Re: [Haskell-cafe] Re: Data.Binary Endianness
On Monday 10 September 2007 21:02, apfelmus wrote: [...] class Put a endian where put :: endian - a - Put [...] Oh, and the 8,16,32 and 64 are good candidates for phantom type/associated data types, too. I think that using any non-H98 feature like MPTC or associated data types for such a generally useful and basic package would be a *big* mistake. Let's follow the KISS principle here. Everybody is free to make a nicer, but non-portable wrapper... Cheers, S. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Data.Binary Endianness
On Monday 10 September 2007 19:50, Thomas Schilling wrote: [...] instance Binary MP3 where get = MP3 $ getHeader * getData -- [*] where getHeader = do magic - getWord32le case magic of ... Of course this works in the sense that it compiles, but Binary is conceptually the wrong class to use. to read a (IEEE) double you use do x - (get :: Double); ... :Where is IEEE mentioned in the docs? Does it use LE/BE/host order? Plain get/put on Float/Double are useless for reading IEEE floating numbers. Cheers, S. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Data.Binary Endianness
sven.panne: On Monday 10 September 2007 19:50, Thomas Schilling wrote: [...] instance Binary MP3 where get = MP3 $ getHeader * getData -- [*] where getHeader = do magic - getWord32le case magic of ... Of course this works in the sense that it compiles, but Binary is conceptually the wrong class to use. I wouldn't go as far as saying `wrong', for protocol-specific data types it seems reasonable for the Haskell serialisation to use an agreed-upon external format, via a Binary instance. It's cute, anyway. -- Don ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Data.Binary Endianness
On Tuesday 11 September 2007 08:14, Don Stewart wrote: sven.panne: On Monday 10 September 2007 19:50, Thomas Schilling wrote: [...] instance Binary MP3 where get = MP3 $ getHeader * getData -- [*] where getHeader = do magic - getWord32le case magic of ... Of course this works in the sense that it compiles, but Binary is conceptually the wrong class to use. I wouldn't go as far as saying `wrong', for protocol-specific data types it seems reasonable for the Haskell serialisation to use an agreed-upon external format, via a Binary instance. The question is: What is the *human reader* suggested when he sees a signature like foo :: Binary a = ... - a - ...? This should probably mean foo is using some portable (de-)serialization, but doesn't care about the actual representation, at least this is how I understand Binary's contract from the Haddock docs. The example above means something completely different, so I propose to add another class (e.g. ExternalBinary, better name needed) to the binary package for such uses. This class wouldn't have any instances in the package itself, but at least it would set a standard, so things are crystal clear when one sees a signature like blah :: ExternalBinary a = ... - a - This situation is very similar to the OO-world, where class inheritance is often overused, just because it looks so handy when written initially and delegation/aggregation/... would be the conceptually right way (i.e. implementation hierarchy vs. interface hierarchy). Cheers, S. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Data.Binary Endianness
On Monday 10 September 2007 19:26, Don Stewart wrote: Yep, just send a patch. Or suggest what needs to happen. OK, I'll see what I can do next weekend, currently I'm busy with packaging/fixing GHC. I have similar code lying around in various places, and it would be nice if there was a more officially sanctioned place to put this. Cheers, S. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Data.Binary Endianness
sven.panne: On Monday 10 September 2007 19:26, Don Stewart wrote: Yep, just send a patch. Or suggest what needs to happen. OK, I'll see what I can do next weekend, currently I'm busy with packaging/fixing GHC. I have similar code lying around in various places, and it would be nice if there was a more officially sanctioned place to put this. Just in case people didn't see, the `binary' package lives on http://darcs.haskell.org/binary/ However, Lennart Kolmodin, Duncan and I are actively maintaining and reviewing patches, so send them to one (or all) of us for review. -- Don ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Data.Binary Endianness
* apfelmus wrote: It's not that related, but I just got struck by an obvious idea, namely to put the endianness in an extra parameter data Endianness = Little | Big | Host putInt32 :: Endianness - Int - Put Please add the endianess to the state of the monad Put. setendianess :: Endianness - Put And for convinience please add the Network constructor to the type Endianness. ,-) ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Can somebody give any advice for beginners?
haskell is greate but i don't know how to start. 2007-09-11 clisper ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Data.Binary Endianness
On Tue, 2007-09-11 at 09:10 +0200, Sven Panne wrote: foo :: Binary a = ... - a - ...? This should probably mean foo is using some portable (de-)serialization, but doesn't care about the actual representation, I'm probably missing something, but: How can the format be portable if the representation isn't unambigously defined? And if it is unabmigously defined, what's wrong with using it for externally defined data formats? -k ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Building production stable software in Haskell
The way I see it as a newcomer, Haskell shifts the typical imperical programming bugs like null pointers and buffer overruns towards space/time leaks, causing programs that either take exponentially long to complete, stack overflow, or fill up the swap file on disc because they consume gigabytes of memory. Other bugs I found are incomplete pattern matches at runtime, but I already got an email of how to fix this using an external tool, although it would be nice if this is part of the compiler/linker itself. How well and how can a Haskell program be tested to make sure it does not cause these space/time bugs? What tools are typically used? Thanks, Peter ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Building production stable software in Haskell
Hi Peter, The way I see it as a newcomer, Haskell shifts the typical imperical programming bugs like null pointers and buffer overruns towards space/time leaks, causing programs that either take exponentially long to complete, stack overflow, or fill up the swap file on disc because they consume gigabytes of memory. Time bugs are quite rare - usually a simple profiling will fix them up, and they are exactly the same sorts of bugs that exist in an imperative programming language. Usually its a case of picking a better algorithm, or thinking clever thoughts. Space leaks are much more tricky - there are profiling tools, but I've never got enough experience using them to say anything more than that. Other bugs I found are incomplete pattern matches at runtime, but I already got an email of how to fix this using an external tool Did the email suggest using Catch? http://www-users.cs.york.ac.uk/~ndm/catch/ If you care enough about pattern matching, you can eliminate them all statically. Thanks Neil ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Can somebody give any advice for beginners?
Because I had a background in videogame development, I purchased The Haskell School of Expression. I found this a great book, but it has a fast pace, so be prepared. To me, Haskell was a bit like climbing a mountain which is largely covered by fog; you don't see anything until you've climbed high enough, and then the view is really beautiful ;-) Peter clisper wrote: haskell is greate but i don't know how to start. 2007-09-11 clisper ___ 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] Licenses and Libraries
Hello, I have some questions connected more with the licenses and libraries as the language itself: Is it possible to: - publish Haskell source code under the BSD3 license - provide an executable binary together with the code including (compiled e.g. with 'ghc --make') standard (in the ghc compiler download) libraries of the base and/or other packages - publish Haskell source code under the BSD3 license which will work with GTK2HS - provide an executable binary together with the code compiled with 'ghc -- make' - does there have to be any special flags set to do so - does there have to be included further notes about the libraries and/or there license -- Thanks in advance, H. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Building production stable software in Haskell
Well, I actually meant more something like the imperative equivalences of code coverage tools and unit testing tools, because I've read rumors that in Haskell, unit testing is more difficult because lazy evaluation will cause the units that got tested to be evaluated completely different depending on how they are used. In strict languages, this is not the case. Neil Mitchell wrote: Hi Peter, The way I see it as a newcomer, Haskell shifts the typical imperical programming bugs like null pointers and buffer overruns towards space/time leaks, causing programs that either take exponentially long to complete, stack overflow, or fill up the swap file on disc because they consume gigabytes of memory. Time bugs are quite rare - usually a simple profiling will fix them up, and they are exactly the same sorts of bugs that exist in an imperative programming language. Usually its a case of picking a better algorithm, or thinking clever thoughts. Space leaks are much more tricky - there are profiling tools, but I've never got enough experience using them to say anything more than that. Other bugs I found are incomplete pattern matches at runtime, but I already got an email of how to fix this using an external tool Did the email suggest using Catch? http://www-users.cs.york.ac.uk/~ndm/catch/ If you care enough about pattern matching, you can eliminate them all statically. Thanks Neil ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Can somebody give any advice for beginners?
On 11/09/2007, Peter Verswyvelen [EMAIL PROTECTED] wrote: To me, Haskell was a bit like climbing a mountain which is largely covered by fog; you don't see anything until you've climbed high enough, and then the view is really beautiful ;-) Either that or: the foothills are glorious, but as soon as you get into the higher altitudes you can fall down a monad and not be able to escape... D. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Building production stable software in Haskell
Hi
Well, I actually meant more something like the imperative equivalences
of code coverage tools and unit testing tools,
hpc and HUnit cover these two things pretty perfectly. hpc will be in
GHC 6.8, and its really cool :-)
because I've read
rumors that in Haskell, unit testing is more difficult because lazy
evaluation will cause the units that got tested to be evaluated
completely different depending on how they are used. In strict
languages, this is not the case.
That's a really weird statement, and one that goes completely opposite
to my view of things. Do you have sources for these rumours? In a pure
language, if you evaluate some code it will do exactly the same thing
every time - there is no different behaviour. If you test the code,
then run it again later, you'll get the same result. Compare that to
something like C where:
int breakRandomly = 0;
int return42()
{
breakRandomly = !breakRandomly;
return (breakRandomly ? 666 : 42);
}
In C you can test this, and it will work, then you can test it twice
with identical values, and it will break.
Lazy evaluation can hide bugs if you only demand some small portion of
the output, but if your property/test is constructed properly, you
shouldn't have any problem.
Thanks
Neil
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Re[2]: [Haskell-cafe] Data.Binary Endianness
Hello Sven, Tuesday, September 11, 2007, 11:10:17 AM, you wrote: Haddock docs. The example above means something completely different, so I propose to add another class (e.g. ExternalBinary, better name needed) to this looks correct form theoretical POV but don't forget that then you will need to redefine each and every function working on Binary instances -- Best regards, Bulatmailto:[EMAIL PROTECTED] ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Data.Binary Endianness
Ketil Malde wrote: On Tue, 2007-09-11 at 09:10 +0200, Sven Panne wrote: foo :: Binary a = ... - a - ...? This should probably mean foo is using some portable (de-)serialization, but doesn't care about the actual representation, I'm probably missing something, but: How can the format be portable if the representation isn't unambigously defined? And if it is unabmigously defined, what's wrong with using it for externally defined data formats? It's portable because it works on other machines also running that exact version of Data.Binary, regardless of their CPU architecture (in particular, word size or endianness). That is the precise sense of 'portable' used here. The actual format used by Data.Binary is not explicitly described in any standard (although in most cases it's moderately obvious, and anyone can read the code), and it's not formally guaranteed that it will never change in a later version (although the maintainers will no doubt try very hard to ensure it doesn't); nor does it contain any automatic support for version-stamping to ensure backwards compatibility in the face of later unlooked-for format changes. For these reasons, although it is very cool, I don't think it can be recommended as a basis for long-term file format definitions. (All of the above speaks of the 'high-level' Data.Binary not the 'low-level'.) Jules ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Data.Binary Endianness
On Tue, 2007-09-11 at 12:01 +0100, Jules Bean wrote: How can the format be portable if the representation isn't unambigously defined? And if it is unabmigously defined, what's wrong with using it for externally defined data formats? It's portable because it works on other machines also running that exact version of Data.Binary, regardless of their CPU architecture (in particular, word size or endianness). That is the precise sense of 'portable' used here. Okay. Data.Binary is not for persistence, then (since the format may change between versions of the library, and presumably between different compilers/RTS), but merely for transient serializing, as over a network connection. This isn't so obvious from the documentation (I myself have blatantly used it for persistence and for reading in externally specified data), and the functions involving FilePaths also tend confusing the issue here. Perhaps it could be made clearer? Another way to avoid abuse of Data.Binary would be to add a unique magic number to each stream, and throw an exception when a mismatching magic number is encountered. -k ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Data.Binary Endianness
Ketil Malde wrote: On Tue, 2007-09-11 at 12:01 +0100, Jules Bean wrote: How can the format be portable if the representation isn't unambigously defined? And if it is unabmigously defined, what's wrong with using it for externally defined data formats? It's portable because it works on other machines also running that exact version of Data.Binary, regardless of their CPU architecture (in particular, word size or endianness). That is the precise sense of 'portable' used here. Okay. Data.Binary is not for persistence, then (since the format may change between versions of the library, and presumably between different compilers/RTS), but merely for transient serializing, as over a network connection. I probably came over stronger than I intended. It is intended for persistence, too. My point is that, should a bug be discovered in Data.Binary, the maintainers may be forced to change the format and there is no mechanism in place for coping with that. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
RE: [Haskell-cafe] Building production stable software in Haskell
That's a really weird statement, and one that goes completely opposite to my view of things. Do you have sources for these rumours? In a pure language, if you evaluate some code it will do exactly the same thing every time - there is no different behaviour. If you test the code, Sorry, I did not express myself correctly I guess. I did not mean different behavior regarding the results that are computed (because that's the great thing about Haskell; this is called referentially transparent isn't it?), but I meant different time/space behavior. I'm not sure where I read this rumor, but if I recall correctly, it had to do with FRP (functional reactive programming), where it was stated that is was really difficult to make sure that no space/time leaks occurred when the user started combining functions in some way. But I might have understood it incorrectly; after all, I'm still in the learning process. Peter ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
RE: [Haskell-cafe] Can somebody give any advice for beginners?
LOL! Another problem is that I always have to descend again for my main job which involves C#/C++, and all that climbing up and down is *very* tiersome. Peter -Original Message- From: Dougal Stanton [mailto:[EMAIL PROTECTED] Sent: Tuesday, September 11, 2007 12:44 PM To: [EMAIL PROTECTED] Cc: clisper; Haskell-Cafe Subject: Re: [Haskell-cafe] Can somebody give any advice for beginners? On 11/09/2007, Peter Verswyvelen [EMAIL PROTECTED] wrote: To me, Haskell was a bit like climbing a mountain which is largely covered by fog; you don't see anything until you've climbed high enough, and then the view is really beautiful ;-) Either that or: the foothills are glorious, but as soon as you get into the higher altitudes you can fall down a monad and not be able to escape... D. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Data.Binary Endianness
On Sep 11, 2007, at 7:01 , Jules Bean wrote: The actual format used by Data.Binary is not explicitly described in any standard (although in most cases it's moderately obvious, and anyone can read the code), and it's not formally guaranteed that it will never change in a later version (although the maintainers will no doubt try very hard to ensure it doesn't); nor does it contain any automatic support for version-stamping to ensure backwards compatibility in the face of later unlooked-for format changes. I will just point out that, while this is one extreme, the other extreme is ASN.1. I think we want to walk the middle path instead -- brandon s. allbery [solaris,freebsd,perl,pugs,haskell] [EMAIL PROTECTED] system administrator [openafs,heimdal,too many hats] [EMAIL PROTECTED] electrical and computer engineering, carnegie mellon universityKF8NH ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: Tiny documentation request
Sven Panne wrote: 2. Could we make is so all items are collapsed initially? (Currently they're all expended initially - which makes it take rather a long time to find anything.) Again this depends on the use case: I'd vote strongly against collapsing the list initially, because that way the incremental search in Firefox won't work without un-collapsing everything. This is exactly why the list is expanded by default. At first I made it default to collapsed, and people complained (possibly Sven, in fact :-). When the index is generated with a more recent Haddock, you get a search field, which does an incremental search, so this might perhaps be more what you are looking for. A more aesthetical note: We should really get rid of the ugly table/CSS layout mixture, the lower part of the page renders a bit ugly and varies between browsers. Switching to pure CSS should be safe in 2007, I guess. Please, please, someone do this for me. I tried, and failed, to get the layout right for the contents list in all browsers at the same time. The semantics of CSS is beyond my comprehension. Cheers, Simon ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Can somebody give any advice for beginners?
On 9/11/07, clisper [EMAIL PROTECTED] wrote: haskell is greate but i don't know how to start. A good place to start is the Haskell wiki: http://haskell.org/haskellwiki/Haskell On the left, look under Learning Haskell -- there's all kinds of great stuff linked from there. I would also suggest hanging out in the #haskell IRC channel on irc.freenode.net -- it's a great place to learn and ask questions. If you give us more information about your programming/mathematics background, why you're learning Haskell, what you hope to get out of it, etc. I'm sure people could also give you some more specific suggestions. -Brent ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: Tiny documentation request
Thomas Schilling wrote: However, regarding the modules list. I think it should be easy to have optional javascript functionality to toggle the visibility of the module tree. The default visibility could be customized using a cookie. I don't know how to make cookies work purely in Javascript - presumably there's a way, though. I'm accepting patches! Cheers, Simon ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Tiny documentation request
Andrew Coppin wrote: OTOH, I recently discovered that GHCi has the ability to show you what's defined in a given module without me having to wait 40 seconds for Firefox to start... Shame you can't scroll its output. (And still no help if you're not sure of the module name.) !!! Run ghci in an environment with a scroll buffer then? Like a non-braindead terminal application, or emacs? (The latter even gives you convenient reverse-incremental-search to search through the info you just printed) Jules ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] haskell and reflection
Haskellians, Am i wrong in my assessment that the vast majority of reflective machinery is missing from Haskell? Specifically, - there is no runtime representation of type available for programmatic representation - there is no runtime representation of the type-inferencing or checking machinery - there is no runtime representation of the evaluation machinery - there is no runtime representation of the lexical or parsing machinery Best wishes, --greg -- L.G. Meredith Managing Partner Biosimilarity LLC 505 N 72nd St Seattle, WA 98103 +1 206.650.3740 http://biosimilarity.blogspot.com ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Building production stable software in Haskell
On Tue, Sep 11, 2007 at 01:59:40PM +0200, Peter Verswyvelen wrote: That's a really weird statement, and one that goes completely opposite to my view of things. Do you have sources for these rumours? In a pure language, if you evaluate some code it will do exactly the same thing every time - there is no different behaviour. If you test the code, Sorry, I did not express myself correctly I guess. I did not mean different behavior regarding the results that are computed (because that's the great thing about Haskell; this is called referentially transparent isn't it?), but I meant different time/space behavior. I'm not sure where I read this rumor, but if I recall correctly, it had to do with FRP (functional reactive programming), where it was stated that is was really difficult to make sure that no space/time leaks occurred when the user started combining functions in some way. But I might have understood it incorrectly; after all, I'm still in the learning process. Yeah, that makes sense. Space leaks are tricky, and unit testing can only verify that under particular usage scenarios they don't occur, but in another case they might pop up. Generally, strict data types can help a lot in preventing space leaks, but can't always solve the problems. I long for a Data.Map.Strict, for instance, because it's so hard to use Data.Map without producing memory leaks... -- David Roundy Department of Physics Oregon State University ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] haskell and reflection
Hi there is no runtime representation of type available for programmatic representation Data.Typeable.typeOf :: Typeable a = a - TypeRep there is no runtime representation of the type-inferencing or checking machinery Pretty much, no. The GHC API may provide some. there is no runtime representation of the evaluation machinery Yhc provides some representation with the Yhc API. there is no runtime representation of the lexical or parsing machinery lex provides some of this. There are various Haskell parsers out there in packages for us. I wouldn't have considered these things reflection - certainly the Java/C# use of the word reflection is quite different. Data.Generics does provide many of the reflection capabilities of Java. Thanks Neil ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] haskell and reflection
Neil, Thanks very much for the detailed response. When we did Rosette, a reflective actor-based language, back in the late '80's and early '90's, we were very much influenced by Brian Cantwell Smith's account of reflection in 3-Lisp and similarly by Friedman and Wand's Mystery of the Tower Revealed. Our analysis suggested the following breakdown - Structural reflection -- all data used in the evaluation of programs has a programmatic representation - Procedural reflection -- all execution machinery used in the evaluation of programs has a programmatic representation The Java notion of reflection is restricted entirely to the first case and then only to the data used once a normalized representation has been achieved. In fact, lexing and parsing are of considerable interest and complexity in the evaluation of programs and reflective access is extremely useful. Likewise, access to the evaluation machinery itself is of more than theoretical interest. For example, in an ATM network management system i wrote in Rosette, i used reflective methods -- where the evaluation itself could be captured, stored and manipulated, much like a 1-shot continuation -- to make a polling interface of an external trouble-ticketing system we were required by business constraints to interface with look like an interrupt-driven interface to the Rosette-based clients. Best wishes, --greg On 9/11/07, Neil Mitchell [EMAIL PROTECTED] wrote: Hi there is no runtime representation of type available for programmatic representation Data.Typeable.typeOf :: Typeable a = a - TypeRep there is no runtime representation of the type-inferencing or checking machinery Pretty much, no. The GHC API may provide some. there is no runtime representation of the evaluation machinery Yhc provides some representation with the Yhc API. there is no runtime representation of the lexical or parsing machinery lex provides some of this. There are various Haskell parsers out there in packages for us. I wouldn't have considered these things reflection - certainly the Java/C# use of the word reflection is quite different. Data.Generics does provide many of the reflection capabilities of Java. Thanks Neil -- L.G. Meredith Managing Partner Biosimilarity LLC 505 N 72nd St Seattle, WA 98103 +1 206.650.3740 http://biosimilarity.blogspot.com ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] haskell and reflection
Greg Meredith wrote: Haskellians, Am i wrong in my assessment that the vast majority of reflective machinery is missing from Haskell? Specifically, * there is no runtime representation of type available for programmatic representation * there is no runtime representation of the type-inferencing or checking machinery * there is no runtime representation of the evaluation machinery * there is no runtime representation of the lexical or parsing machinery As far as they go, those are true. Haskell compiler are permitted to erase types and GHC does so. There is no need to check types at runtime; that's the point of the system! There is no evaluator, or parser, built in to the standard libraries. (The lexer, or a version of it, is embedded in actual fact but that's not very exciting). However, one should not draw too strong negative conclusions from this. It is possible to get suprisingly far with more powerful, more typesafe techniques without surrendering the the pure dynamism of languages that lack compile-time guarantees. Deriving Typeable and Data is one tool which is useful. It is quite possible to embed a haskell compiler, see hs-plugins. Jules ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Data.Binary Endianness
So the answer for persistence is Data.Binary - ASN.1 converter that can be used in extrema? On 11/09/2007, Brandon S. Allbery KF8NH [EMAIL PROTECTED] wrote: On Sep 11, 2007, at 7:01 , Jules Bean wrote: The actual format used by Data.Binary is not explicitly described in any standard (although in most cases it's moderately obvious, and anyone can read the code), and it's not formally guaranteed that it will never change in a later version (although the maintainers will no doubt try very hard to ensure it doesn't); nor does it contain any automatic support for version-stamping to ensure backwards compatibility in the face of later unlooked-for format changes. I will just point out that, while this is one extreme, the other extreme is ASN.1. I think we want to walk the middle path instead -- brandon s. allbery [solaris,freebsd,perl,pugs,haskell] [EMAIL PROTECTED] system administrator [openafs,heimdal,too many hats] [EMAIL PROTECTED] electrical and computer engineering, carnegie mellon universityKF8NH ___ 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] Building production stable software in Haskell
On 9/11/07, Peter Verswyvelen [EMAIL PROTECTED] wrote: How well and how can a Haskell program be tested to make sure it does not cause these space/time bugs? What tools are typically used? I've been fighting this myself. I had an especially nasty stack-overflow that took me weeks to track down. Of course, when I did, I used the tried-and-true divide-and-conquer approach. I found a case where my program consistently crashed, then I added output to see what was executed just before hand (luckily I was already in the IO monad). Finally, I wrote a test program that crashed the same way and was able to fix the bug. ANd, of course, it turned out to be my usage of foldr' - which is what I should have focused on first. Oh well. As for memory usage, I've been using the heap profiling tools in GHC quite a bit. They are scary at first, because they require you to compare postscript graphs, but once you spend some time with them they are actually very useful. This article describes an early version of the tools in GHC: http://citeseer.ist.psu.edu/runciman96heap.html And a web search using Heap profiling for space efficiency in functional programs gives some nice results. Justin ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: Tiny documentation request
On Sep 11, 2007, Simon Marlow wrote: Please, please, someone do this for me. I tried, and failed, to get the layout right for the contents list in all browsers at the same time. The semantics of CSS is beyond my comprehension. Cheers, Simon Hi Simon, On the page http://www.haskell.org/ghc/docs/latest/html/libraries/ index.html, you only need tables to display the foldable lists of modules (HTML tables were commonly used to display many things on a same line), but they can be replaced by nested lists with a bit of CSS : Check this page out : http://la.di.da.free.fr/haddock/ I can help further, if need be. Emmanuel ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Data.Binary Endianness
Jules Bean wrote: For these reasons, although it is very cool, I don't think it can be recommended as a basis for long-term file format definitions. Indeed, the authors have never claimed that this is what it's for. Unfortunately, because the authors haven't *disclaimed* this as a purpose, people have fairly reasonably assumed that this *is* the intent of the package. In conversations with Don and Duncan, they've always been quite clear that Data.Binary is intended to shovel bits rapidly and with a reasonable interface. All of the things of which you speak, and more useful ones such as RTTI and representation of cyclic data, ought to live in a higher-level library. Said library merely hasn't been written yet. (All of the above speaks of the 'high-level' Data.Binary not the 'low-level'.) Data.Binary *is* the low-level Data.Binary :-) b ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Data.Binary Endianness
Bryan O'Sullivan wrote: (All of the above speaks of the 'high-level' Data.Binary not the 'low-level'.) Data.Binary *is* the low-level Data.Binary :-) I was distinguishing between these two levels: (1) High-level = Binary typeclass. Contains instances for many, many useful common types, the internals of which you don't need to understand to use them. But then you wont' understand the format used. Which doesn't matter if all you want to do is pipe stuff around. (2) Low-level = Get and Put typeclasses. Allow you to shovel bytes as you wish, including bundling them up into words of various sizes with explicit endian-ness control. You can sensibly use this to define file formats precisely with some reasonable expectation of speed. You could for example write a TIFF reader (and writer [*]) using these primitives. Jules [*] - exercise for the reader: Can you write a TIFF reader and writer simultaneously, in the sense that you define the file format once and get Get and Put instances for free? ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] haskell and reflection
Jules, Thanks for these comments. i wouldn't judge Haskell solely on the basis of whether it embraced reflection as an organizing computational principle or as a toolbox for programmers. Clearly, you can get very far without it. And, it may be that higher-order functional gives you enough of the 'programs that build programs' capability that 80% of the practical benefits of reflection are covered -- without having to take on the extra level of complexity that reflection adds to typing. i was really just seeking information. Best wishes, --greg On 9/11/07, Jules Bean [EMAIL PROTECTED] wrote: Greg Meredith wrote: Haskellians, Am i wrong in my assessment that the vast majority of reflective machinery is missing from Haskell? Specifically, * there is no runtime representation of type available for programmatic representation * there is no runtime representation of the type-inferencing or checking machinery * there is no runtime representation of the evaluation machinery * there is no runtime representation of the lexical or parsing machinery As far as they go, those are true. Haskell compiler are permitted to erase types and GHC does so. There is no need to check types at runtime; that's the point of the system! There is no evaluator, or parser, built in to the standard libraries. (The lexer, or a version of it, is embedded in actual fact but that's not very exciting). However, one should not draw too strong negative conclusions from this. It is possible to get suprisingly far with more powerful, more typesafe techniques without surrendering the the pure dynamism of languages that lack compile-time guarantees. Deriving Typeable and Data is one tool which is useful. It is quite possible to embed a haskell compiler, see hs-plugins. Jules -- L.G. Meredith Managing Partner Biosimilarity LLC 505 N 72nd St Seattle, WA 98103 +1 206.650.3740 http://biosimilarity.blogspot.com ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: Can somebody give any advice for beginners?
clisper clisper at 163.com writes: haskell is greate but i don't know how to start. Don't! Learning Haskell will change your world! For worse! Really! Don't do that, you still have time to go back! Or be damned like all of us here... Referential transparency will suck up your soul. You'll think about monads as your warm and fuzzy friends. You'll wash your hands after doing IO because you'll feel that your purity suffered. You'll consider unit testing a downgraded form of static typing. When your programs finally compile, they will magically just work. You'll write less and less KLOC, doing more at the same time. Your C#/C++/Java code will look like higher order code after first order transformation done by hand. Your co-workers and friends will not understand what you wrote any more. You'll be like a wizard from another planet for them. You will know the difference between foldl and foldr. All your data structures will be infinite in size. Space leaks will bite you hard. Your functions will be not lazy enough in some arguments and not strict enough in some others at the same time. And even seq will not help you. You'll know what MPTCs and GADTs are. You'll actually understand olegs posts. You'll wonder, what was that OO thing again? You'll take out Java from your CV. Take a friendly advice: go back and forget that you ever heard about Haskell! -- Gracjan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Can somebody give any advice for beginners?
On Tue, 2007-09-11 at 16:55 +, Gracjan Polak wrote: clisper clisper at 163.com writes: haskell is greate but i don't know how to start. Don't! Learning Haskell will change your world! For worse! Really! Don't do that, you still have time to go back! Or be damned like all of us here... Referential transparency will suck up your soul. You'll think about monads as your warm and fuzzy friends. You'll wash your hands after doing IO because you'll feel that your purity suffered. You'll consider unit testing a downgraded form of static typing. When your programs finally compile, they will magically just work. You'll write less and less KLOC, doing more at the same time. Your C#/C++/Java code will look like higher order code after first order transformation done by hand. Your co-workers and friends will not understand what you wrote any more. You'll be like a wizard from another planet for them. You will know the difference between foldl and foldr. And never to use either one. Long live foldl'! All your data structures will be infinite in size. Space leaks will bite you hard. Your functions will be not lazy enough in some arguments and not strict enough in some others at the same time. And even seq will not help you. You'll know what MPTCs and GADTs are. You'll actually understand olegs posts. You'll wonder, what was that OO thing again? You'll take out Java from your CV. Take a friendly advice: go back and forget that you ever heard about Haskell! jcc ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] haskell and reflection
On Tue, Sep 11, 2007 at 07:33:54AM -0700, Greg Meredith wrote: Our analysis suggested the following breakdown - Structural reflection -- all data used in the evaluation of programs has a programmatic representation - Procedural reflection -- all execution machinery used in the evaluation of programs has a programmatic representation The Java notion of reflection is restricted entirely to the first case Then what would you call ClassLoader.defineClass? As for Haskell, there are various tools for both (at least Data.Typeable and hs-plugins), but neither are truly type-safe: it is possible to write code that uses these libraries and type-checks, yet crashes. Static typing makes reflection very difficult to support safely. You might be interested in my MS thesis, where I explored these issues in some more length: http://www.cs.helsinki.fi/u/lealanko/alanko04types.pdf Lauri ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Basic FFI with GHC
How do I create C-libraries that I can load into GHCi? I am trying to
do some basic FFI, and it's not working.
Here's the background. I created three files, foo.h, foo.cpp, and
test_foo.lhs. (source code below)
Note: I am using MinGW/Msys under Windows XP.
If I compile foo.cpp and then try to load test_foo into GHCi, I get an
error. OTOH, if I compile test_foo with GHC, it works. I just don't
understand why it works one way and not the other.
What am I doing wrong?
-- Ron
--
Shell commands
--
$ gcc -c foo.cpp
$ ghci test_foo.lhs foo.o
___ ___ _
/ _ \ /\ /\/ __(_)
/ /_\// /_/ / / | | GHC Interactive, version 6.6.1, for Haskell 98.
/ /_\\/ __ / /___| | http://www.haskell.org/ghc/
\/\/ /_/\/|_| Type :? for help.
Loading package base ... linking ... done.
Loading object (static) foo.o ... done
final link ... done
[1 of 1] Compiling Main ( test_foo.lhs, interpreted )
During interactive linking, GHCi couldn't find the following symbol:
foo
This may be due to you not asking GHCi to load extra object files,
[snip]
$ ghc --make test_foo.lhs foo.o
[1 of 1] Compiling Main ( test_foo.lhs, test_foo.o )
Linking test_foo.exe ...
$ test_foo.exe
Entering main
y = 22
Exiting main
$ ar rcs libfoo.a foo.o
$ ghc --make test_foo.lhs -lfoo
$ test_foo.exe
Entering main
y = 22
Exiting main
$ ghci test_foo.lhs -lfoo
___ ___ _
/ _ \ /\ /\/ __(_)
/ /_\// /_/ / / | | GHC Interactive, version 6.6.1, for Haskell 98.
/ /_\\/ __ / /___| | http://www.haskell.org/ghc/
\/\/ /_/\/|_| Type :? for help.
Loading package base ... linking ... done.
Loading object (dynamic) foo ... failed.
Dynamic linker error message was:
addDLL: unknown error
Whilst trying to load: (dynamic) foo
Directories to search are:
: user specified .o/.so/.DLL could not be loaded.
--
Source code
--
// foo.h
extern C
{
__stdcall int foo(int x);
}
--
// foo.cpp
#include foo.h
__stdcall int foo(int x)
{
return 3 * x + 1;
}
--
test_foo.lhs
{-# OPTIONS_GHC -fglasgow-exts #-}
module Main
where
import Foreign
import Foreign.C
foreign import stdcall unsafe foo
c_Foo :: Word32 - IO Word32
main = do
putStrLn Entering main
let x = 7::Word32
y - c_Foo(x)
putStrLn $ y = ++ show y
putStrLn Exiting main
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Re: [Haskell-cafe] Re: Tiny documentation request
When the index is generated with a more recent Haddock, you get a search field, which does an incremental search, so this might perhaps be more what you are looking for. A more aesthetical note: We should really get rid of the ugly table/CSS layout mixture, the lower part of the page renders a bit ugly and varies between browsers. Switching to pure CSS should be safe in 2007, I guess. Please, please, someone do this for me. I tried, and failed, to get the layout right for the contents list in all browsers at the same time. The semantics of CSS is beyond my comprehension. Well, I'm not a web designer, but I did work with few of them, and it seems to me that you either create a table design in two hours or spend three days trying to create a CSS one and THEN create a table design in two hours. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] haskell and reflection
Op 11-sep-2007, om 18:43 heeft Greg Meredith het volgende geschreven: Thanks for these comments. i wouldn't judge Haskell solely on the basis of whether it embraced reflection as an organizing computational principle or as a toolbox for programmers. Clearly, you can get very far without it. And, it may be that higher-order functional gives you enough of the 'programs that build programs' capability that 80% of the practical benefits of reflection are covered -- without having to take on the extra level of complexity that reflection adds to typing. i was really just seeking information. Template Haskell [1] is a system that lets you write programs that get executed at *compile time*, and that produce parts of the Haskell program to be compiled by manipulating a representation of the program as structured data. It's a form of reflection restricted to compile time, if you'd ask me. Regards, Reinier [1] http://www.haskell.org/haskellwiki/Template_Haskell ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Building production stable software in Haskell
bf3: The way I see it as a newcomer, Haskell shifts the typical imperical programming bugs like null pointers and buffer overruns towards space/time leaks, causing programs that either take exponentially long to complete, stack overflow, or fill up the swap file on disc because they consume gigabytes of memory. Other bugs I found are incomplete pattern matches at runtime, but I already got an email of how to fix this using an external tool, although it would be nice if this is part of the compiler/linker itself. How well and how can a Haskell program be tested to make sure it does not cause these space/time bugs? What tools are typically used? Stress testing is good for catching performance bugs. And space leaks are rare, and usually glaringly obvious. Incomplete pattern matches you can avoid with -Wall and Neil's tool 'Catch'. QuickCheck should also be employed liberally. -- Don ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Building production stable software in Haskell
bf3: Well, I actually meant more something like the imperative equivalences of code coverage tools and unit testing tools, because I've read rumors that in Haskell, unit testing is more difficult because lazy evaluation will cause the units that got tested to be evaluated We have full control over evaluation though, with bang patterns, seq and deep seq. Generally unit testing is generalised to property testing with QuickCheck, though. For code coverage, combined with testing, use HPC, the program coverage tool now in GHC head. -- Don ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Data.Binary Endianness
Don Stewart wrote: Just in case people didn't see, the `binary' package lives on http://darcs.haskell.org/binary/ However, Lennart Kolmodin, Duncan and I are actively maintaining and reviewing patches, so send them to one (or all) of us for review. Right. And this is the real binary package then? (I've seen references to seemingly half a dozen binary packages, some obsolete, some not... It's rather confusing out there!) ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Can somebody give any advice for beginners?
Dougal Stanton wrote: On 11/09/2007, Peter Verswyvelen [EMAIL PROTECTED] wrote: To me, Haskell was a bit like climbing a mountain which is largely covered by fog; you don't see anything until you've climbed high enough, and then the view is really beautiful ;-) Either that or: the foothills are glorious, but as soon as you get into the higher altitudes you can fall down a monad and not be able to escape... At the risk of being told to STHU again... somebody should collect these things and keep them somewhere! ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Can somebody give any advice for beginners?
On 9/11/07, Andrew Coppin [EMAIL PROTECTED] wrote: you can fall down a monad and not be able to escape... It's not so bad. It's in the nature of monads that after you've fallen in once, you can never get trapped any deeper. -- Dan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Can somebody give any advice for beginners?
Dan Piponi wrote: On 9/11/07, Andrew Coppin [EMAIL PROTECTED] wrote: you can fall down a monad and not be able to escape... It's not so bad. It's in the nature of monads that after you've fallen in once, you can never get trapped any deeper. But you can climb higher... (Note: Best viewed in mono-space!) Programmer's Nirvana plane --- Categoric plane --- Co-Monadic plane (Co- everything) - Applicative plane -- Pointless-pointfree plane -- Monadic plane (don't get trapped) ------ Functional plane (Haskell et al!) ------ Imperative plane ASM, C#, Java :) ------ Physical plane (e.g. Silicon) -- Ron ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Can somebody give any advice for beginners?
On 9/11/07, Andrew Coppin [EMAIL PROTECTED] wrote: Dougal Stanton wrote: On 11/09/2007, Peter Verswyvelen [EMAIL PROTECTED] wrote: To me, Haskell was a bit like climbing a mountain which is largely covered by fog; you don't see anything until you've climbed high enough, and then the view is really beautiful ;-) Either that or: the foothills are glorious, but as soon as you get into the higher altitudes you can fall down a monad and not be able to escape... At the risk of being told to STHU again... somebody should collect these things and keep them somewhere! The logical place would be http://haskell.org/haskellwiki/Humor. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Tiny documentation request
Jules Bean wrote: Andrew Coppin wrote: OTOH, I recently discovered that GHCi has the ability to show you what's defined in a given module without me having to wait 40 seconds for Firefox to start... Shame you can't scroll its output. (And still no help if you're not sure of the module name.) !!! Run ghci in an environment with a scroll buffer then? Like a non-braindead terminal application, or emacs? (The latter even gives you convenient reverse-incremental-search to search through the info you just printed) I don't know if Andrew is a windows user, but if so he might not be aware that even with the (otherwise braindead) command window the number of lines buffered is a configurable property (on WinXP at least). I have it set to 1000 lines. The other thing I've found that makes the use of command line tools a lot less painful than it would otherwise be in windows is the Open Command Window Here Power Toy.. http://www.microsoft.com/windowsxp/downloads/powertoys/xppowertoys.mspx It's still nowhere near as good as the old XTree though :-( Regards -- Adrian Hey ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Data.Binary Endianness
andrewcoppin: Don Stewart wrote: Just in case people didn't see, the `binary' package lives on http://darcs.haskell.org/binary/ However, Lennart Kolmodin, Duncan and I are actively maintaining and reviewing patches, so send them to one (or all) of us for review. Right. And this is the real binary package then? (I've seen references to seemingly half a dozen binary packages, some obsolete, some not... It's rather confusing out there!) Yep. Look on hackage to get a sense of what is current. -- Don ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Licenses and Libraries
h._h._h._: Hello, I have some questions connected more with the licenses and libraries as the language itself: Is it possible to: - publish Haskell source code under the BSD3 license - provide an executable binary together with the code including (compiled e.g. with 'ghc --make') standard (in the ghc compiler download) libraries of the base and/or other packages - publish Haskell source code under the BSD3 license which will work with GTK2HS - provide an executable binary together with the code compiled with 'ghc -- make' - does there have to be any special flags set to do so - does there have to be included further notes about the libraries and/or there license You should feel entirely free to do whatever you wish with the language. Particular tools and libraries are licensed individually, and most are BSD, or more rarely LGPL or GPL licensed. BSD is preferred, and required for foundation libraries. -- Don ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] GraphicsMagick binding for Haskell
As a Hackathon project, I'm thinking of trying to write a Haskell binding for the GraphicsMagick image manipulation library (http://www.graphicsmagick.org/). Has anyone done this already? If not, would anyone else besides me use it? If you think there's a better library out there that serves a similar purpose, feel free to tell me about it as well. Cheers, Tim -- Tim Chevalier * catamorphism.org * Often in error, never in doubt Work is there when love is gone -- Greg Brown ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Is take behaving correctly?
Hi take 1000 [1..3] still yields [1,2,3] I thought it was supposed to return an error. Any ideas? Thanks, Paul ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Is take behaving correctly?
On 9/11/07, PR Stanley [EMAIL PROTECTED] wrote: Hi take 1000 [1..3] still yields [1,2,3] I thought it was supposed to return an error. Any ideas? No, that's the behavior for take specified in the Haskell 98 report: http://haskell.org/onlinereport/standard-prelude.html -- take n, applied to a list xs, returns the prefix of xs of length n, -- or xs itself if n length xs. Cheers, Tim -- Tim Chevalier * catamorphism.org * Often in error, never in doubt Modesty...is both alien and irrelevant to people who are happy in themselves, in their beings, in their skins, their natures, their capacities.--Anne Sayre ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Is take behaving correctly?
On 9/11/07, PR Stanley [EMAIL PROTECTED] wrote: Hi take 1000 [1..3] still yields [1,2,3] I thought it was supposed to return an error. Any ideas? Thanks, Paul If for some reason you want a version that does return an error in that situation, you could do something like the following: take' n _ | (n = 0) = [] take' n [] | (n 0) = error take': list too short | otherwise = [] take' n (x:xs) = x : take' (n-1) xs I'm not sure why you'd want that, though. The standard implementation gracefully handles all inputs, and usually turns out to be what you want. Really, if I were you, instead of making a version take' as above, I would just use the standard take but check for the length of the list in the places where it matters. -Brent ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Is take behaving correctly?
I suppose I'm thinking of head or tail - e.g. head [] or tail []. I'm trying to write my own version of the find function. I have a few ideas but not quite sure which would be more suitable in the context of FP. Any advice would be gratefully received - e.g. do I use recursion, list comprehension or what? Thanks, Paul At 00:08 12/09/2007, you wrote: On 9/11/07, PR Stanley [EMAIL PROTECTED] wrote: Hi take 1000 [1..3] still yields [1,2,3] I thought it was supposed to return an error. Any ideas? No, that's the behavior for take specified in the Haskell 98 report: http://haskell.org/onlinereport/standard-prelude.html -- take n, applied to a list xs, returns the prefix of xs of length n, -- or xs itself if n length xs. Cheers, Tim -- Tim Chevalier * catamorphism.org * Often in error, never in doubt Modesty...is both alien and irrelevant to people who are happy in themselves, in their beings, in their skins, their natures, their capacities.--Anne Sayre ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Is take behaving correctly?
byorgey: On 9/11/07, PR Stanley [EMAIL PROTECTED] wrote: Hi take 1000 [1..3] still yields [1,2,3] I thought it was supposed to return an error. Any ideas? Thanks, Paul If for some reason you want a version that does return an error in that situation, you could do something like the following: take' n _ | (n = 0) = [] take' n [] | (n 0) = error take': list too short | otherwise = [] take' n (x:xs) = x : take' (n-1) xs And we'd call it unsafeTake, just like unsafeFromJust and unsafeTail :-) -- Don ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Is take behaving correctly?
On 9/11/07, Don Stewart [EMAIL PROTECTED] wrote: byorgey: On 9/11/07, PR Stanley [EMAIL PROTECTED] wrote: Hi take 1000 [1..3] still yields [1,2,3] I thought it was supposed to return an error. Any ideas? Thanks, Paul If for some reason you want a version that does return an error in that situation, you could do something like the following: take' n _ | (n = 0) = [] take' n [] | (n 0) = error take': list too short | otherwise = [] take' n (x:xs) = x : take' (n-1) xs And we'd call it unsafeTake, just like unsafeFromJust and unsafeTail :-) -- Don Hmm, that's funny, I don't recall ever hearing of those functions... =) ooo, Don has a shiny new e-mail address! -Brent ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Is take behaving correctly?
On Tue, Sep 11, 2007 at 07:38:18PM -0400, Brent Yorgey wrote: On 9/11/07, PR Stanley [EMAIL PROTECTED] wrote: Hi take 1000 [1..3] still yields [1,2,3] I thought it was supposed to return an error. Any ideas? Thanks, Paul If for some reason you want a version that does return an error in that situation, you could do something like the following: take' n _ | (n = 0) = [] take' n [] | (n 0) = error take': list too short | otherwise = [] take' n (x:xs) = x : take' (n-1) xs you could also do something like take' n xs = take n (xs ++ error I want more!) John -- John Meacham - ⑆repetae.net⑆john⑈ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Is take behaving correctly?
Let me get this right, are you saying it's unsafe when it returns an error? Paul At 00:40 12/09/2007, you wrote: byorgey: On 9/11/07, PR Stanley [EMAIL PROTECTED] wrote: Hi take 1000 [1..3] still yields [1,2,3] I thought it was supposed to return an error. Any ideas? Thanks, Paul If for some reason you want a version that does return an error in that situation, you could do something like the following: take' n _ | (n = 0) = [] take' n [] | (n 0) = error take': list too short | otherwise = [] take' n (x:xs) = x : take' (n-1) xs And we'd call it unsafeTake, just like unsafeFromJust and unsafeTail :-) -- Don ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Is take behaving correctly?
prstanley: I suppose I'm thinking of head or tail - e.g. head [] or tail []. I'm trying to write my own version of the find function. I have a few ideas but not quite sure which would be more suitable in the context of FP. Any advice would be gratefully received - e.g. do I use recursion, list comprehension or what? Well, you want to filter all elements from a list that match a predicate, and then return Just the first match, or Nothing? find :: (a - Bool) - [a] - Maybe a Checking the current behaviour: find isSpace haskell is fun Just ' ' My first go would be something like this: ok, so let's start with 'filter': filter Char.isSpace haskell is fun Good, then the natural translation to the Maybe type: listToMaybe . filter isSpace $ haskell is fun Just ' ' And we're almost done. Just firing up QuickCheck: quickCheck $ \p (xs :: [Int]) - find p xs == listToMaybe (filter p xs) OK, passed 100 tests. Seems ok. I hope that gives some insight into the process of deriving Haskell implementations by building up a pipeline of pieces. -- Don ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Is take behaving correctly?
byorgey: On 9/11/07, Don Stewart [EMAIL PROTECTED] wrote: byorgey: On 9/11/07, PR Stanley [EMAIL PROTECTED] wrote: Hi take 1000 [1..3] still yields [1,2,3] I thought it was supposed to return an error. Any ideas? Thanks, Paul If for some reason you want a version that does return an error in that situation, you could do something like the following: take' n _ | (n = 0) = [] take' n [] | (n 0) = error take': list too short | otherwise = [] take' n (x:xs) = x : take' (n-1) xs And we'd call it unsafeTake, just like unsafeFromJust and unsafeTail :-) -- Don Hmm, that's funny, I don't recall ever hearing of those functions... =) ooo, Don has a shiny new e-mail address! And a shiny new job in a shiny new city :-) -- Don ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Is take behaving correctly?
prstanley: Let me get this right, are you saying it's unsafe when it returns an error? Partial functions may crash your program, so that's unsafe by some definitions, yep. We have tools that analyse programs for such bugs, in fact (Neil's `catch' program). -- Don ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Prime monads?
Haskellians, Is there a characterization of prime monads? Here the notion of factorization i'm thinking about is decomposition into adjoint situations. For example, are there monads for which there are only the Kleisli and Eilenberg-Moore decompositions into adjoint situations? Would this be a characterization of quintessentially free or generative? Best wishes, --greg -- L.G. Meredith Managing Partner Biosimilarity LLC 505 N 72nd St Seattle, WA 98103 +1 206.650.3740 http://biosimilarity.blogspot.com ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Is take behaving correctly?
On Tue, 2007-09-11 at 16:48 -0700, Don Stewart wrote: byorgey: On 9/11/07, Don Stewart [EMAIL PROTECTED] wrote: byorgey: On 9/11/07, PR Stanley [EMAIL PROTECTED] wrote: Hi take 1000 [1..3] still yields [1,2,3] I thought it was supposed to return an error. Any ideas? Thanks, Paul If for some reason you want a version that does return an error in that situation, you could do something like the following: take' n _ | (n = 0) = [] take' n [] | (n 0) = error take': list too short | otherwise = [] take' n (x:xs) = x : take' (n-1) xs And we'd call it unsafeTake, just like unsafeFromJust and unsafeTail :-) -- Don Hmm, that's funny, I don't recall ever hearing of those functions... =) ooo, Don has a shiny new e-mail address! And a shiny new job in a shiny new city :-) In a new country. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] GraphicsMagick binding for Haskell
On Tue, Sep 11, 2007 at 03:41:59PM -0700, Tim Chevalier wrote: As a Hackathon project, I'm thinking of trying to write a Haskell binding for the GraphicsMagick image manipulation library (http://www.graphicsmagick.org/). please do! this would be a huge asset for us. image/graphicsmagick and curl are good examples of outstanding existing libraries that are better bound to than rewritten ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
