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ocr'ed version of "The implementation of functional languages"
by Matthew Roberts 31 Jan '05

31 Jan '05

I have just embarked on creating a ocr'ed version of the jpeg images that have been made available for "The implementation of functional languages". However, my ocr software is clunky at best and (not surprisingly) it is slow going. It struch me that someone else might also be hard at work doing this and that there is not point duplicating work. Is anyone else doing this? If so, how can I help? Matt

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JVM-Bridge with Kaffe
by John Goerzen 30 Jan '05

30 Jan '05

Hello, I am attempting to package up the JVM bridge for Debian. As such, I am limited to the purely Free JVM's available within Debian. They include Kaffe, SableVM, GCJ/GIJ, and the Jikes compiler available for most of the above. I could not convince jvm-bridge's Native/configure to even see a gcj environment. Kaffe worked (after updating the include path to /usr/lib/kaffe/include). However, when I tried to start the compile: g++ -DHAVE_CONFIG_H -I. -I. -I. -I/usr/lib/kaffe/include/ -DVM_KAFFE -O3 -W -Wall -fno-rtti -g -O2 -MT JVMBridge.lo -MD -MP -MF .deps/JVMBridge.Tpo -c JVMBridge.cpp -fPIC -DPIC -o .libs/JVMBridge.o JVMBridge.cpp: In function `JNIEnv* JVMBridge_AttachCurrentThread(JavaVM*)': JVMBridge.cpp:57: error: invalid conversion from `JNIEnv**' to `void**' JVMBridge.cpp: In function `jboolean* JVMBridge_GetBooleanArrayRegion(JNIEnv*, _jobject*, int, int)': JVMBridge.cpp:239: warning: unused variable `jboolean foo' JVMBridge.cpp: In function `_jobject* JVMBridge_DefineClass(JNIEnv*, const char*, _jobject*, const jbyte*, int)': JVMBridge.cpp:1187: warning: ignoring #pragma unused JVMBridge.cpp:1188: error: no matching function for call to `_Jv_JNIEnv:: DefineClass(_jobject*&, const jbyte*&, jsize&)' /usr/lib/kaffe/include/jni.h:498: error: candidates are: _jclass* _Jv_JNIEnv::DefineClass(const char*, _jobject*, const jbyte*, int) make[2]: *** [JVMBridge.lo] Error 1 This is jvm-bridge 0.3 and kaffe 1.1.4 (Debian version 1.1.4PRECVS6-1). Thanks, -- John Goerzen Author, Foundations of Python Network Programming http://www.amazon.com/exec/obidos/tg/detail/-/1590593715

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Looking for these libraries...
by John Goerzen 30 Jan '05

30 Jan '05

Hi, I'm looking for libraries / interfaces to these systems from Haskell: LDAP ncurses zlib (the one in darcs doesn't suit my needs) bz2lib Thanks, John

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RE: [Haskell-cafe] File path programme
by Simon Marlow 29 Jan '05

29 Jan '05

On 24 January 2005 22:11, Ben Rudiak-Gould wrote: > Please, let's not ship this with the hierarchical libraries. It's not > ready for prime time. We decided to provide this library for purely pragmatic reasons. It's better than nothing. http://www.haskell.org/pipermail/libraries/2004-October/002605.html Doing a reasonable job on System.FilePath, even if it isn't perfect, will help prevent lots of applications from falling into common traps, and help make more code portable. Cheers, Simon

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field record update syntax
by S. Alexander Jacobson 29 Jan '05

29 Jan '05

I have a lot of code of the form foo {bar = fn $ bar foo} Is there a more concise syntax? I am thinking the record equivalent of C's foo+=5... I imagine there is some operator that does this e.g. foo {bar =* fn} But I don't know what it is... -Alex- ______________________________________________________________ S. Alexander Jacobson tel:917-770-6565 http://alexjacobson.com

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Re: [Haskell-cafe] mathematical notation and functional programming
by Michael Matsko 28 Jan '05

28 Jan '05

Also, Walter Noll of Carnegie Mellon Univ. wrote a book, "Finite-Dimensional Spaces" in 1987 which basically presented undergraduate math in a notationally and conceptually unified manner. Some of the notation and terminology was strange, but consistent. Mike Matsko ----- Original Message ----- From: Fritz Ruehr <fruehr(a)willamette.edu> Date: Friday, January 28, 2005 3:10 pm Subject: Re: [Haskell-cafe] mathematical notation and functional programming > Well, I don't know about modern works which might appeal to > knowledge > of FP languages, but there is a well-known, 2-volume work by Cajori: > > Cajori, F., A History of Mathematical Notations, The Open > Court > Publishing Company, Chicago, 1929 (Available from Dover). > > I know it through Ken Iverson (may he rest in peace), the creator > of > APL. (Dr. Iverson's own notations were not to everyone's taste, but > I > think they were a bigger influence on Backus and the recent wave of > FP > than is generally acknowledged.) > > APL *did* have "implicit maps and zipWiths" in the sense that > scalar > functions would be automatically extended to vectors (and similarly > for > higher dimensions). I think my PhD advisor, Satish Thatte, did some > work on extending this sort of "notational abuse" to Hindley-Milner > systems, but I don't have the citations at hand. > > OK then, googling on Cajori yields this quote from a math history > site: > "He almost single-handedly created the history of mathematics as > an > academic subject in the United States > and, particularly with his book on the history of mathematical > notation, he is still one of the most quoted > historians of mathematics today." > > More googling on "mathematical notation" reveals that there *are* > people concerned about these issues, Steven Wolfram being an > easily-recognized example (he refers to Cajori's work). > > -- Fritz > > On Jan 27, 2005, at 12:14 PM, Henning Thielemann wrote: > > > I wonder if > > mathematical notation is subject of a mathematical branch and > whether> there are papers about this topic, e.g. how one can > improve common > > mathematical notation with the knowledge of functional languages. > > _______________________________________________ > Haskell-Cafe mailing list > Haskell-Cafe(a)haskell.org > http://www.haskell.org/mailman/listinfo/haskell-cafe >

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Nice pedagogical examples of type classes?
by Benjamin Pierce 28 Jan '05

28 Jan '05

My Advanced Programming course is quickly approaching the lectures on type classes, and I am interested in finding a little more (beyond what's in SOE) in the way of examples that illustrate nice uses (especially of more advanced aspects of the class system). I'd be most grateful for pointers to people's favorites. Examples should be reasonably small and depend only on Haskell 98 features. I haven't discussed monads yet, but I'm also interested in good monadic examples for later in the semester. Many thanks, - Benjamin P.S. Suggestions for interesting exercises along these lines are also appreciated!

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RE: Answers to Exercises in Craft of FP
by Christian Hofer 28 Jan '05

28 Jan '05

This should have been sent to haskell-cafe... > > Am 27.01.2005 um 21:28 schrieb Paul Hudak: > >> Chris, I'm not sure that I understand your argument. How about this >> scenario, which is what I do: Students are assigned problems, >> without solutions. They are given some time to work them out and >> turn them in. Then they are given the solutions, most of which I go >> over in class. > > That is perfectly alright with me. The problem that we are discussing > is that it would be helpful to have the solutions to the exercises for > a book that I buy for studying on my own. And this is where I learn > most from. But most of those books (including the Haskell School of > Expression) do not include solutions. In contrast, Pierce's Types and > Programming Languages helps the reader by giving at least solutions to > the most important exercises. And it is just nice to check, if you > have understood the problem correctly and whether there is a more > elegant solution. > > Regards, > Chris >

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RE: [Haskell-cafe] wierd type errros with MPTCs
by Simon Peyton-Jones 28 Jan '05

28 Jan '05

The kind error seems fair enough. GHC looks at the class decl, and decides that indexVal is of kind *. Then the instance declaration uses it with kind (*->*). You may say that it should look at the instance decl too, before deciding kinds, but the instance decl might be in another file. Uncommenting insertIndex allows the compiler to see that indexVal must be of kind (*->*), since it's applied to item in the type of insertIndex. So the compiler does do this much lookahead; the class ops can't be in another module. In GHC you can say class Table table (indexVal :: * -> *) where ... if you like, to make it 100% clear. When you declare a default method, GHC makes up a definition like this: $dmunion :: Table table indexVal => table item -> table item -> table item $dmunion t1 t2 = t1 ("dm" for default method) Then, in the instance decl, if you don't give a declaration for union, GHC makes one up, as if you had written instance Table DBTable IVal where union = $dmunion Now you can see where the error arises. The call to $dmunion gives the constraint (Table DBTable ??) with no way for it to figure out what the ?? is. The type of $dmunion is ambiguous in fact. Now, I agree that the error message, mentioning $dmunion, is rather unhelpful. But I can't see an easy way to improve it. Meanwhile, I hope this helps you make progress. Simon | -----Original Message----- | From: haskell-cafe-bounces(a)haskell.org [mailto:haskell-cafe-bounces@haskell.org] On Behalf Of S. | Alexander Jacobson | Sent: 27 January 2005 17:53 | To: haskell-cafe(a)haskell.org | Subject: [Haskell-cafe] wierd type errros with MPTCs | | This code gives me a Kind error because IVal isn't | applied to enough type arguments. | | import qualified Set | | class Table table indexVal | indexVal->table where | --insertIndex::item->indexVal item -> table item ->table item | union::table item -> table item -> table item | --union t1 t2 = t1 | | data DBTable item = DBTable | data IVal item = Name item | | instance Table DBTable (IVal ) where | | Weirdly, when I uncomment the insertIndex | function, things work. But, if I then uncomment | the default implementation of union, I get: | | No instance for (Table DBTable indexVal) | arising from use of `Main.$dmunion' at example.hs:13 | In the definition of `union': union = Main.$dmunion | In the definition for method `union' | In the instance declaration for `Table DBTable IVal' | | I don't know what this error even means. But it | goes away if I put the union implementation in the | instance rather than in the class. | | Bot these error messages seem unreasonable. Can | someone clarify? | | Note: I am using GHC 6.2.2 | | -Alex- | | | ______________________________________________________________ | S. Alexander Jacobson tel:917-770-6565 http://alexjacobson.com | _______________________________________________ | Haskell-Cafe mailing list | Haskell-Cafe(a)haskell.org | http://www.haskell.org/mailman/listinfo/haskell-cafe

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RE: Answers to Exercises in Craft of FP
by David Owen 27 Jan '05

27 Jan '05

>Gour (gour-haskell-cafe-sender-b3e10c(a)atmarama.org) wrote RE- : > > >Do you know if there are solutions to exersises available somewhere? > >Have you gone through the whole book, i.e. all the exercises? > >Sincerely, >Gour Hi Gour, Unfortuantely I don't know of anywhere that the exercise answers can be found, even after some google searching. I would definitely find them useful though as there are a couple I haven't been able to work out. I can't say I've gone through all the exercises yet but I'll get there one day! I've got as far as the abstract data types chapter. regards DaveO

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fastest Fibonacci numbers in the West
by William Lee Irwin III 27 Jan '05

27 Jan '05

Inspired by a discussion on freenode #haskell, I tried to write the fastest Fibonacci number function possible, i.e. given a natural number input n to compute F_n. mlton seems to enjoy substantially better speed despite equivalent algorithms; it may be enlightening to determine the causes of this, at least for those concerned about performance and the inner workings of the Haskell runtime system(s). In general, I am not usually very concerned about performance, nor am I in this case. But it's something of a mindless microbenchmark or similar. The things I'd normally think of to speed this up would be getting some primitives to find the highest bit of an integer (floor . lg) and to test a given bit of an integer (something vaguely like fromEnum . fromIntegral . (`mod` 2) . (/2^k)), both in some lightweight O(1) with low-hidden-constant manner. This doesn't appear to be a factor in the testing I did, as they're largely 1:1 translations of each other. Still, such things would be useful in various other algorithms, of far greater importance than this one. For the moment, mlton-generated binaries crash computing fib (10^8-1), and there is a 6:1 speed difference for fib (10^7-1) between the two, where mlton-generated binaries take just under 1 minute, and ghc- generated binaries take just under 6 minutes. Anyway, thoughts on how to improve all this from the programmer's point of view, or otherwise explaining what's going on or ameliorating whatever effect is at work here would be appreciated. -- wli

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wierd type errros with MPTCs
by S. Alexander Jacobson 27 Jan '05

27 Jan '05

This code gives me a Kind error because IVal isn't applied to enough type arguments. import qualified Set class Table table indexVal | indexVal->table where --insertIndex::item->indexVal item -> table item ->table item union::table item -> table item -> table item --union t1 t2 = t1 data DBTable item = DBTable data IVal item = Name item instance Table DBTable (IVal ) where Weirdly, when I uncomment the insertIndex function, things work. But, if I then uncomment the default implementation of union, I get: No instance for (Table DBTable indexVal) arising from use of `Main.$dmunion' at example.hs:13 In the definition of `union': union = Main.$dmunion In the definition for method `union' In the instance declaration for `Table DBTable IVal' I don't know what this error even means. But it goes away if I put the union implementation in the instance rather than in the class. Bot these error messages seem unreasonable. Can someone clarify? Note: I am using GHC 6.2.2 -Alex- ______________________________________________________________ S. Alexander Jacobson tel:917-770-6565 http://alexjacobson.com

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Question on "case x of g" when g is a function
by yeoh＠cs.wisc.edu 27 Jan '05

27 Jan '05

Can a kind soul please enlighten me on why f bit0 and f bit1 both return 0? > bit0 = False > bit1 = True > f x = case x of > bit0 -> 0 > bit1 -> 1

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Converting from Int to Double
by Dmitri Pissarenko 27 Jan '05

27 Jan '05

Hello! I have a list of integer numbers (grayscale values from 0 to 255) and want to convert them to a list of double numbers, so that each number is 0 <= x <= 1, where 0 is completely black and 1 is completely white. Before I convert the numbers, I need to convert them to a list of double values (then I can use map to re-scale each element from 0..255 to 0..1). How can I convert an Int into a Double? TIA Dmitri Pissarenko -- Dmitri Pissarenko Software Engineer http://dapissarenko.com

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RE: [Haskell-cafe] File path programme
by Simon Marlow 27 Jan '05

27 Jan '05

On 25 January 2005 19:45, Duncan Coutts wrote: > On Tue, 2005-01-25 at 19:12 +0000, Ben Rudiak-Gould wrote: >> My concern here is that someone will actually use the library once it >> ships, with the following consequences: >> >> 1. Programs using the library will have predictable >> (exploitable) bugs in pathname handling. >> >> 2. It will never be possible to change the current weird >> behavior, because it might break legacy code. The System.FilePath >> library will >> have to remain in GHC forever in its current form, enticing >> programmers with its promise of easy pathname handling and then >> cruelly breaking its contract. >> >> If no one uses it in production code then we can fix it at our >> leisure, and having it out there with "experimental" status isn't >> necessarily a bad thing in that case. It just feels like we're >> playing a dangerous game. > > That's a sufficiently persuasive argument for me! > > Could we just punt this library for this release. After all we can add > libraries in a later point release (eg 6.4.1) you just can't change > existing APIs. We can't add libraries in a point release, because there's no way for code to use conditional compilation to test the patchlevel version number. This seems to be a common misconception, probably brought about by the fact that the time between major releases of GHC is getting quite long. Perhaps I should stop writing email and get some work done :) Cheers, Simon

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RE: [Haskell-cafe] Problem with Hyperlinking Haddock-documentation
by Simon Marlow 27 Jan '05

27 Jan '05

On 27 January 2005 16:54, daniel.is.fischer(a)web.de wrote: > BTW, would it be worthwhile to let haddock use a list of default > interfaces, say on installation it would create a file with > -i /usr/...../base.haddock > -i /usr/...../parsec.haddock &cetera > in it, later a user might add other often used interfaces ? > > Okay, writing one's own script isn't too hard, so there's no real > need for it, but it would be nice for dummies like me. I'd like Haddock to know about installed packages, and in fact we're part of the way there in GHC 6.4 because the package database now includes the locations of the .haddock file and the HTML for each package. I just have to modify Haddock to query the package database... Cheers, Simon

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RE: [Haskell-cafe] Problem with Hyperlinking Haddock-documentation
by Simon Marlow 27 Jan '05

27 Jan '05

On 27 January 2005 09:03, Daniel Fischer wrote: > Am Mittwoch, 26. Januar 2005 21:49 schrieben Sie: >> On Wed, 26 Jan 2005, Daniel Fischer wrote: >>> Maybe somebody can enlighten me. >>> >>> When I run haddock and put the html files e.g. in directory >>> ~/bar/foo, any references to things defined in the Prelude or the >>> libraries are linked to, say ~/bar/foo/Prelude.html#t%3AFractional, >>> which of course does not exist, because the documentation for the >>> Prelude is elsewhere. >>> >>> How can I tell haddock to link such references to where Prelude.html >>> actually is? >> >> I add an option like >> >> -i /usr/local/share/ghc-6.2/html/libraries/base/base.haddock >> > The problem still stands, the link is to ~/bar/foo/Prelude.html, > not to /usr/local/.... > where Prelude.html is. > > Does anybody know what to do? You probably want to invoke Haddock like this: haddock -i/usr/share/ghc-6.2.2/html/libraries/base,/usr/share/ghc-6.2.2/librarie s/base/base.haddock (all on one line). The first path specifies the directory of the HTML for the base package, the second path specifies the .haddock file for the base package. Cheers, Simon

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RE: [Haskell-cafe] Re: library documentation
by Simon Marlow 27 Jan '05

27 Jan '05

On 27 January 2005 10:46, Peter Simons wrote: > Isaac Jones writes: > > > http://www.haskell.org/hawiki/LibraryDocsNeedingHelp > > This is a great idea. > > I have been thinking .... you know what would make > contribution to the library efforts even simpler? If they > were available in a Darcs repository. > > Saying "darcs push" after you've spontaneously added a > three-line explanation into a standard library is a lot more > attractive than "cvs diff", cutting and pasting that diff > into an editor, and e-mailing it to the -libraries list. > (Who submits a diff for three lines of documentation?) > > One of the reasons why Darcs is great is that it makes > submitting changes very simple for _everybody_. This would be great, but unfortunately the activation energy is quite high: we're already pretty committed to CVS, so we either move over to darcs wholesale, or we keep GHC in CVS and libraries in darcs. Neither is particularly attractive right now - darcs isn't ready for projects the size of GHC (at least, last I looked), and having a split repository would be a nightmare. Cheers, Simon

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RE: [Haskell-cafe] Convert to unboxed value? How?
by Simon Marlow 27 Jan '05

27 Jan '05

On 27 January 2005 12:36, Dimitry Golubovsky wrote: > What function should be used to convert an integer value to Int#? This function: f :: Int -> Int# f (I# x) = x > A character to Char#? Similarly: f :: Char -> Char# f (C# c) = c there aren't any library functions that do this for you. Cheers, Simon

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Convert to unboxed value? How?
by Dimitry Golubovsky 27 Jan '05

27 Jan '05

Hi, What function should be used to convert an integer value to Int#? A character to Char#? Dimitry Golubovsky Middletown, CT

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RE: [Haskell-cafe] Question on "case x of g" when g is a function
by Bayley, Alistair 27 Jan '05

27 Jan '05

Another way of looking at it: case peforms pattern matching; it is _not_ an equality test. If you want equality tests, use if-then-else, or something like this (using guards): f x = case () of _ | x == bit0 -> 0 | x == bit1 -> 1 The behaviour that initially threw me was that case works for various literals (numbers and strings), but that's just pattern matching (see 3.17.2, item 7): http://www.haskell.org/onlinereport/exps.html#pattern-matching Another shorthand for f, using guards: f x | x == bit0 = 0 | x == bit1 = 1 > -----Original Message----- > From: Salvador Lucas [mailto:slucas@dsic.upv.es] > Sent: 27 January 2005 09:59 > To: yeoh(a)cs.wisc.edu > Cc: haskell-cafe(a)haskell.org > Subject: Re: [Haskell-cafe] Question on "case x of g" when g > is a function > > Because both bit0 and bit1 are free *local* variables > within the case expression. So, they have nothing > to do with your defined functions bit0 and bit1. > > Best regards, > > Salvador. > > yeoh(a)cs.wisc.edu wrote: > > >Can a kind soul please enlighten me on why f bit0 and f bit1 > >both return 0? > > > > > > > >>bit0 = False > >>bit1 = True > >>f x = case x of > >> bit0 -> 0 > >> bit1 -> 1 > >> ----------------------------------------- ***************************************************************** Confidentiality Note: The information contained in this message, and any attachments, may contain confidential and/or privileged material. It is intended solely for the person(s) or entity to which it is addressed. Any review, retransmission, dissemination, or taking of any action in reliance upon this information by persons or entities other than the intended recipient(s) is prohibited. If you received this in error, please contact the sender and delete the material from any computer. *****************************************************************

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Problem with Hyperlinking Haddock-documentation
by Daniel Fischer 27 Jan '05

27 Jan '05

Maybe somebody can enlighten me. When I run haddock and put the html files e.g. in directory ~/bar/foo, any references to things defined in the Prelude or the libraries are linked to, say ~/bar/foo/Prelude.html#t%3AFractional, which of course does not exist, because the documentation for the Prelude is elsewhere. How can I tell haddock to link such references to where Prelude.html actually is? Please be aware of the fact that I know ///very/// little about html, hyperlinks and such, so be detailed and don't presuppose much. Thanks, Daniel

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List manipulation
by Dmitri Pissarenko 27 Jan '05

27 Jan '05

Hello! I have two lists of Double with equal length and want to create a third one, in which each element is the sum of the corresponding element of the first list and the second list. If list1 is [1, 2, 100] and list2 is [2, 3, 500], then the result of the operation I desire is [3, 5, 600]. I wrote this function <function> add2Img :: [Double] -> [Double] -> [Double] add2Img summand1 summand2 = sum where sum = [ (x+y) | x <- summand1, y <- summand2 ] </function>, but I'm getting [3.0,4.0,501.0,4.0,5.0,502.0,102.0,103.0,600.0] instead of [1, 2, 100]. What is wrong with the function above? TIA Dmitri Pissarenko -- Dmitri Pissarenko Software Engineer http://dapissarenko.com

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QuickCheck properties for Haskell98 Libraries?
by John Meacham 27 Jan '05

27 Jan '05

I was curious if anyone had a collection of QuickCheck rules for testing the Haskell98 Prelude and libraries? It seems like it would be a useful thing to exist as a common resource. In particular, if there were overloaded rules for the various class properties then it would be easier to test whether the instances one writes for standard classes were correct. In fact, it would be nice if the author of every class provided some quickcheck rules for testing the laws instances should obey. John -- John Meacham - ⑆repetae.net⑆john⑈

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What are the MonadPlus laws?
by Jules Bean 27 Jan '05

27 Jan '05

So, anyone? What are the laws that MonadPlus is supposed to satisfy? The obvious ones are that if MonadPlus m then for all types a, (m a) should be a monoid. But, what about the others, because IO does not appear to satisfy a >> mzero == mzero Jules

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RE: [Haskell-cafe] Re: Hugsvs GHC (again)was: Re: Somerandomnewbiequestions
by Simon Marlow 26 Jan '05

26 Jan '05

On 19 January 2005 16:58, Keean Schupke wrote: > Simon Marlow wrote: >> This is what GHC does, if I understand you correctly. The thread >> running select() does so in its own OS thread, while another OS >> thread runs the Haskell code. As long as you use -threaded, that >> is. Oh, and before GHC 6.4 it was done a different way - the >> scheduler used to do the select() between running Haskell threads. >> >> Cheers, >> Simon >> >> > So this means even though the IO calls block, the other Haskell > threads (when run with -threaded) keep running? Yes, unless the IO is to/from disk on a Unix system. Cheers, Simon

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using Map rather than FiniteMap
by S. Alexander Jacobson 26 Jan '05

26 Jan '05

Just did a search after my last post and learned that FiniteMap is bad. Discoverd that Data.Map is the intended replacement. Downloaded it and modified it to work with 6.2. Blazingly fast! Yay. Please ignore the prior message. -Alex- ______________________________________________________________ S. Alexander Jacobson tel:917-770-6565 http://alexjacobson.com

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RE: [Haskell-cafe] using Map rather than FiniteMap
by Simon Marlow 26 Jan '05

26 Jan '05

On 26 January 2005 16:42, S. Alexander Jacobson wrote: > On Wed, 26 Jan 2005, Simon Marlow wrote: >> When using the ordinary 2-generation collector, memory in use will >> tend to be 2-3 times larger than the actual residency, because this >> is a copying collector. > > Ok. Perhaps you want a different name for > this item in the reports? Well, "memory in use" is pretty accurate - it measures the actual amount of memory that the runtime has allocated from the OS. "residency" is a GC term which refers to the amount of live data. I don't think these terms are that confusing, but perhaps my explanation was? >>> On the other hand, I found 10mb, 5mb, and 2.5mb >>> maximum residency, but that is still ~100 bytes >>> per record. > > But 100 bytes per record in a (Map Int Int) seems > awefully high. That 100 bytes includes stack overhead. Remember, when you ran the heap profile which didn't show stack overhead you got a much more reasonable figure. >>> Lastly, I tried "example +RTS -p -K5M -hc" and >>> then looked at the resulting graph (attachment #2) >>> and it shows a total of 1.6Mb heap allocated and >>> if that data is correct, it does correspond >>> roughly to our 20-30 bytes per record estimate. >> >> That profile doesn't include the stack, which sounds reasonable. > > So I guess all the extra memory is actually being > allocated on the stack rather than the heap which > is a sign of a spaceleak. If I solve the > spaceleak I get the 70 bytes per item back. Yup. >> I haven't looked at your code in detail, hopefully someone else can >> shed some light on why you're building up such a large stack in the >> first place. > > The code is just this 6 line program: > > import qualified Map > zipped =zip [1..] [1..100000]::[(Int,Int)] > untup f (x,y) = f x y > produce = foldr (untup Map.insert) Map.empty zipped > fm = length $ Map.keys produce > main = print $ fm > > Can someone tell me what I can do to make this > more efficient? Replace the foldr by a foldl'? import Data.List produce = foldl' (untup (flip Map.insert)) Map.empty zipped (untested) Cheers, Simon

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RE: [Haskell-cafe] using Map rather than FiniteMap
by Simon Marlow 26 Jan '05

26 Jan '05

On 26 January 2005 14:29, S. Alexander Jacobson wrote: > Ah, ok. So I ran the code with 100000 items, > 50000 items, and 25000 items and got total memory > in use of 28Mb, 15Mb, and 8Mb respectively. That > comes to 260-280 bytes per record which is still > an order of magnitude higher than the 20-30 bytes > per record we would expect. When using the ordinary 2-generation collector, memory in use will tend to be 2-3 times larger than the actual residency, because this is a copying collector. > On the other hand, I found 10mb, 5mb, and 2.5mb > maximum residency, but that is still ~100 bytes > per record. Right. > Lastly, I tried "example +RTS -p -K5M -hc" and > then looked at the resulting graph (attachment #2) > and it shows a total of 1.6Mb heap allocated and > if that data is correct, it does correspond > roughly to our 20-30 bytes per record estimate. That profile doesn't include the stack, which sounds reasonable. > Regarding stack, I tried "example +RTS -p -K5M -xt > -hc" and then ran hp2ps and looked at the > resulting graph (attachment #1) SYSTEM appears to > use 4mb of stack at the very beginning (presumably > to create "zipped"), but I don't know why it > would. Then this stack is consumed by the rest of > the program. Stacks never get smaller in GHC, only bigger. If you need 4Mb of stack at one point in your program, you will forever have a 4Mb stack after that (fixing this wouldn't really buy you much; the memory doesn't get traversed or copied by the GC - but one thing you could do is madvise() to tell the OS it doesn't have to page the memory, though). I haven't looked at your code in detail, hopefully someone else can shed some light on why you're building up such a large stack in the first place. Cheers, Simon

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RE: [Haskell-cafe] using Map rather than FiniteMap
by Simon Marlow 26 Jan '05

26 Jan '05

On 25 January 2005 23:27, S. Alexander Jacobson wrote: > Oops. It pays to check your checking code before > making posts like this. > > After actually running the correct test, I am > still getting semi-ridiculous space behavior > (6k/pair)! > > import qualified Map > zipped =zip [1..] [1..100000]::[(Int,Int)] > untup f (x,y) = f x y > produce = foldr (untup Map.insert) Map.empty zipped > fm = length $ Map.keys produce > main = print $ fm > > Has this profile: > > example +RTS -p -K5M -RTS > > total time = 5.10 secs (255 ticks @ 20 ms) > total alloc = 612,534,236 bytes (excludes profiling overheads) > > COST CENTRE MODULE %time %alloc > balance Map 71.8 72.8 > insert Map 12.2 10.8 > size Map 9.0 9.7 > bin Map 2.4 2.2 > rotateR Map 1.6 0.3 > zipped Main 0.8 1.9 > > Notice the 612Mb for storing a mapping from Int > to Int!! Notice that's 612Mb *allocation* to create the finite map and deconstruct it into a list. Not 612Mb of live heap to store the finite map. If you make sure everything is evaluated, and examine the heap profile I'm sure you'll find that the finite map is taking a reasonable amount of space (perhaps 20-30 bytes per node for storing integers, I guess). To get a rough idea of the total live heap without profiling, you can run the program with +RTS -sstderr and look at the memory "in use" figure. Cheers, Simon

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RE: [Haskell-cafe] what is a stack overflow?
by Simon Marlow 26 Jan '05

26 Jan '05

On 25 January 2005 16:04, S. Alexander Jacobson wrote: > Ok. I guessed I was producing a big expression > of the form > > addToFM (addToFM (addToFM (addToFM (addToFM ...) > > I tried to solve it by doing > > (addToFM $! fm) key val > > But still got an error. I then tried the same > with the wrapper code, but still got the error. > > Is there a way to profile stack usage using GHCi > (without compiling) to find the problem? +RTS -xt -RTS will include the stack in a heap profile. See http://www.haskell.org/ghc/docs/latest/html/users_guide/prof-heap.html It will show you the size of the stack over time, but not the contents of the stack. Cheers, Simon

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RE: [Haskell-cafe] Re: Can't do basic time operations with System.Time
by Simon Marlow 26 Jan '05

26 Jan '05

On 25 January 2005 17:17, John Goerzen wrote: > On Tue, Jan 25, 2005 at 03:15:38PM -0000, Simon Marlow wrote: >> normalizeTimeDiff (and TimeDiff in general) is wrong. I wouldn't >> recommend using it. There's the TimeExts library in the lang >> package, which might be useful to you. > > I'm curious about that package. It's in my ghc source tree but not > documented at > http://www.haskell.org/ghc/docs/latest/html/libraries/index.html. > > Is it assumed to be portable and available outside ghc? It's an old non-hierarchical library, unfortunately with no documentation. It'll probably disappear in GHC 6.6, but you can always take the source and use it in your apps. Hopefully by 6.6 there will be a decent date/time library that provides this functionality. Cheers, Simon

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RE: [Haskell-cafe] Re: Visual Programming Languages
by Bayley, Alistair 26 Jan '05

26 Jan '05

> From: Stijn De Saeger [mailto:stijndesaeger@gmail.com] > > Don't know if this is exactly what you were thinking of, but you may > want to have a look at > www.subtextual.org > > if you do, make sure you watch the demo. This was odd... Some cherry-picked quotes from the manifesto: http://alarmingdevelopment.org/index.php?p=5 - Visual languages are not the solution: ... common idea is to replace AST structures with some form of graphical diagram. ... - Programming is not Mathematics - Change is natural: There has been much effort expended to remove the concept of mutable state from programming, to be replaced by immutable values as in mathematics. This is entirely misguided. ... Monads are a reductio ad absurdum. [ Heresy! :-) ] - Control flow considered harmful: ... The primary reason for this is to permit side-effects to be ordered by the programmer. ... [ This appears to contradict the criticism of monads. ] But then the demo shows us how to define a Factorial function using an editor that (AFAICT) is simply operating on AST structures, in a tree-oriented layout. I must be missing something. Alistair. ----------------------------------------- ***************************************************************** Confidentiality Note: The information contained in this message, and any attachments, may contain confidential and/or privileged material. It is intended solely for the person(s) or entity to which it is addressed. Any review, retransmission, dissemination, or taking of any action in reliance upon this information by persons or entities other than the intended recipient(s) is prohibited. If you received this in error, please contact the sender and delete the material from any computer. *****************************************************************

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Re: [Haskell-cafe] How to convert from "IO String" to String
by Dmitri Pissarenko 26 Jan '05

26 Jan '05

Hello! Thanks for your answer! > You probably want something like... > > l = [0, 255, 255, 255, 255, 0, 255, 255, 255, 255, 0, 255, 255, 255, 255, 0] > testConvertToList01 = do img <- readImage "../data-test/diagonalImage.pgm" > return $ TestCase $ assertEqual "" l > (convertToList img) When I use this test case definition, I'm getting an error when constructing the test suite: tests = TestList [testCommentLine01, testCommentLine02, testConvertToList01] GHCi writes TestLik.hs:22: Couldn't match `Test' against `IO Test' Expected type: Test Inferred type: IO Test In the list element: testConvertToList01 In the first argument of `TestList', namely `[testCommentLine01, testCommentLine02, testConvertToList01]' Best regards Dmitri Pissarenko -- Dmitri Pissarenko Software Engineer http://dapissarenko.com

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Re: Visual Programming Languages
by Stijn De Saeger 26 Jan '05

26 Jan '05

> This was odd... > > Some cherry-picked quotes from the manifesto: > http://alarmingdevelopment.org/index.php?p=5 > > - Visual languages are not the solution: ... common idea is to replace AST > structures with some form of graphical diagram. ... > > - Programming is not Mathematics > > - Change is natural: There has been much effort expended to remove the > concept of mutable state from programming, to be replaced by immutable > values as in mathematics. This is entirely misguided. ... Monads are a > reductio ad absurdum. [ Heresy! :-) ] > > - Control flow considered harmful: ... The primary reason for this is to > permit side-effects to be ordered by the programmer. ... [ This appears to > contradict the criticism of monads. ] > > But then the demo shows us how to define a Factorial function using an > editor that (AFAICT) is simply operating on AST structures, in a > tree-oriented layout. I must be missing something. > > Alistair. Yes, it is a bit of a twist. I came across this thing a couple of days ago on the LtU blog, and somehow thought it relevant to the issue of visual programming. I'm curious why the author himself doesn't consider this to be a visual programming language, considering that the language only allows you to program by copying and pasting. stijn.

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Re: Visual Programming Languages
by Stijn De Saeger 26 Jan '05

26 Jan '05

Hi, Don't know if this is exactly what you were thinking of, but you may want to have a look at www.subtextual.org if you do, make sure you watch the demo. cheers, stijn.

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Re: [Haskell] Newbie : How come that cyclic recursive lists areefficient ?
by David Barton 25 Jan '05

25 Jan '05

Benjamin Fransen writes: > There *is no* difference between the two if one views them as pure > mathematical values. Questions of run time speed or memory usage, i.e. > efficiency (which your original question was about) are clearly outside the > realm of pure values, and thus we may perceive them as distinct in this wider > setting. > > My favourite analogy for this is the old joke about a topologist being a > person who cannot see any difference between a cup and a doghnut. The engineer's response, of course, at the thought of ignoring questions about run time speed and memory usage, is that a topologist is a person who doesn't know his ass from a hole in the ground. (I was told this quote was actually from abstract algebraists, when confronted by the famous description of a topologist, but what the heck.) Dave Barton EDAptive Computing

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wxFruit examples
by Dmitri Pissarenko 25 Jan '05

25 Jan '05

Hello! I want to learn to program with wxFruit UI framework. http://zoo.cs.yale.edu/classes/cs490/03-04b/bartholomew.robinson/ Does someone know about any examples apart from paddle ball game? I would like to start with a simple application, which takes a the name of an image file as a command-line argument and displays a window, in which the image is displayed. The window has a "Close" button. If the file in question is not an image, a message box with an error message is displayed. I've looked at the source code of the paddle ball game, but still have no idea how to create the program with aforementioned functionality. TIA Dmitri Pissarenko -- Dmitri Pissarenko Software Engineer http://dapissarenko.com

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Visual Functional Languages
by José Miguel Vilaça 25 Jan '05

25 Jan '05

Hi Im searching for Visual Functional Languages, i.e. languages in which the programmer does diagrams instead of writing textual code. The only language I have found until now is VFPE of Joel Kelso's PhD thesis http://www.csse.uwa.edu.au/~joel/vfpe/ Does anyone know other languages or at least projects on this subject? Thankfully for answers José Miguel Vilaça

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File path programme
by Krasimir Angelov 25 Jan '05

25 Jan '05

Hello, Guys The System.FilePath might not be perfect and might not handle some unusual cases very well. Most of functions in this module are collected from Cabal/Alex/Happy/Haddock. Some of these tools already use their own functions for file path handling. Special care was taken to make them more portable but probably there is still enough room for optimizations. >> What about splitFileExt "foo.bar."? ("foo", "bar.") or ("foo.bar.", "")? > > The latter makes more sense to me, as an extension of the first case > you give and splitting "foo.tar.gz" to ("foo.tar", "gz"). I will take a look at this. I also don't know which case is more natural. > (Win32) > > splitFileName "\\\\server\\share" ==> ("\\\\server","share") > (should probably be ("\\\\server\\share","")) Why? "\\\\server" is the server name and "share" is the directory name on this server. > splitFileName "foo:xyz" ==> ("foo:.","xyz") > (should be (".","foo:xyz") -- this refers to the named stream > xyz of foo) System.FilePath currently doesn't support NTFS streams. I don't care much about them because they are rarely used but the things can be improved. The trouble here is that in some cases the drive letter cann't be easily distinguished. What does "c:foo" mean, file "foo" on drive "c" or stream "foo" of file "c"? > joinPaths "c:\\" "\\foo" ==> "\\foo" > (should be "c:\\foo". I realize that "cd c:\\" on Windows doesn't > actually make "c:\\" the current directory, but ";" doesn't > separate shell commands either.) On Windows there is current drive and current directory on each drive. "\\foo" means top level directory "foo" on the current drive. If the current drive is "c" then I can agree that the joined path is "c:\\foo" but if the current drive is "a" then this is wrong. In both cases "\\foo" is the right answer. If you want something like "c:\\foo" you can use System.Directory.canonicalizePath. canonicalizePath "\\foo" returns either "c:\\foo" or "a:\\foo". > (Posix) > > splitFileName "/foo" ==> ("/","foo"), > splitFileName "/foo/" ==> ("/foo","") > (arguably makes sense, but why isn't it documented?) OK > splitFileName "/foo/bar" ==> ("/foo","bar") > splitFileName "/foo//bar" ==> ("/foo/","bar") > (definitely a bug) Is "/foo//bar" valid file path and what does "//" mean? > pathParents "/foo///bar" ==> ["/","/foo","/foo","/foo","/foo/bar"] Again what does "///" mean? > pathParents "foo/../bar" ==> [".","foo/../bar"] > (what if foo doesn't exist and we wanted to create it?) If "foo" doesn't exist then you can create it or raise an error Cheers, Krasimir

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Newbie Monad question
by Simon Ulfsbäcker 25 Jan '05

25 Jan '05

Hi, I'm a functional programming newbie trying to get the hang of the concept of Monads, but one thing about bind puzzles me. Let's take an IO Monad-example: readLn >>= \i -> readLn >>= \j -> return (i + j) I fail to see how (\j -> return (i + j)) can know about the value of i. Isn't just the value of the previous readLn passed to \j -> return (i + j)? /Smalmatskungen

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How to convert from "IO String" to String
by Dmitri Pissarenko 25 Jan '05

25 Jan '05

Hello! I have a function, which reads the contents of a file into a string: <function1> readImage :: String -> IO String readImage filename = do fileContent <- readFile filename return fileContent </function1> The result of this function is fed into another function, which converts the string content of the file (it is a PGM image file) into a list of integer values (one integer for each pixel, one-dimensional array): <function2> convertToList fileContent = drop 3 fileContentNumbers where fileContentNoComments = removeComments fileContent fileContentTokens = words fileContentNoComments fileContentNumbers = map read (tail fileContentTokens) fileContentNumArr = listArray (1, length fileContentNumbers) fileContentNumbers </function2> Then, I wanted to verify that this function works properly and wrote a test case, which reads an image and tests whether the resulting list is correct: <test-case> testConvertToList01 = TestCase (assertEqual "" [0, 255, 255, 255, 255, 0, 255, 255, 255, 255, 0, 255, 255, 255, 255, 0] (convertToList (readImage "../data- test/diagonalImage.pgm"))) </test-case> When I load the files (you will find them all in attachment) into GHCi, I get following error <error-message> Couldn't match `String' against `IO String' Expected type: String Inferred type: IO String In the application `readImage "../data-test/diagonalImage.pgm"' In the first argument of `convertToList', namely `(readImage "../data-test/diagonalImage.pgm")' </error-message> I suppose that the error is due to this call in the test case: (convertToList (readImage "../data-test/diagonalImage.pgm")) readImage returns IO String and convertToList accepts String. How can I re-write this test case so that it works? Thanks in advance Dmitri Pissarenko -- Dmitri Pissarenko Software Engineer http://dapissarenko.com

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Haskell programs in C
by Dmitri Pissarenko 25 Jan '05

25 Jan '05

Hello! Imagine I wrote a program in Haskell and want to use it on a microcontroller device. AFAIK, Haskell programs are first converted to C code and then compiled by gcc. Is it possible (at least theoretically) to write a program in Haskell, then convert it into C and then compile the C program into an executable, which is optimized for the microcontroller? Thanks in advance Dmitri Pissarenko -- Dmitri Pissarenko Software Engineer http://dapissarenko.com

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~1k memory per elem for FiniteMap!!!?
by S. Alexander Jacobson 25 Jan '05

25 Jan '05

Is it possible/reasonable that Data.FiniteMap takes around 1k per element? I just profiled this code: import Data.FiniteMap zipped =zip [1..] [1..50000] addFMItem (index,item) fm = (addToFM $! fm) item index produce = foldr addFMItem emptyFM zipped fm = take 1 $ keysFM produce main = print $ fm And it apparently consumes more than 45MB of heap and won't run unless I give it at least 3M of stack space. I assume I doing something wrong here, but have no idea what it is. -Alex- ______________________________________________________________ S. Alexander Jacobson tel:917-770-6565 http://alexjacobson.com

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RE: [Haskell-cafe] Re: Can't do basic time operations with System.Time
by Simon Marlow 25 Jan '05

25 Jan '05

On 21 January 2005 21:50, John Goerzen wrote: > On 2005-01-21, Peter Simons <simons(a)cryp.to> wrote: >>> 24 * ((fromIntegral $ tdDay td) + >>> 30 * ((fromIntegral $ tdMonth td) + >>> 365 * (fromIntegral $ tdYear td))))) >> >> I was wondering: Does this calculation account for leap >> years? Does it have to? > > I also wondered about all months being 30 days. But this exact > algorithm is used in fptools' normalizeTimeDiff, and it seems to work > out correctly, so I guess the timeDiff functions assume that every > month has 30 days and every year has 365. normalizeTimeDiff (and TimeDiff in general) is wrong. I wouldn't recommend using it. There's the TimeExts library in the lang package, which might be useful to you. Cheers, Simon

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what is inverse of mzero and return?
by S. Alexander Jacobson 25 Jan '05

25 Jan '05

I assume there is a standard name for this class/function: instance Foo [] where foo [] = mzero foo (x:_) = return x instance Foo (Maybe x) where foo Nothing = mzero foo Just x = return x -Alex- ______________________________________________________________ S. Alexander Jacobson tel:917-770-6565 http://alexjacobson.com

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Re: [Haskell-cafe] what is a stack overflow?
by S. Alexander Jacobson 25 Jan '05

25 Jan '05

Thank you iavor. But the -K option doesn't appear to work with ghci. And I guess the bigger question is what sort of code causes a stack overflow. If 5M is enough stack for most programs then I obviously have some basic coding error which is causing a stack overflow... What sort of code causes that? -Alex- ______________________________________________________________ S. Alexander Jacobson tel:917-770-6565 http://alexjacobson.com On Mon, 24 Jan 2005, Iavor Diatchki wrote: > hi, > programs compile with GHC have a bunch of command line switches. > you can see them by typing: > myProg +RTS -help > one of them enables you to specify stack space, e.g. > myPorg +RTS -K5M > > (very briefly) the stack is a part of memory used by the compiler to > pass around arguments > to functions, and for temporary computations. > -iavor > > > > > On Mon, 24 Jan 2005 17:16:08 -0500 (Eastern Standard Time), S. > Alexander Jacobson <alex(a)alexjacobson.com> wrote: >> GHC assumes the user knows the difference between >> the heap and the stack. I don't. No matter how >> much heap I specify on the GHCi command line, I >> get a stack overflow exception. I have no idea >> what that means or how to remedy it. Hints? >> >> Note: My program is basically creating a few 100k >> item FiniteMaps. I don't think that should exceed >> the memory on my laptop.... >> >> -Alex- >> >> ______________________________________________________________ >> S. Alexander Jacobson tel:917-770-6565 http://alexjacobson.com >> _______________________________________________ >> Haskell-Cafe mailing list >> Haskell-Cafe(a)haskell.org >> http://www.haskell.org/mailman/listinfo/haskell-cafe >> >

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Hugs for Zaurus
by John Goerzen 25 Jan '05

25 Jan '05

Hello, I have built a fixed Hugs for the Zaurus PDA running the OpenZaurus distribution. Download here: http://quux.org/devel/zaurus/hugs_hugs98-Nov2003-r1_arm.ipk Every module except Posix signals appears to be working. -- John

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Recantation and updated views
by Daniel Fischer 25 Jan '05

25 Jan '05

Okay, I was stupid, having ignored my own advice to always look at the sources. I stupidly assumed IO a was not a function-type. On retrospect, I can't imagine, how that came to me. I've looked it up now, and for ghc, I found newtype IO a = IO (State# RealWorld -> (# State# RealWorld, a #)) which is more or less what I've arrived at, eventually. For hugs, it's newtype IO a = IO ((IOError -> IOResult) -> (a -> IOResult) -> IOResult), which I find somewhat more contrived. So I apologize for all the nonsense that came from that and happily agree that getChar &c are well defined values of IO a. Whether we have putStrLn "hello" >> mzero === mzero depends on what raiseIO# exactly does, I've no idea. Again, sorry for all the fuss. Thanks to (in alphabetical order) Jorge, Jules and Ketil for helping me out of my error. Daniel

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RE: [Haskell-cafe] can't 'make install-docs'
by Simon Marlow 25 Jan '05

25 Jan '05

On 21 January 2005 23:24, Daniel Fischer wrote: > I've just installed ghc-6.2.2, but couldn't get the docs made. > I got the following: > Text/Regex.raw-hs Text/Regex/Posix.raw-hs Text/Show.raw-hs > Text/Show/Functions.raw-hs \ > --package=base \ > --dump-interface=base.haddock \ > --use-index=../doc-index.html --use-contents=../index.html \ > > /bin/sh: line 1: t: command not found > gmake[2]: [html/haddock.css] Error 127 (ignored) > /usr/bin/install -c -m 644 html/* > /usr/local/share/ghc-6.2.2/html/libraries/base > /usr/bin/install: cannot stat `html/*': No such file or directory > gmake[2]: *** [install-docs] Error 1 > gmake[1]: *** [install-docs] Error 1 > gmake[1]: Leaving directory `/usr/lib/ghc-6.2.2/libraries' > gmake: *** [install-docs] Error 1 > > What can I do about it? Looks like you need to install Haddock. Cheers, Simon

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