Proposal: Add a few extra members to Foldable and Traversable classes

David Feuer david.feuer at
Fri Sep 19 21:17:13 UTC 2014

On Fri, Sep 19, 2014 at 5:05 PM, Henning Thielemann <
lemming at> wrote:

> On Fri, 19 Sep 2014, David Feuer wrote:
>  Joachim, you may be right about sum and product; I really don't know.
>> Henning: this doesn't change the Data.Foldable API at all. Data.Foldable
>> already exports all of these functions, and the class would give each of
>> them a valid default implementation.
> For consumers of the functions it would not change much. However, user
> instances with custom implementations of the new methods cannot be used
> with older Prelude versions anymore.

Don't we normally blame the person who wrote code that was incompatible
with the library version they wanted to support, rather than the new
library for adding something new that they chose to depend on?
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