Re: [Haskell-cafe] Weird interaction between literate haskell, ghci and OverloadedStrings
Hi, Am Samstag, den 03.12.2011, 16:18 +1100 schrieb Erik de Castro Lopo: I'm working on a literate haskell document (actually TeX, but the example below is just test) and I'm using ByteStrings in the code. I know I can do: ghci -XOverloadedStrings file.lhs or, after ghci is running I can do: Main :set -XOverloadedStrings but I'd like to embed a directive in the file so that when loaded in GHCi, I will automatically get OverloadedStrings. This is mainly so that it JustWorks(tm) when I pass the file on to someone else. Is there a way to do this? There is a short example file below. I'm using ghc-7.0.4 from Debian testing. it does not seem to be related to literate haskell, if I copy the code from your file into a .hs without the , ghci still does not activate the OverloadedStrings extension when loading the file. I’d consider this a bug until the developers explain why this should or cannot be different, and suggest you file it as such. Greetings, Joachim -- Joachim nomeata Breitner m...@joachim-breitner.de | nome...@debian.org | GPG: 0x4743206C xmpp: nome...@joachim-breitner.de | http://www.joachim-breitner.de/ signature.asc Description: This is a digitally signed message part ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] ANNOUNCE: monad-control-0.3
On Sat, 2011-12-03 at 01:35 +0100, Bas van Dijk wrote: Here are some benchmark results that compare the original monad-peel, the previous monad-control-0.2.0.3 and the new monad-control-0.3: http://basvandijk.github.com/monad-control.html Note that the benchmarks use Bryan O'Sullivan's excellent new criterion-0.6 package. btw, how did you manage to get measurements from 2 different versions of the same library (monad-control 0.3 and 0.2.0.3) into a single report? ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Weird interaction between literate haskell, ghci and OverloadedStrings
Joachim Breitner wrote: it does not seem to be related to literate haskell, if I copy the code from your file into a .hs without the , ghci still does not activate the OverloadedStrings extension when loading the file. I hadn't noticed that. I’d consider this a bug until the developers explain why this should or cannot be different, and suggest you file it as such. I agree. I've lodged a bug report here: http://hackage.haskell.org/trac/ghc/ticket/5673 Erik -- -- Erik de Castro Lopo http://www.mega-nerd.com/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] ANNOUNCE: monad-control-0.3
On 3 December 2011 10:18, Herbert Valerio Riedel h...@gnu.org wrote: btw, how did you manage to get measurements from 2 different versions of the same library (monad-control 0.3 and 0.2.0.3) into a single report? By renaming the old package to monad-control2 and using the PackageImports extension. I do wonder why it's not possible to use two different versions of the same package at the same time. Bas ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] ANNOUNCE: monad-control-0.3
On 3 December 2011 00:45, Bas van Dijk v.dijk@gmail.com wrote: Note that Peter Simons just discovered that these packages don't build with GHC-7.0.4 (https://github.com/basvandijk/monad-control/issues/3). I just committed some fixes which enable them to be build on GHC = 6.12.3. Hopefully I can release these fixes this weekend. I just released the fixes: http://hackage.haskell.org/package/monad-control-0.3.0.1 http://hackage.haskell.org/package/lifted-base-0.1.0.1 Cheers, Bas ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Weird interaction between literate haskell, ghci and OverloadedStrings
On 3 December 2011 11:19, Erik de Castro Lopo mle...@mega-nerd.com wrote:
Joachim Breitner wrote:
it does not seem to be related to literate haskell, if I copy the code
from your file into a .hs without the , ghci still does not activate
the OverloadedStrings extension when loading the file.
I hadn't noticed that.
I’d consider this a bug until the developers explain why this should or
cannot be different, and suggest you file it as such.
I agree. I've lodged a bug report here:
http://hackage.haskell.org/trac/ghc/ticket/5673
I think it's very dangerous if language extensions leak from modules
by default. For example if someone creates a library and needs to use
some unsafe language extensions like:
{-# LANGUAGE UndecidableInstances, OverlappingInstances, IncoherentInstances #-}
module SomeLib where ...
You surely don't want to silently enable these in some unsuspecting client:
module MyFirstHaskellModule where
import SomeLib
...
I can imagine having a pragma for explicitly exporting language extensions:
{-# EXPORT_LANGUAGE OverloadedStrings #-}
Cheers,
Bas
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[Haskell-cafe] ismzero operator possible without equal constraint
Hi list, I am using MonadSplit (from http://www.haskell.org/haskellwiki/New_monads/MonadSplit ) for a project and now I want to make a library out of it. This seems to be straightforward, but I got stuck when I tried to move miszero out of the class: miszero :: m a - Bool It tests if the provided monad instance is empty. My naive attempt was: miszero :: (Eq (m a), MonadPlus m) = m a - Bool miszero = ( == mzero ) This works, but not correctly. It adds an Eq constraint that is unneeded. I would prefer to have something like: miszero :: MonadPlus m = m a - Bool Because I am not comparing the contents of the monad. I don't even touch it. Is this possible to write? with kind regards, Edgar ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] ismzero operator possible without equal constraint
Of course it is not possible! Take a simple composition of reader and Maybe functors for an example: miszero :: (b - Maybe a) - Bool I'm pretty sure (b - Maybe a) for a is a MonadPlus, but you can't implement miszero for it. Arseniy. On 3 December 2011 16:55, edgar klerks edgar.kle...@gmail.com wrote: Hi list, I am using MonadSplit (from http://www.haskell.org/haskellwiki/New_monads/MonadSplit ) for a project and now I want to make a library out of it. This seems to be straightforward, but I got stuck when I tried to move miszero out of the class: miszero :: m a - Bool It tests if the provided monad instance is empty. My naive attempt was: miszero :: (Eq (m a), MonadPlus m) = m a - Bool miszero = ( == mzero ) This works, but not correctly. It adds an Eq constraint that is unneeded. I would prefer to have something like: miszero :: MonadPlus m = m a - Bool Because I am not comparing the contents of the monad. I don't even touch it. Is this possible to write? with kind regards, Edgar ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] ismzero operator possible without equal constraint
Hi Arseniy, Yes, I see it now. :) . I had some feeling there should be some structural equality: Just _ == Just _ = True Nothing == Nothing = True _ == _ = False But this doesn't work for functions. Thanks for your answer! Greets, Edgar On Sat, Dec 3, 2011 at 6:23 PM, Arseniy Alekseyev arseniy.alekse...@gmail.com wrote: Of course it is not possible! Take a simple composition of reader and Maybe functors for an example: miszero :: (b - Maybe a) - Bool I'm pretty sure (b - Maybe a) for a is a MonadPlus, but you can't implement miszero for it. Arseniy. On 3 December 2011 16:55, edgar klerks edgar.kle...@gmail.com wrote: Hi list, I am using MonadSplit (from http://www.haskell.org/haskellwiki/New_monads/MonadSplit ) for a project and now I want to make a library out of it. This seems to be straightforward, but I got stuck when I tried to move miszero out of the class: miszero :: m a - Bool It tests if the provided monad instance is empty. My naive attempt was: miszero :: (Eq (m a), MonadPlus m) = m a - Bool miszero = ( == mzero ) This works, but not correctly. It adds an Eq constraint that is unneeded. I would prefer to have something like: miszero :: MonadPlus m = m a - Bool Because I am not comparing the contents of the monad. I don't even touch it. Is this possible to write? with kind regards, Edgar ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] ANNOUNCE: monad-control-0.3
Bas van Dijk v.dijk@gmail.com wrote: It provides lifted versions of functions from the base library. Currently it exports the following modules: * Control.Exception.Lifted * Control.Concurrent.Lifted * Control.Concurrent.MVar.Lifted * System.Timeout.Lifted These are just modules which people have needed in the past. If you need a lifted version of some function, just ask me to add it or send me a patch. Note that Peter Simons just discovered that these packages don't build with GHC-7.0.4 (https://github.com/basvandijk/monad-control/issues/3). I just committed some fixes which enable them to be build on GHC = 6.12.3. Hopefully I can release these fixes this weekend. Just in time! The forkable-monad library seems to fail with base libraries more recent than mine, and I really need a generalized forkIO. =) Thanks for your great work. Greets, Ertugrul -- nightmare = unsafePerformIO (getWrongWife = sex) http://ertes.de/ signature.asc Description: PGP signature ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] ismzero operator possible without equal constraint
On Sat, Dec 3, 2011 at 10:55 AM, edgar klerks edgar.kle...@gmail.com wrote: Hi list, I am using MonadSplit (from http://www.haskell.org/haskellwiki/New_monads/MonadSplit ) for a project and now I want to make a library out of it. This seems to be straightforward, but I got stuck when I tried to move miszero out of the class: miszero :: m a - Bool It tests if the provided monad instance is empty. My naive attempt was: You can write: miszero :: MonadPlus m = m a - m Bool miszero m = (m return False) | return True but that will invoke any monadic effects as well as determining the nature of the value, which may not be what you want. Antoine miszero :: (Eq (m a), MonadPlus m) = m a - Bool miszero = ( == mzero ) This works, but not correctly. It adds an Eq constraint that is unneeded. I would prefer to have something like: miszero :: MonadPlus m = m a - Bool Because I am not comparing the contents of the monad. I don't even touch it. Is this possible to write? with kind regards, Edgar ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] ismzero operator possible without equal constraint
On Sat, Dec 3, 2011 at 3:55 PM, Antoine Latter aslat...@gmail.com wrote: On Sat, Dec 3, 2011 at 10:55 AM, edgar klerks edgar.kle...@gmail.com wrote: Hi list, I am using MonadSplit (from http://www.haskell.org/haskellwiki/New_monads/MonadSplit ) for a project and now I want to make a library out of it. This seems to be straightforward, but I got stuck when I tried to move miszero out of the class: miszero :: m a - Bool It tests if the provided monad instance is empty. My naive attempt was: You can write: miszero :: MonadPlus m = m a - m Bool miszero m = (m return False) | return True but that will invoke any monadic effects as well as determining the nature of the value, which may not be what you want. It's almost certainly not what you want for the list monad. -- Dave Menendez d...@zednenem.com http://www.eyrie.org/~zednenem/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Anonymous, Unique Types, maybe
(Sorry if this email is rather unclear - I know my desired end result, but neither how to acheive nor explain it well. Here goes.) I'm processing lists, using them sortof as streams. (Whether that's a good idea isn't the issue here - but let me know if it isn't!) Fundamentally, there are two types of operations (at least, that are relevant here) - those that change the length of the list and those that don't. Some operators might take more than one list/stream as an argument, combining them in some way or another. Obviously, if the lists were different lengths, the operator would fail. I don't want that to happen at run time, so I want to check for it statically, presumably via the type system. I could do this manually: type AList = [Event] type BList = [Event] type CList = [Event] myMapish :: AList - AList mySelect :: AList - (Event - Bool) - BList myOtherSelect :: BList - CList but I'd rather not have to manually define a new type for every new list length: myMapish :: List a - List a mySelect :: List a - List ? The '?' would be an anonymous, unique type - unless there's a better way to accomplish this. Hope that was clear, and thanks (as always) for the help (and being awesome). -- Scott Lawrence ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] How to get a file path to the program invoked?
On 12/1/11 11:12 AM, dokondr wrote: Hi, When my program starts it needs to know a complete path to the directory from which it was invoked. In terms of standard shell (sh) I need the Haskell function that will do equivalent to: #!/bin/sh path=$(dirname $0) That's not the path to the directory from which the script is invoked (aka, $PWD or, more accurately, the results of `pwd`). That's the path to the directory containing the script. The current working directory (the dir from which the program is invoked, provided the program haven't moved since invocation) can be gotten by System.Directory.getCurrentDirectory in the directory package. Getting the path to the location of the executable is trickier business. -- Live well, ~wren ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] How to get a file path to the program invoked?
On 12/1/11 2:26 PM, dokondr wrote: How to find this path using GHC libraries? There was a discussion about this recently over on libraries@, IIRC. The short answer is that, at present, there is no function to give you $0. We'd like to add such a function, but it's not been done yet. Part of the problem is that, as Alexey says, the first element of argv is just whatever is passed to exec, which is not guaranteed to be a complete path, a canonical path, or any other specific thing we'd desire. It's not at all straightforward to determine the actual location of the executable, especially not in a platform-independent manner. argv[0] can't be trusted, scanning through $PATH isn't guaranteed to find it (and even if you find something of the right name, it's not guaranteed to be the correct executable), etc etc. -- Live well, ~wren ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] ANNOUNCE: monad-control-0.3
On 12/2/11 7:35 PM, Bas van Dijk wrote: On 3 December 2011 00:45, Bas van Dijkv.dijk@gmail.com wrote: * 60 times faster than the previous release! Here are some benchmark results that compare the original monad-peel, the previous monad-control-0.2.0.3 and the new monad-control-0.3: http://basvandijk.github.com/monad-control.html Note that the benchmarks use Bryan O'Sullivan's excellent new criterion-0.6 package. Those are some beautiful benchmarks. Not only is it much faster, but the distribution is much more peaked, which is always a good thing since it makes the performance more predictable. Kudos. -- Live well, ~wren ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Anonymous, Unique Types, maybe
Umm, an obvious point is that if you really are using lists as streams they should appear infinite to the processing code, so you shouldn't encounter operations that fail due to incompatible lengths. Otherwise I think there might be packages on Hackage for fixed sized lists, its a common example for the power of GADTs, though personally I've found size annotated lists unusable at the point where I need `filter` (which you are calling mySelect?). ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] ANNOUNCE: Haskell Communities and Activities Report (21st ed., November 2011)
On behalf of all the contributors, I am pleased to announce that the Haskell Communities and Activities Report (21st edition, November 2011) is now available in PDF and HTML formats: http://haskell.org/communities/11-2011/report.pdf http://haskell.org/communities/11-2011/html/report.html Many thanks go to all the people that contributed to this report, both directly, by sending in descriptions, and indirectly, by doing all the interesting things that are reported. I hope you will find it as interesting a read as I did. If you have not encountered the Haskell Communities and Activities Reports before, you may like to know that the first of these reports was published in November 2001. Their goal is to improve the communication between the increasingly diverse groups, projects, and individuals working on, with, or inspired by Haskell. The idea behind these reports is simple: Every six months, a call goes out to all of you enjoying Haskell to contribute brief summaries of your own area of work. Many of you respond (eagerly, unprompted, and sometimes in time for the actual deadline to the call. The editor collects all the contributions into a single report and feeds that back to the community. When I try for the next update, six months from now, you might want to report on your own work, project, research area or group as well. So, please put the following into your diaries now: = End of April 2012: target deadline for contributions to the May 2012 edition of the HCA Report = Unfortunately, many Haskellers working on interesting projects are so busy with their work that they seem to have lost the time to follow the Haskell related mailing lists and newsgroups, and have trouble even finding time to report on their work. If you are a member, user or friend of a project so burdened, please find someone willing to make time to report and ask them to register with the editor for a simple e-mail reminder in April (you could point me to them as well, and I can then politely ask if they want to contribute, but it might work better if you do the initial asking). Of course, they will still have to find the ten to fifteen minutes to draw up their report, but maybe we can increase our coverage of all that is going on in the community. Feel free to circulate this announcement further in order to reach people who might otherwise not see it. Enjoy! Janis Voigtlaender hcar at haskell.org ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] ismzero operator possible without equal constraint
No not for lists, but it is not a bad direction. If I modify it a bit, I can get an ifmzero function: ifmzero :: (MonadSplit m) = m a - m b - m b - m b ifmzero p b f = join $ mhead $ (liftM (const f) p) `mplus` (return b) mhead :: (MonadSplit m) = m a - m a mhead = liftM fst . msplit Which I think works for all MonadSplit monads. I have some loose rationing, I can show, but am a bit affraid to share :) I have made a small example with a foldl function. Thanks for your example. Greets, Edgar module Control.Monad.MonadSplit where import Control.Monad import Control.Applicative import qualified Data.Sequence as S import Test.QuickCheck class MonadPlus m = MonadSplit m where msplit :: m a - m (a, m a) instance MonadSplit [] where msplit [] = mzero msplit (x:xs) = return (x,xs) instance MonadSplit Maybe where msplit Nothing = mzero msplit (Just x) = return (x, Nothing) ifmzero p b f = join $ mhead $ (liftM (const f) p) `mplus` (return b) mhead :: (MonadSplit m) = m a - m a mhead = liftM fst . msplit foldMSl :: (MonadSplit m) = (b - a - m b) - b - m a - m b foldMSl m i n = ifmzero n (return i) $ do (x, xs) - msplit n i' - m i x foldMSl m i' xs prop_foldMSl_ref = property $ test_foldMSl_ref where test_foldMSl_ref :: Int - [Int] - Bool test_foldMSl_ref x y = (foldMSl (\x y - return $ x - y) x y) == (return (foldl (\x y - x - y) x y)) On Sat, Dec 3, 2011 at 11:39 PM, David Menendez d...@zednenem.com wrote: On Sat, Dec 3, 2011 at 3:55 PM, Antoine Latter aslat...@gmail.com wrote: On Sat, Dec 3, 2011 at 10:55 AM, edgar klerks edgar.kle...@gmail.com wrote: Hi list, I am using MonadSplit (from http://www.haskell.org/haskellwiki/New_monads/MonadSplit ) for a project and now I want to make a library out of it. This seems to be straightforward, but I got stuck when I tried to move miszero out of the class: miszero :: m a - Bool It tests if the provided monad instance is empty. My naive attempt was: You can write: miszero :: MonadPlus m = m a - m Bool miszero m = (m return False) | return True but that will invoke any monadic effects as well as determining the nature of the value, which may not be what you want. It's almost certainly not what you want for the list monad. -- Dave Menendez d...@zednenem.com http://www.eyrie.org/~zednenem/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
