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"Safer" implementation of Data.List.NonEmpty (and some other suggestions)
by 박신환 30 Aug '18

30 Aug '18

Those implementations using the nontotal `fromList`seem inefficient and potentially dangerous. To eliminate those, I wrote a modification of the original file, which is enclosed. Some other suggestions: `insertBy` for `NonEmpty`s `NonEmpty [a]` to `[NonEmpty a]` transposition Add fixity for (:|) as `infixl 4 :|`

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Proposal: add two more Applicative and Monad adapters
by David Feuer 11 Aug '18

11 Aug '18

We currently offer liftA, liftM, liftM2, and ap to implement Functor and Applicative methods in terms of Applicative and Monad ones. But there are a couple other functions in that general vein that are missing. I propose that we should add at least replaceA, and perhaps also beforeM. -- (<$) = replaceA -- This may be better than the default if there is -- an optimized definition of *> (which may be -- based on an optimized >>). replaceA :: Applicative f => a -> f x -> f a replaceA a fa = fa *> pure a -- (<*) = beforeM -- This may be better than the default if there is -- an optimized definition of <$, or if <$ is defined as -- replaceA and *> is optimized. beforeM :: Monad f => f a -> f x -> f a beforeM fa fx = fa >>= \a -> a <$ fx Why a <$ fx and not fx >> pure a? Because <$ could be implemented specially, and is unlikely to be implemented by hand using <* if there isn't a custom <*.

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Lost MonadFix instances
by 박신환 09 Aug '18

09 Aug '18

instance MonadFix Down where mfix f = Down (fix (\x -> let Down x' = f x in x' )) instance MonadFix Proxy where mfix _ = Proxy instance MonadFix U1 where mfix _ = U1 instance MonadFix Complex where mfix f = fix (realPart . f) :+ fix (imagPart . f)

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GC’ing committee memberships
by Joachim Breitner 07 Aug '18

07 Aug '18

Dear Core Library Committee, I am about to switch jobs, and that is a good time to review my responsibilities. I noticed that the GHC Steering Committee is sucking in all my committee-work-time and -energy, leaving none for the CLC, where I have not done any work recently. I would therefore like to officially vacate my seat on the CLC. Cheers, and keep up the good work, Joachim -- Joachim Breitner mail(a)joachim-breitner.de http://www.joachim-breitner.de/

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Extensions to the module name system in H2020
by Marco Zocca 31 Jul '18

31 Jul '18

Hi all, I was wondering if there are plans to extend/revisit/tidy up the module name system (https://wiki.haskell.org/Hierarchical_module_names) in view of Haskell 2020. I'm mostly concerned with scientific/numerical applications, where I find the current state of things to be a bit chaotic (see Numeric/Numerical/Optimisation/Optimization etc.). I would be glad to help out, and gather intelligence from the community as well via e.g. a poll. Best, Marco (github.com/ocramz)

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Map-to-integer for ciphers?
by 박신환 29 Jul '18

29 Jul '18

For use of ciphers (SHA-256, RSA-2048, etc.), a type must be able to be injectively mapped to integers. It seems `Enum` is currently the closest thing that does this. But `Enum` is supposed to be for arithmetic sequences, so it seems better to define a new typeclass. (Here named `Cipherable`) There are some types that aren't members of `Enum`. For example, `Maybe`, `[]`, etc. They seem okay to be Cipherable. Hence: {-# LANGUAGE ScopedTypeVariables #-} instance Cipherable a => Cipherable (Maybe a) where toEnum 0 = Nothing toEnum n = Just (toEnum n) fromEnum Nothing = 0 fromEnum (Just x) = 1 + fromEnum x instance forall a. (Cipherable a, Bounded a) => Cipherable [a] where toEnum 0 = [] toEnum n = let (q,r) = (n-1) `quotRem` (1 + fromEnum (maxBound :: a)) in toEnum r : toEnum q fromEnum [] = 0 fromEnum (x:xs) = 1 + fromEnum x + (1 + fromEnum (maxBound :: a)) * fromEnum xs instance Cipherable Void where toEnum = errorWithoutStackTrace "Cipher.Cipherable.Void.toEnum" fromEnum = absurd (Besides, it is possible to re-write that of `[]` without ScopedTypeVariables? I see no way...)

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atomicModifyIORef' strictness
by David Feuer 14 Jul '18

14 Jul '18

In the process of replacing atomicModifyMutVar#, I noticed that atomicModifyIORef' is just a little bit lazy: atomicModifyIORef' ref (\x -> (x + 1, undefined)) will increment the reference and then throw an exception in the calling thread. We could sometimes avoid creating thunks by changing this, so the above would install undefined in the IORef as well. For example, suppose I write atomicModifyIORef' ref (\x -> (3, x + 5)) This will end up producing a thunk for the second component. That could be avoided using something like atomicModifyIORef' ref (\ !x -> (3, x + 5)) but it seems a little surprising to have to do that in a function that focuses on being strict. I don't really care too much one way or the other, but I figured I should point this out and see what you all think.

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Re: Discussion: New atomic IORef functions
by David Feuer 12 Jul '18

12 Jul '18

On Wed, Jul 11, 2018, 11:32 PM winter <drkoster(a)qq.com> wrote: > OK then, here's some subtle things i want to shout out if you're going to > make the change ; ) > > 1. The proposed naming is just not great, how about these: > > atomicExchangeIORef :: IORef a -> (a -> (a, b)) -> IO (a, (a, b)) > atomicExchangeIORef' :: IORef a -> (a -> (a, b)) -> IO (a, (a, b)) > > atomicApplyIORef :: IORef a -> (a -> a) -> IO (a, a) > atomicApplyIORef :: IORef a -> (a -> a) -> IO (a, a) > > It may not that great but it's more informative IMO. > I agree that my names aren't great, but I think yours are worse. > 3. atomicExchangeIORef should not force the tuple, e.g. don't pattern > match on the tuple result, instead let users choose to force or not. (May > worth adding some document, I'd be happy to help) > I generally disagree. Being lazy in the tuple is pretty much an invitation to memory leaks. I think the lazy version should ideally also be available (it's what the new primop will provide, after all), but I don't think it should be the obvious thing for people to reach for. > 4. atomicExchangeIORef' will not only force the tuple, but also force both > `a` and `b` part to match atomicModifyIORef' 's semantics. > I don't see the need for this. Users can easily force exactly what they want using atomicModifyIORef2 (or if they really want, atomicModifyIORef2Lazy). > 5. atomicApplyIORef(and atomicApplyIORef') deserve its own primop, since > we can skip building selector thunks all together. > Yes, I've implemented that primop already, and it will be added. I'm still looking for an expert to help implement the simplest of the lot, atomicSwapMutVar#, as efficiently as possible.

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Re: Discussion: New atomic IORef functions
by Dr.Koster 12 Jul '18

12 Jul '18

But if you force the pair result, you have to evaluate modifying function isn't it? That's sometime unwanted when you have an very expensive f here, let's say a deep binary search which might not depend previous result. I think that is also why current atomicModifyIORef is designed this way, so I'd rather keep it the old way. 发自我的iPhone ------------------ Original ------------------ From: David Feuer <david.feuer(a)gmail.com> Date: Thu,Jul 12,2018 0:51 AM To: winter <drkoster(a)qq.com> Cc: Haskell Libraries <libraries(a)haskell.org> Subject: Re: Discussion: New atomic IORef functions All the fundamental functions I've defined can be usefully used in the base library. I think that's one good reason to put them there. Another is that while the basic array operations have traditionally been exposed through array, vector, and primitive, and the basic TVar operations have been exposed through stm, the basic IORef and MVar operations have been exposed through base (except, for some reason, casMutVar#). I see no reason to change that. I never proposed a function that forces the previous value unnecessarily, so I don't know why you're complaining about that. The extra laziness I don't like is in the pair result; none of the uses I've seen thus can far make intentional use of that. That's why I tend to think atomicModifyIORef (as it exists today) is almost never what people actually want. Squeezing into a second component leads to extra allocation in what may be a performance-critical function; that said, I'm willing to hold off on higher tuples for now. On Sun, Jul 8, 2018, 3:36 AM winter <drkoster(a)qq.com> wrote: I believe new variations should always be motivated by use-case if there're too many choices, the lazy behavior of old `atomicModifyIORef` is justified by some cases the modifying functions are lazy in its argument, thus a lazy version could win by not forcing previous thunks, we'd want to keep its behavior as how it's documented. As for tuples more than pairs, they're not really needed, user can always squeeze their product into `b` component. IMHO only the addition of `atomicModifyIORef_` is sensible in the context of base, other APIs may go to package like primitives. But if you have a motivated use case with `atomicModifyIORef2`, etc. Please tell me. On 2018年07月08日 03:09, David Feuer wrote: Whoops! I left out the proposal link: https://github.com/ghc-proposals/ghc-proposals/pull/149 Also, what I called atomicModifyIORef_ below should really be called something like atomicModifyIORef'_, since it forces a polymorphic value. Another thing to note: the underlying atomicModifyMutVar2# primop actually supports more than just pairs. It can handle triples, solos, and any other record types whose first components are lifted: atomicModifyIORefSoloLazy :: IORef a -> (a -> Solo a) -> IO (Solo a) atomicModifyIORefSolo :: IORef a -> (a -> Solo a) -> IO a atomicModifyIORef3, atomicModifyIORef3Lazy :: IORef a -> (a -> (a, b, c)) -> IO (a, b, c) etc. Should we add any such? On Sat, Jul 7, 2018, 2:35 PM David Feuer <david.feuer(a)gmail.com> wrote: I have proposed[1] the replacement of the atomicModifyMutVar# primop, and the addition of two cheaper but less capable ones. It seems likely that the proposal will succeed, but that the GHC steering committee will leave the question of user interface changes to the libraries list. I would like to open the discussion here. The new primops lead naturally to several thin wrappers: -- Atomically replace the IORef contents -- with the first component of the result of -- applying the function to the old contents. -- Return the old value and the result of -- applying the function, without forcing the latter. -- -- atomicModifyIORef ref f = do -- (_old, ~(_new, res)) <- atomicModifyIORef2Lazy ref f -- return res atomicModifyIORef2Lazy :: IORef a -> (a -> (a, b)) -> IO (a, (a, b)) -- Atomically replace the IORef contents -- with the result of applying the function -- to the old contents. Return the old and -- new contents without forcing the latter. atomicModifyIORefLazy_ :: IORef a -> (a -> a) -> IO (a, a) -- Atomically replace the IORef contents -- with the given value and return the old -- contents. -- -- atomicWriteIORef ref x = void (atomicSwapIORef ref x) atomicSwapIORef :: IORef a -> a -> IO a Based on the code I've read that uses atomicModifyIORef, I believe that the complete laziness of atomicModifyIORef2Lazy and atomicModifyIORefLazy_ is very rarely desirable. I therefore believe we should also (or perhaps instead?) offer stricter versions: atomicModifyIORef2 :: IORef a -> (a -> (a, b)) -> IO (a, (a, b)) atomicModifyIORef2 ref f = do r@(_old, (_new, _res)) <- atomicModifyIORef2Lazy ref f return r atomicModifyIORef_ :: IORef a -> (a -> a) -> IO (a, a) atomicModifyIORef_ ref f = do r@(_old, !_new) <- atomicModifyIORefLazy_ ref f return r The classic atomicModifyIORef also admits a less gratuitously lazy version: atomicModifyIORefNGL :: IORef a -> (a -> (a,b)) -> IO b atomicModifyIORefNGL ref f = do (_old, (_new, res)) <- atomicModifyIORef2 ref f return res Should we add that as well (with a better name)? Should we even consider *replacing* the current atomicModifyIORef with that version? That could theoretically break existing code, but I suspect it would do so very rarely. If we don't change the existing atomicModifyIORef now, I think we should consider deprecating it: it's very easy to accidentally use it too lazily. _______________________________________________ Libraries mailing list Libraries(a)haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/libraries _______________________________________________ Libraries mailing list Libraries(a)haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/libraries

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Re: Discussion: New atomic IORef functions
by David Feuer 11 Jul '18

11 Jul '18

All the fundamental functions I've defined can be usefully used in the base library. I think that's one good reason to put them there. Another is that while the basic array operations have traditionally been exposed through array, vector, and primitive, and the basic TVar operations have been exposed through stm, the basic IORef and MVar operations have been exposed through base (except, for some reason, casMutVar#). I see no reason to change that. I never proposed a function that forces the previous value unnecessarily, so I don't know why you're complaining about that. The extra laziness I don't like is in the pair result; none of the uses I've seen thus can far make intentional use of that. That's why I tend to think atomicModifyIORef (as it exists today) is almost never what people actually want. Squeezing into a second component leads to extra allocation in what may be a performance-critical function; that said, I'm willing to hold off on higher tuples for now. On Sun, Jul 8, 2018, 3:36 AM winter <drkoster(a)qq.com> wrote: > I believe new variations should always be motivated by use-case if > there're too many choices, the lazy behavior of old `atomicModifyIORef` is > justified by some cases the modifying functions are lazy in its argument, > thus a lazy version could win by not forcing previous thunks, we'd want to > keep its behavior as how it's documented. > > As for tuples more than pairs, they're not really needed, user can always > squeeze their product into `b` component. > > IMHO only the addition of `atomicModifyIORef_` is sensible in the context > of base, other APIs may go to package like primitives. But if you have a > motivated use case with `atomicModifyIORef2`, etc. Please tell me. > > On 2018年07月08日 03:09, David Feuer wrote: > > Whoops! I left out the proposal link: > > https://github.com/ghc-proposals/ghc-proposals/pull/149 > > Also, what I called atomicModifyIORef_ below should really be called > something like atomicModifyIORef'_, since it forces a polymorphic value. > > Another thing to note: the underlying atomicModifyMutVar2# primop actually > supports more than just pairs. It can handle triples, solos, and any other > record types whose first components are lifted: > > atomicModifyIORefSoloLazy > :: IORef a -> (a -> Solo a) -> IO (Solo a) > > atomicModifyIORefSolo > :: IORef a -> (a -> Solo a) -> IO a > > atomicModifyIORef3, atomicModifyIORef3Lazy > :: IORef a -> (a -> (a, b, c)) -> IO (a, b, c) > > etc. > > Should we add any such? > > On Sat, Jul 7, 2018, 2:35 PM David Feuer <david.feuer(a)gmail.com> wrote: > >> I have proposed[1] the replacement of the atomicModifyMutVar# primop, and >> the addition of two cheaper but less capable ones. It seems likely that the >> proposal will succeed, but that the GHC steering committee will leave the >> question of user interface changes to the libraries list. I would like to >> open the discussion here. >> >> The new primops lead naturally to several thin wrappers: >> >> -- Atomically replace the IORef contents >> -- with the first component of the result of >> -- applying the function to the old contents. >> -- Return the old value and the result of >> -- applying the function, without forcing the latter. >> -- >> -- atomicModifyIORef ref f = do >> -- (_old, ~(_new, res)) <- atomicModifyIORef2Lazy ref f >> -- return res >> atomicModifyIORef2Lazy >> :: IORef a -> (a -> (a, b)) -> IO (a, (a, b)) >> >> -- Atomically replace the IORef contents >> -- with the result of applying the function >> -- to the old contents. Return the old and >> -- new contents without forcing the latter. >> atomicModifyIORefLazy_ >> :: IORef a -> (a -> a) -> IO (a, a) >> >> -- Atomically replace the IORef contents >> -- with the given value and return the old >> -- contents. >> -- >> -- atomicWriteIORef ref x = void (atomicSwapIORef ref x) >> atomicSwapIORef >> :: IORef a -> a -> IO a >> >> Based on the code I've read that uses atomicModifyIORef, I believe that >> the complete laziness of atomicModifyIORef2Lazy and >> atomicModifyIORefLazy_ is very rarely desirable. I therefore believe we >> should also (or perhaps instead?) offer stricter versions: >> >> atomicModifyIORef2 >> :: IORef a -> (a -> (a, b)) -> IO (a, (a, b)) >> atomicModifyIORef2 ref f = do >> r@(_old, (_new, _res)) <- atomicModifyIORef2Lazy ref f >> return r >> >> atomicModifyIORef_ >> :: IORef a -> (a -> a) -> IO (a, a) >> atomicModifyIORef_ ref f = do >> r@(_old, !_new) <- atomicModifyIORefLazy_ ref f >> return r >> >> The classic atomicModifyIORef also admits a less gratuitously lazy >> version: >> >> atomicModifyIORefNGL >> :: IORef a -> (a -> (a,b)) -> IO b >> atomicModifyIORefNGL ref f = do >> (_old, (_new, res)) <- atomicModifyIORef2 ref f >> return res >> >> Should we add that as well (with a better name)? Should we even consider >> *replacing* the current atomicModifyIORef with that version? That could >> theoretically break existing code, but I suspect it would do so very >> rarely. If we don't change the existing atomicModifyIORef now, I think we >> should consider deprecating it: it's very easy to accidentally use it too >> lazily. >> > > > _______________________________________________ > Libraries mailing listLibraries@haskell.orghttp://mail.haskell.org/cgi-bin/mailman/listinfo/libraries > > > _______________________________________________ > Libraries mailing list > Libraries(a)haskell.org > http://mail.haskell.org/cgi-bin/mailman/listinfo/libraries >

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