June 2015 - Libraries

zlib-0.6.1 bug?
by Andreas Abel 17 Jun '15

17 Jun '15

Agda sees some segmentation faults when compiled with zlib-0.6.1.x, but not with zlib-0.5.4.2. https://code.google.com/p/agda/issues/detail?can=2&q=1518 You might want to constrain zlib < 0.6 for now. (I reported the issue to the maintainer a couple of weeks ago, but have not gotten any response yet.) Cheers, Andreas -- Andreas Abel <>< Du bist der geliebte Mensch. Department of Computer Science and Engineering Chalmers and Gothenburg University, Sweden andreas.abel(a)gu.se http://www2.tcs.ifi.lmu.de/~abel/

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Math in Haddock
by Dominic Steinitz 17 Jun '15

17 Jun '15

I thought folks might be interested in a little example of what is now possible in Haddock (assuming my PR is accepted): https://hackage.haskell.org/package/Kalman-0.1.0.1/docs/Kalman.html Anyone wanting to live on the edge can build their own haddock and upload their haddocks manually to hackage: https://github.com/idontgetoutmuch/haddock Dominic Steinitz dominic(a)steinitz.org http://idontgetoutmuch.wordpress.com

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Math in Haddock
by Dominic Steinitz 14 Jun '15

14 Jun '15

I thought folks might be interested in a little example of what is now possible in Haddock (assuming my PR is accepted): https://hackage.haskell.org/package/Kalman-0.1.0.1/docs/Kalman.html <https://hackage.haskell.org/package/Kalman-0.1.0.1/docs/Kalman.html> Anyone wanting to live on the edge can build their own haddock and upload their haddocks manually to hackage: https://github.com/idontgetoutmuch/haddock Dominic Steinitz dominic(a)steinitz.org http://idontgetoutmuch.wordpress.com

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Proposal: Add IsList instance for ZipList
by David Feuer 12 Jun '15

12 Jun '15

foo = getZipList $ [f,g,h] <$> [a,b,c] <*> [d,e,i] looks a lot better than bar = getZipList $ ZipList [f,g,h] <$> ZipList [a,b,c] <*> ZipList [d,e,i]

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Re: MonadFail proposal (MFP): Moving fail out of Monad
by Dan Doel 11 Jun '15

11 Jun '15

This is all well defined in the Haskell 1.4 report. Back then Haskell had "unfailable" patterns for desugaring do notation, because there was no fail (it was introduced in H98). I believe a pattern is classified as unfailable there if it is irrefutable or refutable only by bottom. Which of course is the distinction here, (x,y) is unfailable, but not irrefutable. And of course, it seems that GHC never actually stopped implementing unfailable patterns, even though they were removed from the report (or someone added it back at some point). You just have to know how to observe this fact. -- Dan On Thu, Jun 11, 2015 at 12:11 PM, David Turner < dct25-561bs(a)mythic-beasts.com> wrote: > Quoting the Haskell 2010 Report section 3.17.2: Attempting to match a > pattern can have one of three results: it may fail; it may succeed > ...; or it may diverge. Then in paragraph 5: > > Matching the pattern con pat1 ... patn against a value, where con is a > constructor defined by data, depends on the value: > - If the value is of the form con v1 ... vn, sub-patterns are matched > left-to-right against the components of the data value; if all matches > succeed, the overall match succeeds; the first to fail or diverge > causes the overall match to fail or diverge, respectively. > - If the value is of the form con' v1 ... vm, where con is a different > constructor to con', the match fails. > - If the value is ⊥, the match diverges. > > In particular, matching (_,_) can only succeed or diverge: failure is > not an option! Desugaring 'do' handles match failure with a catch-all > case that calls 'fail' but doesn't handle ⊥. > > > > On 11 June 2015 at 16:28, Wolfgang Jeltsch <g9ks157k(a)acme.softbase.org> > wrote: > > Are you sure that desugaring works this way? If yes, this should be > > considered a bug and be fixed, I would say. It is very illogical. > > > > All the best, > > Wolfgang > > > > Am Donnerstag, den 11.06.2015, 16:23 +0100 schrieb David Turner: > >> AIUI the point about ⊥ and (⊥, ⊥) being different doesn't matter here: > >> a bind for a single-constructor datatype never desugars in a way that > >> uses fail (which isn't to say that it can't be undefined) > >> > >> For instance: > >> > >> runErrorT (do { (_,_) <- return undefined; return () } :: ErrorT String > IO ()) > >> > >> throws an exception, even though the bind is in ErrorT where fail just > >> returns left: > >> > >> runErrorT (do { fail "oops"; return () } :: ErrorT String IO ()) > >> > >> => Left "oops" > >> > >> Hope that helps, and hope I understand correctly! > >> > >> David > >> > >> > >> On 11 June 2015 at 16:08, Wolfgang Jeltsch <g9ks157k(a)acme.softbase.org> > wrote: > >> > Hi David, > >> > > >> > thank you very much for this proposal. I think having fail in Monad is > >> > just plain wrong, and I am therefore very happy to see it being moved > >> > out. > >> > > >> > I have some remarks, though: > >> > > >> >> A class of patterns that are conditionally failable are `newtype`s, > >> >> and single constructor `data` types, which are unfailable by > >> >> themselves, but may fail if matching on their fields is done with > >> >> failable paterns. > >> > > >> > The part about single-constructor data types is not true. A > >> > single-constructor data type has a value ⊥ that is different from > >> > applying the data constructor to ⊥’s. For example, ⊥ and (⊥, ⊥) are > two > >> > different values. Matching ⊥ against the pattern (_, _) fails, > matching > >> > (⊥, ⊥) against (_, _) succeeds. So single-constructor data types are > not > >> > different from all other data types in this respect. The dividing line > >> > really runs between data types and newtypes. So only matches against > >> > patterns C p where C is a newtype constructor and p is unfailable > should > >> > be considered unfailable. > >> > > >> >> - Applicative `do` notation is coming sooner or later, `fail` might > >> >> be useful in this more general scenario. Due to the AMP, it is > >> >> trivial to change the `MonadFail` superclass to `Applicative` > >> >> later. (The name will be a bit misleading, but it's a very small > >> >> price to pay.) > >> > > >> > I think it would be very misleading having a MonadFail class that > might > >> > have instances that are not monads, and that this is a price we should > >> > not pay. So we should not name the class MonadFail. Maybe, Fail would > be > >> > a good name. > >> > > >> >> I think we should keep the `Monad` superclass for three main reasons: > >> >> > >> >> - We don't want to see `(Monad m, MonadFail m) =>` all over the > place. > >> > > >> > But exactly this will happen if we change the superclass of > (Monad)Fail > >> > from Monad to Applicative. So it might be better to impose a more > >> > light-weight constraint in the first place. Functor m might be a good > >> > choice. > >> > > >> > All the best, > >> > Wolfgang > >> > > >> > _______________________________________________ > >> > ghc-devs mailing list > >> > ghc-devs(a)haskell.org > >> > http://mail.haskell.org/cgi-bin/mailman/listinfo/ghc-devs > > > > > > _______________________________________________ > > ghc-devs mailing list > > ghc-devs(a)haskell.org > > http://mail.haskell.org/cgi-bin/mailman/listinfo/ghc-devs > _______________________________________________ > ghc-devs mailing list > ghc-devs(a)haskell.org > http://mail.haskell.org/cgi-bin/mailman/listinfo/ghc-devs >

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Re: MonadFail proposal (MFP): Moving fail out of Monad
by Wolfgang Jeltsch 11 Jun '15

11 Jun '15

Are you sure that desugaring works this way? If yes, this should be considered a bug and be fixed, I would say. It is very illogical. All the best, Wolfgang Am Donnerstag, den 11.06.2015, 16:23 +0100 schrieb David Turner: > AIUI the point about ⊥ and (⊥, ⊥) being different doesn't matter here: > a bind for a single-constructor datatype never desugars in a way that > uses fail (which isn't to say that it can't be undefined) > > For instance: > > runErrorT (do { (_,_) <- return undefined; return () } :: ErrorT String IO ()) > > throws an exception, even though the bind is in ErrorT where fail just > returns left: > > runErrorT (do { fail "oops"; return () } :: ErrorT String IO ()) > > => Left "oops" > > Hope that helps, and hope I understand correctly! > > David > > > On 11 June 2015 at 16:08, Wolfgang Jeltsch <g9ks157k(a)acme.softbase.org> wrote: > > Hi David, > > > > thank you very much for this proposal. I think having fail in Monad is > > just plain wrong, and I am therefore very happy to see it being moved > > out. > > > > I have some remarks, though: > > > >> A class of patterns that are conditionally failable are `newtype`s, > >> and single constructor `data` types, which are unfailable by > >> themselves, but may fail if matching on their fields is done with > >> failable paterns. > > > > The part about single-constructor data types is not true. A > > single-constructor data type has a value ⊥ that is different from > > applying the data constructor to ⊥’s. For example, ⊥ and (⊥, ⊥) are two > > different values. Matching ⊥ against the pattern (_, _) fails, matching > > (⊥, ⊥) against (_, _) succeeds. So single-constructor data types are not > > different from all other data types in this respect. The dividing line > > really runs between data types and newtypes. So only matches against > > patterns C p where C is a newtype constructor and p is unfailable should > > be considered unfailable. > > > >> - Applicative `do` notation is coming sooner or later, `fail` might > >> be useful in this more general scenario. Due to the AMP, it is > >> trivial to change the `MonadFail` superclass to `Applicative` > >> later. (The name will be a bit misleading, but it's a very small > >> price to pay.) > > > > I think it would be very misleading having a MonadFail class that might > > have instances that are not monads, and that this is a price we should > > not pay. So we should not name the class MonadFail. Maybe, Fail would be > > a good name. > > > >> I think we should keep the `Monad` superclass for three main reasons: > >> > >> - We don't want to see `(Monad m, MonadFail m) =>` all over the place. > > > > But exactly this will happen if we change the superclass of (Monad)Fail > > from Monad to Applicative. So it might be better to impose a more > > light-weight constraint in the first place. Functor m might be a good > > choice. > > > > All the best, > > Wolfgang > > > > _______________________________________________ > > ghc-devs mailing list > > ghc-devs(a)haskell.org > > http://mail.haskell.org/cgi-bin/mailman/listinfo/ghc-devs

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Re: Time files... and here's another alpha HP for 7.10
by Mark Lentczner 09 Jun '15

09 Jun '15

When you did the cabal install of haddock, which haddock did you get? Isn't 2.16.0 the latest? And that should be what is in the Platform. I guess I should check that the haddock in GHC is actually 2.16.0!

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deepseq:NFData1 class
by Henning Thielemann 08 Jun '15

08 Jun '15

I have the type data NonEmpty f a = NonEmpty a (f a) and want to declare an NFData instance in Haskell 98. With the existing NFData class this is not possible because it requires a (NFData (f a)) constraint which needs FlexibleContexts. A solution would be an NFData1 class analogously to the classes in transformers:Data.Functor.Classes: class NFData1 f where rnf1 :: NFData a => f a -> () instance NFData1 [] where rnf1 = rnf instance (NFData1 f) => NFData1 (NonEmpty f) where rnf1 (NonEmpty x xs) = rnf (x, rnf1 xs) instance (NFData1 f, NFData a) => NFData (NonEmpty f a) where rnf = rnf1

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ANN: bytestring-lexing 0.5.0
by wren romano 06 Jun '15

06 Jun '15

-------------------------------------------- -- bytestring-lexing 0.5.0 -------------------------------------------- The bytestring-lexing package offers extremely efficient bytestring parsers for some common lexemes: namely integral and fractional numbers. In addition, it provides efficient serializers for (some of) the formats it parses. As of version 0.3.0, bytestring-lexing offers the best-in-show parsers for integral values. (According to the Warp web server's benchmark of parsing the Content-Length field of HTTP headers.) And as of this version (0.5.0) it offers (to my knowledge) the best-in-show parser for fractional/floating numbers. -------------------------------------------- -- Changes since 0.4.3 (2013-03-21) -------------------------------------------- I've completely overhauled the parsers for fractional numbers. The old Data.ByteString.Lex.Double and Data.ByteString.Lex.Lazy.Double modules have been removed, as has their reliance on Alex as a build tool. I know some users were reluctant to use bytestring-lexing because of that dependency, and forked their own version of bytestring-lexing-0.3.0's integral parsers. This is no longer an issue, and those users are requested to switch over to using bytestring-lexing. The old modules are replaced by the new Data.ByteString.Lex.Fractional module. This module provides two variants of the primary parsers. The readDecimal and readExponential functions are very simple and should suffice for most users' needs. The readDecimalLimited and readExponentialLimited are variants which take an argument specifying the desired precision limit (in decimal digits). With care, the limited-precision parsers can perform far more efficiently than the unlimited-precision parsers. Performance aside, they can also be used to intentionally restrict the precision of your program's inputs. -------------------------------------------- -- Benchmarks -------------------------------------------- For the Criterion output of the benchmark discussed below, see <http://community.haskell.org/~wren/bytestring-lexing/bench/html/readExponen…>. The main competitors we compare against are the previous version of bytestring-lexing (which already surpassed text and attoparsec/scientific) and bytestring-read which was the previous best-in-show. The unlimited-precision parsers provide 3.3x to 3.9x speedup over the readDouble function from bytestring-lexing-0.4.3.3, as well as being polymorphic over all Fractional values. For Float/Double: these functions have essentially the same performance as bytestring-read on reasonable inputs (1.07x to 0.89x), but for inputs which have far more precision than Float/Double can handle these functions are much slower than bytestring-read (0.30x 'speedup'). However, for Rational: these functions provide 1.26x to 1.96x speedup compared to bytestring-read. The limited-precision parsers do even better, but require some care to use properly. For types with infinite precision (e.g., Rational) we can pass in an 'infinite' limit by passing the length of the input string plus one. For Rational: doing so provides 1.5x speedup over the unlimited-precision parsers (and 1.9x to 3x speedup over bytestring-read), because we can avoid intermediate renormalizations. Whether other unlimited precision types would see the same benefit remains an open question. For types with inherently limited precision (e.g., Float/Double), we could either pass in an 'infinite' limit or we could pass in the actual inherent limit. For types with inherently limited precision, passing in an 'infinite' limit degrades performance compared to the unlimited-precision parsers (0.51x to 0.8x 'speedup'). Whereas, passing in the actual inherent limit gives 1.3x to 4.5x speedup over the unlimited-precision parsers. They also provide 1.2x to 1.4x speedup over bytestring-read; for a total of 5.1x to 14.4x speedup over bytestring-lexing-0.4.3.3! -------------------------------------------- -- Links -------------------------------------------- Homepage: http://code.haskell.org/~wren/ Hackage: http://hackage.haskell.org/package/bytestring-lexing Darcs: http://community.haskell.org/~wren/bytestring-lexing Haddock (Darcs version): http://community.haskell.org/~wren/bytestring-lexing/dist/doc/html/bytestri… -- Live well, ~wren

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Re: Time files... and here's another alpha HP for 7.10
by Mark Lentczner 02 Jun '15

02 Jun '15

On Tue, Jun 2, 2015 at 4:40 AM, George Colpitts <george.colpitts(a)gmail.com> wrote: > I guess I should file a haddock bug as I got the same error installing > threadscope Does ghc --print-libdir display the correct path? (That is, with the full version number.) - Mark

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