Re: [Haskell-cafe] Handling absent maintainers
I patch broken packages in my local repository. I increment a version so the local repository get a precedence over the Hackage. On 16.07.10 03:54, Mark Wotton wrote: 2. run my own hackage server and tell my users to use that instead. -- Best regards, Roman Beslik. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] a patch for base.Foreign.C.String, the current locale
Hi. I have composed a patch that implements Foreign.C.String according to Foreign Function Interface Addendum, i.e. C strings are treated as they are encoded with the current locale. Search Locale.hs in the patch for further directions. Ask if you do not know how to build a patched version of the base library. http://www.beroal.in.ua/prg/haskell/locale.patch -- Best regards, Roman Beslik. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Handling absent maintainers
That works fine for my own stuff, but I'd like it to work for people using my software that relies on those packages. mark On Sat, Jul 24, 2010 at 4:10 PM, Roman Beslik ber...@ukr.net wrote: I patch broken packages in my local repository. I increment a version so the local repository get a precedence over the Hackage. On 16.07.10 03:54, Mark Wotton wrote: 2. run my own hackage server and tell my users to use that instead. -- Best regards, Roman Beslik. -- A UNIX signature isn't a return address, it's the ASCII equivalent of a black velvet clown painting. It's a rectangle of carets surrounding a quote from a literary giant of weeniedom like Heinlein or Dr. Who. -- Chris Maeda ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Handling absent maintainers
One issue that comes up is that when you fork a package, data can no longer be freely exchanged between libraries using the original package's datatypes and libraries using the forked package's datatypes. Something that might help here is the concept of extension or friend packages or modules: packages or modules that could break through to access concrete representations of abstract datatypes or classes. The advantage would be that in many cases, instead of forking a package, you could make the necessary changes through a tightly-coupled but separately-maintained friend package while still maintaining compatibility with the original package. This wouldn't help for the problem of maintaining a package that wouldn't compile. That might be helped by something like a provides or equivalent field, where Cabal could be informed that a new package should be treated as satisfying a dependency on a different package. Alex On Fri, Jul 23, 2010 at 11:36 PM, Mark Wotton mwot...@gmail.com wrote: That works fine for my own stuff, but I'd like it to work for people using my software that relies on those packages. mark On Sat, Jul 24, 2010 at 4:10 PM, Roman Beslik ber...@ukr.net wrote: I patch broken packages in my local repository. I increment a version so the local repository get a precedence over the Hackage. On 16.07.10 03:54, Mark Wotton wrote: 2. run my own hackage server and tell my users to use that instead. -- Best regards, Roman Beslik. -- A UNIX signature isn't a return address, it's the ASCII equivalent of a black velvet clown painting. It's a rectangle of carets surrounding a quote from a literary giant of weeniedom like Heinlein or Dr. Who. -- Chris Maeda ___ 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] Anyone here from New Zealand?
On 24 Jul 2010, at 02:15, Tim Matthews wrote: Any of the haskellers here from NZ? I am in Wellington, Stephen is near Palmerston North. There are a few others elsewhere I think. Are you using haskell in production, internally within your company or just outside of work in your own time? I work on Leksah in my spare time. In Aus they've got hackathons and user groups. Anything even remotely similar here in New Zealand? The last couple of times I have visited my parents in (who live in Palmerston North), Stephen and I have got together for what we jokingly refer to as NZHac or the NZHUG. Our next trip to Palmy will be late August I think. There is an Erlang users group here in Wellington (organised by Lenz) and I attend when I can, there has not been a meeting in some time. It's really more of a FP group in a way as others that attending are not all Erlang users (but most use or would like to use a functional language of some sort). I think if we changed the name to the Wellington FP Users Group or something we might get more interest (especially if we catered to people interested in learning Scala and F#). Hamish ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: ANNOUNCE: Haskell Platform 2010.2.0.0
Don Stewart d...@galois.com writes: We're pleased to announce the fifth release of the Haskell Platform: a single, standard Haskell distribution for everyone. Download the Haskell Platform 2010.2.0.0: http://hackage.haskell.org.nyud.net/platform/ (Caching server). The specification, along with installers (including Windows, Apple and Unix installers for a full Haskell environment) are available. [snip] Just out of curiosity, is the MacPorts version of the Haskell Platform compatible with Mac OS X 10.5.8 Leopard on the PowerPC architecture (as opposed to the Intel one)? -- Benjamin L. Russell -- Benjamin L. Russell / DekuDekuplex at Yahoo dot com http://dekudekuplex.wordpress.com/ Translator/Interpreter / Mobile: +011 81 80-3603-6725 Furuike ya, kawazu tobikomu mizu no oto. -- Matsuo Basho^ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] build and use ghc's rts without a full unregistered ghc port?
Hi, I was just wondering if this is possible, I would like to use a gcc port which cross compiles to the PPC architecture (Wii DevkitPPC to be specifically: http://wiibrew.org/wiki/DevkitPPC) for a platform that is not POSIX compatible I believe (at least not fully or maybe I'm wrong entirely). Ideally I would make an unregistered port of GHC but the problem is because GHC doesn't support true cross compiling yet I need to bootstrap on to the target machine, which isn't running a POSIX environment. Still I did try to attempt to build with both the host and target set to 'powerpc-unknown-linux' and build it with devkitPPC, I did use a custom build.mk which should pull in all the required dependencies, defines, etc for devkitPPC. In the end I didn't get very far with it, it looked like missing posix functions. I didn't want to spend to much time trying to make it work this way (maybe i'm doing it wrong completely). It's quite possible that I could make this work more easily if I used a linux port for the wii but I would like to avoid the need of using linux on the wii because I guess most home-brew users don't have such a setup. So I thought maybe it's possible with less effort to build GHC's RTS and then compile Haskell in C with the RTS as a library dependency. Is this possible? maybe I'm missing something or doing something stupid? Thanks in advance. _ http://clk.atdmt.com/UKM/go/19780/direct/01/ We want to hear all your funny, exciting and crazy Hotmail stories. Tell us now___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] build and use ghc's rts without a full unregistered ghc port?
can't speak as to how difficult it is to get GHC built unregisterised, but you might want to consider JHC if you don't need to use a lot of Hackage. It compiles to C without a special RTS needed, which might make it a lot easier. mark On Sat, Jul 24, 2010 at 8:45 PM, Korcan Hussein korca...@hotmail.com wrote: Hi, I was just wondering if this is possible, I would like to use a gcc port which cross compiles to the PPC architecture (Wii DevkitPPC to be specifically: http://wiibrew.org/wiki/DevkitPPC) for a platform that is not POSIX compatible I believe (at least not fully or maybe I'm wrong entirely). Ideally I would make an unregistered port of GHC but the problem is because GHC doesn't support true cross compiling yet I need to bootstrap on to the target machine, which isn't running a POSIX environment. Still I did try to attempt to build with both the host and target set to 'powerpc-unknown-linux' and build it with devkitPPC, I did use a custom build.mk which should pull in all the required dependencies, defines, etc for devkitPPC. In the end I didn't get very far with it, it looked like missing posix functions. I didn't want to spend to much time trying to make it work this way (maybe i'm doing it wrong completely). It's quite possible that I could make this work more easily if I used a linux port for the wii but I would like to avoid the need of using linux on the wii because I guess most home-brew users don't have such a setup. So I thought maybe it's possible with less effort to build GHC's RTS and then compile Haskell in C with the RTS as a library dependency. Is this possible? maybe I'm missing something or doing something stupid? Thanks in advance. _ http://clk.atdmt.com/UKM/go/19780/direct/01/ We want to hear all your funny, exciting and crazy Hotmail stories. Tell us now___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe -- A UNIX signature isn't a return address, it's the ASCII equivalent of a black velvet clown painting. It's a rectangle of carets surrounding a quote from a literary giant of weeniedom like Heinlein or Dr. Who. -- Chris Maeda ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Weird behavior with arrow commands
El vie, 23-07-2010 a las 23:27 -0400, Ronald Guida escribió:
I am trying to figure out how to use GHC's arrow commands, and I found
some extremely weird behavior.
CC'ed to ghc-users, because this may be a ghc bug.
In GHC's manual, there is a description of arrow commands, which I
don't really understand.
http://www.haskell.org/ghc/docs/latest/html/users_guide/arrow-notation.html#id667303
(Primitive Constructs)
I have two questions:
1. What are arrow commands supposed to do?
2. What is this code supposed to do?
-- start of code --
{-# LANGUAGE Arrows #-}
module Main where
import Control.Arrow
foo :: (b - String) - b, Int), Float), Double) - String) - (b -
String)
foo f g b = f b ++ ++ g (((b, 8), 1.0), 6.0)
bar :: (t - String) - ((Double, Int) - String) - t - String
bar f g = proc x - do
(f - x) `foo` \n m - g - (n)
main = do
putStrLn $ foo show show 17
putStrLn $ bar show show 17
putStrLn $ foo show show 42
putStrLn $ bar show show 42
-- end of code --
Output from GHCi:
17 (((17,8),1.0),6.0)
17 (6.730326920298707e-306,0)
42 (((42,8),1.0),6.0)
42 (6.730326920298707e-306,0)
Output after compiling with GHC:
17 (((17,8),1.0),6.0)
17 (5.858736684536801e-270,0)
42 (((42,8),1.0),6.0)
42 (5.858736684536801e-270,0)
GHC Version:
The Glorious Glasgow Haskell Compilation System, version 6.12.3
This seems to be a bug in ghc. First, let's fix bar to give the full
three arguments (Int, Float, Double) to g:
bar f g = proc x - do
(f - x) `foo` (\n m k - g - (n,m,k))
ghc infers the type:
bar :: (t - String) - ((Double, Float, Int) - String) - t - String
and we see that the argument order in the second argument to bar is
reversed. But the arguments are still given to bar in the order (Int,
Float, Double). For example, the 6.0 in foo is interpreted as an Int and
outputs a 0 (the first 32 bits in such a small double are zeros).
When one varies the numbers in foo, one can see the effects in bar. Can
someone from GHC HQ confirm my understanding, or is this just not
supposed to work with multiple arguments?
Jürgen
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Re: [Haskell-cafe] Weird behavior with arrow commands
On Sat, Jul 24, 2010 at 01:10:56PM +0200, Jürgen Doser wrote: This seems to be a bug in ghc. First, let's fix bar to give the full three arguments (Int, Float, Double) to g: bar f g = proc x - do (f - x) `foo` (\n m k - g - (n,m,k)) ghc infers the type: bar :: (t - String) - ((Double, Float, Int) - String) - t - String and we see that the argument order in the second argument to bar is reversed. But the arguments are still given to bar in the order (Int, Float, Double). For example, the 6.0 in foo is interpreted as an Int and outputs a 0 (the first 32 bits in such a small double are zeros). When one varies the numbers in foo, one can see the effects in bar. Can someone from GHC HQ confirm my understanding, or is this just not supposed to work with multiple arguments? You're right: it's getting the argument order wrong, so -dcore-lint fails on this example and all bets are off. Definitely a bug. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] FGL problem: cannot acces data constructor NodeMap
Hi, I have a problem with the data constructor NodeMap Data.Graph.Inductive.NodeMap of the graph library fgl-5.4.2.3 (also fgl-5.4.2.2): I cannot access the data constructor NodeMap, as the ghci session shows: Prelude :m Data.Graph.Inductive.NodeMap Prelude Data.Graph.Inductive.NodeMap :t NodeMap interactive:1:0: Not in scope: data constructor `NodeMap' However, when I load the source directly it works: Prelude :l Data/Graph/Inductive/NodeMap.hs [1 of 3] Compiling Data.Graph.Inductive.Graph ( Data/Graph/Inductive/Graph.hs, interpreted ) [2 of 3] Compiling Data.Graph.Inductive.Internal.FiniteMap ( Data/Graph/Inductive/Internal/FiniteMap.hs, interpreted ) [3 of 3] Compiling Data.Graph.Inductive.NodeMap ( Data/Graph/Inductive/NodeMap.hs, interpreted ) Ok, modules loaded: Data.Graph.Inductive.Internal.FiniteMap, Data.Graph.Inductive.Graph, Data.Graph.Inductive.NodeMap. *Data.Graph.Inductive.NodeMap :t NodeMap NodeMap :: (Ord a) = FiniteMap a Node - Int - NodeMap a Why is that so? Afterall, my purpose is to get access to the map in a NodeMap and finally to apply lookup to it. But I don't know how to access the map from a NodeMap (the map selector isn't accessible either). Immanuel ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] FGL problem: cannot acces data constructor NodeMap
Immanuel Normann immanuel.norm...@googlemail.com writes: Hi, I have a problem with the data constructor NodeMap Data.Graph.Inductive.NodeMap of the graph library fgl-5.4.2.3 (also fgl-5.4.2.2): I cannot access the data constructor NodeMap, as the ghci session shows: Prelude :m Data.Graph.Inductive.NodeMap Prelude Data.Graph.Inductive.NodeMap :t NodeMap interactive:1:0: Not in scope: data constructor `NodeMap' Well, yes, because you're not meant to. However, when I load the source directly it works: Prelude :l Data/Graph/Inductive/NodeMap.hs [1 of 3] Compiling Data.Graph.Inductive.Graph ( Data/Graph/Inductive/Graph.hs, interpreted ) [2 of 3] Compiling Data.Graph.Inductive.Internal.FiniteMap ( Data/Graph/Inductive/Internal/FiniteMap.hs, interpreted ) [3 of 3] Compiling Data.Graph.Inductive.NodeMap ( Data/Graph/Inductive/NodeMap.hs, interpreted ) Ok, modules loaded: Data.Graph.Inductive.Internal.FiniteMap, Data.Graph.Inductive.Graph, Data.Graph.Inductive.NodeMap. *Data.Graph.Inductive.NodeMap :t NodeMap NodeMap :: (Ord a) = FiniteMap a Node - Int - NodeMap a Why is that so? This works because you're using ghci from within the module, whereas when you import it you're using only its exposed API. Afterall, my purpose is to get access to the map in a NodeMap and finally to apply lookup to it. But I don't know how to access the map from a NodeMap (the map selector isn't accessible either). You're not meant to; the point of NodeMap is to serve as a wrapper around the normal graph types, not for you to use directly (exactly the same as why the constructor for Map isn't exported). May I ask, however, why you want to use Data.Graph.Inductive.NodeMap? -- Ivan Lazar Miljenovic ivan.miljeno...@gmail.com IvanMiljenovic.wordpress.com ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] FGL problem: cannot acces data constructor NodeMap
CC-ing haskell-cafe again: Immanuel Normann immanuel.norm...@googlemail.com writes: 2010/7/24 Ivan Lazar Miljenovic ivan.miljeno...@gmail.com Immanuel Normann immanuel.norm...@googlemail.com writes: Afterall, my purpose is to get access to the map in a NodeMap and finally to apply lookup to it. But I don't know how to access the map from a NodeMap (the map selector isn't accessible either). You're not meant to; the point of NodeMap is to serve as a wrapper around the normal graph types, not for you to use directly (exactly the same as why the constructor for Map isn't exported). May I ask, however, why you want to use Data.Graph.Inductive.NodeMap? Some of my lnodes in the graph have by construction unique labels and I want to lookup the lnode from a graph given only the label of that lnode. Well, from my understanding NodeMap doesn't do what you want, since it assumes that _all_ of the node labels are unique. Furthemore, the way of using it seems to be analogous of how one would use a State monad rather than for actual interactive use throughout. -- Ivan Lazar Miljenovic ivan.miljeno...@gmail.com IvanMiljenovic.wordpress.com ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] FGL problem: cannot acces data constructor NodeMap
Once again cc-ing -cafe; Immanuel, can you please do reply to all
rather than just reply in GMail? :p
Immanuel Normann immanuel.norm...@googlemail.com writes:
2010/7/24 Ivan Lazar Miljenovic ivan.miljeno...@gmail.com
CC-ing haskell-cafe again:
Immanuel Normann immanuel.norm...@googlemail.com writes:
2010/7/24 Ivan Lazar Miljenovic ivan.miljeno...@gmail.com
Some of my lnodes in the graph have by construction unique labels and I
want
to lookup the lnode from a graph given only the label of that lnode.
Well, from my understanding NodeMap doesn't do what you want, since it
assumes that _all_ of the node labels are unique
I wouldn't bother when NodeMap maps also non-unique labels to single nodes,
because I only lookup nodes with unique labels, e.g. assume my label are of
the form
data Label = Unique String | Multi Label
I'm of the suspicion that using NodeMaps in this fashion will have
problem when considering nodes with the same label (even if you don't
explicitly use it for those nodes), as NodeMap seems to assume that node
labels are unique.
For example, mkNode assumes node labels are unique.
Furthemore, the way of using it seems to be analogous of how one would use a
State monad
rather than for actual interactive use throughout.
Could you elaborate this further, please.
http://hackage.haskell.org/packages/archive/fgl/5.4.2.3/doc/html/Data-Graph-Inductive-NodeMap.html#v%3Arun
and
http://hackage.haskell.org/packages/archive/fgl/5.4.2.3/doc/html/Data-Graph-Inductive-NodeMap.html#v%3Arun_
If you just want a mapping from labels to nodes, you may be better off
using your own custom Map (and maybe even defining a new graph type that
has such a Map as part of it).
The successor to FGL-5.x (whatever we'll end up calling it) will allow
you to have custom node types rather than using Ints. However, this
will not work for you in this situation.
The node type is just an _index_ type, analogous to the actual hash
value in a hash{map,array} (as opposed to the value which has the
hashing function applied upon it). It's there to provide a unique
identifier for a particular node. Arguably, an abstract type would be
even better as an Int as it will prevent you from doing silly things
like adding node indices together, but that's beside the point.
If you wish to find a node with a specific label, try using something
like gsel:
http://hackage.haskell.org/packages/archive/fgl/5.4.2.3/doc/html/Data-Graph-Inductive-Basic.html#v%3Agsel
--
Ivan Lazar Miljenovic
ivan.miljeno...@gmail.com
IvanMiljenovic.wordpress.com
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Re: [Haskell-cafe] FGL problem: cannot acces data constructor NodeMap
2010/7/24 Ivan Lazar Miljenovic ivan.miljeno...@gmail.com
Once again cc-ing -cafe; Immanuel, can you please do reply to all
rather than just reply in GMail? :p
Oh, yes I forgot - sorry!
Thanks for all the valuable infos :-)
Immanuel
Immanuel Normann immanuel.norm...@googlemail.com writes:
2010/7/24 Ivan Lazar Miljenovic ivan.miljeno...@gmail.com
CC-ing haskell-cafe again:
Immanuel Normann immanuel.norm...@googlemail.com writes:
2010/7/24 Ivan Lazar Miljenovic ivan.miljeno...@gmail.com
Some of my lnodes in the graph have by construction unique labels and
I
want
to lookup the lnode from a graph given only the label of that lnode.
Well, from my understanding NodeMap doesn't do what you want, since it
assumes that _all_ of the node labels are unique
I wouldn't bother when NodeMap maps also non-unique labels to single
nodes,
because I only lookup nodes with unique labels, e.g. assume my label are
of
the form
data Label = Unique String | Multi Label
I'm of the suspicion that using NodeMaps in this fashion will have
problem when considering nodes with the same label (even if you don't
explicitly use it for those nodes), as NodeMap seems to assume that node
labels are unique.
For example, mkNode assumes node labels are unique.
Furthemore, the way of using it seems to be analogous of how one would
use a
State monad
rather than for actual interactive use throughout.
Could you elaborate this further, please.
http://hackage.haskell.org/packages/archive/fgl/5.4.2.3/doc/html/Data-Graph-Inductive-NodeMap.html#v%3Arun
and
http://hackage.haskell.org/packages/archive/fgl/5.4.2.3/doc/html/Data-Graph-Inductive-NodeMap.html#v%3Arun_
If you just want a mapping from labels to nodes, you may be better off
using your own custom Map (and maybe even defining a new graph type that
has such a Map as part of it).
The successor to FGL-5.x (whatever we'll end up calling it) will allow
you to have custom node types rather than using Ints. However, this
will not work for you in this situation.
The node type is just an _index_ type, analogous to the actual hash
value in a hash{map,array} (as opposed to the value which has the
hashing function applied upon it). It's there to provide a unique
identifier for a particular node. Arguably, an abstract type would be
even better as an Int as it will prevent you from doing silly things
like adding node indices together, but that's beside the point.
If you wish to find a node with a specific label, try using something
like gsel:
http://hackage.haskell.org/packages/archive/fgl/5.4.2.3/doc/html/Data-Graph-Inductive-Basic.html#v%3Agsel
--
Ivan Lazar Miljenovic
ivan.miljeno...@gmail.com
IvanMiljenovic.wordpress.com
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Re: [Haskell-cafe] Heavy lift-ing
I wouldn't-it was a bad example. My only point was that because of the way (=) is implemented for lists the order of the arguments 'a' and 'b' in 'liftM2 f a b' matters. -deech On Sat, Jul 24, 2010 at 1:37 AM, Lennart Augustsson lennart.augusts...@gmail.com wrote: Why would you expect swapped operands to (-) ? Sent from my iPad On Jul 23, 2010, at 20:12, aditya siram aditya.si...@gmail.com wrote: Lists are non-deterministic, but the function taken by liftM2 does not necessarily generate all possible outcomes. In the case of (+) it does, not in the case of (-): liftM2 (-) [0,1] [2,3] = [0-1,0-2,1-2,1-3] = [-2,-3,-1,-2] if all possible cases were generated between the two lists we have to include also: [2-0,2-1,3-0,3-1] -deech On Fri, Jul 23, 2010 at 3:44 PM, Alex Stangl a...@stangl.us wrote: On Fri, Jul 23, 2010 at 11:43:08AM -0700, michael rice wrote: What does it mean to promote a function to a monad? It would seem that the monad values must understand the function that's being promoted, like Ints understand (+). Prelude Control.Monad liftM2 (+) (Just 1) (Just 1) Just 2 But how does one add [0,1] and [0,2] to get [0,2,1,3]? It depends upon the semantics of the particular monad. List monads represent nondeterminism. So, for example, [0,1] represents a 0 or 1, and [0,2] represents a 0 or 2. When you add 0 or 1 to 0 or 2, your possible answers are [0,2,1,3]. Alex ___ 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 ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Heavy lift-ing
On Sat, Jul 24, 2010 at 4:08 PM, aditya siram aditya.si...@gmail.com wrote: I wouldn't-it was a bad example. My only point was that because of the way (=) is implemented for lists the order of the arguments 'a' and 'b' in 'liftM2 f a b' matters. -deech No, it's not. The type of liftM2 makes this clear: liftM2 :: (Monad m) = (a - b - r) - m a - m b - m r The arguments to the function *must* come in the right order, because there is no way to match (a) with (m b) or (b) with (m a). Since liftM2 is parametrically polymorphic in (a) and (b), it can't behave differently in the case where (a = b). --Max ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Heavy lift-ing
Perhaps I'm being unclear again. All I was trying to say was that: liftM2 (-) [0,1] [2,3] /= liftM2 (-) [2,3] [0,1] -deech On Sat, Jul 24, 2010 at 9:30 AM, Max Rabkin max.rab...@gmail.com wrote: On Sat, Jul 24, 2010 at 4:08 PM, aditya siram aditya.si...@gmail.com wrote: I wouldn't-it was a bad example. My only point was that because of the way (=) is implemented for lists the order of the arguments 'a' and 'b' in 'liftM2 f a b' matters. -deech No, it's not. The type of liftM2 makes this clear: liftM2 :: (Monad m) = (a - b - r) - m a - m b - m r The arguments to the function *must* come in the right order, because there is no way to match (a) with (m b) or (b) with (m a). Since liftM2 is parametrically polymorphic in (a) and (b), it can't behave differently in the case where (a = b). --Max ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: New FGL naming survey
For those interested, the overall results are in: http://ivanmiljenovic.wordpress.com/2010/07/25/results-of-fgl-naming-survey/ Ivan Miljenovic ivan.miljeno...@gmail.com writes: Thank you for all the people who have voted; we so far have 42 results in about 12 hours. Some indication of the results so far: * 62% prefer inductive-graphs * 62% have indicated that they use fgl or do some graph-related stuff (no correlation, just an interesting coincidence; I have not as yet done the number crunching to tell what the most popular name is for people that actually use fgl or other graph stuff). * Someone stated that ponies smell sweaty... not sure how that's relevant, but OK. * At least two people prefer the new name as it isn't an acronym (one because acronyms aren't needed and the term functional is redundant, the other because the term graph isn't directly in the package name). * Martin Erwig himself said that he thinks we should keep using the name fgl. So, keep the votes coming in (I actually didn't expect this many already)! On 14 July 2010 00:24, Ivan Lazar Miljenovic ivan.miljeno...@gmail.com wrote: Whether or not the new FGL that Thomas Bereknyei and I are working on should keep the name was a semi-hot issue when we first mentioned the fact that we were working on a new version about a month ago. As such, I've created a survey here to try and find out what the Haskell community overall thinks we should call it: https://spreadsheets.google.com/viewform?formkey=dGpzMmFnUWY3Uktodk5wdHlLQk5kT1E6MA More info can be found on the actual survey page. -- Ivan Lazar Miljenovic ivan.miljeno...@gmail.com IvanMiljenovic.wordpress.com -- Ivan Lazar Miljenovic ivan.miljeno...@gmail.com IvanMiljenovic.wordpress.com ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Heavy lift-ing
Prelude Control.Monad liftM2 (\a b - a : b : []) abc 123 [a1,a2,a3,b1,b2,b3,c1,c2,c3] Prelude Control.Monad Got it! Thanks to all. Michael --- On Sat, 7/24/10, aditya siram aditya.si...@gmail.com wrote: From: aditya siram aditya.si...@gmail.com Subject: Re: [Haskell-cafe] Heavy lift-ing To: Max Rabkin max.rab...@gmail.com Cc: haskell-cafe@haskell.org haskell-cafe@haskell.org, Lennart Augustsson lennart.augusts...@gmail.com Date: Saturday, July 24, 2010, 10:35 AM Perhaps I'm being unclear again. All I was trying to say was that: liftM2 (-) [0,1] [2,3] /= liftM2 (-) [2,3] [0,1] -deech On Sat, Jul 24, 2010 at 9:30 AM, Max Rabkin max.rab...@gmail.com wrote: On Sat, Jul 24, 2010 at 4:08 PM, aditya siram aditya.si...@gmail.com wrote: I wouldn't-it was a bad example. My only point was that because of the way (=) is implemented for lists the order of the arguments 'a' and 'b' in 'liftM2 f a b' matters. -deech No, it's not. The type of liftM2 makes this clear: liftM2 :: (Monad m) = (a - b - r) - m a - m b - m r The arguments to the function *must* come in the right order, because there is no way to match (a) with (m b) or (b) with (m a). Since liftM2 is parametrically polymorphic in (a) and (b), it can't behave differently in the case where (a = b). --Max ___ 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
[Haskell-cafe] default function definitions
Hi, I am studying the Haskell type class system as part of a language comparison thesis. At this point I am looking at how default function definitions are handled in classes. Functions are usually defined in instances, not classes. I appreciate that the code below may not be an appropriate way to write Haskell programs, but it does help me understand how defaults work. I am not trying to construct a running program. Any feedback on the questions below and defaults work in general would be appreciated. Pat module A where data Person = Person String Integer deriving Show data Employee = Employee String Integer deriving Show class C1 c1 where age :: c1 - Integer -- add default impl, can this be defined only once at class level? -- Can this function be redefined in a *class* lower down the heirarchy? age(c1) = 1 -- Is it true that instances must exists before we can run function or make subclasses? instance C1 Person where instance C1 Employee where -- Is it true that C2 can inherit age, provided an instance of C1 exists class C1 c2 = C2 c2 where name :: c2 - String name(c2) = C2 instance C2 Person where instance C2 Employee where -- Is it true that C3 cannot override C1 or C2 existing defaults? -- Is it true that this must be done at instance level? -- class Cx c3 = C3 c3 where --age(c3) = 3 -- This message has been scanned for content and viruses by the DIT Information Services E-Mail Scanning Service, and is believed to be clean. http://www.dit.ie ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
RE: [Haskell-cafe] build and use ghc's rts without a full unregistered ghc port?
I did initially thought about it and had reservations but you convinced me so I've been trying out jhc. Seems a lot more promising but unfortunately I had problems, here's my targets.ini: [wii] cc=powerpc-eabi-gcc byteorder=be gc=static cflags+=-DGEKKO -mrvl -mcpu=750 -meabi -mhard-float executable_extension=.elf bits=32 bits_max=64 Trying to compile a simple hello world haskell program resulted in the following error message: hs.out.elf_code.c:118:2: error: #error Could not determine bitsize hs.out.elf_code.c:150:24: error: sys/select.h: No such file or directory hs.out.elf_code.c:154:25: error: sys/utsname.h: No such file or directory ... ... For the first error I looked at the line and there is some pre-processor conditional code to determine the word size, this seems a bit odd since i've already specified these in the target.ini I would assume that they would get passed in to the compiler as extra defines. More depressing is the last two lines, which looks like a POSIX compatible environment is required with jhc it seems. Having a look at devkitPPC include directory it seems it does implement some POSIX headers but those particular headers certainly do not exist in there. Anyway I'll send a message to the jhc mailing list about it. Date: Sat, 24 Jul 2010 20:51:39 +1000 Subject: Re: [Haskell-cafe] build and use ghc's rts without a full unregistered ghc port? From: mwot...@gmail.com To: korca...@hotmail.com CC: haskell-cafe@haskell.org can't speak as to how difficult it is to get GHC built unregisterised, but you might want to consider JHC if you don't need to use a lot of Hackage. It compiles to C without a special RTS needed, which might make it a lot easier. mark On Sat, Jul 24, 2010 at 8:45 PM, Korcan Hussein wrote: Hi, I was just wondering if this is possible, I would like to use a gcc port which cross compiles to the PPC architecture (Wii DevkitPPC to be specifically: http://wiibrew.org/wiki/DevkitPPC) for a platform that is not POSIX compatible I believe (at least not fully or maybe I'm wrong entirely). Ideally I would make an unregistered port of GHC but the problem is because GHC doesn't support true cross compiling yet I need to bootstrap on to the target machine, which isn't running a POSIX environment. Still I did try to attempt to build with both the host and target set to 'powerpc-unknown-linux' and build it with devkitPPC, I did use a custom build.mk which should pull in all the required dependencies, defines, etc for devkitPPC. In the end I didn't get very far with it, it looked like missing posix functions. I didn't want to spend to much time trying to make it work this way (maybe i'm doing it wrong completely). It's quite possible that I could make this work more easily if I used a linux port for the wii but I would like to avoid the need of using linux on the wii because I guess most home-brew users don't have such a setup. So I thought maybe it's possible with less effort to build GHC's RTS and then compile Haskell in C with the RTS as a library dependency. Is this possible? maybe I'm missing something or doing something stupid? Thanks in advance. _ http://clk.atdmt.com/UKM/go/19780/direct/01/ We want to hear all your funny, exciting and crazy Hotmail stories. Tell us now___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe -- A UNIX signature isn't a return address, it's the ASCII equivalent of a black velvet clown painting. It's a rectangle of carets surrounding a quote from a literary giant of weeniedom like Heinlein or Dr. Who. -- Chris Maeda _ http://clk.atdmt.com/UKM/go/19780/direct/01/ We want to hear all your funny, exciting and crazy Hotmail stories. Tell us now___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] default function definitions
On Saturday 24 July 2010 19:59:26, Patrick Browne wrote: module A where data Person = Person String Integer deriving Show data Employee = Employee String Integer deriving Show class C1 c1 where age :: c1 - Integer -- add default impl, can this be defined only once at class level? -- Can this function be redefined in a *class* lower down the heirarchy? age(c1) = 1 That would normally be written age _ = 1 Yes, a default implementation of a class method can only be given in the class definition, it can't be redefined, but it can be overridden in an instance declaration. For example instance C1 Person where age _ = 3 instance C1 Employee where age (Employee _ n) = n -- Is it true that instances must exists before we can run function or make subclasses? instance C1 Person where instance C1 Employee where You can *call* class methods only for types which are instances of that class. You can define subclasses [not to confuse with OO-subclasses] of C1 even if there are no instances of C1 in scope. -- Is it true that C2 can inherit age, provided an instance of C1 exists class C1 c2 = C2 c2 where name :: c2 - String name(c2) = C2 A compiler/interpreter can accept an instance declaration of C2 for a type only if an instance of C1 for that type in scope [defined in the same module or in a module directly or indirectly imported; class instances are always re-exported from a module]. Since an instance of C2 must also be an instance of C1, all methods of C1 can be applied to that type. instance C2 Person where instance C2 Employee where -- Is it true that C3 cannot override C1 or C2 existing defaults? -- Is it true that this must be done at instance level? -- class Cx c3 = C3 c3 where --age(c3) = 3 -- True. Default methods can only be overridden in instance declarations for the class. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] default function definitions
On Jul 24, 2010, at 10:59 AM, Patrick Browne wrote: class C1 c1 where age :: c1 - Integer -- add default impl, can this be defined only once at class level? -- Can this function be redefined in a *class* lower down the heirarchy? age(c1) = 1 Yes, but keep in mind that the hierarchy is only two levels tall. This mechanism isn't meant for OO-style inheritance. -- Is it true that instances must exists before we can run function or make subclasses? instance C1 Person where instance C1 Employee where Yes, absolutely. -- Is it true that C2 can inherit age, provided an instance of C1 exists class C1 c2 = C2 c2 where name :: c2 - String name(c2) = C2 instance C2 Person where instance C2 Employee where There's no notion of inheritance here. If Person belongs to C2, then it must belong to C1, because you have specifically said that a C2 needs to be a C1 (presumably because you need a person's age to compute their name). So Person will be using C1's age function, in virtue of having a C1 instance. Compare this to: class C4 c4 where name' :: c4 - String instance C1 Person -- gives Person an age function, either default or overridden instance C1 thing = C4 thing -- gives every C1 thing a name, needs Haskell extensions. -- Is it true that C3 cannot override C1 or C2 existing defaults? -- Is it true that this must be done at instance level? -- class Cx c3 = C3 c3 where --age(c3) = 3 Yes, as I said, the hierarchy is two levels tall. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Porting ELF statifier to Haskell!
C K Kashyap schrieb: Hi, At my work we ran into a situation where we started wishing there was a way to take a dynamically linked executable and create a statically linked bundle out of it. Little bit of googling got me to statifier - http://statifier.sourceforge.net/statifier/main.html. I also tried to use statifier in order to run a Haskell program on a remote machine that I compiled locally. I had also no success. :-( ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Type problems
This works:
Prelude System.Random do { randomRIO (1,6) = (\x - putStrLn $ Value = ++
show x) }
Value = 5
So does this:
Prelude System.Random do { x - randomRIO (1,6); putStrLn $ Value = ++ show
x }
Value = 2
But not this:
1 import Control.Monad
2 import System.Random
3
4 foo :: IO ()
5 foo = do
6 x - randomRIO (1,6)
7 putStrLn $ Value = ++ show x
foo.hs:6:18:
Ambiguous type variable `t' in the constraints:
`Num t' arising from the literal `1' at foo.hs:6:18
`Random t' arising from a use of `randomRIO' at foo.hs:6:7-21
Probable fix: add a type signature that fixes these type variable(s)
Failed, modules loaded: none.
Prelude System.Random
Or this:
1 import Control.Monad
2 import System.Random
3
4 foo :: IO ()
5 foo = randomRIO (1,6) = (\x - putStrLn $ Value = ++ show x)
foo.hs:5:17:
Ambiguous type variable `t' in the constraints:
`Num t' arising from the literal `1' at foo.hs:5:17
`Random t' arising from a use of `randomRIO' at foo.hs:5:6-20
Probable fix: add a type signature that fixes these type variable(s)
Failed, modules loaded: none.
How to fix?
Michael
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Re: [Haskell-cafe] Type problems
You have to fix the type of 1 and 6, e.g. by writing
x - randomRIO (1, 6) :: IO Int
or
x - randomRIO (1, 6 :: Int)
GHCi defaults integral numbers to Int, that's why it works there.
On 24 July 2010 21:36, michael rice nowg...@yahoo.com wrote:
This works:
Prelude System.Random do { randomRIO (1,6) = (\x - putStrLn $ Value =
++ show x) }
Value = 5
So does this:
Prelude System.Random do { x - randomRIO (1,6); putStrLn $ Value = ++
show x }
Value = 2
But not this:
1 import Control.Monad
2 import System.Random
3
4 foo :: IO ()
5 foo = do
6 x - randomRIO (1,6)
7 putStrLn $ Value = ++ show x
foo.hs:6:18:
Ambiguous type variable `t' in the constraints:
`Num t' arising from the literal `1' at foo.hs:6:18
`Random t' arising from a use of `randomRIO' at foo.hs:6:7-21
Probable fix: add a type signature that fixes these type variable(s)
Failed, modules loaded: none.
Prelude System.Random
Or this:
1 import Control.Monad
2 import System.Random
3
4 foo :: IO ()
5 foo = randomRIO (1,6) = (\x - putStrLn $ Value = ++ show x)
foo.hs:5:17:
Ambiguous type variable `t' in the constraints:
`Num t' arising from the literal `1' at foo.hs:5:17
`Random t' arising from a use of `randomRIO' at foo.hs:5:6-20
Probable fix: add a type signature that fixes these type variable(s)
Failed, modules loaded: none.
How to fix?
Michael
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Re: [Haskell-cafe] Type problems
Thanks, Tobias. I figured it was something like that but lack the syntax
expertise on where to put it.
MIchael
--- On Sat, 7/24/10, Tobias Brandt tob.bra...@googlemail.com wrote:
From: Tobias Brandt tob.bra...@googlemail.com
Subject: Re: [Haskell-cafe] Type problems
To: michael rice nowg...@yahoo.com
Cc: haskell-cafe@haskell.org
Date: Saturday, July 24, 2010, 3:50 PM
You have to fix the type of 1 and 6, e.g. by writing
x - randomRIO (1, 6) :: IO Int
or
x - randomRIO (1, 6 :: Int)
GHCi defaults integral numbers to Int, that's why it works there.
On 24 July 2010 21:36, michael rice nowg...@yahoo.com wrote:
This works:
Prelude System.Random do { randomRIO (1,6) = (\x - putStrLn $ Value = ++
show x) }
Value = 5
So does this:
Prelude System.Random do { x - randomRIO (1,6); putStrLn $ Value = ++ show
x }
Value = 2
But not this:
1 import Control.Monad
2 import System.Random
3
4 foo :: IO ()
5 foo = do
6 x - randomRIO (1,6)
7 putStrLn $ Value = ++ show x
foo.hs:6:18:
Ambiguous type variable `t' in the constraints:
`Num t' arising from the literal `1' at foo.hs:6:18
`Random t' arising from a use of `randomRIO' at foo.hs:6:7-21
Probable fix: add a type signature that fixes these type variable(s)
Failed, modules loaded:
none.
Prelude System.Random
Or this:
1 import Control.Monad
2 import System.Random
3
4 foo :: IO ()
5 foo = randomRIO (1,6) = (\x - putStrLn $ Value = ++ show x)
foo.hs:5:17:
Ambiguous type variable `t' in the constraints:
`Num t' arising from the literal `1' at foo.hs:5:17
`Random t' arising from a use of `randomRIO' at foo.hs:5:6-20
Probable fix: add a type signature that fixes these type variable(s)
Failed, modules loaded: none.
How to fix?
Michael
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Re: [Haskell-cafe] Type problems
On Saturday 24 July 2010 21:36:14, michael rice wrote:
This works:
Prelude System.Random do { randomRIO (1,6) = (\x - putStrLn $ Value
= ++ show x) } Value = 5
So does this:
Prelude System.Random do { x - randomRIO (1,6); putStrLn $ Value =
++ show x } Value = 2
But not this:
1 import Control.Monad
2 import System.Random
3
4 foo :: IO ()
5 foo = do
6 x - randomRIO (1,6)
7 putStrLn $ Value = ++ show x
foo.hs:6:18:
Ambiguous type variable `t' in the constraints:
`Num t' arising from the literal `1' at foo.hs:6:18
`Random t' arising from a use of `randomRIO' at foo.hs:6:7-21
Probable fix: add a type signature that fixes these type variable(s)
Failed, modules loaded: none.
Prelude System.Random
The x has type
(Num a, Random a) = a
so GHC doesn't know which type to choose.
GHCi uses extended defaulting rules and picks Integer.
Fix, tell GHC which type to choose:
putStrLn $ Value = ++ show (x :: Integer)
or
x - randomRIO (1,6) :: IO Integer
Or this:
1 import Control.Monad
2 import System.Random
3
4 foo :: IO ()
5 foo = randomRIO (1,6) = (\x - putStrLn $ Value = ++ show x)
foo.hs:5:17:
Ambiguous type variable `t' in the constraints:
`Num t' arising from the literal `1' at foo.hs:5:17
`Random t' arising from a use of `randomRIO' at foo.hs:5:6-20
Probable fix: add a type signature that fixes these type variable(s)
Failed, modules loaded: none.
How to fix?
Michael
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Re: [Haskell-cafe] Wildly off-topic: de Boor's algorithm
Andrew Coppin wrote: Given a suitable definition for Vector2 (i.e., a 2D vector with the appropriate classes), it is delightfully trivial to implement de Casteljau's algorithm: de_Casteljau :: Scalar - [Vector2] - [[Vector2]] de_Casteljau t [p] = [[p]] de_Casteljau t ps = ps : de_Casteljau t (zipWith (line t) ps (tail ps)) line :: Scalar - Vector2 - Vector2 - Vector2 line t a b = (1-t) *| a + t *| b Now if you want to compute a given point along a Bezier spline, you can do bezier :: Scalar - [Vector2] - Vector2 bezier t ps = head $ last $ de_Casteljau t ps You can chop one in half with split :: Scalar - [Vector2] - ([Vector2], [Vector2]) split t ps = let pss = de_Casteljau t ps in (map head pss, map last pss) And any other beautiful incantations. Now, de Boor's algorithm is a generalisation of de Casteljau's algorithm. It draws B-splines instead of Bezier-splines (since B-splines generalise Bezier-splines). But I think I may have ACTUALLY MELTED MY BRAIN attempting to comprehend it. Can anybody supply a straightforward Haskell implementation? It took me a while to get around to it, and another while to work it out, but here's what I've come up with. First, here's a restatement of your code with a concrete choice of types (using Data.VectorSpace from the vector-space package) and a few minor stylistic changes just so things will line up with the generalized version better: import Data.VectorSpace interp a x y = lerp x y a deCasteljau [] t = [] deCasteljau ps t = ps : deCasteljau (zipWith (interp t) ps (tail ps)) t bezier ps = head . last . deCasteljau ps split ps t = (map head pss, reverse (map last pss)) where pss = deCasteljau ps t To generalize to De Boor's algorithm, the primary change is the interpolation operation. In De Casteljau's algorithm, every interpolation is over the same fixed interval 0 = x = 1. For De Boor's algorithm we need a more general linear interpolation on the arbitrary interval [x0,x1], because all the interpolations in De Boor's recurrence are between pairs of knots, which have arbitrary values instead of just 0 or 1. Because of Haskell's laziness, we can also take care of searching the result table for the correct set of control points at the same time, just by clamping the input to the desired interval and pre-emptively returning the corresponding 'y' if the input is outside that interval. This way, to find the final interpolant we only need to go to the end of the table, as in 'deCasteljau'. Unlike 'deCasteljau', only a portion of the table is actually computed (a triangular portion with the active control points as base and a path from the vertex of the triangle to the final entry in the table). interp x (x0,x1) (y0,y1) | x x0 = y0 | x = x1 = y1 | otherwise = lerp y0 y1 a where a = (x - x0) / (x1 - x0) Computing the table is now nearly as straightforward as in De Casteljau's algorithm: deBoor p _ [] x = [] deBoor p (_:us) ds x = ds : deBoor (p-1) us ds' x where ds' = zipWith (interp x) (spans p us) (spans 1 ds) Making use of a simple list function to select the spans: spans n xs = zip xs (drop n xs) Note that the algorithm does not make use of @us!!0@ at all. I believe this is correct, based both on the Wikipedia description of the algorithm and the implementations I've seen. De Boor's recurrence seems to require an irrelevant choice of extra control point that would be, notionally, @ds!!(-1)@. This control point has no actual influence inside the domain of the spline, although it /can/ affect values outside the domain (The domain being taken as the central portion of the knot vector where there are @p+1@ non-zero basis functions, forming a complete basis for the degree @p@ polynomials on that interval). This implementation makes the arbitrary but justifiable choice that the extra control point be identical to the first, so that the position of the first knot is irrelevant. It could alternatively be written to take the extra control point as an argument or as a part of @ds@, in which case the caller would be required to supply an additional control point that does not actually influence the spline. I initially found this result difficult to convince myself of even though it seems very plausible mathematically, because it seems to indicate that in general the position of the first and last knots are utterly irrelevant and I never saw any remarks to that effect in any of my reading on B-splines. Empirically, though, it seems to hold. Moving an internal knot at one end of a basis function does not alter the shape of that function in the segment furthest opposite, which is basically the same effect the first knot should have on the first basis function (and the opposite segment is the only one that falls inside the domain of the spline). It still may be that I'm wrong, and if anyone knows I'd love to hear about it, but I'm presently inclined
Re: [Haskell-cafe] default function definitions
Patrick Browne wrote: Hi, I am studying the Haskell type class system as part of a language comparison thesis. At this point I am looking at how default function definitions are handled in classes. Functions are usually defined in instances, not classes. I appreciate that the code below may not be an appropriate way to write Haskell programs, but it does help me understand how defaults work. I am not trying to construct a running program. Any feedback on the questions below and defaults work in general would be appreciated. 1. Stop thinking of Haskell classes being like normal classes in OOP. They are more like what Java calls interfaces. A type can belong to a class, much like in Java any class can implement Runnable (for example). 2. Making one class a subclass of another merely means that before a type can be made an instance of Y, it must first be an instance of X. There is no inheritance in Haskell. And no, if Y is a subclass of X, it cannot change anything in X, just add new stuff. It merely means that if you say I want something that's an instance of Y then it's also guaranteed to be an instance of X, without you having to manually say so. 3. A default implementation is just what it says on the tin: an implementation that will automatically be used if you don't manually supply one. The usual reason for this is if there's an implementation that will always work, but in some cases there may be a more efficient one. The default implementation is then the general version that will always work, and when you write instances for other types, you may specify a better implementation. The other reason is if X can be defined in terms of Y, and Y can be defined in terms of X. Add default implementations for both, and when you write an instance you can implement whichever one is easiest and use the default for the other. HTH. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] data type declaration
Hi, I am trying to understand the data type declaration below. What is the relation between class C3 and the data type Address below? Where is such a technique used? Thanks, Pat module A where data Person = Person String Integer deriving Show data Employee = Employee String Integer deriving Show class C1 c1 where age :: c1 - Integer instance C1 Person where age(Person P1 1) = 1 instance C1 Employee where age(Employee E1 1) = 1 class C1 c2 = C2 c2 where name :: c2 - String instance C2 Person where name(Person P2 1) = P2 instance C2 Employee where name(Employee E2 1) = E2 class C2 c3 = C3 c3 a where address :: c3 - a instance C3 Person String where -- ** What are the semantics or purpose of this construct. -- ** Is the type declared in the context of a class. data C3 c3 a = Address c3 a = Address c3 a instance C3 Person (Address String String) where This message has been scanned for content and viruses by the DIT Information Services E-Mail Scanning Service, and is believed to be clean. http://www.dit.ie ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
RE: [Haskell-cafe] build and use ghc's rts without a full unregistered ghc port?
I managed to get a hello world app working on the Wii! but I had to do some hacking of the generated C code because the devkitPPC is missing 2 posix headers referenced in the generated C code from Jhc. The functions the code used from those headers didn't seem completely essential. Basically I set the define JHC_isPosix to 0, commented out problem code. Of-course this isn't ideal, the solution would be to implement the missing headers for devkitPPC. From: korca...@hotmail.com To: mwot...@gmail.com CC: haskell-cafe@haskell.org Subject: RE: [Haskell-cafe] build and use ghc's rts without a full unregistered ghc port? Date: Sat, 24 Jul 2010 18:25:56 + I did initially thought about it and had reservations but you convinced me so I've been trying out jhc. Seems a lot more promising but unfortunately I had problems, here's my targets.ini: [wii] cc=powerpc-eabi-gcc byteorder=be gc=static cflags+=-DGEKKO -mrvl -mcpu=750 -meabi -mhard-float executable_extension=.elf bits=32 bits_max=64 Trying to compile a simple hello world haskell program resulted in the following error message: hs.out.elf_code.c:118:2: error: #error Could not determine bitsize hs.out.elf_code.c:150:24: error: sys/select.h: No such file or directory hs.out.elf_code.c:154:25: error: sys/utsname.h: No such file or directory ... ... For the first error I looked at the line and there is some pre-processor conditional code to determine the word size, this seems a bit odd since i've already specified these in the target.ini I would assume that they would get passed in to the compiler as extra defines. More depressing is the last two lines, which looks like a POSIX compatible environment is required with jhc it seems. Having a look at devkitPPC include directory it seems it does implement some POSIX headers but those particular headers certainly do not exist in there. Anyway I'll send a message to the jhc mailing list about it. Date: Sat, 24 Jul 2010 20:51:39 +1000 Subject: Re: [Haskell-cafe] build and use ghc's rts without a full unregistered ghc port? From: mwot...@gmail.com To: korca...@hotmail.com CC: haskell-cafe@haskell.org can't speak as to how difficult it is to get GHC built unregisterised, but you might want to consider JHC if you don't need to use a lot of Hackage. It compiles to C without a special RTS needed, which might make it a lot easier. mark On Sat, Jul 24, 2010 at 8:45 PM, Korcan Hussein wrote: Hi, I was just wondering if this is possible, I would like to use a gcc port which cross compiles to the PPC architecture (Wii DevkitPPC to be specifically: http://wiibrew.org/wiki/DevkitPPC) for a platform that is not POSIX compatible I believe (at least not fully or maybe I'm wrong entirely). Ideally I would make an unregistered port of GHC but the problem is because GHC doesn't support true cross compiling yet I need to bootstrap on to the target machine, which isn't running a POSIX environment. Still I did try to attempt to build with both the host and target set to 'powerpc-unknown-linux' and build it with devkitPPC, I did use a custom build.mk which should pull in all the required dependencies, defines, etc for devkitPPC. In the end I didn't get very far with it, it looked like missing posix functions. I didn't want to spend to much time trying to make it work this way (maybe i'm doing it wrong completely). It's quite possible that I could make this work more easily if I used a linux port for the wii but I would like to avoid the need of using linux on the wii because I guess most home-brew users don't have such a setup. So I thought maybe it's possible with less effort to build GHC's RTS and then compile Haskell in C with the RTS as a library dependency. Is this possible? maybe I'm missing something or doing something stupid? Thanks in advance. _ http://clk.atdmt.com/UKM/go/19780/direct/01/ We want to hear all your funny, exciting and crazy Hotmail stories. Tell us now___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe -- A UNIX signature isn't a return address, it's the ASCII equivalent of a black velvet clown painting. It's a rectangle of carets surrounding a quote from a literary giant of weeniedom like Heinlein or Dr. Who. -- Chris Maeda _ http://clk.atdmt.com/UKM/go/19780/direct/01/ We want to hear all your funny, exciting and crazy Hotmail stories. Tell us now _ http://clk.atdmt.com/UKM/go/19780/direct/01/ We want to hear all your funny, exciting and crazy
Re: [Haskell-cafe] Type problems
On 25 July 2010 05:50, Tobias Brandt tob.bra...@googlemail.com wrote: You have to fix the type of 1 and 6, e.g. by writing x - randomRIO (1, 6) :: IO Int or x - randomRIO (1, 6 :: Int) GHCi defaults integral numbers to Int, that's why it works there. The default numeric type is Integer, not Int. -- Ivan Lazar Miljenovic ivan.miljeno...@gmail.com IvanMiljenovic.wordpress.com ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: recommendation for (best) sqlite3 bindings
I am the author of direct-sqlite, and I thank you for the bug report. I'll be fixing this as soon as I'm able. It's always nice to hear about people using my code! On Wed, Jul 21, 2010 at 2:10 AM, Michael Snoyman mich...@snoyman.com wrote: On Wed, Jul 21, 2010 at 8:59 AM, Gour g...@gour-nitai.com wrote: On Wed, 21 Jul 2010 08:06:49 +0300 Michael == Michael Snoyman mich...@snoyman.com wrote: Michael For the sqlite backend for persistent, I took direct-sqlite Michael and modified it slightly. I have a long history of using the Michael sqlite3 C API, so the API felt very familiar to me. So, it seems you're satisfiew with direct-sqlite? What is missing in 1st package (Galois bindings)? I didn't investigate it, I would imagine it's pretty complete if Galois wrote it. I stuck with direct-sqlite just because it was so incredibly simple (single file, ~15 functions). btw, after some research, I've concluded that NOSQL (Redis, MongoDB) are not good solutions in our use-case since we want to have extensive querying support and using sqlite3 with SQL seems better option. That's why I'm sticking with SQL for my current project. Michael If I'm not mistaken, direct-sqlite does not build as-is on Michael hackage because it's missing a reference to the C library. Hmm...you're right. Apparently Archlinux package built OK; but loading it into ghci gives: ghc: /usr/lib/direct-sqlite-1.0/ghc-6.12.1/HSdirect-sqlite-1.0.o: unknown symbol `sqlite3_column_blob' Thank you. Michael However, if you take my approach and just include the code in Michael your library, you can fix that easily enough. It looks it's the problem with package's cabal file... True, it's a very simple fix. In fact, you can just include the sqlite amalgamation file with the code and not worry about library dependencies. Michael ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe -- Dan Knapp An infallible method of conciliating a tiger is to allow oneself to be devoured. (Konrad Adenauer) ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: recommendation for (best) sqlite3 bindings
Sorry I didn't send it earlier, it must have slipped my mind. On Sun, Jul 25, 2010 at 3:07 AM, Dan Knapp dan...@gmail.com wrote: I am the author of direct-sqlite, and I thank you for the bug report. I'll be fixing this as soon as I'm able. It's always nice to hear about people using my code! On Wed, Jul 21, 2010 at 2:10 AM, Michael Snoyman mich...@snoyman.com wrote: On Wed, Jul 21, 2010 at 8:59 AM, Gour g...@gour-nitai.com wrote: On Wed, 21 Jul 2010 08:06:49 +0300 Michael == Michael Snoyman mich...@snoyman.com wrote: Michael For the sqlite backend for persistent, I took direct-sqlite Michael and modified it slightly. I have a long history of using the Michael sqlite3 C API, so the API felt very familiar to me. So, it seems you're satisfiew with direct-sqlite? What is missing in 1st package (Galois bindings)? I didn't investigate it, I would imagine it's pretty complete if Galois wrote it. I stuck with direct-sqlite just because it was so incredibly simple (single file, ~15 functions). btw, after some research, I've concluded that NOSQL (Redis, MongoDB) are not good solutions in our use-case since we want to have extensive querying support and using sqlite3 with SQL seems better option. That's why I'm sticking with SQL for my current project. Michael If I'm not mistaken, direct-sqlite does not build as-is on Michael hackage because it's missing a reference to the C library. Hmm...you're right. Apparently Archlinux package built OK; but loading it into ghci gives: ghc: /usr/lib/direct-sqlite-1.0/ghc-6.12.1/HSdirect-sqlite-1.0.o: unknown symbol `sqlite3_column_blob' Thank you. Michael However, if you take my approach and just include the code in Michael your library, you can fix that easily enough. It looks it's the problem with package's cabal file... True, it's a very simple fix. In fact, you can just include the sqlite amalgamation file with the code and not worry about library dependencies. Michael ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe -- Dan Knapp An infallible method of conciliating a tiger is to allow oneself to be devoured. (Konrad Adenauer) ___ 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] Porting ELF statifier to Haskell!
Looks like the crash is due to ASLR (Address Space Layout Randomization). You need to disable it for it to work. You can disable ASLR very easily - check out http://stackoverflow.com/questions/1455904/how-to-disable-address-space-randomization-for-a-binary-on-linux for instance Statifier worked for me once I disabled ASLR ... On Sun, Jul 25, 2010 at 12:32 AM, Henning Thielemann schlepp...@henning-thielemann.de wrote: C K Kashyap schrieb: Hi, At my work we ran into a situation where we started wishing there was a way to take a dynamically linked executable and create a statically linked bundle out of it. Little bit of googling got me to statifier - http://statifier.sourceforge.net/statifier/main.html. I also tried to use statifier in order to run a Haskell program on a remote machine that I compiled locally. I had also no success. :-( -- Regards, Kashyap ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
