January 2005 - Haskell-Cafe

"Parsing" a string
by Dmitri Pissarenko 08 Feb '05

08 Feb '05

Hello! I have to read a PGM image and transform it into a list of Int values. I read the image (this is an ASCII PGM format) using the readFile function and get a string with the contents of the file. This string contains height and widht of the image at the beginning, and then the pixel values follow. I need to read the height and width, then "cut" them from the string, create an array (or finite map) of Int's (for this I need to know the height and width), and then recursively process the pixel values (i. e. put them into the array). The string is structured as follows: <string> P2 # comment # comment 320<WHITESPACE>243<WHITESPACE>255 130 130 130 130 130 130 130 130 130 130 </string> P2 is the magic number. All lines starting with # are comments and must be ignored. 320 and 243 are width and height. <WHITESPACE> is either a space, or tab, or newline. At the moment, I don't have an idea about how to read width and height. One possible approach would be to convert the string into a list of strings A, using newline as separator. Then, I could create list A' with comments removed. Then, A' can be transformed into a string A'' again. From A'' I know that width is contained between the end of P2 and the first occurrence of whitespace (Char.isSpace). I also know that height is contained between first and second occurrence of white space. I could use some sort of regular expression analogons to access width and height. I have several questions concerning this approach: 1) How can I transform a string into a list of strings, separated by some character (in Java one uses StringTokenizer for this) ? 2) How do the aforementioned "regular expressions' analogons" work in Haskell? Thanks in advance Dmitri Pissarenko -- Dmitri Pissarenko Software Engineer http://dapissarenko.com

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RE: [Haskell-cafe] File path programme
by Simon Marlow 02 Feb '05

02 Feb '05

[ moving to libraries(a)haskell.org ] On 26 January 2005 12:22, Malcolm Wallace wrote: >> 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. > > FWIW, I agree with Duncan, Ben, and Peter, that the new > System.FilePath interface is broken, and the implementation more so. > It would be better to redesign FilePaths as an algebraic datatype. Ok, I'll go with the concensus. System.FilePath in its current state will be removed from the base package. Isaac or Krasimir: can you make the required changes to Cabal? (the code is already duplicated in Distribution.Compat.FilePath, just remove the import for GHC). So let's aim for 6.6 to do it right, and design an abstract type for path names. We have to think about the migration path: Haskell 98 programs must continue to work, so at least IO.FilePath must still be a String, and IO.openFile must still take a String. We can therefore: (a) make System.IO.FilePath be the new type, which is different from, and incompatible with, IO.FilePath. Similarly for System.IO.openFile, System.Directory.removeFile, and so on. (b) or just define a new type, and force you to insert read/show to convert where necessary, eg. before calling openFile. (a) is kind of the right thing, but (b) is a lot less painful in the short term. Since we'll be migrating to a new IO library at some point, (b) is probably fine (the new IO library can use the new FilePaths exclusively), but we'll need to migrate System.Directory too. Would someone like to take up the reigns on the design for the new library? Cheers, Simon

20 58

The Nature of Char and String
by John Goerzen 02 Feb '05

02 Feb '05

Char in Haskell represents a Unicode character. I don't know exactly what its size is, but it must be at least 16 bits and maybe more. String would then share those properties. However, usually I'm accustomed to dealing with data in 8-bit words. So I have some questions: * If I use hPutStr on a string, is it guaranteed that the number of 8-bit bytes written equals (length stringWritten)? + If no, what is the representation written? I'm assuming UTF-8. How could I find out how many bytes were actually written? + If yes, what happens to the upper 8 bits? Are they simply stripped off? * If I run hGetChar, is it possible that it would consume more than one byte of input? How can I determine whether or not this has happend? * Does Haskell treat the "this is a Unicode file" marker special in any way? * Same questions on withCString and related String<->CString conversions. -- John

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RE: [Haskell-cafe] Re: ocr'ed version of "The implementation offunctional languages"
by Simon Peyton-Jones 02 Feb '05

02 Feb '05

Matthew Yes, I'm happy for you to OCR the book, but can I ask that whatever you get be made accessible from my web site, so there's one place people can go to find everything that's available? What would OCR buy us? Searching, I guess, which is a fantastic plus. Anything else? Thanks very much for offering to help. I've replied to haskell-café, so everyone knows what's up, but we can now save everyone's bandwidth by narrowing the thread to Ivan, Marnie (who did the original work), you, and me. If anyone else wants to join in, do yell. Simon | -----Original Message----- | From: haskell-cafe-bounces(a)haskell.org [mailto:haskell-cafe-bounces@haskell.org] On Behalf Of Ivan | Boldyrev | Sent: 31 January 2005 06:48 | To: haskell-cafe(a)haskell.org | Subject: [Haskell-cafe] Re: ocr'ed version of "The implementation offunctional languages" | | On 9005 day of my life Matthew Roberts wrote: | > 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". | | I have high-resolution scans of this books. If Simon permits, I will | create OCR from these scans. But I think, we must obtain author's | permission before OCR'ing. | | PNG version of scans will be released soon. While size of page is | same, quality is much better, probably it will improve speed of | scanning. | | And compact DjVu version will be released too. Perhaps I could use | OCR'ed text for creating searchable version of DjVu? | | > However, my ocr software is clunky at best and (not surprisingly) it is | > slow going. | | What kind of software do you use? | | -- | Ivan Boldyrev | | Assembly of a Japanese bicycle requires greatest peace of spirit. | | _______________________________________________ | Haskell-Cafe mailing list | Haskell-Cafe(a)haskell.org | http://www.haskell.org/mailman/listinfo/haskell-cafe

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Re: [Haskell] Typing in haskell and mathematics
by Iavor Diatchki 02 Feb '05

02 Feb '05

Hello, On Fri, 28 Jan 2005 10:01:33 -0500, Jacques Carette <carette(a)mcmaster.ca> wrote: > The previous post on record syntax reminded me of some 'problems' I had noticed where Haskell and mathematics have a > (deep) usage mismatch. It is interesting that my sentiment is exactly the opposite. Mathematicians (the applied kind, not the pure) tend to be quite sloppy about their notation relaying _a lot_ on the context and the fact that people know what they are talking about. I find that this makes their explanations harder to understand rather than easier. > First, consider a syntax for other component-wise function application? For example, it would be convenient to have > (f,g) @ (x,y) > be (f x, g y). In some languages [with dynamic typing], one can even do (f,g) (x,y) :-) I am not sure what you mean, but you can define exactly that (except for the @ sign which is special syntax already): (f,g) `ap2` (x,y) = (f x, g y) > Yes, I am aware that this untypeable in Haskell, because polymorphism is straight-jacketed by structural rules. What do you mean by this: ap2 :: (a -> b, c - d) -> (a,c) -> (b,d) But > in mathematics, it is convenient and extremely common to: > 1) look at the type a -> b as being a *subtype* of b (though I have never seen it phrased that way in print) I don't think subtyping is what you are thinking of. Perhaps you are referring to the correspondance between b-expressions with a free a-variable, and functions a->b. In Haskell we don't have expressions with free variables as first class values. There might be some interesting things to work out for such beasts. > 2) to consider every 'natural transformation' available and use it (tuples of functions <-> obvious function on > tuples) Are you suggesting that natural transformations should be applied automatically? There are many problems with this: which operations should happen automatically? Type inference (if it works at all) will be hard to do, but perhaps these are technical details. Fundamentally the "sloppy" math notation assumes that what the author wrote is correct and should simply be given "the obvious" meaning. This is pretty much the idea with dynamic typing. I find the restrictions of static typing very convenient (well most of the time :-) as they capture "stupid' errors. > > Seeing a -> b as a subtype of b allows one to take any function f : b -> b -> c (like + ) and 'lift' it to > ff : (a -> b) -> (a -> b) -> (a -> c) > via the obvious definition > ff g h = \x -> f (g x) (h x) > This is done routinely in mathematics. The meaning of the expression (sin + cos) should be immediately obvious. Such > 'lifting' is used even in first-year calculus courses, but not in Haskell. Apart from the fact that this does not seem like a good idea, you can already do things like this in Haskell: liftOp op f g x = f x `op` f x This is all you need, especially if you are prepared to stick to the "usual" mathematical convention of not using curried functions, but instead using tuples to pass multiple arguments. > > The "same" phenomenon is what allows one to 'see' that there is an obvious function > apply_tuple:: (a->b,c->d) -> (a,c) -> (b,d) > so that > (f,g) (a,b) > only has one possible meaning, if the built-in apply function were to be overloaded. There are many interesting things one could do if application was to be overloaded but this hardly seems like a motivating example. You can already use the 'ap2' combinator from above. I can see that it is annoying to have ap2, ap3, etc. You can define a generic "ap_n" using dependent types, or using the encoding tomasz posted, but that hardly seems to be a "deep" problem. > > Similarly, there are "obvious" maps > apply_T :: T (a->b) -> a -> T b > for any datatype constructor T (as has been noticed by all who do 'generic' programming). Is this really true? Consider: data T a = T (a -> Int) What shoud apply_T do? applyT :: (essentially) ((a -> b) -> Int) -> a -> (b -> Int) perhaps: applyT (T f) a = T (\b -> f (const b)) but that probably does not behave as you would like it. Of course you could restrict the datatypes for which apply_T can be derived. This means that > [f, g, h] x == [f x, g x, h x] > but also (in mathematics at least) > {f, g, h} x == {f x, g x, h x} > where {} denotes a set, and the equality above is extensional equality, and so on. I agree that it would be nice to automatically derive functions such as apply_T, etc. This (as you point out) is the idea of generic programming. This however does not suggest that we should replace application... > Note that some computer algebra systems use #1 and #2 above all the time to define the operational meaning of a lot of > syntactic constructs [where I personally extended the use of such rules in the implementation & operational semantics > of Maple]. What hope is there to be able to do something 'similar' in a Haskell-like language? I think it is already possible to do simillar things. I am sure there is room for improvement, but it is important that the consequences of changing a language are worked out in details. It is time for me to go to school :-) bye Iavor

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Problems with building haskell-jvm-bridge-0.3.RC1
by Dmitri Pissarenko 01 Feb '05

01 Feb '05

Hello! I'm trying to build Haskell-JVM bridge (http://sourceforge.net/projects/jvm- bridge/) under Windows (cygwin) and with Java 1.5. I can execute "configure" without errors. When I execute make, I get a lot of errors. Due to a limited size of my buffer, I can show you only the last lines of make's output: JVMBridge.cpp: In function `jboolean JVMBridge_CallNonvirtualBooleanMethodVL(JNIEnv*, _jobject*, _jobject*, _jmethodID*, void*)': JVMBridge.cpp:778: error: `DebugShowPointer' cannot be used as a function JVMBridge.cpp:779: error: `DebugShowPointer' cannot be used as a function JVMBridge.cpp:780: error: `DebugShowPointer' cannot be used as a function JVMBridge.cpp:781: error: `DebugShowPointer' cannot be used as a function JVMBridge.cpp:783: error: `CallNonvirtualBooleanMethodA' undeclared (first use this function) JVMBridge.cpp:785: error: `JVMBridge_DestroyValueList' cannot be used as a function JVMBridge.cpp: In function `jbyte JVMBridge_CallNonvirtualByteMethodVL(JNIEnv*, _jobject*, _jobject*, _jmethodID*, void*)': JVMBridge.cpp:793: error: `DebugShowPointer' cannot be used as a function JVMBridge.cpp:794: error: `DebugShowPointer' cannot be used as a function JVMBridge.cpp:795: error: `DebugShowPointer' cannot be used as a function JVMBridge.cpp:796: error: `DebugShowPointer' cannot be used as a function JVMBridge.cpp:798: error: `CallNonvirtualByteMethodA' undeclared (first use this function) JVMBridge.cpp:800: error: `JVMBridge_DestroyValueList' cannot be used as a function JVMBridge.cpp: In function `jchar JVMBridge_CallNonvirtualCharMethodVL(JNIEnv*, _jobject*, _jobject*, _jmethodID*, void*)': JVMBridge.cpp:808: error: `DebugShowPointer' cannot be used as a function JVMBridge.cpp:809: error: `DebugShowPointer' cannot be used as a function JVMBridge.cpp:810: error: `DebugShowPointer' cannot be used as a function JVMBridge.cpp:811: error: `DebugShowPointer' cannot be used as a function JVMBridge.cpp:813: error: `CallNonvirtualCharMethodA' undeclared (first use this function) JVMBridge.cpp:815: error: `JVMBridge_DestroyValueList' cannot be used as a function JVMBridge.cpp: In function `jshort JVMBridge_CallNonvirtualShortMethodVL(JNIEnv*, _jobject*, _jobject*, _jmethodID*, void*)': JVMBridge.cpp:823: error: `DebugShowPointer' cannot be used as a function JVMBridge.cpp:824: error: `DebugShowPointer' cannot be used as a function JVMBridge.cpp:825: error: `DebugShowPointer' cannot be used as a function JVMBridge.cpp:826: error: `DebugShowPointer' cannot be used as a function JVMBridge.cpp:828: error: `CallNonvirtualShortMethodA' undeclared (first use this function) JVMBridge.cpp:830: error: `JVMBridge_DestroyValueList' cannot be used as a function JVMBridge.cpp: In function `jint JVMBridge_CallNonvirtualIntMethodVL(JNIEnv*, _jobject*, _jobject*, _jmethodID*, void*)': JVMBridge.cpp:838: error: `DebugShowPointer' cannot be used as a function JVMBridge.cpp:839: error: `DebugShowPointer' cannot be used as a function JVMBridge.cpp:840: error: `DebugShowPointer' cannot be used as a function JVMBridge.cpp:841: error: `DebugShowPointer' cannot be used as a function JVMBridge.cpp:843: error: `CallNonvirtualIntMethodA' undeclared (first use this function) JVMBridge.cpp:845: error: `JVMBridge_DestroyValueList' cannot be used as a function JVMBridge.cpp: At global scope: JVMBridge.cpp:850: error: parse error before `*' token JVMBridge.cpp:853: error: `object' was not declared in this scope JVMBridge.cpp:853: error: ISO C++ forbids declaration of `DebugShowPointer' with no type JVMBridge.cpp:853: error: redefinition of `int DebugShowPointer' JVMBridge.cpp:711: error: `int DebugShowPointer' previously defined here JVMBridge.cpp:853: error: initializer list being treated as compound expression JVMBridge.cpp:854: error: ISO C++ forbids declaration of `DebugShowPointer' with no type JVMBridge.cpp:854: error: redefinition of `int DebugShowPointer' JVMBridge.cpp:853: error: `int DebugShowPointer' previously defined here JVMBridge.cpp:854: error: initializer list being treated as compound expression JVMBridge.cpp:855: error: `methodID' was not declared in this scope JVMBridge.cpp:855: error: ISO C++ forbids declaration of `DebugShowPointer' with no type JVMBridge.cpp:855: error: redefinition of `int DebugShowPointer' JVMBridge.cpp:854: error: `int DebugShowPointer' previously defined here JVMBridge.cpp:855: error: initializer list being treated as compound expression JVMBridge.cpp:856: error: `vl' was not declared in this scope JVMBridge.cpp:856: error: ISO C++ forbids declaration of `DebugShowPointer' with no type JVMBridge.cpp:856: error: redefinition of `int DebugShowPointer' JVMBridge.cpp:855: error: `int DebugShowPointer' previously defined here JVMBridge.cpp:856: error: initializer list being treated as compound expression JVMBridge.cpp:857: error: redefinition of `jvalue*valueArray' JVMBridge.cpp:712: error: `jvalue*valueArray' previously defined here JVMBridge.cpp:857: error: `vl' was not declared in this scope JVMBridge.cpp:858: error: parse error before `=' token JVMBridge.cpp:860: error: `vl' was not declared in this scope JVMBridge.cpp:860: error: ISO C++ forbids declaration of ` JVMBridge_DestroyValueList' with no type JVMBridge.cpp:860: error: redefinition of `int JVMBridge_DestroyValueList' JVMBridge.cpp:715: error: `int JVMBridge_DestroyValueList' previously defined here JVMBridge.cpp:861: error: ISO C++ forbids declaration of `DebugShowLong' with no type JVMBridge.cpp:861: error: redefinition of `int DebugShowLong' JVMBridge.cpp:716: error: `int DebugShowLong' previously defined here JVMBridge.cpp:861: error: initializer list being treated as compound expression JVMBridge.cpp:861: error: invalid conversion from `const char*' to `int' JVMBridge.cpp:862: error: parse error before `return' JVMBridge.cpp: In function `jfloat JVMBridge_CallNonvirtualFloatMethodVL(JNIEnv*, _jobject*, _jobject*, _jmethodID*, void*)': JVMBridge.cpp:868: error: `DebugShowPointer' cannot be used as a function JVMBridge.cpp:869: error: `DebugShowPointer' cannot be used as a function JVMBridge.cpp:870: error: `DebugShowPointer' cannot be used as a function JVMBridge.cpp:871: error: `DebugShowPointer' cannot be used as a function JVMBridge.cpp:873: error: `CallNonvirtualFloatMethodA' undeclared (first use this function) JVMBridge.cpp:875: error: `JVMBridge_DestroyValueList' cannot be used as a function JVMBridge.cpp: In function `jdouble JVMBridge_CallNonvirtualDoubleMethodVL(JNIEnv*, _jobject*, _jobject*, _jmethodID*, void*)': JVMBridge.cpp:883: error: `DebugShowPointer' cannot be used as a function JVMBridge.cpp:884: error: `DebugShowPointer' cannot be used as a function JVMBridge.cpp:885: error: `DebugShowPointer' cannot be used as a function JVMBridge.cpp:886: error: `DebugShowPointer' cannot be used as a function JVMBridge.cpp:888: error: `CallNonvirtualDoubleMethodA' undeclared (first use this function) JVMBridge.cpp:890: error: `JVMBridge_DestroyValueList' cannot be used as a function JVMBridge.cpp: In function `_jobject* JVMBridge_CallNonvirtualObjectMethodVL(JNIEnv*, _jobject*, _jobject*, _jmethodID*, void*)': JVMBridge.cpp:898: error: `DebugShowPointer' cannot be used as a function JVMBridge.cpp:899: error: `DebugShowPointer' cannot be used as a function JVMBridge.cpp:900: error: `DebugShowPointer' cannot be used as a function JVMBridge.cpp:901: error: `DebugShowPointer' cannot be used as a function JVMBridge.cpp:903: error: `CallNonvirtualObjectMethodA' undeclared (first use this function) JVMBridge.cpp:905: error: `JVMBridge_DestroyValueList' cannot be used as a function JVMBridge.cpp: In function `void JVMBridge_CallStaticVoidMethodVL(JNIEnv*, _jobject*, _jmethodID*, void*)': JVMBridge.cpp:913: error: `DebugShowPointer' cannot be used as a function JVMBridge.cpp:914: error: `DebugShowPointer' cannot be used as a function JVMBridge.cpp:915: error: `DebugShowPointer' cannot be used as a function JVMBridge.cpp:917: error: `CallStaticVoidMethodA' undeclared (first use this function) JVMBridge.cpp:919: error: `JVMBridge_DestroyValueList' cannot be used as a function JVMBridge.cpp: In function `jboolean JVMBridge_CallStaticBooleanMethodVL(JNIEnv*, _jobject*, _jmethodID*, void*) ': JVMBridge.cpp:925: error: `DebugShowPointer' cannot be used as a function JVMBridge.cpp:926: error: `DebugShowPointer' cannot be used as a function JVMBridge.cpp:927: error: `DebugShowPointer' cannot be used as a function JVMBridge.cpp:929: error: `CallStaticBooleanMethodA' undeclared (first use this function) JVMBridge.cpp:931: error: `JVMBridge_DestroyValueList' cannot be used as a function JVMBridge.cpp: In function `jbyte JVMBridge_CallStaticByteMethodVL(JNIEnv*, _jobject*, _jmethodID*, void*)': JVMBridge.cpp:939: error: `DebugShowPointer' cannot be used as a function JVMBridge.cpp:940: error: `DebugShowPointer' cannot be used as a function JVMBridge.cpp:941: error: `DebugShowPointer' cannot be used as a function JVMBridge.cpp:943: error: `CallStaticByteMethodA' undeclared (first use this function) JVMBridge.cpp:945: error: `JVMBridge_DestroyValueList' cannot be used as a function JVMBridge.cpp: In function `jchar JVMBridge_CallStaticCharMethodVL(JNIEnv*, _jobject*, _jmethodID*, void*)': JVMBridge.cpp:953: error: `DebugShowPointer' cannot be used as a function JVMBridge.cpp:954: error: `DebugShowPointer' cannot be used as a function JVMBridge.cpp:955: error: `DebugShowPointer' cannot be used as a function JVMBridge.cpp:957: error: `CallStaticCharMethodA' undeclared (first use this function) JVMBridge.cpp:959: error: `JVMBridge_DestroyValueList' cannot be used as a function JVMBridge.cpp: In function `jshort JVMBridge_CallStaticShortMethodVL(JNIEnv*, _jobject*, _jmethodID*, void*)': JVMBridge.cpp:967: error: `DebugShowPointer' cannot be used as a function JVMBridge.cpp:968: error: `DebugShowPointer' cannot be used as a function JVMBridge.cpp:969: error: `DebugShowPointer' cannot be used as a function JVMBridge.cpp:971: error: `CallStaticShortMethodA' undeclared (first use this function) JVMBridge.cpp:973: error: `JVMBridge_DestroyValueList' cannot be used as a function JVMBridge.cpp: In function `jint JVMBridge_CallStaticIntMethodVL(JNIEnv*, _jobject*, _jmethodID*, void*)': JVMBridge.cpp:981: error: `DebugShowPointer' cannot be used as a function JVMBridge.cpp:982: error: `DebugShowPointer' cannot be used as a function JVMBridge.cpp:983: error: `DebugShowPointer' cannot be used as a function JVMBridge.cpp:985: error: `CallStaticIntMethodA' undeclared (first use this function) JVMBridge.cpp:987: error: `JVMBridge_DestroyValueList' cannot be used as a function JVMBridge.cpp: At global scope: JVMBridge.cpp:992: error: parse error before `*' token JVMBridge.cpp:995: error: ISO C++ forbids declaration of `DebugShowPointer' with no type JVMBridge.cpp:995: error: redefinition of `int DebugShowPointer' JVMBridge.cpp:856: error: `int DebugShowPointer' previously defined here JVMBridge.cpp:995: error: initializer list being treated as compound expression JVMBridge.cpp:996: error: `methodID' was not declared in this scope JVMBridge.cpp:996: error: ISO C++ forbids declaration of `DebugShowPointer' with no type JVMBridge.cpp:996: error: redefinition of `int DebugShowPointer' JVMBridge.cpp:995: error: `int DebugShowPointer' previously defined here JVMBridge.cpp:996: error: initializer list being treated as compound expression JVMBridge.cpp:997: error: `vl' was not declared in this scope JVMBridge.cpp:997: error: ISO C++ forbids declaration of `DebugShowPointer' with no type JVMBridge.cpp:997: error: redefinition of `int DebugShowPointer' JVMBridge.cpp:996: error: `int DebugShowPointer' previously defined here JVMBridge.cpp:997: error: initializer list being treated as compound expression JVMBridge.cpp:998: error: redefinition of `jvalue*valueArray' JVMBridge.cpp:857: error: `jvalue*valueArray' previously defined here JVMBridge.cpp:998: error: `vl' was not declared in this scope JVMBridge.cpp:999: error: parse error before `=' token JVMBridge.cpp:1001: error: `vl' was not declared in this scope JVMBridge.cpp:1001: error: ISO C++ forbids declaration of ` JVMBridge_DestroyValueList' with no type JVMBridge.cpp:1001: error: redefinition of `int JVMBridge_DestroyValueList' JVMBridge.cpp:860: error: `int JVMBridge_DestroyValueList' previously defined here JVMBridge.cpp:1002: error: ISO C++ forbids declaration of `DebugShowLong' with no type JVMBridge.cpp:1002: error: redefinition of `int DebugShowLong' JVMBridge.cpp:861: error: `int DebugShowLong' previously defined here JVMBridge.cpp:1002: error: initializer list being treated as compound expression JVMBridge.cpp:1002: error: invalid conversion from `const char*' to `int' JVMBridge.cpp:1003: error: parse error before `return' JVMBridge.cpp: In function `jfloat JVMBridge_CallStaticFloatMethodVL(JNIEnv*, _jobject*, _jmethodID*, void*)': JVMBridge.cpp:1009: error: `DebugShowPointer' cannot be used as a function JVMBridge.cpp:1010: error: `DebugShowPointer' cannot be used as a function JVMBridge.cpp:1011: error: `DebugShowPointer' cannot be used as a function JVMBridge.cpp:1013: error: `CallStaticFloatMethodA' undeclared (first use this function) JVMBridge.cpp:1015: error: `JVMBridge_DestroyValueList' cannot be used as a function JVMBridge.cpp: In function `jdouble JVMBridge_CallStaticDoubleMethodVL(JNIEnv*, _jobject*, _jmethodID*, void*)': JVMBridge.cpp:1023: error: `DebugShowPointer' cannot be used as a function JVMBridge.cpp:1024: error: `DebugShowPointer' cannot be used as a function JVMBridge.cpp:1025: error: `DebugShowPointer' cannot be used as a function JVMBridge.cpp:1027: error: `CallStaticDoubleMethodA' undeclared (first use this function) JVMBridge.cpp:1029: error: `JVMBridge_DestroyValueList' cannot be used as a function JVMBridge.cpp: In function `_jobject* JVMBridge_CallStaticObjectMethodVL(JNIEnv*, _jobject*, _jmethodID*, void*)': JVMBridge.cpp:1037: error: `DebugShowPointer' cannot be used as a function JVMBridge.cpp:1038: error: `DebugShowPointer' cannot be used as a function JVMBridge.cpp:1039: error: `DebugShowPointer' cannot be used as a function JVMBridge.cpp:1041: error: `CallStaticObjectMethodA' undeclared (first use this function) JVMBridge.cpp:1043: error: `JVMBridge_DestroyValueList' cannot be used as a function JVMBridge.cpp: In function `jboolean JVMBridge_IsSameObject(JNIEnv*, _jobject*, _jobject*)': JVMBridge.cpp:1051: error: `DebugShowPointer' cannot be used as a function JVMBridge.cpp:1052: error: `DebugShowPointer' cannot be used as a function JVMBridge.cpp: In function `jboolean JVMBridge_IsInstanceOf(JNIEnv*, _jobject*, _jobject*)': JVMBridge.cpp:1059: error: `DebugShowPointer' cannot be used as a function JVMBridge.cpp:1060: error: `DebugShowPointer' cannot be used as a function JVMBridge.cpp: In function `jint JVMBridge_ThrowException(JNIEnv*, _jobject*)': JVMBridge.cpp:1067: error: `DebugShowPointer' cannot be used as a function JVMBridge.cpp: In function `jboolean JVMBridge_ExceptionPending(JNIEnv*)': JVMBridge.cpp:1092: error: `ExceptionCheck' undeclared (first use this function) JVMBridge.cpp: In function `jint JVMBridge_MonitorEnter(JNIEnv*, _jobject*)': JVMBridge.cpp:1105: error: `MonitorEnter' undeclared (first use this function) JVMBridge.cpp: In function `jint JVMBridge_MonitorExit(JNIEnv*, _jobject*)': JVMBridge.cpp:1111: error: `MonitorEnter' undeclared (first use this function) JVMBridge.cpp: In function `char* JVMBridge_GetStringUTFChars(JNIEnv*, _jobject*)': JVMBridge.cpp:1158: error: `GetStringUTFLength' undeclared (first use this function) JVMBridge.cpp:1162: error: `GetStringUTFRegion' undeclared (first use this function) JVMBridge.cpp:1167: error: `GetStringUTFChars' undeclared (first use this function) JVMBridge.cpp:1170: error: `ReleaseStringUTFChars' undeclared (first use this function) JVMBridge.cpp: In function `jint JVMBridge_GetStringUTFLength(JNIEnv*, _jobject*)': JVMBridge.cpp:1178: error: `GetStringUTFLength' undeclared (first use this function) JVMBridge.cpp: In function `_jobject* JVMBridge_DefineClass(JNIEnv*, const char*, _jobject*, const jbyte*, long int)': JVMBridge.cpp:1192: error: `DebugShowPointer' cannot be used as a function make[2]: *** [JVMBridge.lo] Error 1 make[2]: Leaving directory `/cygdrive/c/dapWork/temp/downloads/haskell-jvm- bridg e-0.3.RC1/Native' make[1]: *** [all-recursive] Error 1 make[1]: Leaving directory `/cygdrive/c/dapWork/temp/downloads/haskell-jvm- bridg e-0.3.RC1/Native' make: *** [all] Error 2 Have you an idea what I can do to fix these errors? Thanks in advance Dmitri Pissarenko -- Dmitri Pissarenko Software Engineer http://dapissarenko.com

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Re: mathematical notation and functional programming
by Henning Thielemann 01 Feb '05

01 Feb '05

On Mon, 31 Jan 2005, Chung-chieh Shan wrote: > (Is Lemming the same person as Henning Thielemann?) Yes. :-) > > For the expression '1+x' I > > conclude by type inference that 'x' must be a variable for a scalar > > value, since '1' is, too. But the expression '1/O(n^2)' has the scalar > > value '1' on the left of '/' and a set of functions at the right side. > > Type inference fails, so my next try is to make the operands compatible > > in a somehow natural way. > > It seems to me that your classification of certain notations as "wrong" > and others as "right" assumes a certain type inference system that > allows adding a number to a placeholder but disallows dividing a > function by a set of functions. Let's see if we share a common interpretation of notation before discussing who uses it consistently and who does not. :-) For me 1, x and + are identifiers. The strings "1", "x" and "+" are not mathematical objects. But '1' denotes a unique mathematical object. Only almost, because depending on the underlying explanation it may be identified with the natural number 1, with the rational number 1, with the real 1, with the complex 1, you will probably need a different representation. Further this representation depends on how you represent natural numbers, reals and so on, e.g. by sets. '+' also denotes a mathematical object, more precisely a function, and again we have ambiguities like that for '1', since '+' might be the natural addition, the rational one or even a mixed one. 'x' denotes no special mathematical object but it may be replaced by one, and the special thing is, that within a certain scope all occurences of 'x' must be replaced with the same mathematical object. Functions are special, in the sense that if I write "1+2" I don't want to consider this as the sequence of three objects denoted by "1", "+", "2" but I want that the function denoted by "+" is applied on the values denoted by "1" and "2". So I imagine a layer of notation and a layer of mathematical objects. Do you share this interpretation? What are consequences of this interpretation? "2+2" and "4" denote the same object. A function has only access to the value (the mathematical object) but not to the generating expression. So how can I define e.g. differentation with respect to a variable? I can't, but I don't miss it because I can define it for functions, and yes Jerzy :-), also for other objects. For me differentiation was introduced by limits. The definition of limits don't need expressions as mathematical objects, the differentation of functions don't need them, too. But later we got used to differentiate expression (e.g. x^2 + y^2 is turned into 2*x * dx + 2*y * dy), but no-one defined what that is. What are the consequences of treating expressions as mathematical objects, too? "2+2" and "4" are different expressions. I guess we would still ask for a value, thus we need a mathematical function which maps expressions to values. I think Mathematicas Evaluate is made for this purpose. If mathematical functions can transform expressions - is it possible that they change my writing? ;-) Indeed, I really like this separation: On the one side expression, on the other side mathematical objects. Simplifications of expressions are nothing I allow a mathematical function. But if I simplify an expression I must assert that the denoted mathematical object remains the same. Differentation of a function is possible if you only know its graph, but a computer algebra system can find an expression for the derivation if you have an expression for the function. There are many functions that can be integrated, but a computer algebra system cannot find an expression without the Integrate function for it. When a pupil says "the function can not be integrated" he means that he couldn't find an expression for the integrated function without the integral sign. When a professor teaching calculus says "the function can not be integrated" he means that there is some divergence. It seems to me that in this case the pupil considers expressions as mathematical objects and the professor does not. > Lambda notation also involves much ambiguity and many implicit > conversions. Following the interpretation above I like to see lambda as a notation instead of an mathematical operator. lambda expressions denote functions. I can replace every occurence of lambda expressions textually. If "\A -> B" occurs I can also write "f" and "where holds \forall A f(A)=B". So lambda notation involves no more ambiguities than the rest of the notation. > > You use 'ask' twice in the second expression. Does this mean that there > > may be two different values for 'ask'? If this is the case your second > > interpretation differs from my second interpretation. > > No -- when I use "ask" I mean the one defined in Control.Monad.Reader. Sorry for my imprecise question :-) What I meant was that 'ask' somehow injects a value into the mathematical operation, I wondered if the values it introduces are equal or not.

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Re: mathematical notation and functional programming
by Chung-chieh Shan 01 Feb '05

01 Feb '05

(Is Lemming the same person as Henning Thielemann?) On 2005-01-30T21:24:24+0100, Lemming wrote: > Chung-chieh Shan wrote: > > Wait a minute -- would you also say that "1+x" has no meaning at the > > first glance, because "x" is a variable whereas "1" is an integer, so > > some lifting is called for? > For me 'x' is a place holder for a value. But you can only adds two *numbers* to get a number. It makes no sense to add a number to a placeholder. So it makes no sense to write "1+x", no? > For the expression '1+x' I > conclude by type inference that 'x' must be a variable for a scalar > value, since '1' is, too. But the expression '1/O(n^2)' has the scalar > value '1' on the left of '/' and a set of functions at the right side. > Type inference fails, so my next try is to make the operands compatible > in a somehow natural way. It seems to me that your classification of certain notations as "wrong" and others as "right" assumes a certain type inference system that allows adding a number to a placeholder but disallows dividing a function by a set of functions. > Since mathematical notation invokes many > implicit conversions, it's sometimes no longer unique or obvious what > implicit conversion to use. Many users of O(n^2) seem to consider it as > a placeholder for some expression, where the value of the expression is > bounded by n^2. Lambda notation also involves much ambiguity and many implicit conversions. In particular, "x" can mean the identity function from integers to integers as well as the identity function from booleans to booleans, as well as a function that maps an integer-boolean pair to the integer of the pair, as well as a function that maps an integer-boolean pair to the boolean of the pair, and so on. > > Right; they are control operators in the sense that call/cc is a control > > operator. > So they seem to be operators that work on expressions rather than > values. In this respect they are similar to the lambda operator, aren't > they? Yes. > You use 'ask' twice in the second expression. Does this mean that there > may be two different values for 'ask'? If this is the case your second > interpretation differs from my second interpretation. No -- when I use "ask" I mean the one defined in Control.Monad.Reader. > Church style, System F(-omega), alpha-conversion, lambda calculus, eta > reduction, currying - Where can I find some introduction to them? What > about Haskell Curry? What about Bourbaki? - I have heard they worked > hard to find a unified notation. (I'm sure that other people would have better suggestions, but I rather like Benjamin Pierce's book "Types and programming languages".) Ken -- Edit this signature at http://www.digitas.harvard.edu/cgi-bin/ken/sig War crimes will be prosecuted. War criminals will be punished. And it will be no defense to say, "I was just following orders."' George W. Bush, address to the nation, 2003-03-17 http://www.whitehouse.gov/news/releases/2003/03/20030317-7.html

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RE: UTF-8 BOM, really!? (was: [Haskell-cafe] Re: File path progr amme)
by Bayley, Alistair 01 Feb '05

01 Feb '05

> From: Aaron Denney [mailto:wnoise@ofb.net] > > Better yet would be to have the standard never allow the BOM. > > Since some things can't handle it, on output we should never emit it, > but still must handle it on input. Bah. I don't see how banning it from input would help; as I understand it, it's meant to be ignored anyway, so there's no loss or gain there. Whether or not to emit the BOM on output should be a user choice, surely? > From: Graham Klyne [mailto:GK@ninebynine.org] > > How can it make sense to have a BOM in UTF-8? UTF-8 is a sequence of > octets (bytes); what ordering is there here that can > sensibly be varied? >From http://www.unicode.org/faq/utf_bom.html#BOM : "Q: Where is a BOM useful? A: A BOM is useful at the beginning of files that are typed as text, but for which it is not known whether they are in big or little endian format..." i.e. it helps when you need to guess what the encoding of a given file might be. 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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File paths and internationalization/localization
by Graham Klyne 31 Jan '05

31 Jan '05

I don't offer any answers, but the problems raised on this list concerning file paths using local language characters would appear to have some parallels in the world of URIs. Martin Duerst and others at W3C have been working on the problem of internationalization (I18N) of URIs, and their proposals were recently published as a Proposed Standard RFC [1]. If this area is being considered in the design of Haskell libraries, there may be some lessons there to be copied. #g -- [1] ftp://ftp.rfc-editor.org/in-notes/rfc3987.txt ------------ Graham Klyne For email: http://www.ninebynine.org/#Contact

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