Difference between revisions of "FP Laboratory 11"

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         Container - Footer
 
         Container - Footer
 
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<div class="mw-collapsible mw-collapsed" data-collapsetext="Hide solution" data-expandtext="Show solution">
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<syntaxhighlight lang="Haskell">
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instance Show Position where
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    show (Position (Point col row) width height) = "(" ++ show col ++ "," ++ show row ++ ")["++ show width++","++ show height++"]"
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instance Show Component where
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    show :: Component -> String
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    show gui = showIndent "" gui where
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        showIndent ind (TextBox name position text) = ind ++ show position ++ " TextBox[" ++ name ++ "]: " ++ text ++"\n"
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        showIndent ind (Button name position text click) = ind ++ show position ++ " Button[" ++ name ++ "]: " ++ text ++"\n"
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        showIndent ind (Container name children) = let
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            inner = concat[showIndent (ind++"\t") c |c<-children]
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            in ind ++ "Container - " ++ name ++ "\n" ++ inner
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</syntaxhighlight>
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</div>
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<div style="clear:both"></div>
  
 
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Revision as of 12:07, 15 November 2023

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