The original intent had been to have a discussion about deprecating the generalized combinators in Data.List in 7.12 and removing them in 7.14 once we had the ability to deprecate a re-export.

This path gives a 2 year window for the much smaller pool of users who import Data.List qualified and also use List.foldr to drop "List." from their code, and a way to gracefully provide warnings, without immediately breaking the larger pool of users who import Data.List unqualified and just reach for members that aren't in the Prelude and rely on the lack of conflicts today.

I don't see a path that results in monomorphic members of Data.List for those particular combinators that doesn't require a sharp shock in which a bunch of code breaks for a large pool of users without us being able to warn them first.

-Edward

-Edward

On Wed, Feb 4, 2015 at 12:05 PM, Johan Tibell <johan.tibell@gmail.com> wrote:

On Wed, Feb 4, 2015 at 9:01 AM, Edward Kmett <ekmett@gmail.com> wrote:

The current step was to generalize them so that code that imported Data.List so that they don't conflict with the Prelude versions.

The intent was that once we gained the ability to deprecate re-exports that we'd remove them entirely. We now have a patch that enables us to do such things.

It turns out that if you look at hackage, for the most part folks are actually importing Data.List unqualified to bring into scope foldl' or sort. Almost nobody invokes foldr from it.

The "generalization and subsequent re-export deprecation" path breaks less code than the "leaving them monomorphic and breaking everyone who uses Data.List unqualified" path, even if it leads to an intermediate state that is a bit awkward, and doesn't lead easily to a final state where monomorphic versions of those combinators are available.

I didn't quite follow this. Does this mean that the Data.List functions will be generalized for now but eventually monomorphized again?

 

-Edward

On Wed, Feb 4, 2015 at 11:13 AM, Christopher Done <chrisdone@gmail.com> wrote:

> Looking at the generalizations in Data.List I find them pretty odd now when
> I think about it. I'd expect Data.List functions to be monomorphic to
> lists, just like I expect functions in Data.Map to be monomorphic to maps.
> Now there might be generalized versions of these functions in e.g. the
> Prelude, but generalizing Data.List means that I don't even have the
> monomorphic versions available if I want to resolve ambiguity by using
> them*.

Sums up my feelings exactly. Data.Map, Data.List, etc. should be
monomorphic. Adding generalized functions in Data.List is a little
baffling.

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