FP Laboratory 11/cs

Complex data structure

Consider following data structure representing some kind of GUI.

data Point = Point {column::Int,row::Int} 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}
  | 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",
          Button "btn_open" (Position (Point 100 0) 100 20) "Open",
          Button "btn_close" (Position (Point 200 0) 100 20) "Close"
        ],
      Container "Body" [TextBox "textbox_1" (Position (Point 0 20) 300 500) "Some text goes here"],
      Container "Footer" []
    ]

• Přidejte typ Component do typove třídy Show.

Výsledek pro naše data z předchozího příkladu by měl vypadat takto.

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) = 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

• Vytvořte funkci insertInto, která vloží prvek do existujícího kontejneru z GUI. Parametry funkce budou:
  • prvním parametrem bude GUI, do kterého budeme vkládat nový prvek;
  • druhým parametrem bude název kontejneru, do kterého vkládáme nový prvek, lze bezpečně předpokládat, že bude vždy existovat. Prvek bude v kontejneru umístěn jako poslední;
  • posledním parametrem je vložený prvek.

insertInto :: Component -> String -> Component -> Component

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

• Rozšiřte definici tlačítka v našem GUI takto.

data Event = MouseEvent Point
           | KeyEvent {keyPressed::Char} deriving (Show)
...
  | Button {name :: String, position :: Position, text :: String, onClick :: Maybe (Event -> String)}
...

Naše onClick je funkce, která se spustí po kliknutí na tlačítko. Parametrem této funkce jsou data popisující událost, která se osluhu spustila.

...
[ Button "btn_new" (Position (Point 0 0) 100 20) "New" (Just (\event -> "Clicked on new button.")),
  Button "btn_open" (Position (Point 100 0) 100 20) "Open" Nothing,
  Button "btn_close" (Position (Point 200 0) 100 20) "Close" (Just (\event -> "Clicked on close button.")) ]
...

• Vytvořte funkci clickOnButton, která dostane naše GUI a nějakou událost. Pokud je parametrem instance MouseEvent a pozice, na kterou jsme klikli, je uvnitř některého z tlačítek GUI, pak vyhodnotí odpovídající funkci onClick a výsledkem bude získáný řetězec. Ve všech ostatních případech bude výsledkem Nothing.

clickOnButton :: Component -> Event -> Maybe String

ghci> clickOnButton gui (MouseEvent (Point 5 5))
Just "Clicked on new button."
ghci> clickOnButton gui (MouseEvent (Point 205 5))
Just "Clicked on close button."
ghci> clickOnButton gui (MouseEvent (Point 205 50))
Nothing

isInside :: Point -> Position -> Bool
isInside (Point pCol pRow) (Position (Point cornerCol cornerRow) width height) =
     cornerCol <= pCol && pCol <= cornerCol + width && cornerRow <= pRow && pRow <= cornerRow + height

getFirstOrNothing :: [Maybe a] -> Maybe a
getFirstOrNothing [] = Nothing
getFirstOrNothing (Nothing:xs) = getFirstOrNothing xs
getFirstOrNothing (Just x: xs) = Just x

clickOnButton :: Component -> Event -> Maybe String
clickOnButton (Button {position = pos, onClick = (Just func)}) (MouseEvent point) | isInside point pos = Just (func (MouseEvent point))
clickOnButton (Container {children=inner}) event = getFirstOrNothing [clickOnButton c event |c<-inner]
clickOnButton _ _ = Nothing

Doplňková cvičení

• Uvažujme následující definici a příklad m-árního stromu.

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 [])]

• Vytvořte funkci, která sečte všechny hodnoty uložené ve stromu m-ary.

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