added some more to Chapter3

seed/Chapter3/Step_3_4.hs

@@ -10,7 +10,7 @@ page = thehtml <<
         ]
     ]
 
--- Rewrite all of this to use a type synonym.
+-- Rewrite all of this to use a type synonym for the tuple.
 
 toDoItems :: [(Bool, String)] -- a list of tuples: each a Bool and String
 toDoItems =

seed/Chapter3/Step_3_5.hs

@@ -0,0 +1,57 @@
+module Step_3_5 where
+
+import Slides
+
+page = slideDeck "Chapter 3"
+    [ codeSlide "Not that safe"
+        "Type synonyms are quick and easy and often the right choice, but \
+        \don't offer as much type saftey as possible. Consider:"
+        [ "type Range = (Int, Int)"
+        , "inRange :: Range -> Int -> Bool"
+        , "inRange (lo,hi) x = lo <= x && x <= hi"
+        , ""
+        , "type Point = (Int, Int)"
+        , "p :: Point"
+        , "p = (3,7)"
+        , ""
+        , "ick = inRange p 4 -- compiles!"
+        ]
+    , codeSlide "Data Types"
+        "Data types let you create a type that is distinct. When you so you \
+        \define a constructor that builds values of the type:"
+        [ "data Range = Range Int Int"
+        , "inRange :: Range -> Int -> Bool"
+        , "inRange (Range lo hi) x = lo <= x && x <= hi"
+        , ""
+        , "data Point = Point Int Int"
+        , "p :: Point"
+        , "p = Point 3 7"
+        , ""
+        , "ick = inRange p 4 -- now this is a compile error"
+        ]
+    , codeSlide "Multiple Constrcutors"
+        "Data types are very powerful. They can have more than one constructor \
+        \and each constructor can have any number of values:"
+        [ "data Direction = North | East | South | West"
+        , "  deriving (Eq, Show)"
+        , ""
+        , "data Weather = Sunny | Rainy Double | Windy Double Direction"
+        , "describe :: Weather -> String"
+        , "describe Sunny = \"lovely\""
+        , "describe (Rainy inches) | inches < 0.2 = \"drizzle\""
+        , "                        | otherwise    = \"wet\""
+        , "describe (Windy speed dir) = "
+        , "    \"blowin' \" ++ show speed ++ \" from \" ++ show dir"
+        ]
+    , codeSlide "Wait, Deriving What?"
+        "The deriving clause on the data declaration is a bit of boilerplate \
+        \saver that will make your data do more. Here are some of the things \
+        \you can 'derive' for your data automatically:"
+        [ "Eq      -- works with == and /= operators"
+        , "Ord     -- works with <, >, etc.."
+        , "Show    -- works with show"
+        , "Read    -- works with read"
+        , "Enum    -- convertable to/from integers"
+        , "Bounded -- has a min and max value"
+        ]
+    ]

seed/Chapter3/Step_3_6.hs

@@ -0,0 +1,59 @@
+module Step_3_6 where
+
+import Text.Html
+
+page = thehtml <<
+    [ header << (thetitle << "Output")
+    , body <<
+        [ h1 << "A to do list:"
+        , thediv << toDoHtml
+        , h1 << "# people invited:"
+        , p << show (headcount invited)
+        ]
+    ]
+
+-- We've written two lists.
+
+data ToDo = ToDo String | Done String
+
+toDoItems :: [ToDo]
+toDoItems =
+    [ Done "Pick up avacados"
+    , Done "Make snacks"
+    , ToDo "Clean house"
+    , ToDo "Have party"
+    ]
+
+
+data Invite = Invite String Int
+
+who :: Invite -> String
+who (Invite name count) = name
+
+invited :: [Invite]
+invited =
+    [ Invite "Amy" 1
+    , Invite "Bob" 7  -- he's got lots of kids
+    , Invite "Cam" 2
+    , Invite "Doris" 3
+    , Invite "Edgar" 2
+    , Invite "Fran" 2
+    ]
+
+formatToDo :: ToDo -> Html
+-- Try writing this
+
+renderToDo :: [ToDo] -> [Html]
+renderToDo ts = map formatToDo ts
+
+toDoHtml :: Html
+toDoHtml = ulist << renderToDo toDoItems
+
+-- NEXT
+
+-- Write this function
+
+headcount :: [Invite] -> Int
+headcount is = 0 -- this list was just a place holder, delete it
+
+

seed/Chapter3/Step_3_7.hs

@@ -0,0 +1,86 @@
+module Step_3_7 where
+
+import Text.Html
+
+page = thehtml <<
+    [ header << (thetitle << "Output")
+    , body <<
+        [ h1 << "A to do list:"
+        , thediv << toDoHtml
+        , reminderHtml
+        , h1 << "# people invited:"
+        , p << show (headcount invited)
+        ]
+    ]
+
+data ToDo = ToDo String | Done String
+
+toDoItems :: [ToDo]
+toDoItems =
+    [ Done "Pick up avacados"
+    , Done "Make snacks"
+    , ToDo "Clean house"
+    , ToDo "Have party"
+    ]
+
+-- We need a function to return the next item to do.
+-- Something like:
+--        whatToDoNext :: [ToDo] -> ToDo
+
+-- But what should it return if they are all done?
+-- Enter Maybe:
+whatToDoNext :: [ToDo] -> Maybe String
+
+-- The return type is Maybe String -- in the same way [String] is a type 'built'
+-- from the String type, Maybe String is a type 'built' from the String type. But
+-- rather than a list, values of type Maybe String can have one of two forms:
+--         Just someString
+--         Nothing
+whatToDoNext (Done item : ts) = whatToDoNext ts
+whatToDoNext (ToDo item : ts) = Just item
+whatToDoNext []               = Nothing
+
+formatNotice :: Maybe String -> Html
+formatNotice Nothing = noHtml
+formatNotice (Just item) = h1 << ("*** DO THIS: " ++ item ++ " ***")
+
+reminderHtml :: Html
+reminderHtml = formatNotice $ whatToDoNext toDoItems
+
+
+formatToDo :: ToDo -> Html
+formatToDo (ToDo item) = li << bold << item
+formatToDo (Done item) = li << item
+
+renderToDo :: [ToDo] -> [Html]
+renderToDo ts = map formatToDo ts
+
+toDoHtml :: Html
+toDoHtml = ulist << renderToDo toDoItems
+
+-- Try changing the toDoItems to be all Done and see how this works
+
+
+-- NEXT
+-- Add an optional partner or spouse to the invite data type.
+-- Add a list of invitiees (and optional partners!) to the page.
+
+data Invite = Invite String Int
+
+who :: Invite -> String
+who (Invite name count) = name
+
+invited :: [Invite]
+invited =
+    [ Invite "Amy" 1
+    , Invite "Bob" 7  -- he's got lots of kids
+    , Invite "Cam" 2
+    , Invite "Doris" 3
+    , Invite "Edgar" 2
+    , Invite "Fran" 2
+    ]
+
+headcount :: [Invite] -> Int
+headcount [] = 0
+headcount (Invite who count : is) = count + headcount is
+

seed/lib/Tutorial.hs

@@ -69,6 +69,9 @@ steps =
     , Step 3 2 Code
     , Step 3 3 Slides
     , Step 3 4 Code
+    , Step 3 5 Slides
+    , Step 3 6 Code
+    , Step 3 7 Code
     ]
 
 stepUrls :: [String]