[clean-list] Understanding Generics

[Alexsandro Soares]

Hi all,

   I'm trying to figure out how to implement a generic
version of the function "sub". This function takes an
element and returns a list of this element and all its
subtrees. Examples:

  sub [1,2,3] = [[1,2,3], [2,3], [3], []] 
  sub (B (L 1) (L 2)) = [(B (L 1) (L 2)), (L 1), (L
2)]

  Reading the Clean manual I couldn't understand how
to use generics for this case. Can anyone help me? 

Cheers,
  Alex
   
P.S.:  The non-generic implemention would be

---- Sub.icl
------------------------------------------
module Sub
import StdGeneric, StdEnv

:: Tree a = L a | B (Tree a) (Tree a)
:: List a = Nil | Cons a (List a)

t1 = B (L 1) (L 2)
l1 = Cons 1 (Cons 2 (Cons 3 Nil))

subTree :: (Tree a) -> [(Tree a)]
subTree (L a) = [L a]
subTree (t=:(B l r)) = [t:subTree l] ++ subTree r

subList :: (List a) -> [(List a)]
subList Nil = [Nil]
subList (l=:(Cons x xs)) = [l : subList xs]

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