November 2010 - Haskell-Cafe

Re: [Haskell-cafe] DPH and GHC 7.0.1
by Andrew Coppin 30 Nov '10

30 Nov '10

On 29/11/2010 01:42 AM, Manuel M T Chakravarty wrote: > Andrew Coppin: >> I was wondering about this myself, actually. I'm especially surprised since I thought the DPH implementation was hard-wired into the compilter itself (in which case, how can you distribute it seperately?) >> >> Then again, I've never yet even tried using DPH. (The wiki page looks very out of date, so I don't know how much to trust its information.) > As David said, we will release the DPH libraries separately, but at the same time as GHC 7.0.2. DPH consists essentially of two components (a) the vectoriser, a program transformer hardwired into GHC and (b) the DPH libraries. At the request of the Haskell Platform people we separated the DPH library packages from the standard GHC distribution and will distribute them via Hackage. > > The wiki page will be updated in time for that release. > > Manuel I would have thought that the two components would be so tightly coupled that this wouldn't work. But then again, you presumably know a lot more about it than I ever will. Anyway, thanks for the clarification.

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System.Console.Haskeline
by michael rice 30 Nov '10

30 Nov '10

How do I load this module? Michael ============= *Main> :m + System.Console.Haskeline <no location info>: Could not find module `System.Console.Haskeline': it is not a module in the current program, or in any known package. *Main>

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Crazy idea, building ghc with cabal?
by Joris Putcuyps 30 Nov '10

30 Nov '10

Hello Could it be done and would it be interesting, building 'ghc' using cabal? * 'lhc' does it * Use 'cabal-rpm' and 'cabal2arch' to create packages for linux distributions * As ordinary user, install specific versions in your home directory. cabal install ghc => $HOME/.cabal/bin/ghc * Get base packages as a dependency. Greetings Joris

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Transparent identity instances
by Jafet 29 Nov '10

29 Nov '10

Hi, Does it make sense to declare a transparent identity instance for Functor, Applicative, Monad, etc? For example, I might want to generalize ($) = (<*>) where > ($) :: (a -> b) -> a -> b > (<*>) :: (Functor f) => f (a -> b) -> f a -> f b The traditional definition makes Identity a newtype: > newtype Identity a = Identity a > instance Applicative Identity where > pure a = Identity a > (Identity f) <*> (Identity a) = Identity (f a) But using this instance becomes unwieldy. If using Identity was transparent, eg. if it was a type synonym > {-# LANGUAGE TypeSynonymInstances #-} > type Identity a = a > instance Applicative Identity where > -- something like > pure a = a > f <*> a = f a But GHC does not accept type synonym instances unless they are fully applied. Is it sound for such an instance to exist? If so, how might it be defined? -- Jafet

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Load testing
by Tony Morris 29 Nov '10

29 Nov '10

Does there exist a package for convenient load-testing against a website? e.g. making lots of HTTP requests against a server, including timing, and collecting the results? -- Tony Morris http://tmorris.net/

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Re: Template Haskell: exchanging information between 'splicers'
by jean-christophe mincke 29 Nov '10

29 Nov '10

Oleg, I am using GHC 6.12.3 Here a reproduction: in the file Template.hs proc () = runIO $ do runQ [|1+1|] proc' () = [|1+1|] In the file Main.hs i1 = $(proc ()) -- fails at compile time with "Segmentation fault/access violation in generated code". Maybe is it the expected behavior, I do not know. i2 = $(proc' ()) -- sucessfull i3 = proc() -- sucessful but proc is executed at "runtime" main = ... Hope it is clear enough otherwise let me know. Regards J-C On Mon, Nov 29, 2010 at 4:45 AM, <oleg(a)okmij.org> wrote: > > Hello! > > > But, please, correct me if I am wrong, in your example, the splicer are > > executed at run time and not at compile time. > > With TH, it becomes a bit difficult to tell what is exactly `compile > time'. One can say however that when the code is ready to be spliced > in at the top level, the IO actions in its splices must have been > completed. > > > I have modified your example to make it run at compile time and I get a > > (compile time) segmentation fault. > > As I mentioned, the code was specifically designed to cause something > like segmentation fault. Sneaking out free variables is definitely the > bad thing. The principle of exchanging data between splices (using > runQ/runIO) is valid and could be used for good things, too. > > I am wondering though what GHC version and command-line parameters are > you using? On my system. with GHC 6.10.3, I tried running the original > and modified code in GHCi and GHC (with and without -O2) and did not > get segmentation fault. Could you provide more details about your > system so to reproduce the segfault? I think Simon Peyton-Jones would > really like to know all that. > > Cheers, > Oleg >

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DPH and GHC 7.0.1
by Gregory Propf 29 Nov '10

29 Nov '10

I was hoping to play around with Data.Parallel.Haskell (dph) but noticed that it seems to have been exiled from ghc 7.0.1 which I just installed. It also doesn't seem to be in cabal. Anybody know how to use dph with 7.0.1 or has it been abandoned or something?

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Re: [Haskell] haskell.org downtime: Tuesday Nov 30th
by Henning Thielemann 28 Nov '10

28 Nov '10

Ian Lynagh schrieb: > We plan to have some haskell.org downtime on Tuesday Nov 30th, while we > migrate to the new server. Is there a simple way for me to get a local copy of the Wiki content? I have contributed to several articles and could rest more easily with a local backup before the server is migrated. :-)

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ANNOUNCE: iteratee-compress 0.1.2
by Maciej Piechotka 28 Nov '10

28 Nov '10

Iteratee-compress provides compressing and decompressing enumerators including flushing. Currently only gzip is provided but at bzip and LZMA are planned. This is bug-fixing release Changes from previous version: - Fix infinite loop/segfault bug - Fix bug in which part of the output was lost - Support for iteratee 0.5 and 0.6 Next goals: - BZip support - LZMA support - Generic interface for flushing To think about: - Should inner iteratee be able to request flushing? Regards

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ANNOUNCE: iteratee-parsec 0.0.6
by Maciej Piechotka 28 Nov '10

28 Nov '10

Iteratee-parsec is a library which allows to have a parsec (3) parser in Iteratee monad. It contains 2 implementations: - John Lato's on public domain. It is based on monoid and design with short parsers in mind. - Mine on MIT. It is based on single-linked mutable list. It seems to be significantly faster for larger parsers - at least in some cases - but it requires a monad with references (such as for example IO or ST). The version 0.0.6 uses reference library. Regards

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