Re: [Haskell-cafe] Re: Slightly humorous: Headhunters toolbox (example for Germany)
* Ertugrul Soeylemez wrote: Good to know that Saxony-Anhalt is the state in Germany with leading interest in Haskell. :-) I would like to know, whether this is due to Magdeburg or Halle. Saxony-Anhalt is the state in Germany with leading number of Google searches regarding Haskell. And that means, that the two people playing with Haskell at the university of Halle (located in Saxony-Anhalt) has Internet access an know to use a search engine. Lutz, using good old Altavista via 64kbps in Jena, Thuringia. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Why Either = Left | Right instead of something like Result = Success | Failure
* Ionut G. Stan wrote: I was just wondering if there's any particular reason for which the two constructors of the Either data type are named Left and Right. Yes. The basic function on this type is either. either a b (Left x) = Left (a x) either a b (Right x) = Right (b x) So the names of the constuctors are natural. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Bug with [Double]
* Ben Millwood wrote: Prelude [1,1+2/3..10] :: [Rational] [1 % 1,5 % 3,7 % 3,3 % 1,11 % 3,13 % 3,5 % 1,17 % 3,19 % 3,7 % 1,23 % 3,25 % 3,9 % 1,29 % 3,31 % 3] Same result. This sounds like a bug to me. The section of the Haskell Report that deals with the Enum class mentions Float and Double, not Rational, and there's really no sensible reason why Rationals would exhibit this behaviour given that they don't have rounding error. Double is not better: Prelude [9,9+2/3..10] [9.0,9.666,10.332] Prelude [7,9 .. 10] [7,9] ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] (liftM join .) . mapM
* Tony Morris wrote: Can (liftM join .) . mapM be improved? (Monad m) = (a - m [b]) - [a] - m [b] a) liftM concat . mapM -- list handling . monad handling b) (sequence .) . map -- monad handling . list handling ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] semantics of type synonym
* pbrowne wrote: semantics). I used the following type synonym: type String = [Char] type Name = String String, Name and [Char] are synonyms, which means every expression is identically to the others. There is no difference besides that String and Name are type aliases while [Char] is a type construct. getName :: String - Name getName n = n I checked the types with two tests: -- test 1 :t ww ww :: [Char] The type interference system determines that you have an array of characters, hence a [Char]. All those existing type aliases are suppressed by the module. Otherwise the list get's very long ... -- test 2 :t getName(ww) getName(ww) :: Name From the definition of getName, the compiler knows which type alias is prefered from the set of equivalent names. Obviously I get two different types. You get two different representations of the same type. In the case of the function Haskells type system seems to pick up enough information to determine that “ww” is a Name. Nope. ww is still a [Char] for the compiler. And you do not even check for the type of ww. :t snd . (\x - (getName x, x)) $ ww ... :: String ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] about Haskell code written to be too smart
* Claus Reinke wrote: Continuing our adventures into stylistic and semantic differences:-) It's good practice to keep a simple minded version of the code and using quickcheck to try to find differences between the optimized and trivial version. It's good practice to even check, that the optimized version is really faster/smaller than the simple one. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] about Haskell code written to be too smart
* Manlio Perillo wrote: But this may be really a question of personal taste or experience. What is more natural? 1) pattern matching 2) recursion or 1) function composition 2) high level functions Composition of library functions is usually much more readable than hand written recursion, simply because the typical idiom is highlighted instead of checking yourself, that there is no strange matching against the obvious case. Composition of library functions is usually much more efficient and preferable than hand written recursion, simply because the fine tuned fusion capabilities. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] type metaphysics
* Martijn van Steenbergen wrote: Int has 2^32 values, just like in Java. Haskell Report 6.4 (revised): The finite-precision integer type Int covers at least the range [ - 2^29, 2^29 - 1]. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: tensor product of dynamic-sized bits
* Ahn, Ki Yung wrote: This is why I am looking for existing work, because I am not yet very sure about my code I'm using. http://www.galois.com/technology/communications_security ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: sort and lazyness (?)
* Daniel Kraft wrote: Otherwise, how can one handle such amounts in data anyway? Only using arrays? Data.Array or some problem specific data structure. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Bit Field Marshalling
* Michael D. Adams wrote: But as far as I can tell, hsc2hs doesn't support bit fields. On top of that I'm not sure I can make any safe assumptions about what order the bit fields are packed (LSB or MSB first). C standard allows padding and reorder of struct entries in order to match alignment requirements. The only exeption are bitfields, which must not reordered and padded. This way bit fields are the only portable way to define the binary representation in C. Unfortunly the C standard does not specify any bit order for bit fields, but almost all implementations use the machine specific bit order, in order to ease access to multiple bits wide bit field and fill LSB to MSB. But there is no guarantee. I run into this problem when writing an low level kernel interface in SPARK. The ABI (binary representation) of the kernel API depends on the C compiler flags (i.e. #pragma packed). Especially kernels of commericial unicies might generate this problem, because the developer uses gcc instead of the native compiler. The only portable way to get access to C defined structures is involving a C compiler, either using hsc or a C helper module. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Poor libraries documentation
* Jonathan Cast wrote: On 30 Jan 2008, at 7:19 PM, Anton van Straaten wrote: quickCheck $ x - cos (x + 2*pi) == cos x Falsifiable, after 2 tests: -1.0 Test.QuickCheck.quickCheck $ \x - abs (cos x - cos (x + 2*pi)) 0.1 OK, passed 100 tests. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: cryptographic hash functions in darcs (re: announcing darcs 2.0.0pre3)
* zooko wrote: This makes the choice of SHA-1 for the patch-id-generation function wholly inappropriate. We already know that SHA-1 doesn't have collision resistance, and there is reason to suspect that in the near future it will turn out that it doesn't have second-pre-image resistance either. Calm down! The found collisions in SHA-1 require some very specific environment choices. I doubt darcs will allow those preconditions. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Why functional programming matters
* Isaac Dupree wrote: fewer frustratingly unsolvable bugs down-the-road? I personally like the refactoring speed. Due to pureness it's easy to refactor and that's why I can generalize more and more often. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [darcs-devel] [Haskell-cafe] Re: announcing darcs 2.0.0pre3
* zooko wrote: On the one hand, SHA-1 is cryptographically fragile and is deprecated for use in applications that require collision-resistance and pre- image resistance. Such a cryptographically strong requirement is not given in the darcs case. SHA-1 is still used in almost all existing cryptographic protocols and secure against the known attacks, because the protocol itself prohibits the attacking preconditions. SHA-2 is the current standard for those applications It's not known, if SHA-2 will suffer from the same attack principle or not. If you really consider the current known attacks against SHA-1 as important, you have to leave the whole family an choose i.e. RIPEMD-160. On the other hand, why does darcs need a cryptographically secure hash function at all? Wouldn't MD5 or a sufficiently wide CRC, such as the one used in ZFS [2], do just as well? They would certainly be a lot faster to compute. SHA-1 is the current standard for quick and dirty checksumming an new applications. Using MD5 or any CRC is only for software acheologists. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Field updates in a state monad
* Michael Roth wrote:
Exists there a way to write this cleaner without writing countless
set_xyz helper functions?
The syntactic sugar for record modifications is simply that: sugar.
You might write your own modifier functions:
set_bla x y = x { bla = y }
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Re: [Haskell-cafe] Show instances for error messages (Was: Refactoring status)
* Henning Thielemann wrote: happen. Paradoxical. It would be interesting if it is possible to tunnel Show class dictionaries through to an 'error' like IO is tunneled to 'trace'. unsafeShow :: (forall a . Show a = a) - String ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Haskell-cafe reply-to etiquette
* Justin Bailey wrote: When I joined the haskell-cafe mailing list, I was surprised to see the reply-to header on each message was set to the sender of a given message to the list, rather than the list itself. That's good practice. That seemed counter to other mailing lists I had been subscribed to, but I didn't think too much about it. Please search for Reply-To considered harmful and send this text to the admins of the other lists. The discussion is older than Google. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: DSL question -- was: New slogan for haskell.org
* Steve Lihn wrote: Thanks for the example. I am particularly amazed GHC is complaining at '/', not '+'. The type mismatch occurs (is reported) at much lower level. It would be nice if there is a way to bump it up a couple levels... Add type signatures for mu and dont_try_this. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Haskell performance
* Simon Peyton-Jones wrote: Does anyone feel like doing this? It'd be a great service. No need to know anything much about GHC. I'd like to do that. For a lecture I'm already generated performance tests for various sorting algorithms. It's designed about a function performance :: Size - IO RunsPerSecond. So with unsafePerformIO it is a good candidate for quickCheck. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Haskell performance
* Malcolm Wallace wrote: Something along these lines already exists - the nobench suite. Ok, your turn. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] OOP'er with (hopefully) trivial questions.....
* Tillmann Rendel wrote: My conclusion: To make Haskell a better OO language Haskell is not an OO language and never should be. (Since it's not the goal of Haskell to be any OO language at all this may not be a problem) Ack. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] type classes
* Peter Padawitz wrote: I'd like to define several instances of the same type class with the same type variable instance. Only method instances differ. How can I do this without writing copies of the type class? Define the type class in a module named MyClass. Define the each instance in a module named MyInstanceX where X is a version number. Include only the MyInstanceX module, you currently need. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] St. Petersburg Game
* [EMAIL PROTECTED] wrote: I'm trying to program an implementation of the St. Petersburg game in Haskell. There is a coin toss implied, and the random-number generation is driving me quite mad. So far, I've tried this: import Random import System.Random -- time goes on, interfaces change increment :: Int - Int increment b = b + 1 main = dolet b = 0 let c = randomRIO (1,2) until (c == 1) increment b return b In Haskell you take it the other side around: - Given a random number generator System.Random.newStdGen :: IO StdGen - you generate an infinite list of coin flip results System.Random.randoms :: (RandomGen g) = g - [a] System.Random.randomRs :: (RandomGen g) = (a,a) - g - [a] - you are interested in the the first elements of a given value takeWhile :: (a - Bool) - [a] - [a] - and need to compute the length of this list length :: [a] - Int To model the result of a coin flip, you need two possible values. Your choice [1,2] is possible, but the boolean values are much easier. Let's choose True for number up and False otherwise. Put it together: main :: IO () main = do rnd - newStdGen let result = computeResult rnd print result computeResult :: (RandomGen g) = g - Int computeResult = length . takeWhile not . randoms Or in short: main = print . length . takeWhile not . randoms = newStdGen ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Learning hierarchy
Hi, in order to upload my teaching programms to hackage, I look for an accepted hierarchy to put the modules into. My current version is Learning.Donnerhacke.Algorithms.Sort ... etc. pp. Would such a hierarchy make sense? Is the a hope for inclusion of other modules? The main purpose of this moduls in my special case are: Implementation of the algorithms from Sedgewick's famous book. They are combined with a ver short program ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Learning hierarchy
* Lutz Donnerhacke wrote: The main purpose of this moduls in my special case are: Implementation of the algorithms from Sedgewick's famous book. ... Sorry, I hit the send button a bit too early. ... They are used with very small main programms containing a FFI inclusion of a external C object and a main calling Test.QuickCheck between the C function and the library function (from Learning...). This way the studends are teached to learn C. The Makefile compiles the C code to a object file and links it with the main programm to generate test cases for their work. A secondary function is exported via FFI to display the used data structures at the C level in an additional X11 window. This is offered to ease debugging of their programms. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: [Haskell] Re: Trying to install binary-0.4
* Simon Marlow wrote: further sub-versions may be added after the x.y, their meaning is package-defined. Ordering on versions is lexicographic, given multiple versions that satisfy a dependency Cabal will pick the latest. x.y.z should be ordered numerically, if possible. As suggested by various people in this thread: we change the convention so that dependencies must specify a single x.y API version, or a range of versions with an upper bound. Cabal or Hackage can refuse to accept packages that don't follow this convention (perhaps Hackage is a better place to enforce it, and Cabal should just warn, I'm not sure). Ack. Hackage is a good place to reject. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Is take behaving correctly?
* Neil Mitchell wrote: There are 4 variants of tail: tail :: [a] - [a] -- normal tailDef :: [a] - [a] - [a] -- returns the first argument on [] tailMay :: [a] - Maybe [a] -- returns a Nothing tailNote :: String - [a] - [a] -- crashes, but with a helpful message tailSafe :: [a] - [a] -- returns [] on [] From the logical point of view tailMay is the right one. It pushes the error handling to the caller programm. tail = fromJust . tailMay ___ 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
Re: [Haskell-cafe] Parsing binary data.
* Tony Finch wrote: http://erlang.org/doc/programming_examples/bit_syntax.html#4 The IP header example in the latter is a brilliant real-world example. Unfortunly this example does not handle bit and byte order. Take a look at Ada's representation clauses for such topics. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Slow IO or bad code?
* Vimal wrote:
Beginning of CODE
loop t function
| t == 1 = do function
| otherwise = do { function; loop (t - 1) function }
prod [] [] = 0
prod (a:as) (b:bs) = a*b + prod as bs
prod = sum . zipWith (*)
to_int :: [String] - [Integer]
to_int [] = []
to_int (x:xs) = (read x) : to_int xs
This is the slow part. Prelude.read ist really slow.
Futhermore use the recusion pattern again:
to_int = map read
doit = do
n - getLine
a - getLine
b - getLine
let la = to_int (words a);
lb = to_int (words b); in
print (prod la lb)
What is n used for?
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Re: [Haskell-cafe] Re: monad subexpressions
* Bulat Ziganshin wrote: Hello apfelmus, I still think that this syntax extension has profound impact and is a bad idea. can you please rewrite *p++=*q++ in haskell? p = q ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Definition of the Haskell standard library
* Simon Peyton-Jones wrote: Then, in effect, the standard library is all the X packages. I wonder if it'd help to have some descriptions such as those above (better worded), and use them? Cabal already has a stability indication, and that might serve, but we'd want to articulate much more clearly what it meant. You need an external indicator, not an indicator from the package author. It might be interesting to transform the dependency graph of cabalized packaged at hackage into a ranking indicator. It's like the Google Pagerank: Same benefit, same illness. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Maintaining the community
* Malcolm Wallace wrote: If anything, Usenet is even worse than mailing lists for volume, especially of spam. Also, very few sites maintain their nntp servers adequately these days - e.g. comp.lang.haskell has never made it to where I work. I beg to differ. Of course, I'm an Usenet admin and involved in Usenet administration since years. Saing no Usenet is usually a sign of the famous not invented here syndrom. I'd sugest to keep the 30+ years experience with large volume distributed mass communication, instead of throwing good and infrastructure and user interfaces away. Wikis, Webformus and a lot of other Web 2.0 hypes are doomed to redo every mistake which is solved since 20+ years. MMDV. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Maintaining the community
* Magnus Therning wrote: One obvious solution is to split the list into several, more specialised lists. It's far from obvious, at least to me, how to do that with this list though. Switch to Usenet. The new haskell group will die, if the traffic will not increase. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Updated urlcheck
I'm proud to announce an updated version of dons' concurrent urlcheck. It's a bad and buggy rewrite from scratch. It can check a file of urls or the consistency of the transitive hull of a website incl. the existance of the border urls. Futhermore the warnings from TagSoup parsing can be reported. Main bugs are memory leaks in conjunction with unnecessary retrieval of binary files, and missing documentation. If somebody has enough time in the next weeks: Many thanks in advance. URL: http://www.iks-jena.de/mitarb/lutz/haskell/urlcheck-0.0.tar.gz ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] (pre)compiled Haskell compiler for True64/Alpha
Does anyone have a haskell compiler for True64 (formerly known as OSF/1) on Alpha hardware? I'm currently unable to compile the first bootstrap compiler. Any hint which compiler should I start with? I'll send detailed error reports only if I do not succeed in the next hours. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] (pre)compiled Haskell compiler for True64/Alpha
On Wed, Jun 06, 2007 at 10:00:15PM +1000, Donald Bruce Stewart wrote: I think the last ghc I ran on OSF/1 alpha was hmm, 5.04.2? Yep. I found that, because it was heavily described. There were quite a number of bugs with 64bit code. This are the same problems I have with nhc or hugs (sizeof (void*) != sizeof int). Hugs simply crashes while nhc does not compile (yet). You might be able to get a newer one working though. The 6.x series is fairly easy to bootstrap (there's alpha/debian for example), so if you run into problems, let glasgow-haskell-users@ know. Thank you. I do not have Linux, so a Debian packet does not help that much. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: wanted: haskell one-liners (in the perl sense of one-liners)
* Thomas Hartman wrote: You contributed #12:14 Thunder @pl s - drop (length s - n) s #12:14 lambdabot drop = subtract n . length But, on second thought, 1) I can't use this as a drop-in replacement for the non points free (right term?) version, and 2) I don't really understand it. I did not contribute, but polluted the channel with my own test. In order to understand this construct you have to switch to the (- a) Monad: drop = subtract n . length == do x - subtract n . length drop x This construct consists of partially applied functions, i.e. functions waiting for an argument. If you apply an argument to the whole construct, it is applied to each line seperatly. So drop = subtract n . length $ s becomes: let x = subtract n . length $ s in drop x s == let x = length s - n in drop x s == drop (length s - n) s I did not expect this monadic approach from lambdabot and was somewhat surprised. I assumed an application of liftM2 drop instead. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
