January 2005 - Haskell-Cafe

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 28 Jan '05

28 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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