FP Laboratory 11

Complex data structure

Consider following data structure representing some kind of GUI.

data Point = Point {column::Int,row::Int} deriving (Show)

data Event = MouseEvent Point
           | KeyEvent {keyPressed::Char} deriving (Show)

data Position = Position {leftTopCorner :: Point, width :: Int, height :: Int} 

data Component
  = TextBox {name :: String, position :: Position, text :: String}
  | Button {name :: String, position :: Position, text :: String, onClick :: Maybe ((Event, Component) -> String)}
  | Container {name :: String, children :: [Component]}

As an example, we can use following data structure.

gui :: Component
gui =
  Container
    "My App"
    [ Container
        "Menu"
        [ Button "btn_new" (Position (Point 0 0) 100 20) "New" Nothing,
          Button "btn_open" (Position (Point 100 0) 100 20) "Open" Nothing,
          Button "btn_close" (Position (Point 200 0) 100 20) "Close" Nothing
        ],
      Container "Body" [TextBox "textbox_1" (Position (Point 0 20) 300 500) "Some text goes here"],
      Container "Footer" []
    ]

• Add the data type Component into the type class Show.

The result for our data from previous example should be something like this.

ghci> gui
Container - My App
        Container - Menu
                (0,0)[100,20] Button[btn_new]: New
                (100,0)[100,20] Button[btn_open]: Open
                (200,0)[100,20] Button[btn_close]: Close
        Container - Body
                (0,20)[300,500] TextBox[textbox_1]: Some text goes here
        Container - Footer

instance Show Position where
    show (Position (Point col row) width height) = "(" ++ show col ++ "," ++ show row ++ ")["++ show width++","++ show height++"]"

instance Show Component where
    show :: Component -> String
    show gui = showIndent "" gui where
        showIndent ind (TextBox name position text) = ind ++ show position ++ " TextBox[" ++ name ++ "]: " ++ text ++"\n" 
        showIndent ind (Button name position text click) = ind ++ show position ++ " Button[" ++ name ++ "]: " ++ text ++"\n"
        showIndent ind (Container name children) = let 
            inner = concat[showIndent (ind++"\t") c |c<-children]
            in ind ++ "Container - " ++ name ++ "\n" ++ inner

• Cerate a function insertInto, it will insert an element into the existing container from a GUI. The functions parameters will be:
  • first parameter will be the GUI, where we are inserting the new element;
  • second parameter is the name of the container, where we insert the new element, you can safely assume, that it will always exist. The element will be placed as last in the container;
  • last parameter is the inserted element.

ghci> insertInto gui "Footer" (TextBox "Done" (Position (Point 0 500) 300 10) "We are done!")
Container - My App
        Container - Menu
                (0,0)[100,20] Button[btn_new]: New
                (100,0)[100,20] Button[btn_open]: Open
                (200,0)[100,20] Button[btn_close]: Close
        Container - Body
                (0,20)[300,500] TextBox[textbox_1]: Some text goes here
        Container - Footer
                (0,500)[300,10] TextBox[Done]: We are done!

insertInto :: Component -> String -> Component -> Component
insertInto (Container cName children ) toName element 
    | cName == toName = Container cName (children++[element]) 
    | otherwise = Container cName [insertInto c toName element  |c<-children]
insertInto x toName element = x

Additional exercises

• Consider the following definition and the example of the m-ary tree.

data MTree a = MTree a [MTree a]

testTree1 :: MTree Int            
testTree1 = MTree 1 [(MTree 2 [(MTree 3 []),(MTree 4 [(MTree 5 []),(MTree 6 [])]), (MTree 7 []),(MTree 8 [])]), (MTree 9 [])]

• Create a function that sums all values stored in the m-ary tree.

msum :: MTree Int -> Int

• Create a function that extracts all values from the m-ary tree into a list.

mToList :: MTree a -> [a]

• Create a function that counts all leaves in the m-ary tree.

mLeafCount :: MTree a -> Int

• Create a function that finds a maximum value stored in the m-ary tree.

mMaxTree :: Ord a => MTree a -> a

• Create a function that checks whether a given element is stored in the m-ary tree.

mContains :: Eq a => MTree a -> a -> Bool

• Create a function that returns a number of elements greater than a given value.

mGreaterThan :: Ord a => MTree a -> a -> Int