Should foldl' be added to the post-"Plan FTP" Prelude

David Feuer david.feuer at gmail.com
Mon Mar 2 00:35:47 UTC 2015


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" <ben.franksen at online.de> 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 <kazu at iij.ad.jp> 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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