May 2011 - Haskell-Cafe

Apache license, any drawbacks for Haskell packages?
by Magnus Therning 09 May '11

09 May '11

Are there any drawbacks to using the Apache license for Haskell packages? /M -- Magnus Therning OpenPGP: 0xAB4DFBA4 email: magnus(a)therning.org jabber: magnus(a)therning.org twitter: magthe http://therning.org/magnus I invented the term Object-Oriented, and I can tell you I did not have C++ in mind. -- Alan Kay

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repa Shape help
by briand＠aracnet.com 09 May '11

09 May '11

Howdy, as usual, the haskell type system complete defeats me in the simplest of applications: import Data.Array.Repa as A import Data.Array.Repa.Index import Data.Array.Repa.Shape as AS main = do let x = A.fromList (AS.shapeOfList [2, 2]) ([1.0, 2.0, 3.0, 4.0]::[Double]) putStrLn $ show x test_repa.hs:10:13: Ambiguous type variable `sh' in the constraint: `Shape sh' arising from a use of `show' at test_repa.hs:10:13-18 Probable fix: add a type signature that fixes these type variable(s) Failed, modules loaded: none. After much staring at the type signatures I finally figured out that adding a type annotation to x of : :: Array DIM2 Double would fix the problem, but I'm not completely clear as to why. after all fromList is typed: (Shape sh, Elt a) => sh -> [a] -> Array sh a Since it knows [a] is [Double] and sh must be - well I'm not really clear on what sh is supposed to be. therein lies my problem. Although it does seem that sh can be darn near anything, which is probably why it was ambiguous. At one point I had tried something like (2 :. 2) and got a whole host of errors for that too, except that DIM2 is defined in exactly that way, so it's not at all obvious why that didn't work. I was hoping someone could clarify on what's going on. Thanks, Brian

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trying to cabal install lambdabot, failure on 'random' package
by Sean Perry 09 May '11

09 May '11

/usr/bin/ghc --make -package-name show-0.4.1.1 -hide-all-packages -fbuilding-cabal-package -i -idist/build -i. -idist/build/autogen -Idist/build/autogen -Idist/build -optP-include -optPdist/build/autogen/cabal_macros.h -odir dist/build -hidir dist/build -stubdir dist/build -package-id QuickCheck-2.4.0.1-5898cfb0116fc1d6ecef04b3f053c323 -package-id base-4.3.1.0-167743fc0dd86f7f2a24843a933b9dce -package-id random-1.0.0.3-749b78c54a8a99991b32dbb45d98a91b -package-id smallcheck-0.4-008eb21a2943dfdde26401dbc145c45b -package-id syb-0.3-8db7bc4339a1cb8a6f2a46c40447ef0b -O -Wall -XHaskell98 ShowQ ShowFun SimpleReflect <command line>: cannot satisfy -package-id random-1.0.0.3-749b78c54a8a99991b32dbb45d98a91b: random-1.0.0.3-749b78c54a8a99991b32dbb45d98a91b is shadowed by package random-1.0.0.3-57524486875e0c4c260dd22788921013 (use -v for more information) World file is already up to date. cabal: Error: some packages failed to install: lambdabot-4.2.3.2 depends on show-0.4.1.1 which failed to install. lambdabot-utils-4.2.1 failed during the building phase. The exception was: ExitFailure 1 readline-1.0.1.0 failed during the configure step. The exception was: ExitFailure 1 show-0.4.1.1 failed during the building phase. The exception was: ExitFailure 1 I have ghc 7.0.,3 and cabal $ cabal --version cabal-install version 0.10.2 using version 1.10.1.0 of the Cabal library From the recent Haskell Platform for OS X. Ideas?

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Re: [Haskell-cafe] For Project Euler #24 you don't need to generate all the lexicographic permutations <Spoiler>
by KC 08 May '11

08 May '11

I see from the solutions on Project Euler others did think of this way but at least on my last IQ test I did get an 'A'; 95. I am a jenius. :D -- -- Regards, KC

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For Project Euler #24 you don't need to generate all the lexicographic permutations <Spoiler>
by caseyh＠istar.ca 08 May '11

08 May '11

For Project Euler #24 you don't need to generate all the lexicographic permutations by Knuth's method or any other. You're only looking for the millionth lexicographic permutation of "0123456789" Problem 24 A permutation is an ordered arrangement of objects. For example, 3124 is one possible permutation of the digits 1, 2, 3 and 4. If all of the permutations are listed numerically or alphabetically, we call it lexicographic order. The lexicographic permutations of 0, 1 and 2 are: 012 021 102 120 201 210 What is the millionth lexicographic permutation of the digits 0, 1, 2, 3, 4, 5, 6, 7, 8 and 9? <Spoiler> <Spoiler> <Spoiler> Plan of attack: -- The "x"s are different numbers -- 0xxxxxxxxx represents 9! = 362880 permutations/numbers -- 1xxxxxxxxx represents 9! = 362880 permutations/numbers -- 2xxxxxxxxx represents 9! = 362880 permutations/numbers -- 20xxxxxxxx represents 8! = 40320 -- 21xxxxxxxx represents 8! = 40320 -- 23xxxxxxxx represents 8! = 40320 -- 24xxxxxxxx represents 8! = 40320 -- 25xxxxxxxx represents 8! = 40320 -- 26xxxxxxxx represents 8! = 40320 -- 27xxxxxxxx represents 8! = 40320 etc. <Spoiler> <Spoiler> -- lexOrder "0123456789" 1000000 "" lexOrder digits left s | len == 0 = s ++ digits | quot > 0 && rem == 0 = lexOrder (digits\\(show (digits!!(quot-1)))) rem (s ++ [(digits!!(quot-1))]) | quot == 0 && rem == 0 = lexOrder (digits\\(show (digits!!len))) rem (s ++ [(digits!!len)]) | rem == 0 = lexOrder (digits\\(show (digits!!(quot+1)))) rem (s ++ [(digits!!(quot+1))]) | otherwise = lexOrder (digits\\(show (digits!!(quot)))) rem (s ++ [(digits!!(quot))]) where len = (length digits) - 1 facLen = factorial len (quot,rem) = quotRem left facLen

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no time profiling on my MacBookPro8,1
by Nicolas Frisby 08 May '11

08 May '11

For this vanilla program > module Main where > > main = print $ fib 40 > > fib 0 = 1 > fib 1 = 1 > fib n = fib (n - 1) + fib (n - 2) with these commands $ ghc -prof -auto-all -rtsopts -O --make Main.hs -o Main $ ./Main +RTS -p all of the %time cells in the generated Main.prof file are 0.0, as is the total time count (0.00 secs and 0 ticks). The %alloc cells seem normal. Andy Gill noticed that if you compile with -threaded, the %time cells seem normal. I scanned the GHC Trac tickets specific to Mac OS X, but saw no titles that looked similar. Is this a known issue? Thanks.

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For Project Euler #1 isn't it more efficient to generate just the numbers you need? <Spoiler>
by caseyh＠istar.ca 07 May '11

07 May '11

-- Instead of this -- sumMultiples3or5 s = sum [x | x <- [3..s-1], x `mod` 3 == 0 || x `mod` 5 == 0] -- Isn't this faster sumMultiples3or5 s = sum ([x | x <- [3,6..s-1]] `merge` [x | x <- [5,10..s-1]]) merge xs [] = xs merge [] ys = ys merge txs@(x:xs) tys@(y:ys) | x < y = x : xs `merge` tys | x > y = y : txs `merge` ys | otherwise = x : xs `merge` ys

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Server hosting
by Andrew Coppin 07 May '11

07 May '11

OK, so strictly this is unrelated to Haskell as such. However, there's enough people doing webby stuff with Haskell that some of you must have wanted to run your code on a real, Internet-accessible web server. So does anybody have any suggestions on which companies offer the most favourable tools / pricing? I currently have a website, but it supports only CGI *scripts* (i.e., Perl or PHP). It does not support arbitrary CGI *binaries*, which is what I'd want for Haskell. In fact, I don't have control over the web server at all; I just put content on there. The same provider can offer me a virtual server, but at 3x the price I'm currently paying. I simply cannot afford that kind of money just for silly toy projects. What does everybody else use?

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lambdabot install error
by epsilonhalbe 07 May '11

07 May '11

hey haskellers, i'm fresh into haskell and love it. so to do faster easier haskell i wanted to install lambdabot but had to face some errors - i don't understand them at all here is some error output from zsh: http://hpaste.org/46401/bot_install_error can anyone help me - i'm working on a debian (crunchbang) y.t epsilonhalbe (ε/2)

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Manatee-0.2.1 release!
by Lazycat Manatee 07 May '11

07 May '11

Hi all, Manatee-0.2.1 release! (Detail see: http://goo.gl/MkVw http://goo.gl/PnPbq http://goo.gl/OSpz8) New features in new version: * Show welcome page when you first time use Manatee, make manatee easier to use. * Keymap helper, you just need hit Ctrl+/ or Ctrl+? if you don't know keymap. * Window layout save/restore, you play Manatee and shutdown, all window layout will restore when you next startup. * Tab position save when you switch to other tab-group, and restore tab position when you switch back. * Use new input-framework instead manatee-anything package. * Many detail improve and bug fixed. Enjoy! -- Andy

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