Proposal: Add a catamorphism on Trees

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David Feuer

17 May 2016 17 May '16

5:03 p.m.

Daniel Wagner would like to add the following straightforward function to Data.Tree. I think this is a grand idea. foldTree :: (a -> [b] -> b) -> Tree a -> b foldTree f = go where go (Node x ts) = f x (map go ts)

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Joachim Breitner

17 May 17 May

5:18 p.m.

Hi, Am Dienstag, den 17.05.2016, 17:03 -0400 schrieb David Feuer:

...

Daniel Wagner would like to add the following straightforward function to Data.Tree. I think this is a grand idea.

foldTree :: (a -> [b] -> b) -> Tree a -> b foldTree f = go where go (Node x ts) = f x (map go ts)

LGTM Joachim -- Joachim “nomeata” Breitner mail@joachim-breitner.de • https://www.joachim-breitner.de/ XMPP: nomeata@joachim-breitner.de • OpenPGP-Key: 0xF0FBF51F Debian Developer: nomeata@debian.org

Michael Walker

5:19 p.m.

On Tue, 17 May 2016 17:03:31 -0400 David Feuer wrote:

...

Daniel Wagner would like to add the following straightforward function to Data.Tree. I think this is a grand idea.

foldTree :: (a -> [b] -> b) -> Tree a -> b foldTree f = go where go (Node x ts) = f x (map go ts)

+1 Nice, simple, and useful. -- Michael Walker (http://www.barrucadu.co.uk)

Edward Kmett

6:35 p.m.

No objection here. +1 On Tue, May 17, 2016 at 5:03 PM, David Feuer wrote:

...

Daniel Wagner would like to add the following straightforward function to Data.Tree. I think this is a grand idea.

foldTree :: (a -> [b] -> b) -> Tree a -> b foldTree f = go where go (Node x ts) = f x (map go ts) _______________________________________________ Libraries mailing list Libraries@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/libraries

Alp Mestanogullari

18 May 18 May

8:52 a.m.

+1, have implemented it in a few occasions already. On Tue, May 17, 2016 at 11:03 PM, David Feuer wrote:

...

Daniel Wagner would like to add the following straightforward function to Data.Tree. I think this is a grand idea.

foldTree :: (a -> [b] -> b) -> Tree a -> b foldTree f = go where go (Node x ts) = f x (map go ts) _______________________________________________ Libraries mailing list Libraries@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/libraries

-- Alp Mestanogullari

Jake McArthur

8:55 a.m.

+1 from me as well. I think I'm unlikely to ever turn down a straightforward catamorphism or anamorphism. On Wed, May 18, 2016, 8:52 AM Alp Mestanogullari wrote:

...

+1, have implemented it in a few occasions already.

On Tue, May 17, 2016 at 11:03 PM, David Feuer wrote:

...
Daniel Wagner would like to add the following straightforward function to Data.Tree. I think this is a grand idea.

foldTree :: (a -> [b] -> b) -> Tree a -> b foldTree f = go where go (Node x ts) = f x (map go ts) _______________________________________________ Libraries mailing list Libraries@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/libraries

-- Alp Mestanogullari _______________________________________________ Libraries mailing list Libraries@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/libraries

amindfv＠gmail.com

11:28 a.m.

+1 Tom

...

El 18 may 2016, a las 08:55, Jake McArthur escribió:

+1 from me as well. I think I'm unlikely to ever turn down a straightforward catamorphism or anamorphism.

...
On Wed, May 18, 2016, 8:52 AM Alp Mestanogullari wrote: +1, have implemented it in a few occasions already.

...
On Tue, May 17, 2016 at 11:03 PM, David Feuer wrote: Daniel Wagner would like to add the following straightforward function to Data.Tree. I think this is a grand idea.

foldTree :: (a -> [b] -> b) -> Tree a -> b foldTree f = go where go (Node x ts) = f x (map go ts) _______________________________________________ Libraries mailing list Libraries@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/libraries

-- Alp Mestanogullari _______________________________________________ Libraries mailing list Libraries@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/libraries

Libraries mailing list Libraries@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/libraries

Tikhon Jelvis

11:32 a.m.

I was just thinking about refactoring some code to a tree fold—I had assumed it was in the library already, and only realized it wasn't when I saw this thread. Definite +1. On May 18, 2016 8:28 AM, wrote:

...

+1

Tom

El 18 may 2016, a las 08:55, Jake McArthur escribió:

+1 from me as well. I think I'm unlikely to ever turn down a straightforward catamorphism or anamorphism.

On Wed, May 18, 2016, 8:52 AM Alp Mestanogullari wrote:

...
+1, have implemented it in a few occasions already.

On Tue, May 17, 2016 at 11:03 PM, David Feuer wrote:

...
Daniel Wagner would like to add the following straightforward function to Data.Tree. I think this is a grand idea.

foldTree :: (a -> [b] -> b) -> Tree a -> b foldTree f = go where go (Node x ts) = f x (map go ts) _______________________________________________ Libraries mailing list Libraries@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/libraries

-- Alp Mestanogullari _______________________________________________ Libraries mailing list Libraries@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/libraries

_______________________________________________ Libraries mailing list Libraries@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/libraries

_______________________________________________ Libraries mailing list Libraries@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/libraries

Edward Kmett

11:44 a.m.

Interestingly, I just noticed I'm missing a similar combinator in `free` for the Cofree comonad. https://github.com/ekmett/free/issues/136 On Wed, May 18, 2016 at 11:32 AM, Tikhon Jelvis wrote:

...

I was just thinking about refactoring some code to a tree fold—I had assumed it was in the library already, and only realized it wasn't when I saw this thread.

Definite +1. On May 18, 2016 8:28 AM, wrote:

...
+1

Tom

El 18 may 2016, a las 08:55, Jake McArthur escribió:

+1 from me as well. I think I'm unlikely to ever turn down a straightforward catamorphism or anamorphism.

On Wed, May 18, 2016, 8:52 AM Alp Mestanogullari wrote:

...
+1, have implemented it in a few occasions already.

On Tue, May 17, 2016 at 11:03 PM, David Feuer wrote:

...
Daniel Wagner would like to add the following straightforward function to Data.Tree. I think this is a grand idea.

foldTree :: (a -> [b] -> b) -> Tree a -> b foldTree f = go where go (Node x ts) = f x (map go ts) _______________________________________________ Libraries mailing list Libraries@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/libraries

-- Alp Mestanogullari _______________________________________________ Libraries mailing list Libraries@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/libraries

_______________________________________________ Libraries mailing list Libraries@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/libraries

_______________________________________________ Libraries mailing list Libraries@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/libraries

_______________________________________________ Libraries mailing list Libraries@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/libraries