- Libraries - Haskell.org

What replaces prime.haskell.org?
by Gershom B 20 May '20

20 May '20

With prime.haskell.org gone (perhaps permanently?) what becomes of its archives, in particular of libraries committee related material? In particular, I was looking up the three release policy, and the canonical link for it seems to be http://web.archive.org/web/20190422080453/https://prime.haskell.org/wiki/Li… Is this available elsewhere, or will it be migrated elsewhere? Thanks, Gershom

3 2

Potential space leak in transpose
by David Feuer 15 May '20

15 May '20

In Data.List, we define transpose :: [[a]] -> [[a]] transpose [] = [] transpose ([] : xss) = transpose xss transpose ((x : xs) : xss) = (x : [h | (h : _) <- xss]) : transpose (xs : [t | (_ : t) <- xss]) The potential difficulty is that we essentially mapMaybe over the xss list twice in the third case. So we hang on to the heads where we need the tails and the tails where we need the heads. We could fix that with something like this: transpose ((x : xs) : xss) = (x : fronts) : transpose (xs : rears) where (fronts, rears) = unzip [(h,t) | (h : t) <- xss] I don't know how much that'll cost in practice.

5 15

Better API for BaudRate
by Travis Whitaker 14 May '20

14 May '20

Hello fellow Haskellers, In my line of work I have the (mis)fortune of making extensive use of the POSIX TTY API. The System.Posix.Terminal module from the unix package is mostly fine for this, except for handling baud rates. The trouble is that POSIX stipulates the presence of a small set of baud rate options as CPP macros in the range 0 - 38400, but this is far too slow for any modern device. Linux, macOS, and likely other Unixes conditionally define many additional CPP macros for baud rates: Linux's termbits.h goes all the way up to 4000000. So, we know from CPP at compile time which baud rate values should work with the TTY syscalls. Given this, I'd propose a set of definitions for baud rates similar to what Ed Kmett uses in his "gl" package: represent baud rates as their C type, and use CPP to define bidirectional pattern synonyms for the present baud rate constants. This eliminates a key problem with the current API: baud rate code can fail at compile time (BaudRate constructors are conditionally present based on CPP) _or_ runtime (there are CPP-conditional partial functions on BaudRate in the API). With the pattern synonyms approach, all failures due to missing baud rate CPP definitions will occur at compile time, and total functions on baud rate must be defined in terms of a conversion to the underlying numeric type. There is a sketch of this technique here: https://github.com/haskell/unix/pull/145 I'm eager to hear others' thoughts on how the baud rate API might be improved. Travis Whitaker

3 2

Questions regarding Bounded
by Simon Jakobi 09 May '20

09 May '20

Hi! I was surprised not to find any documentation regarding interactions of Ord and Bounded. Are there any instances where minBound <= x == True and maxBound >= x == True don't hold for every x? Possibly relatedly, I was looking for Bounded instances for Maybe and Either. To me the following instances seem sensible: instance Bounded a => Bounded (Maybe a) where minBound = Nothing maxBound = Just maxBound instance (Bounded a, Bounded b) => Bounded (Either a b) where minBound = Left minBound maxBound = Right maxBound Are these instances omitted for a reason? Interestingly, both types do have corresponding Ord instances. Lastly, I noticed that Natural has a lower bound (0) but not an upper one, and therefore cannot have a Bounded instance. Is anyone aware of some prior art regarding a LowerBounded class or similar? Cheers, Simon

6 13

Ord methods are surprisingly strict
by Simon Jakobi 08 May '20

08 May '20

Hi! Generally, when using libraries, I expect functions to be as lazy as possible, unless they are documented to have different strictness properties. My impression was that this rule of thumb is fairly widely accepted. If this is not a good rule to work with, please do correct me! In any case, I noticed that many instances of Ord in base are an exception to that rule: (>=), max, etc. tend to evaluate both arguments, although a result could often be produced based on the value of only one argument. For example (True >= x) could return True without evaluating x, but it doesn't. The most blatant and trivial example would be () where the ordering can be determined without looking at any argument. However: $ ghci GHCi, version 8.10.1: https://www.haskell.org/ghc/ :? for help > () >= undefined *** Exception: Prelude.undefined CallStack (from HasCallStack): error, called at libraries/base/GHC/Err.hs:79:14 in base:GHC.Err undefined, called at <interactive>:13:7 in interactive:Ghci1 > undefined >= () *** Exception: Prelude.undefined CallStack (from HasCallStack): error, called at libraries/base/GHC/Err.hs:79:14 in base:GHC.Err undefined, called at <interactive>:14:1 in interactive:Ghci1 The code where I first noticed the issue looked a bit like this: data Const = Type | Kind | Sort deriving (Eq, Ord, Show) f :: NonEmpty Const -> Const f = maximum Ideally f would stop traversing the list once it encounters the first Sort. Yet it doesn't: > f (Sort :| [undefined]) *** Exception: Prelude.undefined Redefining the Ord instance is trickier than expected too: instance Ord Const where Type <= _ = True Kind <= Kind = True Kind <= Sort = True Sort <= Sort = True _ <= _ = False This is insufficient to fix max, since its default implementation is biased towards the second argument: max x y = if x <= y then y else x > max Sort undefined *** Exception: Prelude.undefined So I customize max: max Type x = x max Kind Sort = Kind max Kind _ = Kind max Sort _ = Sort (f (Sort :| [undefined])) still fails! This turns out be due to NonEmpty's Foldable instance relying on the default definition for maximum: maximum :: forall a . Ord a => t a -> a maximum = fromMaybe (errorWithoutStackTrace "maximum: empty structure") . getMax . foldMap (Max #. (Just :: a -> Maybe a)) The problem here is that Maybe's Semigroup instance is strict in both arguments! So I have to define f = foldr1 max …to finally get > f (Sort :| [undefined]) Sort So my questions are: Why are derived Ord instances and most Ord instances in base so surprisingly strict? How come the entire tooling around Ord seems so biased towards strict Ord implementations? Cheers, Simon

7 15

Give alternate default definition for (<=)
by Dannyu NDos 08 May '20

08 May '20

I have following datatype for representing arbitrary computable numbers: newtype Computable = Inexact (Word -> Integer) "Inexact" encapsulates Cauchy sequences. min and max will halt: instance Ord Computable where min (Inexact f) (Inexact g) = Inexact (\n -> min (f n) (g n)) max (Inexact f) (Inexact g) = Inexact (\n -> max (f n) (g n)) But comparison functions won't halt for same numbers: compare (Inexact f) (Inexact g) = go 0 where go n = compare (f n) (g n) <> go (n+1) So in this case, it would be inappropriate to defaultly define min and max. It would be nice if there was a function for alternately defining comparison functions: defaultLessThan :: Ord a => a -> a -> Bool defaultLessThan x y = x == y || x == min x y Then we can let (<=) = defaultLessThan. Also I have to mention that the "realAbs" function I suggested in January must be the following definition in this regard: realAbs x = max x (negate x)

2 2

No fixity declaration for deepseq
by Christiaan Baaij 13 Apr '20

13 Apr '20

Hello list, Is the following behavior intended? or an oversight? Prelude Control.DeepSeq> tail ((undefined :: ()) `seq` 1 : []) *** Exception: Prelude.undefined CallStack (from HasCallStack): error, called at libraries/base/GHC/Err.hs:80:14 in base:GHC.Err undefined, called at <interactive>:5:8 in interactive:Ghci2 Prelude Control.DeepSeq> tail ((undefined :: ()) `deepseq` 1 : []) [] If you're wondering what's happening, there is a (builtin) fixity declaration for 'seq': infixr `seq` 0 But there isn't one for `deepseq`. So undefined `seq` 1 : [] is parsed as undefined `seq` (1 : []) while undefined `deepseq` 1 : [] is parsed as (undefined `deepseq` 1) : [] In a real-life use-case, changing `seq` to `deepseq` actually resulted in a (very unanticipated) space-leak for me. So again, is the lack of fixity declaration for deepseq intentional? or an accidental omission? Best regards, Christiaan

2 1

On the state of 'tar'
by hasufell 08 Apr '20

08 Apr '20

Friends, 'tar' [0][1] is an excellent native haskell implementation of the tar format. However, there are currently a lot of unattended issues: * unicode filepaths broken due to Char8 use [2] * executable bits handled improperly [3] * no support for long filepath extension [4][5] * doesn't handle hardlinks properly [6] * handles symbolic links too strictly [7] Most of these issues are 2 to 4 years old, some of them have PRs that have never been reviewed. 'tar' fails to unpack our own ghc bindists even [4]. I consider it, in this state, too unreliable for production use. Since it is in the 'haskell' namespace on github and probably the first hit on hackage, this needs to be improved quickly, IMO. Users currently can use tar-bytestring [8] (no windows support) or libarchive [9] (not a native implementation), but 'tar' should ultimately be fixed and maintained properly. -- [0] https://hackage.haskell.org/package/tar [1] https://github.com/haskell/tar [2] https://github.com/haskell/tar/issues/6 [3] https://github.com/haskell/tar/issues/25 [4] https://github.com/haskell/tar/issues/49 [5] https://github.com/haskell/tar/issues/27 [6] https://github.com/haskell/tar/issues/51 [7] https://github.com/haskell/tar/issues/32 [8] https://github.com/hasufell/tar-bytestring [9] https://hackage.haskell.org/package/libarchive -- Cheers, Julian

4 6

[bzlib] [PATCH] Fix build with base >= 4.13
by hasufell 07 Apr '20

07 Apr '20

https://gist.github.com/hasufell/a5f1091646d1b891e6d2a73714dbb50e Last time I pinged duncan he seemed to have forgotten it. If you don't mind sharing maintainership, please do so.

3 4

Re: intent to enable 2fa requirement for github.com/haskell org
by Carter Schonwald 25 Mar '20

25 Mar '20

Yeah, there’s def an incredible diversity of tools that are great in this space. And there’s at this point decent tools for almost every platform constraint imaginable. On Wed, Mar 25, 2020 at 1:30 PM Giorgio Marinelli <giorgio(a)marinel.li> wrote: > I use the following 2fa tools. They offer also import/export > functionalities. > > - andOTP (Android) https://github.com/andOTP/andOTP > - OTPClient (Linux) https://github.com/paolostivanin/OTPClient > > Regards, > > > Giorgio > > On Wed, 25 Mar 2020 at 17:48, Carter Schonwald > <carter.schonwald(a)gmail.com> wrote: > > > > Duncan, David, please figure out 2fa tools that work for you and enable > them, > > > > > > https://github.com/tadfisher/pass-otp > > > > https://github.com/solokeys/solo > > > > https://github.com/herrjemand/awesome-webauthn#hardware-authenticators > > > > https://1password.com/ > > > > https://keepass.info/download.html > > > > > > if you are having trouble figuring out tools you're comfortable using, > please share with us those constraints we can help you! > > > > im here to help (and i'm delaying enabling another day or two to provide > help to some active contributors who are having their own difficulties > setitng up this stuff) > > > > On Wed, Mar 18, 2020 at 6:16 PM Duncan Coutts <duncan(a)dcoutts.me.uk> > wrote: > >> > >> On Wed, 2020-03-18 at 14:46 -0400, Carter Schonwald wrote: > >> > hey everyone, because so much important stuff for the community, it > >> > makes sense to add 2fa required for the org, are there any good > >> > reasons to either wait to do this, or not do it? Feedback welcome! > >> > >> I think I might get cut off. > >> > >> Is it not still the case that github's 2fa needs a program running on a > >> mobile phone, or an SMS-capable mobile phone? Is there any support for > >> normal tools running on a normal Linux machine? > >> > >> (I think last time I tried to use the SMS route, it refused to send SMS > >> messages to my landline, despite the fact that I can receive them) > >> > >> > >> Duncan > >> > > _______________________________________________ > > ghc-devs mailing list > > ghc-devs(a)haskell.org > > http://mail.haskell.org/cgi-bin/mailman/listinfo/ghc-devs >

1 0