Re: [Haskell-cafe] Building a tree?

[michael rice]

Example understood. Thanks.

Is there a module for binary trees?

Michael

--- On Wed, 6/10/09, wren ng thornton w...@freegeek.org wrote:

From: wren ng thornton w...@freegeek.org
Subject: Re: [Haskell-cafe] Building a tree?
To: haskell-cafe@haskell.org
Date: Wednesday, June 10, 2009, 8:13 PM

michael rice wrote:
 Here's a function from Data.Tree:
 
 unfoldTree :: (b - (a, [b])) - b - Tree a
 Build a tree from a seed value
 
 Could someone please give me a brief example of usage.

    Data.Tree let t = unfoldTree (\i - (show i, [i`div`2..i-1]))
    Data.Tree putStr . drawTree $ t 8

-- Live well,
~wren
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Re: [Haskell-cafe] Building a tree?

[wren ng thornton]

michael rice wrote:

Example understood. Thanks.

Is there a module for binary trees?


Not that I know of off hand. Trees are one of those data structures with 
so many different variants that people end up rolling their own based on 
whatever they need at the time. Hence Data.Tree, Data.Sequence, 
Data.Set, Data.Map, Data.IntMap, Data.Trie,...


--
Live well,
~wren
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[Haskell-cafe] Building a tree?

[michael rice]

Here's a function from Data.Tree:

unfoldTree :: (b - (a, [b])) - b - Tree a
Build a tree from a seed value

Could someone please give me a brief example of usage.

Michael




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Re: [Haskell-cafe] Building a tree?

[Henning Thielemann]

On Wed, 10 Jun 2009, michael rice wrote:


Here's a function from Data.Tree:

unfoldTree :: (b - (a, [b])) - b - Tree a
Build a tree from a seed value

Could someone please give me a brief example of usage.


unfoldTree (\n - (chr (n + ord 'a'), replicate n (n-1))) 3


Or did you expect a real world example? :-)
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Re: [Haskell-cafe] Building a tree?

[wren ng thornton]

michael rice wrote:

Here's a function from Data.Tree:

unfoldTree :: (b - (a, [b])) - b - Tree a
Build a tree from a seed value

Could someone please give me a brief example of usage.


Data.Tree let t = unfoldTree (\i - (show i, [i`div`2..i-1]))
Data.Tree putStr . drawTree $ t 8

--
Live well,
~wren
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Re: [Haskell-cafe] Building a tree?

[wren ng thornton]

michael rice wrote:

Here's a function from Data.Tree:

unfoldTree :: (b - (a, [b])) - b - Tree a
Build a tree from a seed value

Could someone please give me a brief example of usage.



In as far as understanding it, it may be easier if you look at the 
generalized version of the anamorphism:



newtype Fix f = Fix { unFix :: f (Fix f) }

type Tree a = Fix (Node a)

data Node a b = Node a [b]

instance Functor (Node a) where
fmap f (Node a bs) = Node a (map f bs)



unfoldTree f = Fix . fmap (unfoldTree f) . f


--
Live well,
~wren
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