[Haskell-beginners] Re: How to delete a range from AVL tree.

[Alexander.Vladislav.Popov]

Excuse me for the repost.
I'm sending it again because I have not find a reply from
beginners-bounces at haskell.org and I want to exclude (possible) problems
related to the mailing list.
I would be very much appritiated for any help or advice.

Alexander.

2010/9/16 Alexander.Vladislav.Popov <alexander.vladislav.popov at gmail.com>

> Hi.
>
> Help me to solve the problem I faced with.
> I'm trying to delete items from the AVL tree 'itree' that are between 0 and
> 2.
> But as you can see the result tree contains value of 1.
>
>
> > import Data.Tree.AVL
> > import Data.COrdering
>
> > mydelete' :: (Ord a) => a -> a -> AVL a -> AVL a
> > mydelete' p1 p2 tree = let res = delete cmp tree in
> >                        case contains res cmp of
> >                          True      -> mydelete' p1 p2 res
> >                          otherwise -> res
> >                        where
> >                          cmp  = between p1 p2
>
> > between a b x = if x < a
> >                 then LT
> >                 else if x > b
> >                      then GT
> >                      else EQ
>
>
> > itree = push ((sndByCC compare) 3) 3 (pair 1 2)
> > idel  = mydelete' 0 2
>
> *Main> idel itree
> P (Z E 1 E) 3 E
> *Main> idel $ idel itree
> P (Z E 1 E) 3 E
> *Main>
>
> Explain me why I got following results and where I made error.
>
> *Main> (mydelete' 0 3) itree
> E
> *Main> (mydelete' 0 2) itree
> P (Z E 1 E) 3 E
> *Main> (mydelete' 1 2) itree
> P (Z E 1 E) 3 E
> *Main> (mydelete' 1 1) itree
> Z (Z E 1 E) 2 (Z E 3 E)
> *Main> (mydelete' 2 1) itree
> Z (Z E 1 E) 2 (Z E 3 E)
> *Main> (mydelete' 0 1) itree
> Z (Z E 1 E) 2 (Z E 3 E)
> *Main> (mydelete' 0 2) itree
> P (Z E 1 E) 3 E
> *Main> (mydelete' (-1) 2) itree
> P (Z E 1 E) 3 E
>
> Alexander
>
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