January 2005 - Haskell-Cafe

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 25 Jan '05

25 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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