RE: Parsing qualified types
Consider the following two Modules: File A.lhs: == module A where data A a = MkA a == File B.lhs: == module B where import qualified A type A a = A.A a--- Problem! == ghc-4.03 (current sources) complains while compiling B.lhs: B.lhs:5: parse error on input `.' Fixed, thanks for the report. Cheers, Simon
RE: CVS Snapshot Bug?
CVS Snapshot Bug? Please let me know if you need more information. Fixed today, thanks for the report. Cheers, Simon
RE: Help: Segfault | Where is the *.hc for 4.02 ?
I've tried `ghc-4.02-i386-unknown-linux.tar.gz' in-place, but even "hello world" will dump core. Some info about my box: glibc-2.1.1 I think the conclusion is that recent glibcs don't work with ghc. Unfortunately we don't have a box here to test on, so if anyone can help narrow down the problem and/or mail those responsible we'd be grateful. BTW, I've tried to give ghc `-optc-g', but all ghc-4.02 versions which I have, include those being compiled by myself, cause `ld' to dump core, even with glibc-2.0.7 and gcc 2.7.2.3 :-( We don't support/reccommend compiling with -optc-g :-) The reason is that ghc post-processes the assembly output from gcc, and the script simply doesn't understand the debugging info inserted by -g. Nevertheless, ld shouldn't dump core. As per the well-known joke, "Don't do that then!" Simon
digits of large integer
Anatoli Tubman wrote: T How can I *efficiently* print (i.e. find the decimal, or in T general N-ary, representation of) large Integers, like factorial of 1? Lennart Augustsson [EMAIL PROTECTED] replied A Use hbc? It uses the gmp routine to convert an Integer to a String. A Converting 1! to a String takes much less time than computing it. The cost of computing N-ary digit(s) of some f(n) may change in many times, depending on what special method is applied for the given f. Consider, for example, 8-ary digits for 2^n. They cost almost nothing. Probably, the initial question concerns mathematics rather than programming, or a programming tool choice. -- Sergey Mechveliani [EMAIL PROTECTED]
Re: how to write a simple cat
Hello! On Fri, Jun 04, 1999 at 12:18:31PM +0200, Friedrich Dominicus wrote: [...] splitFilterMap unSplitFn afterMap filterPredicate beforeMap splitFn = unSplitFn . map afterMap . filter filterPredicate . map beforeMap . splitFn [...] sorry this looks morre terrible to me than all solutions before, IMO way to much parameters and the names don't give me a good hint of what e.g beforeMap does. That's a HOF that first splits something up to a list using splitFn (or with the generalization I mentioned, to a monad), then maps a function over that list (namely beforeMap, because it's mapped *before* the filter), filters something out (using the filterPredicate), then again maps a function (namely afterMap, because it's mapped *after* the filter), then somehow joins the list (or monad), using unSplitFn. splitFilter unSplitFn filterPred splitFn = splitFilterMap unSplitFn id filterPred id splitFn That's just a specialization if there's no need for mapping a function over the list before or after the filtering. lenGt limit list = length list limit That's used as filter predicate. processFile limit = splitFilter unlines (lenGt limit) lines -- for the unnumbered version OR I think s.th in that directin is somewhar what I like more numberElems = zip [1..] number2str (nr,l) = show nr ++ '\t' : l I would not call it number2 s.th it does not expplain to me that something is printed so maybe print_number_str_pair or the like would be fine for me But the function doesn't print either. It converts to a string. Therefore 2str. You could call it numberStrPair2String more accurately. processFile limit = splitFilterMap unlines number2str (lenGt limit . snd) id (numberElems . lines) I don't think that I could work with splitFilterMap. Nevertheless is shows me all way lead to ROME ;-) Hmmm. I think using higher order functions to encapsulate programming structures (i.e. function concatenations, applications, etc.) is one thing that makes up functional programming. Just consider standard combinators like map, filter, foldl, foldr, sequence (Monads ahead :-) ), ... I re-wrote that stuff in Python and I've to admit it's way easier to understand for me (not even talking of writing). But I think it was a good example to learn how FP-trained would do it. It's a long long way to go;-) Did you use the more functional parts of Python there? map? filter? :-) Regards Friedrich Regards, Hannah.
y2k compliance
Hi I would like to know whether haskell compilers (hugs, hbc and lmlc) are fuly y2k compliant. Can anyone fill me in on this? Thanks Hugo -- Dr Hugo Bouckaert - Systems Administrator, Computer Science UWA Tel: +(61 8) 9380 2878 / Fax: +(61 8) 9380 1089 Email: [EMAIL PROTECTED] / Web: http://www.cs.uwa.edu.au/~hugo
RE: Language Feature Request: String Evaluation
In principle I can do this, but: 1. how do I hide the import of show String to replace it w/ my own? 2. If I do replce show String what else will break? 3. If instead I define an eshow function that strips "", how do I minimize the perforamnce hit of quote stripping? 4. If I want to share my code, I have to share both the actual codebase as well as the preprocessor code. This seems like sucha basic language syntax issue that I shouldn't have to worry about which version of haskell your collaborators are running. Everyone writing their own preprocessor will severely balkanize the language. Hm, it seems to me that that is the cost of being a maverick. 5. How does the use of this pre-processor interact w/ tools like Derive and PolyP which are also implemented as preprocessors? That being said, I would be happy to take a shot at HacWrite if it had a shot of becoming part of the language definition (or if it was a standard part of the various haskell distributions: ghc, hugs, hbc,etc.) and if Magnus would allow it. Is there a good lanugage reason to object to this feature? It seems like a no brainer imprpovement. (Allow me to play devil's advocate.) Not everyone uses Haskell to do web page processing or text processing, and Haskell already has too much syntactic sugar. I don't like your notion of changing the semantics of Show String, and I don't like the implicit show coercions for variables that get substituted into a string. (Whenever coercions get to be a pain, my instinct is to hide them in the plumbing of a set of combinators.) Preprocessing introduces another stage into the compilation process, and makes it that much more difficult to understand a program; interaction between preprocessors can be tricky (as you pointed out). --FC
Re: how to write a simple cat
Hello! On Wed, Jun 02, 1999 at 01:29:12AM -0700, Simon Peyton-Jones wrote: [...] - Would people actually add stuff? I'm a bit skeptical, but it would be great to have my skepticism proved unfounded. I think, Friedrich and those who helped him could have posted their questions and suggestions and answers to a Wiki-Wiki similarly easily like to the Haskell mailing list. Anyway, I think the interested questions of a learning person are a good motor to provide answers, explanations, and so on that are comprehensible for a "newbie" (as incomprehensible answers provoke further questions, that often finally lead to something that's understood by at least the one asking the questions, except s/he gave up). Simon Hannah.
Re: y2k compliance
Hugo Bouckaert wrote: I would like to know whether haskell compilers (hugs, hbc and lmlc) are fuly y2k compliant. Can anyone fill me in on this? ... and , if you are already here,... could somebody explain, please, what does it mean to have a compiler which is *NOT* y2k compliant, what is the difference between "full" and "not full" compliance, and why should we really care. (Please, - if I might be a little rigid - don't tell me about false dates returned by the OS, etc. I want to know how a language compiler may have anything to do with this Nessie...) Jerzy Karczmarczuk Caen, France. June 9th, year -237 before the Really New Functional Era (*) (*) At that moment our beloved Pope will finally decide that the True Doctors might be promoted Saints, and they need not go to Hell even if their wifes were Episcopal Church priests.
Re: Language Feature Request: String Evaluation
S. Alexander Jacobson writes: In principle I can do this, but: 1. how do I hide the import of show String to replace it w/ my own? 2. If I do replce show String what else will break? I'd rather let the preprocessor insert calls to eshow, and leave show as it is. 3. If instead I define an eshow function that strips "", how do I minimize the perforamnce hit of quote stripping? Maybe you could make eshow a member in a class EShow, which defaults to show, and make a special instance for Char (add a member eshowList). 4. If I want to share my code, I have to share both the actual codebase as well as the preprocessor code. This seems like sucha basic language syntax issue that I shouldn't have to worry about which version of haskell your collaborators are running. Everyone writing their own preprocessor will severely balkanize the language. I think it's a good idea to use a preprocessor for experimenting with your own language extensions. When (and if) the extensions settle and turn out to be useful, you could consider proposing them as part of a language definition. 5. How does the use of this pre-processor interact w/ tools like Derive and PolyP which are also implemented as preprocessors? I don't know. Buth the HacWrite preprocessor is simpleminded, it only looks for the new text lexemes, and doesn't know about the Haskell syntax. If you run such a preprocessor first, I think it would work. That being said, I would be happy to take a shot at HacWrite if it had a shot of becoming part of the language definition (or if it was a standard part of the various haskell distributions: ghc, hugs, hbc,etc.) and if Magnus would allow it. Is there a good lanugage reason to object to this feature? It seems like a no brainer imprpovement. I don't see any need to put something like this into the language definition for the moment. But if you want to use HacWrite, I could try to put it on some web page. /M -Alex- ___ S. Alexander JacobsonShop.Com 1-212-697-0184 voice The Easiest Way To Shop On Tue, 8 Jun 1999, Lennart Augustsson wrote: "S. Alexander Jacobson" wrote: HacWrite certainly seems like an improvement over Haskell. However, it is just not as good as the scripting languages. HacWrite still requires the author to differentiate between strings and other types, still requires explicit use of show and still requires more typing and curly balancing. Isn't this nicer? "insert into mytable values (NULL,'$var1','$(var2+var3)','$var3') So add your own little modification to HacWrite. It would be easy enough to add $ interpolation. -- Lennart
Re: y2k compliance
On Wed 09 Jun, Jerzy Karczmarczuk wrote: ... and , if you are already here,... could somebody explain, please, what does it mean to have a compiler which is *NOT* y2k compliant, I have found that some compilers put the date and time of compilation in the resulting object files, so it is possible that such a complier might suffer a Y2K problem, even on a Y2K compliant OS. what is the difference between "full" and "not full" compliance, I don't know, this looks like IT salesman speak to me. Perhaps "not full" compliance means it will get dates wrong, but won't do anything worse (like crash or destroy files). and why should we really care. This can be a real pain if you're working under a QA system that demands that software builds are repeatable (I.E. they will always generate the byte for byte identical object files, given the same sources). I suppose this is true whether or not the the compiler is Y2K compliant, but as a point of principal I would expect all information generated by a compiler to be correct. You never know when you might end up using that information (to update libraries for example). Regards -- Adrian Hey
RE: y2k compliance
Hi Hugo, | I would like to know whether haskell compilers (hugs, hbc and lmlc) are | fuly y2k compliant. Can anyone fill me in on this? My understanding is that none of the current Haskell implementors can afford to answer a question like this because none of us have the developer, support, or legal resources that would be required to back it up. It must therefore be left to individuals or groups of users to determine an appropriate notion of y2k compliance for their own use, and to take responsibility for determining whether the appropriate systems meet those standards. We already provide source and documentation to help with any such assessment, but we cannot take it any further. Of course, if someone does carry out a y2k evaluation on one or more Haskell systems, and chooses to publish their results, then everybody can benefit. All the best, Mark
Re: how to write a simple cat
Hannah Schroeter wrote: Hello! On Fri, Jun 04, 1999 at 12:29:45PM +0200, Friedrich Dominicus wrote: [...] What is difficult is that by using some predefined function, one can express very much in very small code. I believe Haskell is even more expressive than most OO languages with comparable libraries (perhaps except Smalltalk, as that has also a very compact syntax). I havn't made my mind if that is positive of negative. Sometimes it remind me of Perl and I'm not a big lover from it. Somehow that's not really fair towards Haskell. Perl is made up of many special cases, and in some other places, you have to use major hackery to achieve some goal (mind the "OO" part of Perl, for just one example). Now Haskell is on the other hand not quite fair to me. It makes me look as if I never have seen or programmed. I'm not thinking I'm the king of hacking, but I'm quite able to write some pieces of code. If using Haskell I have the feeling to ran against a wall, if I have s.th whih is trivial in e.g Python I have to fight to find a solution in Haskell. Maybe that's unfairf but it's quite different from all the things I know. Another difficulty is monadic I/O. Perhaps you should exercise programming with standard higher-order functions without I/O a bit more, so that you master that difficulty and don't have to *simultaneously* understand both the HOF things and I/O. That might be good advice but I/O is one of the most essential things and I have to know how to use it proper for writing small skripts. I think exercise with the purely functional, non-I/O core (and perhaps interact like someone else suggested) teaches you the mode of thinking in purely functional languages. That thinking can also help you understand the way I/O is implemented in a referentially transparent way. I disagree, small scripts spend most of the time doing I/O if I don't understand how to do that I'm not able to even write the most simple things. This is eg. true for my cat ... Till then Friedrich
Re: how to write a simple cat
Hello! On Fri, Jun 04, 1999 at 12:29:45PM +0200, Friedrich Dominicus wrote: [...] What is difficult is that by using some predefined function, one can express very much in very small code. I believe Haskell is even more expressive than most OO languages with comparable libraries (perhaps except Smalltalk, as that has also a very compact syntax). I havn't made my mind if that is positive of negative. Sometimes it remind me of Perl and I'm not a big lover from it. Somehow that's not really fair towards Haskell. Perl is made up of many special cases, and in some other places, you have to use major hackery to achieve some goal (mind the "OO" part of Perl, for just one example). Haskell has a very small, rather regular core syntax, with a bit of syntactical sugar on top (type classes [translated to records of "methods"], list comprehensions, monadic do-expressions), but that syntax allows to define rather high level functions *in Haskell itself* (see the Hugs prelude for the definitions and see that very few of those definitions are actually references to primitives, for example), and usually with very clean definitions (though the GHC prelude implementation sometimes uses hacks to get more efficient implementations). Another difficulty is monadic I/O. Perhaps you should exercise programming with standard higher-order functions without I/O a bit more, so that you master that difficulty and don't have to *simultaneously* understand both the HOF things and I/O. That might be good advice but I/O is one of the most essential things and I have to know how to use it proper for writing small skripts. I think exercise with the purely functional, non-I/O core (and perhaps interact like someone else suggested) teaches you the mode of thinking in purely functional languages. That thinking can also help you understand the way I/O is implemented in a referentially transparent way. [...] This comments helped me. So I think I will put them under my pillow;-) Regards and thanks Friedrich Regards, Hannah.
