Re: foldable flexible bridges (putting foldable+traversable in prelude) Re: Burning bridges

of course things will break. Things also break in easily fixable ways every major ghc version (and that doesn't stop each new GHC major version from being progressively more awesom). And thats ok. "all of hackage" isnt an informative test. Its ok, we have a type system, we'll know exactly what to change to make it all better again, thats kinda a big upside to having a type system after all. Mostly just adding some ":: [sometypehere]" constraints and then problems solved. thats a wonderfully easy breakage, an eminently patchable one even. There will no doubt be much patching of many actively maintained libs around ghc 7.8's release anyways, so why not amortize that effort to improve prelude while we're at it? Thats a great time to improve things. On Tue, May 21, 2013 at 1:18 AM, Krzysztof Skrzętnicki wrote:

I'm not convinced nothing will break. From my experience if you change anything in such high impact place as Prelude you are unlikely not to break anything. You are making some functions more generic and this can easily create ambiguity.

Just try compiling whole Hackage with modified Prelude and see what the results are.

Best regards, Krzysztof Skrzętnicki

On Tue, May 21, 2013 at 7:06 AM, Carter Schonwald < carter.schonwald@gmail.com> wrote:

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lets see what concerns there are

1) will any code break? Nope! In fact, it's trivial to provide a shim that only exposes the list monomorphic versions.

2) does the change make learning the language more challenging? No. In fact, i've encountered *many* more smart people getting confused as to why the map / fold etc in prelude are all list specific than i've seen people struggle with type classes. The various list specific versions of the foldable codes actually **confuses** smart software folks who are starting to learn haskell for fun.

I can't explain to a smart engineer *any* reason why minimum :: Ordhttp://www.haskell.org/ghc/docs/latest/html/libraries/base/Prelude.html#t:Or... a => [a] -> a exists in prelude. I *can* explain why something like minimum :: ( Foldablehttp://www.haskell.org/ghc/docs/latest/html/libraries/base/Data-Foldable.htm... t, Ordhttp://www.haskell.org/ghc/docs/latest/html/libraries/base/Data-Ord.html#t:O... a) => t a -> a would be useful and deserving of being in the standard prelue.

I've actually had to explain to a smart python engineering friend who's learning haskell this very problem. (that the list only versions are there for no deep reason aside from some pedagogical approach from over a decade ago that is no longer used)

tl;dr no code will break, there will be less inessential nonuniformity that doesn't aid in engineering or learning with haskell, so a win in every direction.

lets make things happen.

-Carter

On Mon, May 20, 2013 at 11:04 PM, wrote:

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Whoa! I don't think that replacing list-monomorphic functions in the prelude with more-general ones is going to cause the community to split down the middle!

Most of the changes we're talking about won't even break any legacy code! Of course, some typeclass-rearranging will break things, but not the prelude replacements that we've been discussing. The biggest impact is that existing teaching texts may have old information about the type signatures of standard functions.

As much as I *love* imagining the Haskell community in a bridge-burning, rival GHC HQ deathmatch (Simon vs. Simon! Edward vs. Edward!), I really think this change won't attract the interest of any tabloids.

That said, I definitely agree that it should take more than a few +1s to move this forward. I'd suggest a relative-consensus on the libraries list, then a "Here's our plan; are we crazy?" email on haskell-cafe.

Tom

El May 20, 2013, a las 6:59 PM, Felipe Almeida Lessa < felipe.lessa@gmail.com> escribió:

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IMHO, the problem is that the community isn't large enough to be able to suffer a split. Case in point: how are we going to have two GHC HQs?

If we're going to burn bridges, perhaps we should follow a Python-3-esque path of releasing a major upgrade together with:

- A refactoring tool to aid with the transition.

- A deadline of, say, 2-3 years during which the latest GHC for current Haskell would receive bugfixes while GHC 8 moves along as usual.

Cheers,

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On 5/19/13 7:25 PM, Anthony Cowley wrote:

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I think this issue may be too big to rely on mailing list +1s. Is

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any precedent for having a web-based poll of some sort? We often get more engagement in debates on IRC and /r/haskell than the mailing list, so let's not let the choice of forum drive the result.

Indeed.

Personally, I'm all for blessing Foldable/Traversable as "built-in" and getting rid of the monomorphic legacy. But then, I'm also all for making Applicative a superclass of Monad, not having all the mtl modules re-export everything from Control.Monad, etc. However, all of these issues have a long history of discord, and that discord cannot be resolved on this list IMO.

I'm generally a staunch advocate of backward compatibility. However,

On Mon, May 20, 2013 at 7:49 PM, wren ng thornton wrote: there these

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issues are ones where we've known the right answer for a long time (unlike refactoring the numeric type class hierarchy), and we've simply been unwilling to burn bridges in order to do the right thing. I love Haskell, and I respect the haskell' committee, but I think it's time to just burn it all down.

Let us not forget the original reasons for many of these warts. Some of them stem from ignorance or oversight (superclasses of Monad); others stem from the desire to help newcomers (monomorphism); and others stem from circularities in the language definition (the existence of the Prelude). As Haskell has developed, we have learned more ---therefore we should not embrace prior ignorance---, our standard idioms have evolved ---therefore clinging to list-monomorphism *causes* confusion rather than alleviating it---, and we've tried to remove much of the circularity involved in desugaring the various built-in notations for lists, arithmetic sequences, do-notation, etc.

With all that has changed in the last 15 years, I think it's high time to fork Haskell, tear off all the bandaids, and begin afresh. This won't solve all the problems, of course. We will still despair of the numeric hierarchy; we will still despair of the partial functions demanded by the Haskell spec; we will still worry about how to resolve things like MPTCs, type families, and all that. But at least we can finally put these particular ghosts to rest. Alas, to fork the language is to split the community. And while I advocate such drastic measures, they are measures which cannot be resolved either on this list or by the (intentionally conservative) haskell' committee.

-- Live well, ~wren

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-- Felipe.

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