Определение геометрической фигуры

data Font = Courier | Fixedsys | Lucida deriving (Eq, Show)
 
data Figure = Circle Float Float Float | Rectangle Float Float Float Float | Triangle Float Float Float Float Float Float 
              | TextBox  Float Float Font String deriving (Eq, Show)
 
fromJust :: Maybe a -> a
fromJust (Just a) = a
fromJust Nothing  = error "bad value"
              
getLetterSize :: Font -> Float
getLetterSize Courier  = 8
getLetterSize Fixedsys = 10
getLetterSize Lucida   = 12
 
getArea :: Figure -> Float
getArea (Rectangle x1 y1 x2 y2) = (x2-x1)*(y2-y1)
getArea (Circle _ _ r) = 3.14159536 * r * r
getArea (Triangle x1 y1 x2 y2 x3 y3) = x1*x2-y1*y2
getArea (TextBox _ _ f s) = (fromIntegral (length s)) * (getLetterSize f)
 
getRectangles :: [Figure] -> [Figure]
getRectangles [] = []
getRectangles ((Rectangle x1 y1 x2 y2):fs) = (Rectangle x1 y1 x2 y2) : (getRectangles fs)
getRectangles ((Circle _ _ _):fs)          = (getRectangles fs)
getRectangles ((Triangle _ _ _ _ _ _):fs)  = (getRectangles fs)
getRectangles ((TextBox _ _ _ _):fs)       = (getRectangles fs)
 
move :: Figure -> Float -> Float -> Figure
move (Rectangle x1 y1 x2 y2) dx dy      = (Rectangle (x1+dx) (y1+dy) (x2+dx) (y2+dy))
move (Circle x y r) dx dy               = (Circle (x+dx) (y+dy) r)
move (TextBox x y f s) dx dy            = (TextBox (x+dx) (y+dy) f s)
move (Triangle x1 y1 x2 y2 x3 y3) dx dy = (Triangle (x1+dx) (y1+dy) (x2+dx) (y2+dy) (x3+dx) (y3+dy))
              
getBound :: Figure -> Figure
getBound (Rectangle x1 y1 x2 y2)     = (Rectangle x1 y1 x2 y2)            
getBound (Circle x y r)              = (Rectangle (x-r) (y-r) (x+r) (y+r))
getBound (TextBox x y f s)           = (Rectangle x (y-(getLetterSize f)) (x+(fromIntegral (length s)) * (getLetterSize f)) y)
getBound (Triangle x1 y1 x2 y2 x3 y3)= (Rectangle (min x1 (min x2 x3)) (max y1 (max y2 y3)) (max x1 (max x2 x3)) (min y1 (min y2 y3)))
 
getX1 :: Figure -> Maybe Float
getX1 (Rectangle x1 _ _ _ )  = Just x1
getX1 (Triangle _ _ _ _ _ _) = Nothing
getX1 (Circle  _ _ _)        = Nothing
getX1 (TextBox _ _ _ _)      = Nothing
 
getX2 :: Figure -> Maybe Float
getX2 (Rectangle _ _ x2 _)   = Just x2
getX2 (Triangle _ _ _ _ _ _) = Nothing
getX2 (Circle  _ _ _)        = Nothing
getX2 (TextBox _ _ _ _)      = Nothing
 
getY1 :: Figure -> Maybe Float
getY1 (Rectangle _ y1 _ _ )  = Just y1
getY1 (Triangle _ _ _ _ _ _) = Nothing
getY1 (Circle  _ _ _)        = Nothing
getY1 (TextBox _ _ _ _)      = Nothing
 
getY2 :: Figure -> Maybe Float
getY2 (Rectangle _ _ _ y2)   = Just y2
getY2 (Triangle _ _ _ _ _ _) = Nothing
getY2 (Circle  _ _ _)        = Nothing
getY2 (TextBox _ _ _ _)      = Nothing
 
getFigure :: [Figure] -> (Float,Float) -> Maybe Figure
getFigure [] (_,_) = Nothing
getFigure (fg:fgs) (xx,yy) |  ((xx <= x2) && (xx >= x1) && (yy <= y1) && (yy >= y2)) = Just fg
                           |  otherwise = getFigure fgs (xx,yy)
                              where x1=(fromJust (getX1 (getBound fg)));
                                    x2=(fromJust (getX2 (getBound fg))); 
                                    y1=(fromJust (getY1 (getBound fg)));
                                    y2=(fromJust (getY2 (getBound fg)))

getRectangles [(Circle 1 2 3), (Rectangle 1 2 3 4), (Rectangle 11 22 33 44), (Circle 11 22 33)]

getRectangles :: [Figure] -> [Figure]
getRectangles [] = []
getRectangles ((Rectangle x1 y1 x2 y2):fs) = (Rectangle x1 y1 x2 y2) : (getRectangles fs)
getRectangles (_:fs)          = (getRectangles fs)
 
getX1 :: Figure -> Maybe Float
getX1 (Rectangle x1 _ _ _ ) = Just x1
getX1 _                     = Nothing
 
getX2 :: Figure -> Maybe Float
getX2 (Rectangle _ _ x2 _)  = Just x2
getX2 _                     = Nothing
 
getY1 :: Figure -> Maybe Float
getY1 (Rectangle _ y1 _ _ ) = Just y1
getY1 _                     = Nothing
 
getY2 :: Figure -> Maybe Float
getY2 (Rectangle _ _ _ y2) = Just y2
getY2 _                    = Nothing

isRectangle (Rectangle _ _ _ _) = True
isRectangle _ = False
 
getRectangles = filter isRectangle