Re: [Haskell-cafe] Re: Hack (web) and apache configuration
On Jun 25, 2009, at 13:31 , Henry Laxen wrote: It reminds me of a saying I heard once. If carpenters built houses the way programmers write programs, you could walk into any house, remove any single nail, and the structure would collapse into pieces no larger than toothpicks. Weinberg's Law: If carpenters built houses the way programmers write programs, then the first woodpecker that came along would destroy civilization. -- brandon s. allbery [solaris,freebsd,perl,pugs,haskell] allb...@kf8nh.com system administrator [openafs,heimdal,too many hats] allb...@ece.cmu.edu electrical and computer engineering, carnegie mellon universityKF8NH PGP.sig 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] coding standard question
On Thu, Jun 25, 2009 at 3:27 AM, wren ng thorntonw...@freegeek.org wrote:
If certain warnings truly are spurious and unavoidable, then it's best to
document this explicitly in the code by pragmas to disable the relevant
warnings. This way the spurious nature of the warning is documented (for
future maintainers, including yourself) and the distracting output of the
compiler is removed as well. Unfortunately, GHC only gives whole-file scope
for disabling warnings, but that could be fixed with enough work.
Hello all,
Forgive me if I'm a bit out of topic, but following this thread, I
decided to add -Wall -Werror for a program I'm working on.
I've spend a bit of time correcting quite a lot of warnings, most of
them being about missing type signatures. I've corrected them all, but
there remains one that I can't : ghc refuses the type signature it
suggests me.
Anyone has any idea ?
=
da...@pcdavid2:~/projets/haskell/caimonitor$ ./g
[3 of 4] Compiling Bdd ( Bdd.hs, Bdd.o )
Bdd.hs:27:0:
Warning: Definition but no type signature for `connecter'
Inferred type: connecter :: IO
HDBC-mysql-0.6:Database.HDBC.MySQL.Connection.Connection
no location info:
Failing due to -Werror.
=
Here's part of the code : without -Werror, the code compiles and works fine.
==
module Bdd where
import Database.HDBC
import Database.HDBC.MySQL
import Text.Printf
import Messages
mysqlInfo :: MySQLConnectInfo
mysqlInfo = defaultMySQLConnectInfo { mysqlHost =xxx.xxx.xxx.xxx
, mysqlUser =
, mysqlPassword =
, mysqlDatabase = xx
, mysqlPort = 0
, mysqlUnixSocket =
}
--connecter :: IO Database.HDBC.MySQL.Connection.Connection
connecter= connectMySQL mysqlInfo
...
...
...
==
Thanks,
David
___
Haskell-Cafe mailing list
Haskell-Cafe@haskell.org
http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] coding standard question
Am Freitag 26 Juni 2009 11:30:32 schrieb david48:
On Thu, Jun 25, 2009 at 3:27 AM, wren ng thorntonw...@freegeek.org wrote:
If certain warnings truly are spurious and unavoidable, then it's best to
document this explicitly in the code by pragmas to disable the relevant
warnings. This way the spurious nature of the warning is documented (for
future maintainers, including yourself) and the distracting output of the
compiler is removed as well. Unfortunately, GHC only gives whole-file
scope for disabling warnings, but that could be fixed with enough work.
Hello all,
Forgive me if I'm a bit out of topic, but following this thread, I
decided to add -Wall -Werror for a program I'm working on.
I've spend a bit of time correcting quite a lot of warnings, most of
them being about missing type signatures. I've corrected them all, but
there remains one that I can't : ghc refuses the type signature it
suggests me.
Anyone has any idea ?
=
da...@pcdavid2:~/projets/haskell/caimonitor$ ./g
[3 of 4] Compiling Bdd ( Bdd.hs, Bdd.o )
Bdd.hs:27:0:
Warning: Definition but no type signature for `connecter'
Inferred type: connecter :: IO
HDBC-mysql-0.6:Database.HDBC.MySQL.Connection.Connection
no location info:
Failing due to -Werror.
=
Here's part of the code : without -Werror, the code compiles and works
fine.
==
module Bdd where
import Database.HDBC
import Database.HDBC.MySQL
import Text.Printf
import Messages
mysqlInfo :: MySQLConnectInfo
mysqlInfo = defaultMySQLConnectInfo { mysqlHost =xxx.xxx.xxx.xxx
, mysqlUser =
, mysqlPassword =
, mysqlDatabase = xx
, mysqlPort = 0
, mysqlUnixSocket =
}
--connecter :: IO Database.HDBC.MySQL.Connection.Connection
Looks like you must also
import Database.HDBC.MySQL.Connection
or, if the type Connection is exported from one of the imported modules, use it
unqualifed
or qualified with that module name.
connecter= connectMySQL mysqlInfo
...
...
...
==
Thanks,
David
___
Haskell-Cafe mailing list
Haskell-Cafe@haskell.org
http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: FFI and heap memory usage limit
On 22/06/2009 23:48, Bulat Ziganshin wrote: Hello Marcin, Tuesday, June 23, 2009, 2:31:13 AM, you wrote: Now this took an odd turn, because the simulation started crashing with out-of-memory errors _after_ completing (during bz2 compression). I'm fairly certain this is a GC/FFI bug, because increasing the max heap didn't help. Moving the bz2 compression to a separate process provided a reasonable solution. What I think is happening is that after the simulation completes, almost all of the available memory (within the -M limit) is filled with garbage. Then I run bzlib which tries to allocate more memory (from behind FFI?) to compress the results, which in turn causes an out-of-memory error instead of triggering a GC collection. i can propose a quick fix - alloc 10 mb using allocBytes before starting your algorithm, and free it just before starting bzlib. it may help i agree that this looks like a deficiency of memory allocator. it's better to write at ghc-users maillist (or at least make a copy to Simon Marlow) to attract attention to your message Maybe bzlib allocates using malloc()? That would not be tracked by GHC's memory management, but could cause OOM. Another problem is that if you ask for a large amount of memory in one go, the request is usually honoured immediately, and then we GC shortly afterward. If this is the problem for you, please submit a ticket and I'll see whether it can be changed. You could work around it by calling System.Mem.performGC just before allocating the memory. Cheers, Simon ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Haskell on JVM
Incidentally, I am looking for someone well versed in the JVM who wants to help spearhead a JVM back end for jhc. I would love to see this! With the current advent of all those languages targeting at the JVM (Groovy, Scala, Clojure) I think a JVM backend for a Haskell compiler could, together with proper Java interop, make for a major breakthrough of Haskell in general. Unforunately, as I can tell from my halfknowledge, the JVM lacks some important functionality required for properly targeting functional language features on the JVM. And here comes my question: If there is anybody with proper knowledge about this issue, I would really like to know what are those things that are missing? For example, Clojure lacks proper tail recrusion optimization due to some missing functionality in the JVM. But does anybody know the details? Thanks, Timo ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Haskell on JVM
Although I don't know what the current JVM lacks to properly act as a functional backend, it appears that JVM 1.7 will be at least better suitable to support dynamic languages. See: The Da Vinci Machine Project http://openjdk.java.net/projects/mlvm/ Arvid On Fri, Jun 26, 2009 at 2:09 PM, Timo B. Hübelt...@gmx.info wrote: Incidentally, I am looking for someone well versed in the JVM who wants to help spearhead a JVM back end for jhc. I would love to see this! With the current advent of all those languages targeting at the JVM (Groovy, Scala, Clojure) I think a JVM backend for a Haskell compiler could, together with proper Java interop, make for a major breakthrough of Haskell in general. Unforunately, as I can tell from my halfknowledge, the JVM lacks some important functionality required for properly targeting functional language features on the JVM. And here comes my question: If there is anybody with proper knowledge about this issue, I would really like to know what are those things that are missing? For example, Clojure lacks proper tail recrusion optimization due to some missing functionality in the JVM. But does anybody know the details? Thanks, Timo ___ 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] Haskell on JVM
On 26 Jun 2009, at 14:09, Timo B. Hübel wrote: And here comes my question: If there is anybody with proper knowledge about this issue, I would really like to know what are those things that are missing? For example, Clojure lacks proper tail recrusion optimization due to some missing functionality in the JVM. But does anybody know the details? Basically, the JVM lacks a native ability to do tail calls. It does not have an instruction to remove/replace a stack frame without executing an actual return to the calling method/function. With the heavy use of recursion in functional programs, this is an important feature in a language implementation to avoid stack overflows. Some language implementations (Scala) can do partial workarounds by turning the generated code into a loop in the compiler, but this is frequently limited to only deal with self-recursive calls, and does not deal with the general case (X-calls-Y-calls-Z-calls-X...), which a proper implementation of tail- calls at the JVM level would allow. At the JIT level (below the JVM spec level) some implementations may actually do the tail call optimization anyway, but this is beyond the control of a language implementation, and would result in a situation where the behaviour of your program depends on particular implementations/versions/parameters of the JVM running it. That is something to be avoided if possible. Maarten Hazewinkel maarten.hazewin...@gmail.com ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Haskell on JVM
There has been a scheme with tail recursion on the JVM for a long time IIRC. SISC right? At least I am fairly certain it does. On Friday, June 26, 2009, Timo B. Hübel t...@gmx.info wrote: Incidentally, I am looking for someone well versed in the JVM who wants to help spearhead a JVM back end for jhc. I would love to see this! With the current advent of all those languages targeting at the JVM (Groovy, Scala, Clojure) I think a JVM backend for a Haskell compiler could, together with proper Java interop, make for a major breakthrough of Haskell in general. Unforunately, as I can tell from my halfknowledge, the JVM lacks some important functionality required for properly targeting functional language features on the JVM. And here comes my question: If there is anybody with proper knowledge about this issue, I would really like to know what are those things that are missing? For example, Clojure lacks proper tail recrusion optimization due to some missing functionality in the JVM. But does anybody know the details? Thanks, Timo ___ 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] Multi-module scripts
Is it possible to write a Haskell script that uses a module that is also going to be interpreted? Like, say: #!/usr/bin/runhaskell module Main (main) where import OtherModule main = (...) where OtherModule is available in, say, OtherModule.hs and not in the already compiled and installed library? Thanks, Maurício ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Haskell on JVM
Hi Timo, On Fri, Jun 26, 2009 at 5:09 AM, Timo B. Hübel t...@gmx.info wrote: Incidentally, I am looking for someone well versed in the JVM who wants to help spearhead a JVM back end for jhc. I would love to see this! With the current advent of all those languages targeting at the JVM (Groovy, Scala, Clojure) I think a JVM backend for a Haskell compiler could, together with proper Java interop, make for a major breakthrough of Haskell in general. Unforunately, as I can tell from my halfknowledge, the JVM lacks some important functionality required for properly targeting functional language features on the JVM. And here comes my question: If there is anybody with proper knowledge about this issue, I would really like to know what are those things that are missing? For example, Clojure lacks proper tail recrusion optimization due to some missing functionality in the JVM. But does anybody know the details? My brief research into why the JVM lacks tail calls indicated that tail calls do not play nicely with the JVM security model and make stack traces harder to manage. Although, I have also heard that tail call of some form is expected to appear in java 1.7. Jason ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Haskell on JVM
On Fri, Jun 26, 2009 at 7:12 AM, David Leimbach leim...@gmail.com wrote: There has been a scheme with tail recursion on the JVM for a long time IIRC. SISC right? Ah SISC is interpreted. Clojure is compiled. At least that may be the key difference to making it work or not. At least I am fairly certain it does. On Friday, June 26, 2009, Timo B. Hübel t...@gmx.info wrote: Incidentally, I am looking for someone well versed in the JVM who wants to help spearhead a JVM back end for jhc. I would love to see this! With the current advent of all those languages targeting at the JVM (Groovy, Scala, Clojure) I think a JVM backend for a Haskell compiler could, together with proper Java interop, make for a major breakthrough of Haskell in general. Unforunately, as I can tell from my halfknowledge, the JVM lacks some important functionality required for properly targeting functional language features on the JVM. And here comes my question: If there is anybody with proper knowledge about this issue, I would really like to know what are those things that are missing? For example, Clojure lacks proper tail recrusion optimization due to some missing functionality in the JVM. But does anybody know the details? Thanks, Timo ___ 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] Haskell on JVM
For example, Clojure lacks proper tail recrusion optimization due to some missing functionality in the JVM. But does anybody know the details? |Basically, the JVM lacks a native ability to do tail calls. It does |not have an instruction to remove/replace a stack frame without |executing an actual return to the calling method/function. There is a conflict between preserving stack layout and efficient tail calls. Unfortunately, stack inspection appears to be used for security aspects in JVM. That doesn't make tail calls impossible, but may have slowed down progress as this argument always comes up in discussing tail calls on the JVM (since its byte code isn't just an internal detail, but an externally used API). None of the various partial workarounds are quite satisfactory (jumps work only locally, there is an upper size limit on how much code can be considered as local, trampolines return before each call, there are alternatives that clear the stack not before each call, but every n calls, ..., see the various Haskell to Java/JVM papers). I was curious about the current state (the issue is as old as JVM), and here's what I've found so far (more concrete/official info would be appreciated): tail calls in the VM [2007] http://blogs.sun.com/jrose/entry/tail_calls_in_the_vm RFE: Tail Call Optimization [2002] http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=4726340 [2009] http://wikis.sun.com/display/mlvm/TailCalls Tail Call Optimization in the Java HotSpot(TM) VM [2009] http://www.ssw.uni-linz.ac.at/Research/Papers/Schwaighofer09Master/ Still cooking, still not done, it seems, but perhaps closer than ever? Claus ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Why is Bool no instance of Num and Bits?
Agreed. I wound up having to add a horrible Num instance for Bool in 'monoids' in order to support a decent Boolean Ring type. http://comonad.com/haskell/monoids/dist/doc/html/monoids/Data-Ring-Boolean.html I would much rather be able to get rid of it! The only problem with eliminating the constraint is that any code that uses Bits polymorphically might have to pick up a Num annotation, but I can't see it being a serious problem. -Edward Kmett On Wed, Jun 24, 2009 at 8:13 AM, John Meacham j...@repetae.net wrote: On Fri, May 08, 2009 at 04:36:41PM +0200, Stephan Friedrichs wrote: When looking for an xor function, I found one in Data.Bits but couldn't use it for Bool, because Bool is no instance of Bits and of Num (which would be necessary, because it's class (Num b) = Bits b). My question is: Why not? This has bothered me too. However, I think the root problem is that 'Num' is a superclass of 'Bits'. There is no reason it should be, all the default instances can be specified without the Num dependency. John -- John Meacham - ⑆repetae.net⑆john⑈ - http://notanumber.net/ ___ 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] Haskell on JVM
Since the JVM doesn't seem to support tail call optimization, I suppose one could could directly manipulate the bytecodes generated by jhc to do TCO. One challenge would be the garbage collector, since Haskell and Java have very different working sets of what is still being used. -- Regards, Casey ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Haskell on JVM
JVM 7 has tail calls, and if you don't want to wait for that, goto works perfectly well for self-recursive functions. Other techniques can deal with mutual recursion, albeit at the cost of performance. Regards, John A. De Goes N-Brain, Inc. The Evolution of Collaboration http://www.n-brain.net|877-376-2724 x 101 On Jun 26, 2009, at 6:26 AM, Maarten Hazewinkel wrote: On 26 Jun 2009, at 14:09, Timo B. Hübel wrote: And here comes my question: If there is anybody with proper knowledge about this issue, I would really like to know what are those things that are missing? For example, Clojure lacks proper tail recrusion optimization due to some missing functionality in the JVM. But does anybody know the details? Basically, the JVM lacks a native ability to do tail calls. It does not have an instruction to remove/replace a stack frame without executing an actual return to the calling method/function. With the heavy use of recursion in functional programs, this is an important feature in a language implementation to avoid stack overflows. Some language implementations (Scala) can do partial workarounds by turning the generated code into a loop in the compiler, but this is frequently limited to only deal with self-recursive calls, and does not deal with the general case (X-calls-Y-calls-Z-calls-X...), which a proper implementation of tail-calls at the JVM level would allow. At the JIT level (below the JVM spec level) some implementations may actually do the tail call optimization anyway, but this is beyond the control of a language implementation, and would result in a situation where the behaviour of your program depends on particular implementations/versions/parameters of the JVM running it. That is something to be avoided if possible. Maarten Hazewinkel maarten.hazewin...@gmail.com ___ 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] Haskell on JVM
Maybe the JVM could be abused so that all of the haskell code is within one function, so as to avoid java's notion of a function boundary and implement our own using just goto? Or does the JIT operate on entire functions at a time? On Fri, Jun 26, 2009 at 1:23 PM, John A. De Goesj...@n-brain.net wrote: JVM 7 has tail calls, and if you don't want to wait for that, goto works perfectly well for self-recursive functions. Other techniques can deal with mutual recursion, albeit at the cost of performance. Regards, John A. De Goes N-Brain, Inc. The Evolution of Collaboration http://www.n-brain.net | 877-376-2724 x 101 On Jun 26, 2009, at 6:26 AM, Maarten Hazewinkel wrote: On 26 Jun 2009, at 14:09, Timo B. Hübel wrote: And here comes my question: If there is anybody with proper knowledge about this issue, I would really like to know what are those things that are missing? For example, Clojure lacks proper tail recrusion optimization due to some missing functionality in the JVM. But does anybody know the details? Basically, the JVM lacks a native ability to do tail calls. It does not have an instruction to remove/replace a stack frame without executing an actual return to the calling method/function. With the heavy use of recursion in functional programs, this is an important feature in a language implementation to avoid stack overflows. Some language implementations (Scala) can do partial workarounds by turning the generated code into a loop in the compiler, but this is frequently limited to only deal with self-recursive calls, and does not deal with the general case (X-calls-Y-calls-Z-calls-X...), which a proper implementation of tail-calls at the JVM level would allow. At the JIT level (below the JVM spec level) some implementations may actually do the tail call optimization anyway, but this is beyond the control of a language implementation, and would result in a situation where the behaviour of your program depends on particular implementations/versions/parameters of the JVM running it. That is something to be avoided if possible. Maarten Hazewinkel maarten.hazewin...@gmail.com ___ 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] Haskell on JVM
On Fri, Jun 26, 2009 at 10:44 AM, Daniel Peeblespumpkin...@gmail.com wrote: Maybe the JVM could be abused so that all of the haskell code is within one function, so as to avoid java's notion of a function boundary and implement our own using just goto? Or does the JIT operate on entire functions at a time? As I recall, this has been tried, but there's a limit (64k?) on function body size that you immediately run in to. Also, this would seem likely to get seriously in the way of optimizations and use of the JVM's slightly-higher-than-assembly level of abstraction. I think the second reason, for example, is why people (to my knowledge) haven't tried the otherwise well suited Cheney-on-the-MTA scheme...Stack as nursery is cute, but I think you want to work with the JVM, not against it. AHH ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Haskell on JVM
JVM 7 has tail calls, Source, please? JSR-292 seems the most likely candidate so far, and its draft doesn't seem to mention tail calls yet. As of March this year, the people working on tail calls for mlvm [1], which seems to be the experimentation ground for this, did not seem to expect any fast route: http://mail.openjdk.java.net/pipermail/mlvm-dev/2009-March/000405.html There have been years of rumours and plans, so it would be nice to have concrete details, before any fp-on-jvm implementation design starts to rely on this. Claus [1] http://openjdk.java.net/projects/mlvm/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Haskell on JVM
I don't have a source, but I know tail calls have been implemented (in a patch) and tested, and at the JVM Summit everyone was saying this was definitely going to be released in JVM 7. Regards, John A. De Goes N-Brain, Inc. The Evolution of Collaboration http://www.n-brain.net|877-376-2724 x 101 On Jun 26, 2009, at 11:27 AM, Claus Reinke wrote: JVM 7 has tail calls, Source, please? JSR-292 seems the most likely candidate so far, and its draft doesn't seem to mention tail calls yet. As of March this year, the people working on tail calls for mlvm [1], which seems to be the experimentation ground for this, did not seem to expect any fast route: http://mail.openjdk.java.net/pipermail/mlvm-dev/2009-March/000405.html There have been years of rumours and plans, so it would be nice to have concrete details, before any fp-on-jvm implementation design starts to rely on this. Claus [1] http://openjdk.java.net/projects/mlvm/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Multi-module scripts
As long as OtherModule is in the same directory, Main should have no trouble finding it. Do you mean like this? $ ls Greet.hs hello* $ cat hello #!/usr/bin/env runghc module Main where import Greet main = putStrLn (greet world) $ cat Greet.hs module Greet (greet) where greet :: String - String greet s = hello ++ s $ ./hello hello world Greg On 2009-Jun-26, Maurício wrote: Is it possible to write a Haskell script that uses a module that is also going to be interpreted? Like, say: #!/usr/bin/runhaskell module Main (main) where import OtherModule main = (...) where OtherModule is available in, say, OtherModule.hs and not in the already compiled and installed library? Thanks, Maurício ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe -- ___ ___ __ _ / _ \ / _ \| || | Gregory D. Weber, Associate Professor / /_\// / | | | /\ | | Indiana University East / /_\\/ /__| | |/ \| | http://mypage.iu.edu/~gdweber/ \/\_/\___/\__/ Tel. (765) 973-8420; FAX (765) 973-8550 ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] download, download-curl ...
Hello Cafe, I'm looking to make it possible for people to use urls directly in my haskell program (TxtSushi) and I'd like your suggestions if you have any. I really like the API's for download and download-curl, but I'm wondering what the practical differences are between the two? Is download-curl a replacement for download? Will it build OK on any platform or do I have to use something like the HTTP library if I want it to work for people with Windows? (I really like the fact that the download APIs support FTP too though) Thank You Keith -- keithsheppard.name ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] download, download-curl ...
keithshep: Hello Cafe, I'm looking to make it possible for people to use urls directly in my haskell program (TxtSushi) and I'd like your suggestions if you have any. I really like the API's for download and download-curl, but I'm wondering what the practical differences are between the two? Is download-curl a replacement for download? Will it build OK on any platform or do I have to use something like the HTTP library if I want it to work for people with Windows? (I really like the fact that the download APIs support FTP too though) They're essentially identical, but under the hood one is using curl, one is using libdownload. libdownload isn't really portable outside of linux. -- Don ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] System.Vacuum.Ubigraph
Hi, The package seems to have a connection problem on my machine. Prelude import System.Vacuum.Ubigraph Prelude System.Vacuum.Ubigraph view (0,1) Loading package syb ... linking ... done. Loading package base-3.0.3.1 ... linking ... done. Loading package parsec-2.1.0.1 ... linking ... done. Loading package network-2.2.1.3 ... linking ... done. Loading package array-0.2.0.0 ... linking ... done. Loading package containers-0.2.0.1 ... linking ... done. Loading package bytestring-0.9.1.4 ... linking ... done. Loading package old-locale-1.0.0.1 ... linking ... done. Loading package old-time-1.0.0.2 ... linking ... done. Loading package pretty-1.0.1.0 ... linking ... done. Loading package filepath-1.1.0.2 ... linking ... done. Loading package unix-2.3.2.0 ... linking ... done. Loading package directory-1.0.0.3 ... linking ... done. Loading package process-1.0.1.1 ... linking ... done. Loading package random-1.0.0.1 ... linking ... done. Loading package haskell98 ... linking ... done. Loading package mtl-1.1.0.2 ... linking ... done. Loading package time-1.1.3 ... linking ... done. Loading package vacuum-0.0.95 ... linking ... done. Loading package HTTP-4000.0.7 ... linking ... done. Loading package HaXml-1.13.3 ... linking ... done. Loading package dataenc-0.13.0.0 ... linking ... done. Loading package haxr-3000.2.1 ... linking ... done. Loading package vacuum-ubigraph-0.1.0.3 ... linking ... done. *** Exception: user error (Error calling ubigraph.clear: �: openFile: does not exist (No such file or directory)) In ubigraph.clear: �: openFile: the part between clear and openFile is not always the same character or sequence of characters! I guess it's a problem with Network.XmlRpc.Client but couldn't locate it. Anyone else that has (had) this problem? Best Regards, Cetin Sert ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Haskell on JVM
On Fri, Jun 26, 2009 at 03:26:34PM +0200, Maarten Hazewinkel wrote: On 26 Jun 2009, at 14:09, Timo B. Hübel wrote: And here comes my question: If there is anybody with proper knowledge about this issue, I would really like to know what are those things that are missing? For example, Clojure lacks proper tail recrusion optimization due to some missing functionality in the JVM. But does anybody know the details? Basically, the JVM lacks a native ability to do tail calls. It does not have an instruction to remove/replace a stack frame without executing an actual return to the calling method/function. With the heavy use of recursion in functional programs, this is an important feature in a language implementation to avoid stack overflows. This is part of the reason I think jhc might be a good haskell compiler for the jvm, it requires no special tail call support of its back end. It translates all recursion into explicit code flow operations. (even complex things, like co-recursive functions and join points) John -- John Meacham - ⑆repetae.net⑆john⑈ - http://notanumber.net/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Rigid type variable error
From: Darryn djr...@aapt.net.au To: beginn...@haskell.org Subject: Rigid type variables match error Date: Sat, 27 Jun 2009 10:18:13 +0930 Hi, I wonder if anyone can explain what is going on here and what to do about it. I'm fairly new to Haskell, so apologies in advance if my question seems naive. I've cut my code down to a minimum that reproduces the problem. I receive an error in GHCI in the following code, complaining that it cannot match the rigid type variables for the instance definition for Ainst for the function a3. Can anyone advise about what to do about it? class A a where a1 :: a a2 :: a - a a3 :: (B b) = b - a class B b where b1 :: Int - b data (B b) = Ainst b = I | J (Ainst b) | K b instance (B b) = A (Ainst b) where a1 = I -- a2 :: (B b, A a) = a - a a2 = J -- a3 :: (B b, A a) = b - a a3 = K -- Error! -- a3 = K `asTypeOf` a3 -- Error even with this! data Binst = Val Int instance B Binst where b1 = Val Test5.hs:17:9: Couldn't match expected type `b1' against inferred type `b' `b1' is a rigid type variable bound by the instance declaration at Test5.hs:12:12 `b' is a rigid type variable bound by the type signature for `a3' at Test5.hs:5:13 Expected type: b - Ainst b1 Inferred type: b - Ainst b In the expression: K `asTypeOf` a3 In the definition of `a3': a3 = K `asTypeOf` a3 Failed, modules loaded: none. Thanks in advance for any help anyone can provide. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
