Various enhancements and additions

slides/Course03.hs

@@ -161,3 +161,22 @@ mkEmailSafe user host ext =
               ++ show s
               ++ ". Expected one of: [\"com\", \"fr\"]")
 
+mkEmailSafe' :: String -> String -> String -> Either String String
+mkEmailSafe' user host ext = do
+  username <- checkUsername user
+  extension <- checkExt ext
+  pure (username ++ "@" ++ host ++ "." ++ extension)
+  where
+    checkUsername :: String -> Either String String
+    checkUsername s =
+      if all isLower s
+        then Right s
+        else Left ("Username should be lowercase, but found: " ++ s)
+    checkExt :: String -> Either String String
+    checkExt "com" = Right "com"
+    checkExt "fr" = Right "fr"
+    checkExt s =
+      Left ("Unexpected extension: "
+              ++ show s
+              ++ ". Expected one of: [\"com\", \"fr\"]")
+

slides/Course04.hs

@@ -85,3 +85,32 @@ data Interval a = Interval {
   }
   deriving Functor
 
+-- | @makeURL "http" "google.fr" "search/advanced"@ returns
+-- @"http://www.google.fr/search/advanced"@
+makeURL :: String -> String -> String -> String
+makeURL = undefined
+
+newtype Protocol = Protocol String
+
+newtype Hostname = Hostname String
+
+newtype Segments = Segments [String]
+
+makeURL' :: Protocol -> Hostname -> Segments -> String
+makeURL' = undefined
+
+data User = User { name :: String, avatar :: FilePath, id :: Int }
+
+-- | @authenticate user password@ tries to authenticate @user@ with @password@
+authenticate :: User -> String -> Bool
+authenticate = undefined
+
+data Guest
+data Authenticated
+
+-- @type@ defines aliases (shortcuts)
+type UserWithAuthStatus a = User
+
+authenticate' :: User -> String -> UserWithAuthStatus Authenticated
+authenticate' = undefined
+

slides/course-01.md

@@ -446,6 +446,7 @@ Property-based testing:
 
 # Recommended Reading
 
+- https://learnyouahaskell.github.io/chapters.html
 - http://book.realworldhaskell.org/read/getting-started.html
 
 <!-- Machinery for making the snippets valid, not shown, only

slides/course-03.md

@@ -431,8 +431,8 @@ Functional toolbox:
 
 # Recommended Reading
 
-- http://learnyouahaskell.com/syntax-in-functions
-- http://learnyouahaskell.com/higher-order-functions
+- https://learnyouahaskell.github.io/syntax-in-functions.html
+- https://learnyouahaskell.github.io/higher-order-functions.html
 
 ---
 
@@ -531,7 +531,7 @@ If done at this point and time remains:
 
 ---
 
-# More composition
+# More composition: monads
 
 ```bash
 > :type (>>=)
@@ -561,6 +561,36 @@ mkEmailSafe user host ext =
               ++ ". Expected one of: [\"com\", \"fr\"]")
 ```
 
+---
+
+# User friendly monads: the `do` notation
+
+```bash
+> :type (>>=)
+(>>=) :: Monad m => m a -> (a -> m b) -> m b
+```
+
+```hs
+mkEmailSafe' :: String -> String -> String -> Either String String
+mkEmailSafe' user host ext = do
+  username <- checkUsername user
+  extension <- checkExt ext
+  pure (username ++ "@" ++ host ++ "." ++ extension)
+  where
+    checkUsername :: String -> Either String String
+    checkUsername s =
+      if all isLower s
+        then Right s
+        else Left ("Username should be lowercase, but found: " ++ s)
+    checkExt :: String -> Either String String
+    checkExt "com" = Right "com"
+    checkExt "fr" = Right "fr"
+    checkExt s =
+      Left ("Unexpected extension: "
+              ++ show s
+              ++ ". Expected one of: [\"com\", \"fr\"]")
+```
+
 <!-- Machinery for making the snippets valid, not shown, only
      used by exdown (see check.sh).
 

slides/course-04.md

@@ -396,6 +396,74 @@ frequency :: [(Int, Gen a)] -> Gen a
 
 ---
 
+# `newtype`
+
+```hs
+-- | @makeURL "http" "google.fr" "search/advanced"@ returns
+-- @"http://www.google.fr/search/advanced"@
+makeURL :: String -> String -> String -> String
+makeURL = undefined
+```
+
+<center>
+  What's error prone about this function for callers?
+</center>
+
+--
+
+```hs
+newtype Protocol = Protocol String
+
+newtype Hostname = Hostname String
+
+newtype Segments = Segments [String]
+
+makeURL' :: Protocol -> Hostname -> Segments -> String
+makeURL' = undefined
+```
+
+`newtype`:
+* Cost-free (runtime) disambiguation 💪
+* ⚠️ It's just names! ⚠️
+
+---
+
+# Phantom Types
+
+```hs
+data User = User { name :: String, avatar :: FilePath, id :: Int }
+
+-- | @authenticate user password@ tries to authenticate @user@ with @password@
+authenticate :: User -> String -> Bool
+authenticate = undefined
+```
+
+<center>
+  How to model that a user is authenticated to the system?
+</center>
+
+--
+
+```hs
+data Guest
+data Authenticated
+
+-- @type@ defines aliases (shortcuts)
+type UserWithAuthStatus a = User
+
+authenticate' :: User -> String -> UserWithAuthStatus Authenticated
+authenticate' = undefined
+```
+
+--
+
+Phantom types:
+
+* Use type parameters as markers to distinguish data
+* Could you do that in Java?
+
+---
+
 # Recap
 
 Typeclasses:
@@ -409,10 +477,16 @@ Typeclasses:
 
 # Recommended reading
 
-- http://learnyouahaskell.com/types-and-typeclasses#typeclasses-101
+- https://learnyouahaskell.github.io/types-and-typeclasses.html#typeclasses-101
 - http://book.realworldhaskell.org/read/using-typeclasses.html
 - https://wiki.haskell.org/Typeclassopedia
 
+---
+
+# Type Applications
+
+TODO for next year
+
 <!-- Machinery for making the snippets valid, not shown, only
      used by exdown (see check.sh).
 

tps/TP1.hs

@@ -3,8 +3,9 @@
 -- Load me in the REPL with: cabal repl TP1.hs, then use :r to reload the code upon changing
 
 --
--- In this file, you need to replace the @undefined@ calls by real code
+-- In this file, you need to replace the @undefined@ calls by real code.
 --
+-- Resource for the syntax of functions: https://learnyouahaskell.github.io/syntax-in-functions.html
 
 module Main where
 

tps/TP5.hs

@@ -109,3 +109,14 @@ main = do
           html "<h1>Hello</h1>"
   where
     port :: Int = 3000
+
+data User = User { name :: String, avatar :: FilePath, id :: Int }
+
+-- | @authenticate user password@ tries to authenticate @user@ with @password@
+authenticate :: User -> String -> UserWithAuthStatus Authenticated
+authenticate = undefined
+
+data Guest
+data Authenticated
+
+type UserWithAuthStatus a = User