- Libraries - Haskell.org

Whither split base?
by Carter Schonwald 22 Nov '18

22 Nov '18

I just remembered that it was one of the ongoing things the CLC was involved with, for a while. Has there been recent action there ?

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Bootstrap cabal-install in sandbox
by Harley Leyton 22 Nov '18

22 Nov '18

Building cabal-install with bootstrap.sh --sandbox seems to run into https://github.com/haskell/cabal/issues/5391. Any workarounds?

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Re: Proposal: Num instance for (a -> b)
by Anthony Clayden 17 Nov '18

17 Nov '18

> relevant reddit comment thread: ... Are you people completely nuts? Haven't you wreaked enough havoc with the Foldable Traversable Piffle? Why ref pointy-headed discussion on reddit when you could also ref far more frequent complaints: https://blog.plover.com/prog/haskell/type-errors.html "I think there must be something really wrong with the language design here. I don't know exactly what it is, but I think someone must have made the wrong tradeoff at some point." https://blog.plover.com/prog/haskell/evaluation-functor-2.html https://blog.plover.com/prog/haskell/evaluation-functor.html (It's by no means only that author complaining; it's just that was easiest to grab.) No, EKmett, including `length` in `Foldable` with a `((,) a)` instance is a lot more serious than "somewhat unfortunate". > At what point is it better to put "weird" stuff into its own libraries (or newtypes) and keep base clean? Always the standard Prelude should be clean of "weird" stuff. So that beginners don't have to go round the houses to exclude the standard and get a sensible Prelude. A beginner has more than enough to cope with without piling the import mechanism on them. Whereas it's no burden on the pointy-heads to import WeirdPrelude. If the CLC process were to do anything useful, I'd expect yous to be organising that. And then I could leave yew lot to turn your Haskell into Perl, where any composition of symbols can acquire some meaning. As it is, the only reason I monitor the Libraries list is to complain about proposals for nuttiness. AntC

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Generalizing some type signatures involving Int
by Vanessa McHale 15 Nov '18

15 Nov '18

Would it be possible to generalize replicate and length to have type signatures replicate :: Integral a => a -> b -> [b] and length :: (Integral a, Foldable t) => t b -> a ? There have been a few instances where such a thing would have been useful to me. Cheers

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Proposal: Num instance for (a -> b)
by Daniel Cartwright 12 Nov '18

12 Nov '18

relevant reddit comment thread: https://www.reddit.com/r/haskell/comments/9vtis5/the_universe_of_discourse_… instance Num b => Num (a -> b) where f + g = \x -> f x + g x f * g = \x -> f x * g x f - g = \x -> f x - g x negate f = \x -> negate (f x) abs f = \x -> abs (f x) signum f = \x -> signum (f x) fromInteger i = \x -> fromInteger (f x)

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Proposal to add mapAccumL function to vector package
by John Ky 08 Nov '18

08 Nov '18

Hello, I'd like to add the mapAccumL function to the vector package. Specifically the Data.Vector.Storable module, but it would also be useful other vector modules. This is my attempt at an implementation: {-# LANGUAGE ScopedTypeVariables #-} mapAccumL :: forall a b c. (Storable b, Storable c) => (a -> b -> (a, c)) -> a -> DVS.Vector b -> (a, DVS.Vector c) mapAccumL f a vb = DVS.createT $ do vc <- DVSM.unsafeNew (DVS.length vb) a' <- go 0 a vc return (a', vc) where go :: Int -> a -> DVS.MVector s c -> ST s a go i a0 vc = if i < DVS.length vb then do let (a1, c1) = f a0 (DVS.unsafeIndex vb i) DVSM.unsafeWrite vc i c1 go (i + 1) a1 vc else return a0 {-# INLINE mapAccumL #-} The implementation should obey the following law: import qualified Data.List as L import qualified Data.Vector.Storable as DVS (DVS.toList <$> DVS.mapAccumL f a (DVS.fromList bs)) === L.mapAccumL f a bs Cheers, -John

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Taking over maintainership of cpphs, HaXml, hscolour, and polyparse
by Peter Simons 05 Nov '18

05 Nov '18

Fellow Haskell Hackers, it appears that Malcolm Wallace has lost interest in maintaining his packages on Hackage. Some of them are rather important dependencies for others, and therefore I'd like to take over maintenance of the following libraries: - cpphs - HaXml - hscolour - polyparse Polyparse, in particular, needs a maintenance update to fix build issues with GHC 8.6.1. The absence of a working release blocks packages like hlint from supporting that compiler [1]. I tried to contact Malcolm on 2018-09-24 via e-mail. Others have also tried to reach him through WhatsApp other channels. Unfortunately, no-one has received a response, which is why we decided to go through with this process. Best regards, Peter [1] https://github.com/haskell-infra/hackage-trustees/issues/186

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Proposal: give Ptr a nominal role
by David Feuer 04 Nov '18

04 Nov '18

Currently, we have data Ptr a = Ptr Addr# type role Ptr phantom This is weird: accidentally coercing a pointer to a different type is very bad. The only reason Ptr has this role is that without it, castPtr and such may not be free or will involve unsafe coercions. Thankfully, we have enough power to fix this now. data Addr = Ptr_ Addr# newtype Ptr a = Ptr_ Addr type role Ptr nominal pattern Ptr :: Addr# -> Ptr a pattern Ptr a# = Ptr_ (Addr a#) castPtr :: Ptr a -> Ptr b castPtr (Ptr a) = Ptr a ptrCoercible :: ((forall a b. Coercible (Ptr a) (Ptr b)) => r) -> r ptrCoercible r = r ptrCoercion :: Coercion (Ptr a) (Ptr b) ptrCoercion = Coercion I propose that we do this.

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Proposal: Add a splitBy / splitOn in Data.List
by Saurabh Nanda 03 Nov '18

03 Nov '18

This has certainly been discussed before. A quick Google search turned up the following past discussions: - https://mail.haskell.org/pipermail/libraries/2006-July/005494.html - https://mail.haskell.org/pipermail/libraries/2012-July/018228.html Is there anything blocking this discussion & implementation? Anything that can be done to unblock it? -- Saurabh.

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Proposal: Move primitive-Data.Primitive.Addr API into base
by Daniel Cartwright 03 Nov '18

03 Nov '18

Motivation: There are a lot of places in base where 'Ptr a' is used in place of 'Addr', because in base there is no 'Addr', only 'Addr#'. The problem lies in the fact that many of these uses of 'Ptr a' are lying; the 'a' value is meaningless. Authors of functions therein have used things like 'Ptr ()', 'Ptr Word8', 'Ptr a', but these types do not mean what they say they mean - they're just Addr. There are probably other motivations for this that I can't think of off the top of my head right now.

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