2012/1/8 Sergey Mironov ier...@gmail.com
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
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