4 ms·

Perhaps we have different definitions of OOP. To me, it's not OOP without subclasses and private mutable state. What does OOP mean to you? I'm guessing you're t

• dllthomas 12y ago
  You can implement private mutable state (and dynamic polymorphism behind an interface) with records of closures. Depending on what you mean by "subclasses" here, they may follow trivially. Haskell typeclasses are a poor match to OOP, as you say.
  • jarrett 12y ago
    > with records of closures. Interesting. Can you point me to an example?
    • Jtsummers 12y ago
      http://c2.com/cgi/wiki?ClosuresAndObjectsAreEquivalent http://c2.com/cgi/wiki?ClosuresAndObjectsAreEquivalent http://okmij.org/ftp/Scheme/oop-in-fp.txt http://okmij.org/ftp/Scheme/oop-in-fp.txt http://stackoverflow.com/questions/2954642/methods-and-properties-in-scheme-is-oop-possible-in-scheme http://stackoverflow.com/questions/2954642/methods-and-prope... http://mitpress.mit.edu/sicp/full-text/book/book-Z-H-20.html http://mitpress.mit.edu/sicp/full-text/book/book-Z-H-20.html Some examples. The first is a discussion on it. The second and third have examples in scheme. I'd type more but I'm on my iPad. If I get time later I'll steal time on someone's computer to type up more.
    • dllthomas 12y ago
      Jtsummers gave some links, but in the interest of having something here: data Surface = Surface -- presumably provided by drawing backend data Shape = Shape { shapeGetCenter :: (Int, Int) , shapeSetCenter :: Int -> Int -> Shape , shapeDraw :: Surface -> IO () , shapeScale :: Double -> Shape , shapeGetAABB :: (Int, Int, Int, Int) , shapeShow :: String } instance Show Shape where show = shapeShow circle r x y = Shape { shapeGetCenter = (x, y) , shapeSetCenter = circle r , shapeDraw = undefined -- draw shape to surface , shapeScale = \ f -> circle (f * r) x y , shapeGetAABB = ( floor $ fromIntegral x - r/2 , floor $ fromIntegral y - r/2 , ceiling $ fromIntegral x + r/2 , ceiling $ fromIntegral y + r/2 ) , shapeShow = unwords [ "circle", show r, show x, show y ] } box w h theta x y = Shape { shapeGetCenter = (x, y) , shapeSetCenter = box w h theta , shapeDraw = undefined -- draw shape to surface , shapeScale = \ f -> box (w * f) (h * f) theta x y , shapeGetAABB = let w' = h * abs (sin theta) + w * abs (cos theta) h' = w * abs (sin theta) + h * abs (cos theta) in ( floor $ fromIntegral x - w'/2 , floor $ fromIntegral y - h'/2 , ceiling $ fromIntegral x + w'/2 , ceiling $ fromIntegral y + h'/2 ) , shapeShow = unwords [ "box", show w, show theta, show x, show y ] }