- Haskell-Cafe - Haskell.org

Second Request for code review - Knuth Morris Pratt for Data.Sequence
by Justin Bailey 11 Sep '07

11 Sep '07

Using the code developed for ByteStrings by myself, Christ Kuklewicz and Daniel Fischer, I've implemented Knuth-Morris-Pratt substring searching on Data.Sequence "Seq" values. Attached you'll find the library in kmp.zip.safe. The algorithm is implemented in the module Data.Sequence.KMP. At the root, SpeedTest.hs can be compiled on Windows with the "prof_compile.bat" file included (you'll need to install the "regex-dfa" and "regex-base" packages from Hackage to build). SpeedTest searches for a known value in the 7 MB file "endo.dna" (which can be downloaded from http://www.icfpcontest.org/endo.zip) using several different algorithms and methods: strict and lazy bytestrings, regular expressions, and the KMP algorithm for "Seq" values. SpeedTest is pretty fast but I worry about its space usage. It may just be the nature of Seq values, but I cannot get it to run in constant space when I think it should be. I'm especially interested in help here. All comments and feedback are welcome. Since the zip file includes a darcs context file, feel free to send patches. Justin

1 0

WinHugs shortcut keys
by Peter Verswyvelen 10 Sep '07

10 Sep '07

Winhugs seems to have some shortcut keys, like F5 for run. It does not seem to have shortcut keys for reload, edit, etc... These would be really handy. It is possible to customize the shortcuts assigned to the commands? If not, can it be build from source? Thanks, Peter

2 3

Installation of GLUT package
by Ronald Guida 10 Sep '07

10 Sep '07

About a month ago, I asked about how to install freeglut and get GHC to recognize it. I was side-tracked; I finally decided to try to get it working, and I'm just stuck. I have GHC 6.6.1 and freeglut 2.4.0. Freeglut successfully compiled "out of the box" in MS Visual Studio.Net 2003 on my Windows XP box. GHC won't recognize freeglut; I found out that I need to recompile the GLUT package to get things working. Today I downloaded the GLUT package from hackage.haskell.org and attempted to install it. The installation blows up. According to Cabal/How_to_install_a_Cabal_package, I need to download the package, unzip it, and then run the following three commands. 1. runghc Setup.hs configure 2. runghc Setup.hs build 3. runghc Setup.hs install The first command, "runghc Setup.hs configure", fails, reporting that it can't find "sh". Naturally, I'm on a Windows box, so I don't have the Unix shell on my system. So now I'm stuck... * Is there an easy way to work around the absence of "sh"? * Is there an easy way to get "sh" on my Windows box? * <joke> GHC was available pre-compiled for Windows. Is there an easy way to get someone else to compile the GLUT package for me? :-) </joke> * Is it feasible to walk past a cut and "upgrade" to Linux? Most Windows programs can be replaced by open-source equivalents, but my sticky issue is that there's no Linux version of iTunes. -- Ron PS, Here's the output of configure. Do I really need all this stuff just for the GLUT package? C:\GLUT\GLUT-2.0>runghc Setup.hs configure Configuring GLUT-2.0... configure: Dependency base-any: using base-2.1.1 configure: Dependency OpenGL-any: using OpenGL-2.2.1 configure: Using install prefix: C:\Program Files configure: Binaries installed in: C:\Program Files\Haskell\bin configure: Libraries installed in: C:\Program Files\Haskell\GLUT-2.0\ghc-6.6.1 configure: Private binaries installed in: C:\Program Files\GLUT-2.0 configure: Data files installed in: C:\Program Files\Common Files\GLUT-2.0 configure: Using compiler: C:\ghc\ghc-6.6.1\bin\ghc.exe configure: Compiler flavor: GHC configure: Compiler version: 6.6.1 configure: Using package tool: C:\ghc\ghc-6.6.1\bin\ghc-pkg.exe configure: Using ar found on system at: C:\ghc\ghc-6.6.1\bin\ar.exe configure: No haddock found configure: No pfesetup found configure: No ranlib found configure: Using runghc found on system at: C:\ghc\ghc-6.6.1\bin\runghc.exe configure: No runhugs found configure: No happy found configure: No alex found configure: Using hsc2hs: C:\ghc\ghc-6.6.1\bin\hsc2hs.exe configure: No c2hs found configure: No cpphs found configure: No greencard found Setup.hs: Cannot find: sh

5 12

ANN: The Monad.Reader - Issue 8
by Wouter Swierstra 10 Sep '07

10 Sep '07

I am pleased to announce that the latest issue of The Monad.Reader is now available: http://www.haskell.org/haskellwiki/The_Monad.Reader Issue 8 consists of the following two articles: * Brent Yorgey Generating Multiset Partitions * Conrad Parker Type-Level Instant Insanity The Monad.Reader is a quarterly magazine about functional programming. It is less-formal than journal, but somehow more enduring than a wiki page or blog post. If you'd like to submit something to the next issue of The Monad.Reader, please get in touch. I haven't fixed the deadline for the next issue just yet; I hope to send out an official call for copy in the coming weeks. I'd also like to point out that you can now order TMR apparel from: http://www.cafepress.com/TheMonadReader. Enjoy! Wouter This message has been checked for viruses but the contents of an attachment may still contain software viruses, which could damage your computer system: you are advised to perform your own checks. Email communications with the University of Nottingham may be monitored as permitted by UK legislation.

1 0

Re: [Haskell-cafe] Tiny documentation request
by manu 10 Sep '07

10 Sep '07

Neil Mitchell wrotes : > Replicating actual tables with CSS is a nightmare - you shouldn't use > table's for lots of things, I agree > but there are sometimes when it really is > the best option. Which isn't the case here ! Nested lists would easily do the trick... > Fixing up the CSS and still keeping tables is a > perfectly valid option. yes it's true... E.D

1 0

Re: [Haskell-cafe] Speed of character reading in Haskell
by Miguel Mitrofanov 10 Sep '07

10 Sep '07

> I started with the obvious > main = getContents >>= print . tokenise > where tokenise maps its way down a list of characters. This is very > simple, very pleasant, and worked like a charm. > However, the language has an INCLUDE directive, so I'm going to have > to call readFile or something in the middle of tokenising, so the > main tokeniser loop can't be a pure String -> [Token] function any > more. What about > tokenise :: [String] -> ([Token],[FilePath]) > main = print . fst =<< mfix process where > process (tokens,paths) = do > mainContents <- getContents > includes <- mapM readFile paths > return $ tokenise $ mainContents : includes I guess, it would be useful to replace ([Token],[FilePath]) with Writer [FilePath] [Token] > Method 1A (pure list processing) > main = getContents >>= print . doit 0 > doit n ('\n':cs) = doit (n+1) cs > doit n ( _ :cs) = doit n cs > doit n [] = n I think, you should use something like (doit $! n+1) cs here. > In *retrospect*, it is really obvious why this was > necessary, but I must say that in *prospect* I wasn't expecting it. In fact, I was expecting this to be an issue even for 1A. I suppose, GHC is smart enough to suppress lazyness in the first method.

6 7

Elevator pitch for Haskell.
by Paul Johnson 10 Sep '07

10 Sep '07

This page (http://www.npdbd.umn.edu/deliver/elevator.html) has a template for an "elevator pitch". This is what you say to someone when you have 30 seconds to explain your big idea, for instance if you find yourself in an elevator with them. I thought I'd try instantiating it for Haskell. For software developers who need to produce highly reliable software at minimum cost, Haskell is a pure functional programming language that reduces line count by 75% through reusable higher order functions and detects latent defects with its powerful static type system. Unlike Ada and Java, Haskell allows reusable functions to be combined without the overhead of class definitions and inheritance, and its type system prevents the hidden side effects that cause many bugs in programs written in conventional languages. Comments? Paul.

20 29

Re: [Haskell-cafe] Where would I find fromInt?
by Tom Harper 10 Sep '07

10 Sep '07

Hi Paul -- The function you want is called fromIntegral, and works for all Integral types. Using it, you can add a type signature to specify what you want to change the number to (Float, Double, other Integral type, etc. Example: > fromIntegral (4 :: Int) :: Double 4.0 Hope this helps! -- Tom Harper rtharper(a)aftereternity.co.uk +1 949 235 0185 Public Key: http://aftereternity.co.uk/rth.asc On 9/9/07, PR Stanley <prstanley(a)ntlworld.com> wrote: > Hi > Where would I find the fromInt function, please? > Better still, would anyone know how to write a func for converting > int to float and vice versa? > Thanks, Paul > > _______________________________________________ > Haskell-Cafe mailing list > Haskell-Cafe(a)haskell.org > http://www.haskell.org/mailman/listinfo/haskell-cafe > -- Tom Harper rtharper(a)aftereternity.co.uk +1 949 235 0185 Public Key: http://aftereternity.co.uk/rth.asc

1 0

Help understanding type error
by Levi Stephen 10 Sep '07

10 Sep '07

Hi, I'm after some help understanding either what I'm doing wrong, or why this error occurs. I have a data type: > data T a = forall b. (Show b) => T b a and I want to use/extract 'b' from this. > extShow (T b _) = b This gives the following compilation error: extest.hs:5:0: Inferred type is less polymorphic than expected Quantified type variable `b' escapes When checking an existential match that binds $dShow :: {Show b} b :: b The pattern(s) have type(s): T t The body has type: b In the definition of `extShow': extShow (T b _) = b I tried adding a type signature: > extShow' :: (Show b) => T a -> b > extShow' (T b _) = b Now I get a different error: extest.hs:8:19: Couldn't match expected type `b' (a rigid variable) against inferred type `b1' (a rigid variable) `b' is bound by the type signature for `extShow'' at extest.hs:7:18 `b1' is bound by the pattern for `T' at extest.hs:8:10-14 In the expression: b In the definition of `extShow'': extShow' (T b _) = b It seems (to newbie me ;) ) like it should be possible to extract the first part of T, and deduce that it is an instance of the class 'Show'. The following seems ok: > doShow (T b _) = putStrLn (show b) Thanks, Levi

7 7

Hackage and GHC 6.8
by Neil Davies 09 Sep '07

09 Sep '07

Given that GHC 6.8 is just around the corner and, given how it has re-organised the libraries so that the dependencies in many (most/all) the packages in the hackage DB are now not correct. Is there a plan of how to get hackage DB up to speed with GHC 6.8 ? Cheers Neil

5 6