[clean-list] Understanding Generics

[Alexsandro Soares]

Arjen,

   I'm trying to make a Clean version of the genetic
programming system originally written in Haskell using
PolyP. The online reference is:

http://www.cs.chalmers.se/~patrikj/poly/others/geneticalgorithmsinhaskellwithpolytypicprogramming.ps.gz


There, the author uses a paramorphism to implement the
function "sub" (called "scan", in the original
system), in this way:

------------------------------------------------

--para :: Regular d => (d a -> FunctorOf d a b -> b)
-> d a -> b
para i x = i x (fmap id (para i) (out x)) 

polytypic fchildren :: (f a [b] -> [b]) 
= case f of 
    Const t -> \x -> [] 
    Empty   -> \x -> [] 
    Par     -> \x -> [] 
    Rec     -> \x -> x 
    f * g   -> \(x,y) -> fchildren x ++ fchildren y 
    f + g   -> either fchildren fchildren 

--scan :: d a -> [d a] 
scan = para (\x -> \y -> x : fchildren y) 

----------------------------------------------

  I think the result of sub [[1, 2], [3], [4, 5, 6]]
is
  
   [ [[1, 2], [3], [4, 5, 6]], 
     [[3], [4, 5, 6]], 
     [[4, 5, 6]], 
     [[]] 
   ]
  
  But I'm not sure.

  Regards,
  Alex
  
  
--- Arjen van Weelden <A.vanWeelden at cs.ru.nl>
escreveu:

> Sorry for the reply to self.
> 
> There is another issue with this not so elegant
> solution:
> it give a run-time error on lists of lists, e.g.,
> [[Int]].
> Alex, what do you want in this case?
> What should be the result of sub [[1, 2], [3], [4,
> 5, 6]]?
> 
> regards,
> 	Arjen
> 



		
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