Re: Proposal: improve the Data.Tree API

I was thinking of: length :: Tree a -> Int length = L.length . flatten But to be honest, I don't have strong feelings about this, I'm willing to drop this particular function (length) from the proposal, if there is no consensus. João 2014-02-24 10:50 GMT+00:00 Ivan Lazar Miljenovic :

On 24 February 2014 21:39, João Cristóvão wrote:

...

Hello,

The Data.Tree API seems rather poor. Some research on hackage shows some additional functions being defined in very unrelated packages:

http://hackage.haskell.org/package/debian-3.81/docs/Debian-Apt-Dependencies....

...

http://hackage.haskell.org/package/hledger-lib-0.22.1/docs/Hledger-Utils.htm...

...

I propose the addition of the following functions, that seem rather

...

forward to me:

-- | get the sub-tree rooted at the first (left-most, depth-first) occurrence -- of the specified node value lookupTree :: Eq a => a -> Tree a -> Maybe (Tree a)

-- | get the sub-tree rooted at the first (left-most, depth-first) value that -- matches the provided condition findTree :: (a -> Bool) -> Tree a -> Maybe (Tree a)

-- | keep only the elements that match the provided condition filter :: (a -> Bool) -> Tree a -> Tree a

The 'Tree' is appended in the name, to distinguish from the Foldable instances, that return the value, and not a sub-tree.

Additionally, the following two functions might also be useful (even if

straigh the

...

implementation is very simple in the second case): -- | get the sub-tree for the specified node value in the first tree in -- forest in which it occurs. lookupTreeInForest :: Eq a => a -> [Tree a] -> Maybe (Tree a)

-- | Length of the tree length :: Tree a -> Int

What is the length of a tree? The number of sub-trees of that particular root node? The overall width of the tree? The number of nodes?

...

There are probably more useful functions to add, so suggestions are welcomed.

Previous discussion: https://github.com/haskell/containers/issues/39#issuecomment-35799628

Discussion period: 2 weeks

Cheers, João

_______________________________________________ Libraries mailing list Libraries@haskell.org http://www.haskell.org/mailman/listinfo/libraries

-- Ivan Lazar Miljenovic Ivan.Miljenovic@gmail.com http://IvanMiljenovic.wordpress.com