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

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