accounts
-    & filter (\Account{balance} -> balance > 1000000)
-    & filter (\Account{email} -> "ponzi" `isInfixOf` email)
-    & filter (\Account{name} -> case name of Nothing -> True; Just _ -> False)
+    & filter (\account -> account.balance > 1000000)
+    & filter (\account -> "ponzi" `isInfixOf` account.email)
+    & filter (\account -> case account.name of Nothing -> True; Just _ -> False)
     & map email
 
 

slides/check.sh

@@ -3,7 +3,7 @@
 # Continously build the *.hs files extract from
 # snippets of the *.md files
 
-ls *.md *.cabal | grep course | entr "./build_hs.sh" &
+ls *.md | grep course | entr "./extract_hs.sh && cabal build" &
 
 declare -r HS_CHECKER_PID="$!"
 

slides/course-02.md

@@ -405,8 +405,8 @@ instance Collection Maybe where
   size = \case Nothing -> 0; Just _ -> 1
   toList = \case Nothing -> []; Just x -> [x]
 
-instance Mappable [] where
-  map f = \case [] -> []; (x : xs) -> f x : Course02.map f xs
+instance Mappable Maybe where
+  map _f = undefined
 ```
 
 ---
@@ -437,35 +437,6 @@ Right 0
 Left "Prelude.read: no parse"  # Not the best error message
 ```
 
---
-
-**Cette fin de slide naze, parceque la syntaxe `Collection (Either a)` apparaît trop bizarre**
-
-* Abstracting over `Either`
-
-<!-- exdown-skip -->
-```hs
-instance Collection (Either a) where
-  size _ = undefined
-  isEmpty _ = undefined
-  toList _ = undefined
-
-instance Mappable (Either a) where
-  map f _ = undefined
-```
-
-???
-
-```hs
-instance Collection (Either a) where
-  size _ = 1
-  isEmpty _ = False
-  toList = \case Left _ -> []; Right b -> [b]
-
-instance Mappable (Either a) where
-  map f = \case Left a -> Left a; Right b -> Right (f b)
-```
-
 ---
 
 # Types: records
@@ -509,6 +480,25 @@ setBalance n account = account { balance = n } -- functional update
 
 ---
 
+# Abstracting over a record: `Interval`
+
+```hs
+data Interval a = Interval {
+  start :: a,
+  end :: a
+}
+
+instance Collection Interval where
+  size _ = undefined
+  isEmpty _ = undefined
+  toList _ = undefined
+
+instance Mappable Interval where
+  map _f _ = undefined
+```
+
+---
+
 # Common abstractions
 
 ```hs

slides/course-03.md

@@ -316,9 +316,9 @@ data Account = Account {
 dubious :: [Account] -> [String]
 dubious accounts =
   accounts
-    & filter (\Account{balance} -> balance > 1000000)
-    & filter (\Account{email} -> "ponzi" `isInfixOf` email)
-    & filter (\Account{name} -> case name of Nothing -> True; Just _ -> False)
+    & filter (\account -> account.balance > 1000000)
+    & filter (\account -> "ponzi" `isInfixOf` account.email)
+    & filter (\account -> case account.name of Nothing -> True; Just _ -> False)
     & map email
 ```
 

slides/course-04.md

@@ -365,6 +365,8 @@ class Functor f where
 
 # Be lazy, rely on the compiler
 
+From course 2:
+
 ```hs
 data Interval a = Interval {
     start :: a,
@@ -373,7 +375,6 @@ data Interval a = Interval {
   deriving Functor
 ```
 
-- What can this type represent?
 - Write `Functor Interval`
 
 ---