Same here (+1 foldl', -1 foldr') On 24 February 2015 at 21:44, Chris Allen wrote:

(+1) on foldl', (-1) on foldr' for the reasons outlined in the other mailing list.

On 02/24/2015 02:42 PM, Bob Ippolito wrote:

(Cross-posted from haskell-cafe as suggested by Carter Schonwald)

I would love to have foldl' as part of the Prelude. I use it quite frequently and it seems like a beginner trap to have foldl but not foldl' (which is almost always the better choice). I see that foldMap has been added (in addition to all of Monoid and Traversable), why was foldl' left out?

It might be good measure to add foldr' as well, although I use that much less frequently.

-bob

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-- *Λ\ois* http://twitter.com/aloiscochard http://github.com/aloiscochard

No, that is not a way now that we have FTP. On Wed, Feb 25, 2015 at 7:31 PM, Kazu Yamamoto wrote:

...

I would love to have foldl' as part of the Prelude. I use it quite frequently and it seems like a beginner trap to have foldl but not foldl' (which is almost always the better choice). I see that foldMap has been added (in addition to all of Monoid and Traversable), why was foldl' left out?

That is one way but I think another way is to make foldl strict:

http://www.well-typed.com/blog/90/

I'm tired of explaining the difference of foldl and foldl' to beginners. :-)

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

FTP sets up the expectation that foldl has a specific relationship to foldMap. I suppose you could go against that, and also break any code relying on the current foldl semantics, but I'd personally be very much opposed to that. On Mar 1, 2015 5:13 PM, "Ben Franksen" wrote:

Why not?

David Feuer wrote:

...

No, that is not a way now that we have FTP.

On Wed, Feb 25, 2015 at 7:31 PM, Kazu Yamamoto wrote:

...

...

I would love to have foldl' as part of the Prelude. I use it quite frequently and it seems like a beginner trap to have foldl but not foldl' (which is almost always the better choice). I see that foldMap has been added (in addition to all of Monoid and Traversable), why was foldl' left out?

That is one way but I think another way is to make foldl strict:

http://www.well-typed.com/blog/90/

I'm tired of explaining the difference of foldl and foldl' to beginners. :-)

--Kazu

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On Sat, Mar 7, 2015 at 6:08 PM, Ben Franksen wrote:

David Feuer wrote:

...

FTP sets up the expectation that foldl has a specific relationship to foldMap.

How does foldl have a more specific relationship with foldMap than foldl'? Both are currently methods of class Foldable, BTW.

Yes, and each is expected to have a specific relationship to foldMap. Changing the foldl for lists breaks that. David