2012/1/8 Sergey Mironov
Hi list! Could you please give me a quick example of navigating throw Data.Typeable.Zipper built on top of a Rose Tree? eg. (See ??? in the last line - is my question)
{-#LANGUAGE TemplateHaskell, DeriveDataTypeable, TypeOperators #-}
import Data.Typeable.Zipper
data Tree k a = Tree { _rules :: [(k,Tree k a)] } deriving(Show, Typeable)
$(mkLabelsNoTypes [''Tree])
atree = Tree [(1, Tree []), (2, Tree []), (3, Tree [(11, Tree [])])]
moveToLeftmostChild :: (Typeable k, Typeable a) => Zipper1 (Tree k a) -> Zipper1 (Tree k a) moveToLeftmostChild z = moveTo ??? z
Thanks, Sergey
Heh, look like I've found the solution by myself! Here is the missing part: get_child n t = ((_rules t) !! n) -- fast'n'diry set_child n c t = t{ _rules = (hs ++ (c:ts)) } where (hs,ts) = splitAt n (_rules t) focus_child :: Int -> Tree k a :-> (k, Tree k a) focus_child n = lens (get_child n) (set_child n) moveToLeftmostChild :: (Ord k, Typeable k, Typeable a) => Zipper (Tree k a) (Tree k a) -> Zipper (Tree k a) (k, Tree k a) moveToLeftmostChild z = moveTo (focus_child 0) z Thanks, Sergey