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> Now OOP is taken for granted and assumed that all languages should be able to produce objects. Not really. There are OOP languages, there are multi-paradigm

• chowells 12y ago
  What Haskell lacks is hierarchies of subtyping. It certainly can be used for OOP. I've written object-oriented code in Haskell. It's not common, but it's not hard. And on rare occasions it's the best solution to a problem.
  • bunderbunder 12y ago
    What's that old chestnut about design patterns just being workarounds for missing language features? Multi-paradigm languages: I'll admit they're usually woefully lacking in sex appeal. When it comes to getting @$#@% done and moving on with your life, though, they be awesome.
    • dllthomas 12y ago
      There is a difference between "this isn't provided by the language, but I can easily implement it" and "this is impossible (or absurdly messy) in the language, but these work-arounds can make me care less".
  • jarrett 12y ago
    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 thinking of Haskell's typeclasses as an analogue to Java's interfaces. Any other features?
    • 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 ] }
  • dllthomas 12y ago
    Haskell does not have OOP facilities built into the language. But then, Haskell arguably doesn't have sequencing of IO built into the language. Standard libraries get the latter done, in many ways better than it's done in other languages. The former lacks a canonical representation provided by any standard (or nearly standard) library I'm aware of, but it's pretty easy to implement the pieces you need yourself once you're aware of the patterns.