- Libraries - Haskell.org

RE: Proposal: Make gcd total
by Simon Peyton-Jones 08 Jun '11

08 Jun '11

| > So if someone actually follows through with this as an official | > libraries submission (with a patch, deadline, etc.), the odds seem in | > favor of it. | | I'll try to see it through, although the process seems rather daunting. | It has annoyed me for too long. I think there is general agreement that * The library submission process is too daunting, especially because you have to come up with a complete implementation of a proposal before you even know whether it's going to fly. * The process gets stuck because achieving universal consensus is too difficult * The maintainer "libraries(a)haskell.org" means that no individual feels responsible for making a decision on a proposal. What we need is something to put in its place. Simon and I have been cooking up a proposal. Here it is: http://www.haskell.org/haskellwiki/Library_submissions/NewDraft It is aimed just at libraries whose maintainer is listed as libraries(a)haskell.org. (The thousands of other libraries with named maintainers can obviously do whatever their maintainer wants, although perhaps this new draft may be useful for them too.) It's a draft. What do you think of it? Do you think it would be better than the status quo? Can you suggest any improvements? ALSO: does anyone (or two or three people) want to volunteer to act as maintainer for any of the "Volunteer needed" packages? Johan, I was thinking you might serve for 'containers', perhaps in harness with someone else since it is such a crucial package. Simon

13 24

Re: [Haddock] bug with haddock || hackage || hackage "Ocean" style
by David Waern 06 Jun '11

06 Jun '11

2011/5/27 Drew Day <drewday(a)gatech.edu>: > I stumbled upon this rendering bug on hackage: > > http://hackage.haskell.org/packages/archive/Cabal/1.10.1.0/doc/html/Languag… > > About 3/4ths down the page, there is a floating rendering containing the > text: > > import "network" Network.Socket > Simple investigation of the contents reveals that this comes from: > > -- | [GHC § 7.3.18] Allow imports to be qualified by the package > -- name the module is intended to be imported from, e.g. > -- > -- > import "network" Network.Socket > | PackageImports > > I include a screenshot for completeness. Thanks for the report. Looks like a CSS bug. Mark: do you know what's going wrong here? David

1 0

Lazy functors and friends
by Henning Thielemann 05 Jun '11

05 Jun '11

I have written a Wiki article where I argue, that Functor instances should match their arguments strictly in order to comply with the laws. However for the Traversable class I did not find laws, thus I invented one myself: sequenceA (fmap Identity x) == Identity x What do you think of it? Are there more laws that would be reasonable? http://www.haskell.org/haskellwiki/Lazy_functors

2 1

seq -> force
by Henning Thielemann 05 Jun '11

05 Jun '11

For a datatype like data T a = Cons a I could define 'seq' myself as seq (Cons _) x = x if it would be a type class method. Is there a type class for generating the constructor independently from the input, as in: force ~(Cons x) = Cons x ?

3 2

Re: Proposal: Make gcd total
by Ross Paterson 02 Jun '11

02 Jun '11

On 28 May 2011 11:59, Daniel Fischer wrote: > I would like to propose the elimination of the special error case > > gcd 0 0 = error "Prelude.gcd: gcd 0 0 is undefined" Just deleting that line sounds good. For documentation, I'd suggest: gcd x y is the non-negative factor of both x and y of which every common factor of x and y is also a factor; for example gcd 4 6 = 2, gcd (-4) 6 = 2, gcd (-4) (-6) = 2, gcd 0 4 = 4, gcd 0 0 = 0. (That is, the common divisor that is "greatest" in the divisibility ordering.)

4 3

Re: Libraries Digest, Vol 93, Issue 21
by John Lato 31 May '11

31 May '11

> > > Message: 3 > Date: Sun, 22 May 2011 06:52:49 -0400 > From: "Edward Z. Yang" <ezyang(a)MIT.EDU> > Subject: Re: Proposal: Value strict versions of containers > To: Milan Straka <fox(a)ucw.cz> > Cc: libraries <libraries(a)haskell.org> > Message-ID: <1306061483-sup-1713@ezyang> > Content-Type: text/plain; charset=UTF-8 > > Excerpts from Milan Straka's message of Sun May 22 06:50:07 -0400 2011: > > - the types Data.IntMap.IntMap, Data.IntMap.Lazy.IntMap and > > Data.IntMap.Strict.IntMap should be equal -- so I can use strict > > methods on IntMap someone else created with lazy methods. That is > > simple in absence of type classes. > > Comment: This would mean you would get no static assurances against > mixing up a strict IntMap with a lazy IntMap; for all intents and purposes, > this is equivalent to implementing strict versions of all functions on top > of a lazy data type. > Another consequence to this design is that, should someone want to have > class MapC m key value | m -> key, m -> value where it becomes impossible to directly write > instance MapC (Data.IntMap.Strict.IntMap Int a) Int a where > > instance MapC (Data.IntMap.Lazy.IntMap Int a) Int a where because the two instances are the same. Regardless, +1 for Milan's proposal either with one type or separate types for strict and lazy. John Lato

2 4

parallel package: minor error in the documentation of Control.Parallel.Strategies.parMap
by Tsuyoshi Ito 31 May '11

31 May '11

Hello, I think that the documentation of the parallel package version 3.1.0.1 contains a minor error (I hope that this is the right place to report such an issue). Namely, the documentation of Control.Parallel.Strategies.parMap (see http://hackage.haskell.org/packages/archive/parallel/3.1.0.1/doc/html/Contr…) contains the following remark: > parMap strat f = withStrategy strat . map f but this is incorrect. Being new to Parallel Haskell, I had been confused by this remark, wondering why this means that the elements are evaluated in parallel, until I found out that the actual implementation was: > parMap strat f = (`using` parList strat) . map f or equivalently: parMap strat f = withStrategy (parList strat) . map f Please fix the documentation. Thank you in advance. Best regards, Tsuyoshi Tsuyoshi Ito Institute for Quantum Computing, University of Waterloo http://www.cs.uwaterloo.ca/~tito/

2 1

Re: Proposal: Make gcd total
by Ross Paterson 30 May '11

30 May '11

On 29 May 2011 01:21, wren ng thornton wrote: >On 5/28/11 8:38 AM, Daniel Fischer wrote: >> (By the way, non-negative, like the current positive, is not entirely true, >> for bounded signed integer types [with twos' complement representation], >> gcd minBound minBound = gcd minBound 0 = minBound< 0, >> should that special case be mentioned or should we ignore it like we >> currently do?) > > That's a sticky issue, but one that needs to be documented. Given that > the result is always positive with the exception of gcd 0 0, gcd > minBound minBound, gcd minBound 0, and gcd 0 minBound, I think these > corner cases should be specifically enumerated. There is a difference: gcd 0 0 follows from a general rule, but the minBound ones are the sort of corner wierdness we get for using fixed-size types. (That is, the former should be mentioned as a non-obvious consequence, the latter as an exception/bug.) Incidentally, gcd (minBound::Int) n currently gives negative results for quite a few values of n.

3 2

Proposal: remove datatype contexts from base
by Ross Paterson 29 May '11

29 May '11

The Haskell' committee decided to remove datatype contexts from the language: http://www.haskell.org/pipermail/haskell-prime/2011-January/003335.html (though this doesn't seem to be in the Report yet.) In the base package there are 4 of these: Data/Complex.hs:data (RealFloat a) => Complex a GHC/Arr.lhs:data Ix i => Array i e GHC/Real.lhs:data (Integral a) => Ratio a = !a :% !a deriving (Eq) Control/Arrow.hs:newtype ArrowApply a => ArrowMonad a b = ArrowMonad (a () b) As far as I know, removing them won't break any code that compiles now, so let's do it.

11 10

Clipboard package: Unicode update
by Daniel Díaz Casanueva 26 May '11

26 May '11

Hi all, Clipboard is a package for interacting with the (Windows only, currently) system [1]. Recently, I have received a patch that, to avoid problems with unicode characters, saves the content in the clipboard in Unicode format (instead of normal text). I thought that this is a change in the behaviour of the function (though the interface remains equal), so I'm hesitating if I must add this feature in a new function or to modify the current declaration. I await your opinions. Daniel Díaz, Clipboard maintainer. -- References [1] http://hackage.haskell.org/package/Clipboard

1 0