On 26 August 2010 11:51, Ozgur Akgun
But that's because you use Show while defining the Obj data type. You can implement other functionalities, by introducing a custom type class, and implementing functionalities in instance declarations.
Hi Ozgur This is well known, of course, Ralf Lammel (umlauts on the a in Lammel) and Klaus Ostermann have a catalogue of "shoehorns" to fit OO design into Haskell: http://homepages.cwi.nl/~ralf/gpce06/paper.pdf However these styles aren't exemplary [*] - little Haskell code that I've seen in the wild makes use of them. For instance, having a type class for each operation as per CustomTC seems exorbitant, likewise adding type class contexts to datatype definitions quickly becomes unwieldy: data Obj = forall a. (Show a, AquaticLifeform a, ...) => Obj a Best wishes Stephen [*] Caveat - Figure 16 is quite reminiscent of the "finally tagless" style which is now widely used.