Re: [Haskell-cafe] Efficient functional idiom for histogram
On Sat, Aug 1, 2009 at 4:44 PM, Paul Moorep.f.mo...@gmail.com wrote: PS I know my code is probably fairly clumsy - I'd appreciate style suggestions, but my main interest here is whether a beginner, with a broad programming background, a basic understanding of Haskell, and access to Google, put together a clear, efficient, program (ie, the case where my usual scripting language is too slow and I want to knock something up quickly in a high-level, high-performance language). Here is one way to rewrite your program. It improved the speed somewhat for me. I timed both programs on my computer. I suppose one could try using an array for calculating the histogram as well, but I only tried the simples thing here. I hope someone can weigh in with a more thorough analysis. Please note how I've avoided including the IO Monad in some type signatures by extracting the data from it locally (with -). It is quite possible to apply the histogram function to the data before going through the IO Monad as well, but it doesn't appear to change the execution speed much here. Caveat: My testing wasn't extensive. I just compiled with -O and timed the programs a couple of times. import System.Random import qualified Data.Map as Map import Data.Map (Map) import Data.List diceRolls :: Int - IO [Int] diceRolls highVal = do generator - getStdGen return (randomRs (1, highVal) generator) groupDice :: Int - [Int] - [[Int]] groupDice chunk rolls = map (take chunk) $ iterate (drop chunk) rolls simulate :: Int - Int - Int - IO [Int] simulate count m n = do rolls - diceRolls n let sums = map sum $ groupDice m rolls return (take count sums) histogram :: Ord a = [a] - [(a,Int)] histogram = Map.assocs . foldl f Map.empty where f m k = Map.insertWith (+) k 1 m simulation = do lst - simulate 10 3 6 return (histogram $ lst) main = do s - simulation putStrLn (show s) ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Haskell haikus
On Sat, Dec 6, 2008 at 1:18 AM, Gwern Branwen [EMAIL PROTECTED] wrote: So: does anybody have a haiku I missed? Or even better, is anyone feeling poetically inspired tonight? :) There's one by shapr in HaskellQuotes at the Wiki. shapr the snow falls slowly, the lambdas are lifting, weak head normal form Here's one by me: Without a kigo / or requisite syllables / haiku don't typecheck Pekka Karjalainen ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: [Haskell] GHC 6.10 and OpenGL
On Tue, Dec 2, 2008 at 6:55 PM, Claus Reinke [EMAIL PROTECTED] wrote: I finally got round to trying cabal-install with OpenGL/GLUT, using a freshly built ghc head, a cygwin bash, and [...] C:\Program Files\Haskell\GLUT-2.1.1.2\ghc-6.11.20081202/libHSGLUT-2.1.1.2.a(Window.o):fake: (.text+0x15): undefined reference to `glutWarpPointer' [...] I believe these errors are caused by the wrong calling convention being used in the Haskell bindings. This part in the configure script tests the build (host) platform: case $host in *-mingw32) CALLCONV=stdcall ;; *) CALLCONV=ccall ;; esac Since it doesn't test for Cygwin, you end up with the calling convention being ccall, which leads to the linker errors because of associated name mangling (you would also see run-time crashes if you managed to somehow link your program). Pekka ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] (OT) Has GHC stopped being the Glorious Glasgow Haskell Compiler?
On Thu, Nov 20, 2008 at 6:26 AM, Benjamin L.Russell [EMAIL PROTECTED] wrote: Am I missing something, or has the nickname been changed? Well, 'ghc --version' tells me that I am using The Glorious Glasgow Haskell Compilation System, version 6.10.1... ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Linker errors to OpenGL with GHC 6.10.1
2008/11/13 Greg Fitzgerald [EMAIL PROTECTED]: Do you know how I can fix these linker errors? C:\projects\funcat HelloWorld.hs import Graphics.Rendering.OpenGL import Graphics.UI.GLUT main = do (progname, _) - getArgsAndInitialize createWindow Hello World displayCallback $= clear [ColorBuffer] mainLoop C:\projects\funls lib GlU32.Lib glut32.lib OpenGL32.Lib glut.def glut32.dll C:\projects\funghc -Llib -lglut32 -lglu32 -lopengl32 HelloWorld.hs --make Linking HelloWorld.exe ... C:\Program Files\Haskell\GLUT-2.1.1.2\ghc-6.10.1/libHSGLUT-2.1.1.2.a(Begin.o):fake:(.text+0x1cb): undefined reference to `glutGet' [...] Thanks, Greg I'm assuming this is on Windows because of C:\... These kinds of linker errors happened to me when I built libHSGLUT with a wrong type of calling convention (by accident). There are two callconvs, and they are called stdcall and ccall on the Haskell side. The 'runhaskell setup configure' step is supposed to detect the correct one to use, so you should run it and then grep for lines with CALLCONV. They should say stdcall on Windows. If you find them saying ccall, that's likely the cause of all the linker errors. (Most Windows dynamic libraries use stdcall, but for extra configuration fun OpenAL uses ccall.) If this is the problem, you can change the offending ccall in the configuration files to stdcall and rebuild the library. Grepping for CALLCONV will also show the places you need to change this way. In my case the wrong configuration came from using the sh program from Cygwin. With the MSYS variety there was no problem. To be exact, it came down to the $host variable checked by the configuration script. Pekka ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Extract source code from literate Haskell (LHS) files
On 9/30/07, Peter Verswyvelen [EMAIL PROTECTED] wrote: This is of course very easy to do manually, but does a command line tool exist for extracting source code from literate Haskell files? There are a lot of good answers already. You can also use some GHC command line options. Please see: http://haskell.org/haddock/haddock-html-0.8/invoking.html#cpp Pekka ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Hints for Euler Problem 11
On 8/15/07, Mathias Biilmann Christensen [EMAIL PROTECTED] wrote: Spotted this thread as I was working on a Haskell solution for this one myself - here's the solution I came up with: [ ... ] raw_matrix = 08 02 22 97 38 15 00 40 00 75 04 05 07 78 52 12 50 77 91 08 ++ 49 49 99 40 17 81 18 57 60 87 17 40 98 43 69 48 04 56 62 00 ++ 81 49 31 73 55 79 14 29 93 71 40 67 53 88 30 03 49 13 36 65 ++ [ ... ] A little style issue here on the side, if I may. You don't need to use (++) to join multiline string literals. text = If you want to have multiline string literals \ \in your source code, you can break them up with \ \backslashes. Any whitespace characters between \ \two backslashes will be ignored. (The Haskell 98 Report calls them backslants.) Pekka ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] A few questions on primes generating.
On 8/13/07, L.Guo [EMAIL PROTECTED] wrote: Hi All: Hello, I am reading http://www.haskell.org/haskellwiki/Prime_numbers The code in sector 1 Bitwise prime sieve. I have 3 questions about it. 1) In function go, what does the number 46340 mean ? Is it sqrt(MAX_LONG) ? Yes, it appears so. In a 32 bit implementation I get: Prelude sqrt $ fromIntegral (maxBound :: Int) 46340.950001051984 2) We have this type definition : pureSieve :: Int - Int Why there is no error (type mismatch) of this call in func main : pureSieve 1000 If you have integer literals in your program, the compiler sees a fromInteger in front of them. So the value is just converted to type Int automatically, because that is expected here. You can give different numeric default declarations in your own modules. Please see sections 10.3 (for overloaded literals) and 10.4 (for defaults) here: http://www.haskell.org/tutorial/numbers.html Sometimes you can get an overflow like this: Prelude 1000 :: Int -159383552 3) In main again, what does expression [| x |] mean ? Why this cannot be execute in GHCi ? It's Template Haskell, and is used there for some kind of optimisation (I think). Template Haskell needs to be enabled with a command line switch for it to work. Please see the documentation for more information. It's section 7.6 in your User's Guide. Though in this case you can probably just remove it to try out the program. Perhaps someone else can explain what actual effect it has here. Pekka ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] RLE in Haskell: why does the type variable get instantiated?
On 7/31/07, Chris Eidhof [EMAIL PROTECTED] wrote: Hey Haskell-Cafe, I was trying out the code in Dons's article [1], and I noticed a weird thing when doing it in GHCi. When binding the function composition to a variable, the type suddenly changes. I'm not completely sure why this happens. Is this because GHCi is in a monad and wants to find an instance for the type variable? Here's my GHCi session: [ ... ] Apfelmus already explained why it happens. I'd like to add one thing. If you are experimenting with GHCi, you can turn the restriction off with the option -fno-monomorphism-restriction. In GHCi itself this is given as follows: Prelude :set -fno-monomorphism-restriction After giving this and entering the same things as in your original message, the type of encode came out to be as follows: Prelude Control.Arrow Data.List let encode = map (length head) . group Prelude Control.Arrow Data.List :t encode encode :: (Eq a) = [a] - [(Int, a)] This option also saves some typing (of the variety you do on the keyboard!) when you just want to use GHCi as a calculator: Prelude Control.Arrow Data.List let x = 5 Prelude Control.Arrow Data.List let y = 6.3 Prelude Control.Arrow Data.List x*y 31.5 Instead of Integer, the type of x is now x :: (Num t) = t without the restriction, and I don't need to add fromInteger to the multiplication. I don't recommend you to use this option all the time, of course. It's just a convenience. Pekka ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: partitions of a multiset
On 7/24/07, Brent Yorgey [EMAIL PROTECTED] wrote: I'm not sure what a formal mathematical definition would be off the top of my head; but in Haskell, given a list L :: [a], I'm looking for all partitions P :: [[a]] where (sort . concat $ P) == (sort L). Here is quick attempt that requires Ord [a] and expects a sorted list. It may very well not be correct, but it seemed to get all the simple cases I tried right. Can you find a counterexample where it doesn't work? import Data.List (nub, (\\)) subsets [] = [[]] subsets xs = []:[ a:b | a - nub xs, let (_:tl) = dropWhile (/=a) xs, b - subsets tl ] multiPart [] = [[]] multiPart xs = [ a:b | a - takeWhile ((head xs ==) . head) $ tail $ subsets xs, b - multiPart $ xs \\ a, null b || a = head b ] It would be nice if one could get rid of the (=) and hence Ord without allowing duplicates. Furthermore, I haven't worried at all about space or time efficiency while writing this. I'd want to get it right first. Pekka ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
