- Haskell-Cafe - Haskell.org

Newbie terminology for partial application
by Peter Verswyvelen 28 Aug '07

28 Aug '07

A while ago I confused "currying" with "partial application", which was pointed out by members of this community, and the wiki pages got adapted so that newbies like me don't make the same mistake twice ;) That's great. Anyway, at the risk of making mistakes again, I'm looking for good terminilogy when talking about "partial application". For example: -- uncurried form *f (x,y)* = -- whatever -- curried form *g x y *= f (x,y) -- partial application *h x *= g x But when writing text documents, I guess it is common to say "/g is curried/", but is it also common to say /"g is partially applied"? /The latter sounds silly to a non-native speaker like myself... Or shouldn't it be? / /And what is "application"? I guess it means that (g x y) is internally translated to ((g $ x) $ y) which is translated into (apply (apply g x) y) where apply is a primitive function? Thanks, Peter PS: sorry for the poor English! / /

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Re: [Haskell-cafe] Ideas
by Andrew Coppin 27 Aug '07

27 Aug '07

Neil Mitchell wrote: > HI > > >>> Flippi (google: Haskell Flippi) >>> >> ...and yet haskell.org uses WikiMedia? (Which is written in something >> bizzare like Perl...) >> > > Yes, but WikiMedia is a result of years of work, Flippi is a lot less. > Wikipedia uses WikiMedia - its a tried and proven solution. > Well, I guess... I just thought, you know, the Tcl wiki is written in Tcl, why isn't the Haskell wiki written in Haskell? Hey, aren't we trying to tell people is a *useful* language that people should learn and use? ;-) >>>> - A "graphical programming tool". (You add boxes and put in lines, it >>>> constructs a "program" that you can run.) >>>> >> Have you ever played with KLogic? You draw boxes and lines, and it makes >> some logic. (As in the digital electronics sense of "logic".) >> >> I have some (very expensive) software called Reaktor. You draw boxes and >> lines, it does DSP algorithms. You build synthesizers and effects boxes >> with it. >> > > That sounds exactly like PureData - you can also do graphics as well > with PureData, the demo I saw was very cool. Of course, PureData is > written in C with Haskell as an extension language. > Oh. Ah well.. > The last two ideas you mentioned require a graphical user interface, > which is an area of Haskell which is comparatively weak, compared to > the rest of Haskell. > Yeah, I noticed. Though actually Gtk2hs isn't too bad. (There's a few corners that require bit-flipping and other low-level strangeness...)

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Help understanding a partial application
by Levi Stephen 27 Aug '07

27 Aug '07

Hi, I was browsing through the source code for Data.Foldable and having trouble comprehending it (which was kind of the point of browsing the code, so I could learn something ;) ) I'm looking at foldl foldl :: (c -> d -> c) -> c -> t d -> c foldl f z t = appEndo (getDual (foldMap (Dual . Endo . flip f) t)) z But, I haven't got very far. I'm still trying to follow: Endo . flip f f is of type c->d->c, so this makes flip f of type d->c->c. I think the Endo constructor is of type (a->a)->Endo a I think a is binding to a function type here, but can not work out what. (From memory) ghci reports > :t Endo . flip (+) Num a => a -> Endo a So, this looks like a partial application of the constructor? But, this still isn't helping me understand. Any thoughts or pointers that might help me comprehend what's happening? Thanks, Levi lstephen.wordpress.com

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Style
by Arie Groeneveld 27 Aug '07

27 Aug '07

Hi, I defined several functions for calculating the number of trailing zero's of n! tm = sum . takeWhile(>0) . iterate f . f where f = flip div 5 tm1 n = sum . takeWhile(>0) . map (div n . (5^)) $ [1..] tm2 n = sum . takeWhile(>0) . map (div n) $ iterate ((*)5) 5 tm3 = sum . takeWhile(>0) . flip map (iterate ((*)5) 5) . div Questions: Which one is the most elegant one generally speaking? Which one is most natural in Haskell? Is there more 'beauty' to possible? My personal choice is 'tm'. I like 'tm3' (a revised version of tm2) in terms of pointlessness and not having a 'where', but I think it's a bit contrived because of the 'flip'. Comments? Thanks @@i

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Re: [Haskell-cafe] Norvig's Sudoku Solver in Haskell
by Yitzchak Gale 27 Aug '07

27 Aug '07

I wrote: >> Perhaps you would gain something if you used Data.Map.! >> instead of your "lookup". Manu wrote: > I'm not sure I understand, do you mean I should have use a strict Map > constructor ? > like : Map !key !value ? No, there is an operator in Data.Map called "!". > how can it replace the lookup function ? Use > import qualified Data.Map as M > import Data.Map (!) Then, instead of "lookup k m" use "m ! k". >> Other than that, I'm not >> sure why your code runs slower than mine. Malte Milatz wrote: MM> The use of "length" here is not an actual MM> performance problem... Maybe not there, but I think Malte's suggestion might actually improve performance if you do the same thing a few lines further down, where you wrote: > case length dPlaces of By using Malte's idea there instead of length, you might allow some calculations inside dPlaces to be lazily skipped. Regards, Yitz

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arrows-.02 fails when rebuilding ghc 6.6.1
by Luc TAESCH 27 Aug '07

27 Aug '07

I try download and build 6.6.1 ( as ubntu has just 6.6 on package) and most went ok ( compiler and most libs) but arrows i tried and download arrow 0.2 from hackage but no more success any ideas ? ( knowing 6.6 is also on the machine if that matters) luc@haserv:~/src/arrows-0.2$ runghc Setup.hs build Preprocessing library arrows-0.2... Building arrows-0.2... [ 1 of 13] Compiling Data.Stream ( Data/Stream.hs, dist/build/Data/Stream.o ) [ 2 of 13] Compiling Control.Arrow.Transformer ( Control/Arrow/Transformer.hs, dist/build/Control/Arrow/Transformer.o ) [ 3 of 13] Compiling Control.Arrow.Operations ( Control/Arrow/Operations.hs, dist/build/Control/Arrow/Operations.o ) [ 4 of 13] Compiling Control.Arrow.Transformer.CoState ( Control/Arrow/Transformer/CoState.hs, dist/build/Control/Arrow/Transformer/CoState.o ) [ 5 of 13] Compiling Control.Arrow.Internals ( Control/Arrow/Internals.hs, dist/build/Control/Arrow/Internals.o ) [ 6 of 13] Compiling Control.Arrow.Transformer.Automaton ( Control/Arrow/Transformer/Automaton.hs, dist/build/Control/Arrow/Transformer/Automaton.o ) Control/Arrow/Transformer/Automaton.hs:98:0: Illegal instance declaration for `ArrowWriter w (Automaton a)' (the Coverage Condition fails for one of the functional dependencies; Use -fallow-undecidable-instances to permit this) In the instance declaration for `ArrowWriter w (Automaton a)' Control/Arrow/Transformer/Automaton.hs:104:0: Illegal instance declaration for `ArrowError r (Automaton a)' (the Coverage Condition fails for one of the functional dependencies; Use -fallow-undecidable-instances to permit this) In the instance declaration for `ArrowError r (Automaton a)' Control/Arrow/Transformer/Automaton.hs:115:0: Illegal instance declaration for `ArrowReader r (Automaton a)' (the Coverage Condition fails for one of the functional dependencies; Use -fallow-undecidable-instances to permit this) In the instance declaration for `ArrowReader r (Automaton a)' Control/Arrow/Transformer/Automaton.hs:120:0: Illegal instance declaration for `ArrowState s (Automaton a)' (the Coverage Condition fails for one of the functional dependencies; Use -fallow-undecidable-instances to permit this) In the instance declaration for `ArrowState s (Automaton a)' Control/Arrow/Transformer/Automaton.hs:126:0: Illegal instance declaration for `ArrowAddWriter w (Automaton a) (Automaton a')' (the Coverage Condition fails for one of the functional dependencies; Use -fallow-undecidable-instances to permit this) In the instance declaration for `ArrowAddWriter w (Automaton a) (Automaton a')' I discovered recently that my ubuntu package were providing only 6.6 and the latest cabal needs 6.6.1. when rebuilding this one from the tar ( not the head on darcs) most went ok but the arrows lib. I also tried to get it from hackage, but idem: ( I also have 6.6 on the machaine dos it matters ?) here is the build from hacakge with runghc : luc@haserv:~/src/arrows-0.2$ runghc Setup.hs build Preprocessing library arrows-0.2... Building arrows-0.2... [ 1 of 13] Compiling Data.Stream ( Data/Stream.hs, dist/build/Data/Stream.o ) [ 2 of 13] Compiling Control.Arrow.Transformer ( Control/Arrow/Transformer.hs, dist/build/Control/Arrow/Transformer.o ) [ 3 of 13] Compiling Control.Arrow.Operations ( Control/Arrow/Operations.hs, dist/build/Control/Arrow/Operations.o ) [ 4 of 13] Compiling Control.Arrow.Transformer.CoState ( Control/Arrow/Transformer/CoState.hs, dist/build/Control/Arrow/Transformer/CoState.o ) [ 5 of 13] Compiling Control.Arrow.Internals ( Control/Arrow/Internals.hs, dist/build/Control/Arrow/Internals.o ) [ 6 of 13] Compiling Control.Arrow.Transformer.Automaton ( Control/Arrow/Transformer/Automaton.hs, dist/build/Control/Arrow/Transformer/Automaton.o ) Control/Arrow/Transformer/Automaton.hs:98:0: Illegal instance declaration for `ArrowWriter w (Automaton a)' (the Coverage Condition fails for one of the functional dependencies; Use -fallow-undecidable-instances to permit this) In the instance declaration for `ArrowWriter w (Automaton a)' Control/Arrow/Transformer/Automaton.hs:104:0: Illegal instance declaration for `ArrowError r (Automaton a)' (the Coverage Condition fails for one of the functional dependencies; Use -fallow-undecidable-instances to permit this) In the instance declaration for `ArrowError r (Automaton a)' Control/Arrow/Transformer/Automaton.hs:115:0: Illegal instance declaration for `ArrowReader r (Automaton a)' (the Coverage Condition fails for one of the functional dependencies; Use -fallow-undecidable-instances to permit this) In the instance declaration for `ArrowReader r (Automaton a)' Control/Arrow/Transformer/Automaton.hs:120:0: Illegal instance declaration for `ArrowState s (Automaton a)' (the Coverage Condition fails for one of the functional dependencies; Use -fallow-undecidable-instances to permit this) In the instance declaration for `ArrowState s (Automaton a)' Control/Arrow/Transformer/Automaton.hs:126:0: Illegal instance declaration for `ArrowAddWriter w (Automaton a) (Automaton a')' (the Coverage Condition fails for one of the functional dependencies; Use -fallow-undecidable-instances to permit this) In the instance declaration for `ArrowAddWriter w (Automaton a) (Automaton a')' Control/Arrow/Transformer/Automaton.hs:135:0: Illegal instance declaration for `ArrowAddReader r (Automaton a) (Automaton a')' (the Coverage Condition fails for one of the functional dependencies; Use -fallow-undecidable-instances to permit this) In the instance declaration for `ArrowAddReader r (Automaton a) (Automaton a')' Control/Arrow/Transformer/Automaton.hs:144:0: Illegal instance declaration for `ArrowAddState r (Automaton a) (Automaton a')' (the Coverage Condition fails for one of the functional dependencies; Use -fallow-undecidable-instances to permit this) In the instance declaration for `ArrowAddState r (Automaton a) (Automaton a')' luc@haserv:~/src/arrows-0.2$ ------------------------------------------------------- here is a make from the build in the libraries tree under ghc 6.6.1 luc@haserv:~/Desktop/ghc-6.6.1-src/ghc-6.6.1/libraries/arrows$ make gcc -E -undef -traditional -P \ -DIMPORT_DIR='"/home/luc/Desktop/ghc-6.6.1-src/ghc-6.6.1/libraries/arrows"' \ -DLIB_DIR='"/home/luc/Desktop/ghc-6.6.1-src/ghc-6.6.1/libraries/arrows"' \ -DINCLUDE_DIR='"/home/luc/Desktop/ghc-6.6.1-src/ghc-6.6.1/libraries/arrows/include"' \ -DDATA_DIR='"/home/luc/Desktop/ghc-6.6.1-src/ghc-6.6.1/libraries/arrows"' \ -DHTML_DIR='"/home/luc/Desktop/ghc-6.6.1-src/ghc-6.6.1/libraries/arrows/html"' \ -DHADDOCK_IFACE='"/home/luc/Desktop/ghc-6.6.1-src/ghc-6.6.1/libraries/arrows/html/arrows.haddock"' \ -DFPTOOLS_TOP_ABS='"/home/luc/Desktop/ghc-6.6.1-src/ghc-6.6.1"' \ -x c -I../../includes -Iinclude -DPACKAGE=arrows -DVERSION=0.2.1 -DPKG_LIBDIR='"/usr/local/lib/ghc-6.6.1"' -DPKG_DATADIR='"/usr/local/share/ghc-6.6.1"' package.conf.in | \ grep -v '^#pragma GCC' | \ sed -e 's/""//g' -e 's/:[ ]*,/: /g' >package.conf.inplace gcc -E -undef -traditional -P -DINSTALLING \ -DIMPORT_DIR='"/usr/local/lib/ghc-6.6.1/imports"' \ -DLIB_DIR='"/usr/local/lib/ghc-6.6.1"' \ -DINCLUDE_DIR='"/usr/local/lib/ghc-6.6.1/include"' \ -DDATA_DIR='"/usr/local/share/ghc-6.6.1"' \ -DHTML_DIR='"/usr/local/share/ghc-6.6.1/html/libraries/arrows"' \ -DHADDOCK_IFACE='"/usr/local/share/ghc-6.6.1/html/libraries/arrows/arrows.haddock"' \ -x c -I../../includes -Iinclude -DPACKAGE=arrows -DVERSION=0.2.1 -DPKG_LIBDIR='"/usr/local/lib/ghc-6.6.1"' -DPKG_DATADIR='"/usr/local/share/ghc-6.6.1"' package.conf.in | \ grep -v '^#pragma GCC' | \ sed -e 's/""//g' -e 's/:[ ]*,/: /g' >package.conf.installed ../../utils/ghc-pkg/ghc-pkg-inplace update - --force-files <package.conf.inplace Reading package info from stdin ... done. /home/luc/Desktop/ghc-6.6.1-src/ghc-6.6.1/libraries/arrows/include doesn't exist or isn't a directory (ignoring) cannot find libHSarrows.a on library path (ignoring) Saving old package config file... done. Writing new package config file... done. ../../utils/ghc-pkg/ghc-pkg-inplace update - -f ../../driver/package.conf --force-files <package.conf.installed Reading package info from stdin ... done. cannot find libHSarrows.a on library path (ignoring) Saving old package config file... done. Writing new package config file... done. ../../compiler/ghc-inplace -H16m -O -fallow-undecidable-instances -package-name arrows-0.2.1 -O -Rghc-timing -fgenerics -package base -fgenerics -split-objs -c Control/Arrow/Internals.hs -o Control/Arrow/Internals.o -ohi Control/Arrow/Internals.hi Control/Arrow/Internals.hs:29:0: Failed to load interface for `Control.Arrow.Operations': Use -v to see a list of the files searched for. <<ghc: 24450740 bytes, 4 GCs, 136484/136484 avg/max bytes residency (1 samples), 16M in use, 0.00 INIT (0.00 elapsed), 0.16 MUT (0.51 elapsed), 0.07 GC (0.20 elapsed) :ghc>> make: *** [Control/Arrow/Internals.o] Error 1 luc@haserv:~/Desktop/ghc-6.6.1-src/ghc-6.6.1/libraries/arrows$

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Re: [Haskell-cafe] Norvig's Sudoku Solver in Haskell
by manu 27 Aug '07

27 Aug '07

> From: Malte Milatz <malte(a)gmx-topmail.de> > Subject: Re: [Haskell-cafe] Norvig's Sudoku Solver in Haskell > > Your program was wrapped by your mail client, so you may want to > hpaste > your program for easier digestion. > here it is : http://hpaste.org/2452 > > Your profiling output suggests that much time is consumed by the > lookup > function. Since you're using (fromJust . lookup) everywhere anyway, a > data structure not envolving the Maybe type is probably a more succint > choice. And why bother with characters and strings? > no rationale except that's what the original Python script did use >> newV2 <- case length newCell of >> 0 -> Nothing >> 1 -> do let peersOfS = [ s' | s' <- lookup s peers ] >> res <- foldM eliminate newV (zip peersOfS >> (cycle newCell)) >> return res >> _ -> return newV > > The use of “length” here is not an actual performance problem, but > unnecessary. Simply write: case newCell of [] -> ... > [_] -> ... > _ -> ... > > The same is valid for your other use of length. > > Malte I see, thanks ! E.D

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Norvig's Sudoku Solver in Haskell
by manu 27 Aug '07

27 Aug '07

Hello, After reading Peter Norvig's take on writing a Sudoku solver (http:// norvig.com/sudoku.html) I decided that I would port his program to Haskell, without changing the algorithm, that'll make a nice exercise I thought and should be fairly easy... Boy, was I wrong ! Anyway, I eventually managed to tiptoe around for loops, mutable state, etc... However, when I run my program against the test data provided (http:// norvig.com/top95.txt) I find it takes around 1m20 s to complete (compiled with -fvia-C and - O2, on a MacBook Pro 2.33GHz Intel Core 2 Duo). That's roughly 8 times longer than Norvig's Python script. That's not what I expected ! My program is also longer than the Python version. Being a beginner, I am convinced my implementation is super naive and non idiomatic. A seasonned Haskeller would do much shorter and much faster. I don't know how to improve it though ! Should I introduce more strictness ? replace lists with more efficient data structures (ByteStrings, Arrays) ? Here is my program, and part of the profiling (memory allocation looks huge !) I hope this post wasn't too long. Thanks for any advice ! Emmanuel. {- This is an attempt to implement in Haskell, Peter Norvig's sudoku solver : "Solving Every Sudoku Puzzle" (http://norvig.com/sudoku.html) In Norvig's program, methods which change a grid return either a new grid, either False (failure). Here I use Maybe, and return Just grid or Nothing in case of failure -} module Main where import Prelude hiding (lookup) import Data.List hiding (lookup) import qualified Data.Map as M import Control.Monad import Maybe import System.IO -------------------------------------------------- -- Types type Digit = Char type Square = String type Unit = [Square] -- We represent our grid as a Map type Grid = M.Map Square [Digit] -------------------------------------------------- -- Setting Up the Problem rows = "ABCDEFGHI" cols = "123456789" digits = "123456789" cross :: String -> String -> [String] cross rows cols = [ r:c:[] | r <- rows, c <- cols ] squares :: [Square] squares = cross rows cols -- ["A1","A2","A3",...] unitlist :: [Unit] unitlist = [ cross rows [c] | c <- cols ] ++ [ cross [r] cols | r <- rows ] ++ [ cross rs cs | rs <- ["ABC","DEF","GHI"], cs <- ["123","456","789"]] units :: M.Map Square [Unit] units = M.fromList [ (s, [ u | u <- unitlist, elem s u ]) | s <- squares ] peers :: M.Map Square [Square] peers = M.fromList [ (s, set [[ p | p <- e, p /= s ] | e <- lookup s units ]) | s <- squares ] where set = nub . concat -------------------------------------------------- -- Wrapper around M.lookup used in list comprehensions lookup :: (Ord a, Show a) => a -> M.Map a b -> b lookup k v = case M.lookup k v of Just x -> x Nothing -> error $ "Error : key " ++ show k ++ " not in map !" -- lookup k m = fromJust . M.lookup k m -------------------------------------------------- -- Parsing a grid into a Map parsegrid :: String -> Maybe Grid parsegrid g = do regularGrid g foldM assign allPossibilities (zip squares g) where allPossibilities :: Grid allPossibilities = M.fromList [ (s,digits) | s <- squares ] regularGrid :: String -> Maybe String regularGrid g = if all (\c -> (elem c "0.-123456789")) g then (Just g) else Nothing -------------------------------------------------- -- Propagating Constraints assign :: Grid -> (Square, Digit) -> Maybe Grid assign g (s,d) = if (elem d digits) then do -- check that we are assigning a digit and not a '.' let toDump = delete d (lookup s g) res <- foldM eliminate g (zip (repeat s) toDump) return res else return g eliminate :: Grid -> (Square, Digit) -> Maybe Grid eliminate g (s,d) = let cell = lookup s g in if not (elem d cell) then return g -- already eliminated -- else d is deleted from s' values else do let newCell = delete d cell newV = M.insert s newCell g -- newV2 <- case length newCell of -- contradiction : Nothing terminates the computation 0 -> Nothing -- if there is only one value (d2) left in square, remove it from peers 1 -> do let peersOfS = [ s' | s' <- lookup s peers ] res <- foldM eliminate newV (zip peersOfS (cycle newCell)) return res -- else : return the new grid _ -> return newV -- Now check the places where d appears in the units of s let dPlaces = [ s' | u <- lookup s units, s' <- u, elem d (lookup s' newV2) ] case length dPlaces of 0 -> Nothing -- d can only be in one place in unit; assign it there 1 -> assign newV2 (head dPlaces, d) _ -> return newV2 -------------------------------------------------- -- Search search :: Maybe Grid -> Maybe Grid search Nothing = Nothing search (Just g) = if all (\xs -> length xs == 1) [ lookup s g | s <- squares ] then (Just g) -- solved else do let (_,s) = minimum [ (length (lookup s g),s) | s <- squares, length (lookup s g) > 1 ] g' = g -- copie of g foldl' some Nothing [ search (assign g' (s,d)) | d <- lookup s g ] where some Nothing Nothing = Nothing some Nothing (Just g) = (Just g) some (Just g) _ = (Just g) -------------------------------------------------- -- Display solved grid printGrid :: Grid -> IO () printGrid = putStrLn . gridToString gridToString :: Grid -> String gridToString g = let l0= map snd (M.toList g) -- [("1537"),("4"),...] l1 = (map (\s -> " " ++ s ++ " ")) l0 -- [" 1 "," 2 ",...] l2 = (map concat . sublist 3) l1 -- [" 1 2 3 "," 4 5 6 ",...] l3 = (sublist 3) l2 -- [[" 1 2 3 "," 4 5 6 "," 7 8 9 "],...] l4 = (map (concat . intersperse "|")) l3 -- [" 1 2 3 | 4 5 6 | 7 8 9 ",...] l5 = (concat . intersperse [line] . sublist 3) l4 in unlines l5 where sublist n [] = [] sublist n xs = take n xs : sublist n (drop n xs) line = hyphens ++ "+" ++ hyphens ++ "+" ++ hyphens hyphens = take 9 (repeat '-') -------------------------------------------------- main :: IO () main = do h <- openFile "top95.txt" ReadMode grids <- hGetContents h let solved = mapMaybe (search . parsegrid) (lines grids) mapM_ printGrid solved hClose h ************************************************************************ *** Sun Aug 26 13:44 2007 Time and Allocation Profiling Report (Final) sudoku_norvig +RTS -p -hc -RTS total time = 49.40 secs (988 ticks @ 50 ms) total alloc = 6,935,777,308 bytes (excludes profiling overheads) COST CENTRE MODULE %time %alloc lookup Main 65.7 22.6 eliminate Main 32.4 70.3 search Main 1.8 6.3 individual inherited COST CENTRE MODULE no. entries % time %alloc %time %alloc MAIN MAIN 1 0 0.0 0.0 100.0 100.0 main Main 190 1 0.0 0.0 100.0 100.0 printGrid Main 214 95 0.0 0.0 0.0 0.1 gridToString Main 215 665 0.0 0.1 0.0 0.1 search Main 208 427143 1.8 6.3 99.4 99.2 assign Main 210 468866 0.1 0.6 90.4 90.3 eliminate Main 212 30626903 32.2 69.8 89.9 89.6 lookup Main 213 172203504 57.7 19.9 57.7 19.9 lookup Main 211 468866 0.4 0.1 0.4 0.1 lookup Main 209 22447632 7.2 2.6 7.2 2.6 parsegrid Main 192 95 0.0 0.0 0.6 0.7 assign Main 198 7695 0.0 0.0 0.6 0.7 eliminate Main 201 51054 0.2 0.5 0.6 0.7 lookup Main 202 1239860 0.4 0.1 0.4 0.1 lookup Main 200 1953 0.0 0.0 0.0 0.0 ... (more innocuous stuff)

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Re: [Haskell-cafe] Re: Parsec is being weird at me
by Andrew Coppin 27 Aug '07

27 Aug '07

Chris Casinghino wrote: > On 8/25/07, Andrew Coppin <andrewcoppin(a)btinternet.com> wrote: > >> >> I thought the whole *purpose* of the endBy combinator was to keep >> applying one parser until the other one succeeds? >> > > > I don't think this is a lookahead problem, but rather just a > misreading of the spec of endBy. Here it is: > > (endBy p sep) parses zero or more occurrences of p, seperated and > ended by sep. Returns a list of values returned by p. > > The key text is "seperated and ended by sep". Not just ended by. > ...so then what does sepEndBy do?

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nested datatypes
by Thomas Girod 27 Aug '07

27 Aug '07

Hi there. recently I was trying to represent complex data by defining several datatypes and nesting them, such as data Foo = Foo { foo :: Bar } deriving (Eq,Show) data Bar = Bar { bar :: Int } deriving (Eq,Show) To change only a part of the data, syntactic sugar is quite convenient. But it seems to be quite painful with nested datatypes. b = Bar 10 f = Foo b foobar :: Int -> Foo -> Foo foobar i f = let nb = (foo f){bar = i} in f{foo = nb} So, my question is : is there a nifty way to modify data within a nested datatype, similar to the f{foo = bar} style ? If not, anyone is using some kind of workaround for this ?

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Hugs on Zaurus
by Ulrich Vollert 27 Aug '07

27 Aug '07

> Haskell could run on such a platform". Ofcourse this is completly > other way around in terms of power and memory. :) > > But anyway, did anyone do it? I compiled Hugs for my Sharp Zaurus SL-C3200 (http://www.trisoft.de) which is a PDA with an ARM processor. (System: Lineo uLinux , CPU: Intel® XScale™ (PXA270, 416 MHz)) Hugs was compiled by gcc 2.95.3 and can be used in the console, additionally under a special X/Qt-Environment called pdaXqtrom (http://www.users.on.net/~hluc/myZaurus/) So, it is possible to use graphics on the Zaurus, too. I didnt dare to port ghc or Yhc - which would be great to use on the Zaurus, too. Regards, Ulrich

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renderString problems
by Dave Tapley 26 Aug '07

26 Aug '07

Hi all, I'm having a lot of trouble using renderString from Graphics.UI.GLUT.Fonts. All my attempts to render a StrokeFont have so far failed. Using a BitmapFont I can get strings to appear but they demonstrate the odd behaviour of translating themselves a distance equal to their length every time my displayCallback function is evaluated. My requests are: * Does anyone know how to keep the position fixed? * Are there any good examples of (working) GLUT code available on the web, I'm finding it very hard to make any progress at the moment. Certainly not at Haskell speed :( I am using the following code: > import Graphics.UI.GLUT > main = do > getArgsAndInitialize > createWindow "" > displayCallback $= update > actionOnWindowClose $= ContinueExectuion > mainLoop > > update = do > clear [ColorBuffer] > renderString Fixed8By13 $ "Test string" > flush Cheers, Dave

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is there a way to run tests at compile time using TH
by Alex Jacobson 26 Aug '07

26 Aug '07

I'd like to have code not compile if it doesn't pass the tests. Is there a way to use TH to generate compiler errors if the tests don't pass? -Alex-

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:, infix operator, infix constructor, et cetera
by dbast0s＠yahoo.com.br 26 Aug '07

26 Aug '07

There is something called infix constructors and something else called infix operators. I'm guessing that an infix operator is really a function, and an infix constructor I don't know what it is. How would you guys describe them? (*) More questions. I learned how to define (++), and then I wanted to see how (:) would be defined. The Haskell 98 Report mentions that -- The (:) operator is built-in syntax, and cannot legally be given -- a fixity declaration; but its fixity is given by: -- infixr 5 : What does ``built-in syntax'' mean? Paul Hudak, in ``The Haskell School of Expression'' mentions that he defines (:) legally, in Appendix A. After writing data [a] = [] | a : [a] -- more pseudo-code infixr 5 : and making a couple of observations about it, he writes: ``The way (:) is defined here is actually legal syntax. Infix constructors are permitted in *data* declarations, and are distinguished from infix operators (for pattern-matching purposes) by the fact that they must begin with a colon (a property trivially satisfied by ":").'' So I'm not sure what ``legal syntax'' and ``pseudo-code'' exactly mean. The program > module Main where > data [a] = [] | a : [a] > infixr 5 : > main = putStrLn "hello world" gives %runhugs.exe Colon.lhs runhugs: Error occurred ERROR "Colon.lhs":3 - Syntax error in data declaration (unexpected `[') (*) The 5. What does that 5 do in ``infixr 5 :''?

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Converting CTime -> Int
by Rob Hoelz 26 Aug '07

26 Aug '07

Hello everyone, I'm writing an interface to C code, and one of the functions I'm wrapping returns time_t. I see that this maps to CTime in Foreign.C.Types, but I can't figure out how to convert it to an Int (or any other useful Haskell type, for that matter) for the life of me. I've poured over the standard library docs, but to no avail. Could someone give me a hint? Thanks, Rob Hoelz

6 6

Text.Xhtml.Strict
by Marco Túlio Gontijo e Silva 26 Aug '07

26 Aug '07

Hello there. I don't know if it's off topic, but I don't know where else to ask. I've been using Text.Xhtml.Strict, and I'm wondering why the functions are mostly Html -> Html and not HTML a => a -> Html, or something similar. If they were like this, << and toHtml would be not needed, what would make it simpler to call the functions with arguments that are not Html. The question is specific to this library, but I think it's a very general one: isn't it better to have more generic functions with type changing inside? It seems to me that it would make things better from the users point of view. What do you think? -- Marco Túlio Gontijo e Silva Blog: http://marcotmarcot.blogspot.com/ Página: http://marcotmarcot.googlepages.com/ Correio, Jabber, GTalk, MSN: marcotmarcot(a)gmail.com IRC: marcotmarcot(a)irc.freenode.net IRC: marcotmarcot(a)irc.indymedia.org Skype: marcotmarcot Telefone: 33346720 Celular: 98116720 Endereço: Rua Paula Cândido, 257/201 Gutierrez 30430-260 Belo Horizonte/MG Brasil

2 1

Files for Hugs on Zaurus
by Ulrich Vollert 26 Aug '07

26 Aug '07

Hi Phillipa, Hugs is fast enough for me to work on the Zaurus. I packed together all the files which belong to Hugs on my Zaurus and I hope that I didnt miss something. Unpack them to /, the files will stay in usr/local/bin, usr/local/lib and usr/local/share. If you want to use Hugs not only under the console, but with pdaxqtrom (which includes a X-Server, a gcc-Compiler and tons of other stuff), go to http://www.users.on.net/~hluc/myZaurus/custom.html Please tell me, whether Hugs is working for you. Regards, Ulrich

1 0

"GHC from source" makes a great hardware test
by Dave Bayer 26 Aug '07

26 Aug '07

I recently did the classic "push a shopping cart down the aisle at Fry's" to build a Core 2 Quad computer, with Linux swap and a soft raid array spread across three 750 GB sata hard disks. I had some potential "first build" issues, notably a mishap with the lawn of copper grass that passes for a 775 cpu socket, followed by an hour of brain-surgery with a magnifying glass and a tiny screwdriver. I was very curious to test the stability of this system when it booted up after all; the best hardware test I could think of was multiple processes building GHC from source, with each iteration using the previous GHC binary as the compiler for the new build. Four iterating GHC builds in parallel is enough to peg all four cores at 100% indefinitely, with considerable disk activity to the soft raid array. The most I had going at once was 30 GHC builds; the system remained responsive enough for me to gracefully change my mind in the morning. Building multiple copies of GHC generates a lot of heat; going full tilt, the computer was drawing 220 watts at the wall. I don't use air conditioning for my summer office, so I ended up taping a small bathroom exhaust fan and dimmer switch into the back of a cardboard box, to collect the hot air from the back of the computer and send it out the window through a dryer hose. This kept the cores at 40 C (the enclosure itself has all possible fans) and my office cooler. A previous passive dryer hose arrangement kept the computer at 50 C, which is cooler than my MacBook cpu at full tilt, but I like to build things. Cardboard is an awesome quick prototyping material. Someone else in the same boat might save some time by modifying my Bash script. I ran hundreds of GHC builds without a mishap, and concluded that my system is stable. > #!/bin/bash > > # ghc-test.sh > > # Bash script to iteratively build ghc from source > # http://www.haskell.org/ghc > > # usage: > # ghc-test iters [ghc] > > # Bash scripting reference: Advanced Bash-Scripting Guide > # http://tldp.org/LDP/abs/html/index.html > > # Customize these parameters to local installation: > > sourcedir="/home/me/ghc-6.6.1" > src1="${sourcedir}/ghc-6.6.1-src.tar.bz2" > src2="${sourcedir}/ghc-6.6.1-src-extralibs.tar.bz2" > > testdir="/media/raid/ghc-test" > log="${testdir}/log.txt" > ghcdir="ghc-6.6.1" > binarypath="driver/ghc/ghc" > > > # determine build directory > time=$(date +'%Y%m%d-%H%M%S') > builddir="${testdir}/${time}" > > > # determine number of iterations > if [[ -z "$1" ]] > then > iters=2 > else > iters=$1 > fi > > > # choose ghc binary to use > if [[ -n "$2" && -f $2 && -x $2 ]] > then > ghc=$2 > else > ghc=$(which ghc) > fi > > > # check ghc binary for pulse > fib=`${ghc} -e 'let x = 0 : 1 : zipWith (+) x (tail x) in x !! 99'` > if [[ ${fib} != "218922995834555169026" ]] > then > echo "** bad ** ${ghc} ${iters} ${time}" >> ${log} > ghc=$(which ghc) > else > echo "ok ${ghc} ${iters} ${time}" >> ${log} > fi > > > # do an iteration if $iters > 0 > let iters=iters-1 > if [[ ${iters} -gt 0 ]] > then > > # build new copy of ghc from source > mkdir -p ${builddir} > cd ${builddir} > tar -jxf ${src1} > tar -jxf ${src2} > cd ${ghcdir} > ./configure --with-ghc=${ghc} > make > > # delete previous build directory, now that we're done with $ghc > if [[ -n "$3" && -d "$3" ]] > then > rm -rf $3 > fi > > # iterate > newghc="${builddir}/${ghcdir}/${binarypath}" > ${sourcedir}/ghc-test.sh ${iters} ${newghc} ${builddir} > > else > > # delete previous build directory > if [[ -n "$3" && -d "$3" ]] > then > rm -rf $3 > fi > > fi

3 2

Re: [Haskell-cafe] Re: Parsec is being weird at me
by Andrew Coppin 26 Aug '07

26 Aug '07

Chris Casinghino wrote: > On 8/25/07, Chris Casinghino <chris.casinghino(a)gmail.com> wrote: > >> I'm not sure there is a built in combinator for what you want, >> >> > > I guess I should have looked harder. What you want is manyTill: > > "manyTill :: GenParser tok st a -> GenParser tok st end -> GenParser tok st [a] > > (manyTill p end) applies parser p zero or more times until parser end > succeeds. Returns the list of values returned by p." > Yeah, OK, that looks good...

1 0

Re: [Haskell-cafe] Re: Parsec is being weird at me
by Chris Casinghino 26 Aug '07

26 Aug '07

The following two messages didn't make it to the list the first time because I sent from the wrong address. oops! Hopefully these answer the question. Message 1: On 8/25/07, Andrew Coppin <andrewcoppin(a)btinternet.com> wrote: > Stefan O'Rear wrote: > > There is one other little bit of documented behavior. Parsec's normal > > combinators only parse LL(1) grammars. Consult any work on formal > > languages for the exact meaning and all the consequences, however for > > this example it serves to note that after seeing abc, the single > > character of lookahead '#' is not sufficient to determine the correct > > parse. > > > > I thought the whole *purpose* of the endBy combinator was to keep > applying one parser until the other one succeeds? I don't think this is a lookahead problem, but rather just a misreading of the spec of endBy. Here it is: (endBy p sep) parses zero or more occurrences of p, seperated and ended by sep. Returns a list of values returned by p. The key text is "seperated and ended by sep". Not just ended by. Of course, the lookahead restriction is real, so just writing do {s <- many anyToken; char '#'; return s} won't work either. I'm not sure there is a built in combinator for what you want, but you could perhaps write: do {s <- many (satisfy (/= '#')); char '#'; return s} perhaps there is a more efficient way. --Chris ------ Message 2: > > I'm not sure there is a built in combinator for what you want, > I guess I should have looked harder. What you want is manyTill: "manyTill :: GenParser tok st a -> GenParser tok st end -> GenParser tok st [a] (manyTill p end) applies parser p zero or more times until parser end succeeds. Returns the list of values returned by p." --Chris

1 0

Parsec is being weird at me
by Andrew Coppin 26 Aug '07

26 Aug '07

Anybody want to explain to me why this doesn't work? ___ ___ _ / _ \ /\ /\/ __(_) / /_\// /_/ / / | | GHC Interactive, version 6.6.1, for Haskell 98. / /_\\/ __ / /___| | http://www.haskell.org/ghc/ \____/\/ /_/\____/|_| Type :? for help. Loading package base ... linking ... done. Prelude> :m Text.ParserCombinators.Parsec Prelude Text.ParserCombinators.Parsec> parseTest (endBy anyToken (char '#')) "abc#" Loading package parsec-2.0 ... linking ... done. parse error at (line 1, column 1): unexpected "b" expecting "#"

4 5

Re: [Haskell-cafe] Ideas
by Andrew Coppin 26 Aug '07

26 Aug '07

Iain Lane wrote: >> - Blogging software. (Because there isn't enough of it in the world yet.) >> > > In addition (because a little competition can't help ;), I'm going to > be experimenting with writing a blog engine for my final year project > at Uni next year - 2007/08. Hopefully some good will come of it, i.e. > something that people (I) can actually use. It'll probably be more > blog less CMS than Hope. At the minute I'm looking at using HAppS for > most of it. Should be fun! > Good luck with that - should be enjoyable at least. ;-) I'm going to have a go at it myself as well. My current blog uses something called "word press", and I don't like it especially much. (It *insists* on chewing up all my carefully applied formatting. And the people providing it have locked it down so there's loads I can't change...) So I'm hoping to write something nice to replace it with. But we'll see...

1 0

Re: [Haskell-cafe] Ideas
by Andrew Coppin 26 Aug '07

26 Aug '07

Bertram Felgenhauer wrote: > Hi, > > You wrote: > >> - An interactive function plotter. (GNUplot is nice, but it can't plot >> recursive functions...) >> > > Actually you can express a lot of those with the ?: operator. > Ooo... interesting. I don't recall seeing *that* in the manual! > gnuplot> f(x) = x < 1 ? 0 : f(x/2) + 1 > gnuplot> plot f(x) > > works just as expected. Mutually recursive functions defined that > way work, too. > > Still, support could be a lot better here. > OK... so how do I plot a graph of the Fibonacci numbers? Similarly, how do I plot (what Haskell calls) interate f 0?

1 0

newbie - how to call a Haskell interpreter from C
by Brock Peabody 26 Aug '07

26 Aug '07

Hi, I've been trying to find place to use Haskell at work, and I think a good opportunity will be to use it for our scripting language. To do that, I need to be able to invoke an interpreter directly from another language. I've investigated using HaskellScript (too web/ActiveX centric), but really I just want to compile ghci or hugs into my executable/library. It seems like this is something I should be able to figure out easily, but so far I've failed and have not found any reference to others succeeding. any advice? thanks in advance, Brock

3 3

Question of a manual computation on Reader Monad.
by Peter Cai 25 Aug '07

25 Aug '07

Hi all, In order to improve my understanding of monad, I am trying to do some manual computation on "Reader Monad" but I got some problem. The computation is like this: --instance Monad (Reader e) where -- return a = Reader $ \e -> a -- (Reader r) >>= f = Reader $ \e -> f (r e) e runReader (do { b <- Reader $ show; return b } ) -- This is the initial expression, it should equals "show" runReader (Reader $ show >>= \b -> return b) -- remove do notion runReader (Reader $ \e -> return( show e ) e) -- apply the definition of ">>=" runReader (Reader $ \e -> (Reader $ \e1 -> show(e)) e) -- apply the definition of "return" But the last expression is incorrect, and I don't know how to go on. Could anyone explain this for me? Thanks in advance! Reference : http://www.haskell.org/all_about_monads/html/readermonad.html

3 2

RE: [Haskell-cafe] How to fix linker errors when creating a package using cabal
by Peter Verswyvelen 25 Aug '07

25 Aug '07

Indeed, adding the non-exposed modules to the other-modules fixed it. Thanks Allan! Cheers, Peter -----Original Message----- From: Allan Clark [mailto:a.d.clark@ed.ac.uk] Sent: Saturday, August 25, 2007 2:28 PM To: Peter Verswyvelen Subject: Re: [Haskell-cafe] How to fix linker errors when creating a package using cabal Peter Verswyvelen wrote: > I'm trying to make a package of Ben.Lippmeier's very nice ANUPlot graphics > library (http://cs.anu.edu.au/people/Ben.Lippmeier) > > IMHO this would be a great contribution to the Haskell library, it's very > clean code for newbies :) > > I created the following cabal file: > > name: Plot > version: 1.1 > license: AllRightsReserved > maintainer: Ben.Lippmeier(a)anu.edu.au > exposed-modules: > Graphics.Plot.Display, > Graphics.Plot.Picture, > Graphics.Plot.Primitive, > Graphics.Plot.Render, > Graphics.Plot.Colors, > Graphics.Plot.Util, > Graphics.Plot.RenderState, > Graphics.Plot.Animate, > Graphics.Plot.View, > Graphics.Plot.Wrapper, > Graphics.Plot > Build-Depends: base, OpenGL, GLUT > ghc-options: -fglasgow-exts > > and then tried > runhaskell Setup.hs configure > runhaskell Setup.hs build > runhaskell Setup.hs install > > which all seemed to work fine (see log below). > > However, when building an example that uses that package, I get a lot of > linker errors (see log below) > > Is this because I configured the cabal files incorrectly, or do I have to > adjust the module sources so they explicitly export the missing symbols? > > Thanks, > Peter > [ snip ] > Files\Haskell\Plot-1.1\ghc-6.6.1/libHSPlot-1.1.a(Wrapper.o)(.text+0x2f1):fak > e: undefined reference to > `Plotzm1zi1_GraphicsziPlotziCallback_Display_con_info' > Hi, I'm not cabal expert, but basically I had a similar problem, and I fixed it by adding a missing module in the 'exposed-modules' part. Basically where is con_info defined, it's probably in a module which isn't exposed. If so then either put it in the 'exposed-modules' section or if you do not wish to expose it then maybe you could try putting it in a 'other-modules' section. regards allan

1 0

Haskellnet could not find network-any dependency.
by Edward Ing 25 Aug '07

25 Aug '07

Hi, I am trying to install Haskellnet. But the configuration breaks on dependency of network-any in GHC 6.6. I thought network-any was part of Hierarchical libraries? If not where do I get it? Edaward.

2 1

How to fix linker errors when creating a package using cabal
by Peter Verswyvelen 25 Aug '07

25 Aug '07

I'm trying to make a package of Ben.Lippmeier's very nice ANUPlot graphics library (http://cs.anu.edu.au/people/Ben.Lippmeier) IMHO this would be a great contribution to the Haskell library, it's very clean code for newbies :) I created the following cabal file: name: Plot version: 1.1 license: AllRightsReserved maintainer: Ben.Lippmeier(a)anu.edu.au exposed-modules: Graphics.Plot.Display, Graphics.Plot.Picture, Graphics.Plot.Primitive, Graphics.Plot.Render, Graphics.Plot.Colors, Graphics.Plot.Util, Graphics.Plot.RenderState, Graphics.Plot.Animate, Graphics.Plot.View, Graphics.Plot.Wrapper, Graphics.Plot Build-Depends: base, OpenGL, GLUT ghc-options: -fglasgow-exts and then tried runhaskell Setup.hs configure runhaskell Setup.hs build runhaskell Setup.hs install which all seemed to work fine (see log below). However, when building an example that uses that package, I get a lot of linker errors (see log below) Is this because I configured the cabal files incorrectly, or do I have to adjust the module sources so they explicitly export the missing symbols? Thanks, Peter ------------------ LOG ------------------------------- L:\3rdParty\ANUPlot\src>runhaskell Setup.hs unregister Unregistering Plot-1.1... Saving old package config file... done. Writing new package config file... done. L:\3rdParty\ANUPlot\src>runhaskell Setup.hs clean cleaning... L:\3rdParty\ANUPlot\src>runhaskell Setup.hs configure --global Configuring Plot-1.1... configure: Dependency base-any: using base-2.1.1 configure: Dependency OpenGL-any: using OpenGL-2.2.1 configure: Dependency GLUT-any: using GLUT-2.1.1 configure: Using install prefix: C:\Program Files configure: Binaries installed in: C:\Program Files\Haskell\bin configure: Libraries installed in: C:\Program Files\Haskell\Plot-1.1\ghc-6.6.1 configure: Private binaries installed in: C:\Program Files\Plot-1.1 configure: Data files installed in: C:\Program Files\Common Files\Plot-1.1 configure: Using compiler: c:\app\ghc\bin\ghc.exe configure: Compiler flavor: GHC configure: Compiler version: 6.6.1 configure: Using package tool: c:\app\ghc\bin\ghc-pkg.exe configure: Using ar found on system at: c:\app\ghc\bin\ar.exe configure: No haddock found configure: No pfesetup found configure: No ranlib found configure: Using runghc found on system at: c:\app\ghc\bin\runghc.exe configure: No runhugs found configure: No happy found configure: No alex found configure: Using hsc2hs: c:\app\ghc\bin\hsc2hs.exe configure: No c2hs found configure: No cpphs found configure: No greencard found L:\3rdParty\ANUPlot\src>runhaskell Setup.hs build Preprocessing library Plot-1.1... Building Plot-1.1... L:\3rdParty\ANUPlot\src>runhaskell Setup.hs register Registering Plot-1.1... Reading package info from ".installed-pkg-config" ... done. Saving old package config file... done. Writing new package config file... done. L:\3rdParty\ANUPlot\src>runhaskell Setup.hs install Installing: C:\Program Files\Haskell\Plot-1.1\ghc-6.6.1 & C:\Program Files\Haskell\bin Plot-1.1... Registering Plot-1.1... Reading package info from ".installed-pkg-config" ... done. Saving old package config file... done. Writing new package config file... done. Linking AnimClock.exe ... C:\Program Files\Haskell\Plot-1.1\ghc-6.6.1/libHSPlot-1.1.a(Wrapper.o)(.text+0x2f1):fak e: undefined reference to `Plotzm1zi1_GraphicsziPlotziCallback_Display_con_info' C:\Program Files\Haskell\Plot-1.1\ghc-6.6.1/libHSPlot-1.1.a(Wrapper.o)(.text+0xc7c):fak e: undefined reference to `Plotzm1zi1_GraphicsziPlotziUtilOp_zhzh_closure' C:\Program Files\Haskell\Plot-1.1\ghc-6.6.1/libHSPlot-1.1.a(Wrapper.o)(.text+0xdcb):fak e: undefined reference to `Plotzm1zi1_GraphicsziPlotziCallback_Idle_con_info' C:\Program Files\Haskell\Plot-1.1\ghc-6.6.1/libHSPlot-1.1.a(Wrapper.o)(.text+0xdfc):fak e: undefined reference to `Plotzm1zi1_GraphicsziPlotziCallback_Display_con_info' C:\Program Files\Haskell\Plot-1.1\ghc-6.6.1/libHSPlot-1.1.a(Wrapper.o)(.text+0xe3b):fak e: undefined reference to `Plotzm1zi1_GraphicsziPlotziCallback_Display_con_info' C:\Program Files\Haskell\Plot-1.1\ghc-6.6.1/libHSPlot-1.1.a(Wrapper.o)(.text+0xe68):fak e: undefined reference to `Plotzm1zi1_GraphicsziPlotziCallback_Display_con_info' C:\Program Files\Haskell\Plot-1.1\ghc-6.6.1/libHSPlot-1.1.a(Wrapper.o)(.rodata+0x54):fa ke: undefined reference to `Plotzm1zi1_GraphicsziPlotziUtilOp_zhzh_closure' C:\Program Files\Haskell\Plot-1.1\ghc-6.6.1/libHSPlot-1.1.a(RenderState.o)(.text+0x3d6) :fake: undefined reference to `Plotzm1zi1_GraphicsziPlotziUtilOp_zlzhzhzg_closure' C:\Program Files\Haskell\Plot-1.1\ghc-6.6.1/libHSPlot-1.1.a(RenderState.o)(.text+0x652) :fake: undefined reference to `Plotzm1zi1_GraphicsziPlotziUtilOp_zlzhzhzg_closure' C:\Program Files\Haskell\Plot-1.1\ghc-6.6.1/libHSPlot-1.1.a(RenderState.o)(.text+0x8ce) :fake: undefined reference to `Plotzm1zi1_GraphicsziPlotziUtilOp_zlzhzhzg_closure' C:\Program Files\Haskell\Plot-1.1\ghc-6.6.1/libHSPlot-1.1.a(RenderState.o)(.text+0xb4a) :fake: undefined reference to `Plotzm1zi1_GraphicsziPlotziUtilOp_zlzhzhzg_closure' C:\Program Files\Haskell\Plot-1.1\ghc-6.6.1/libHSPlot-1.1.a(RenderState.o)(.text+0xdc8) :fake: undefined reference to `Plotzm1zi1_GraphicsziPlotziCallback_KeyMouse_con_info' C:\Program Files\Haskell\Plot-1.1\ghc-6.6.1/libHSPlot-1.1.a(RenderState.o)(.rodata+0x10 ):fake: undefined reference to `Plotzm1zi1_GraphicsziPlotziUtilOp_zlzhzhzg_closure' C:\Program Files\Haskell\Plot-1.1\ghc-6.6.1/libHSPlot-1.1.a(View.o)(.text+0x190b):fake: undefined reference to `Plotzm1zi1_GraphicsziPlotziUtilOp_zlzhzhzg_closure' C:\Program Files\Haskell\Plot-1.1\ghc-6.6.1/libHSPlot-1.1.a(View.o)(.text+0x19cc):fake: undefined reference to `Plotzm1zi1_GraphicsziPlotziUtilOp_zhzh_closure' C:\Program Files\Haskell\Plot-1.1\ghc-6.6.1/libHSPlot-1.1.a(View.o)(.text+0x1b9b):fake: undefined reference to `Plotzm1zi1_GraphicsziPlotziUtilOp_zlzhzhzg_closure' C:\Program Files\Haskell\Plot-1.1\ghc-6.6.1/libHSPlot-1.1.a(View.o)(.text+0x1c5c):fake: undefined reference to `Plotzm1zi1_GraphicsziPlotziUtilOp_zhzh_closure' C:\Program Files\Haskell\Plot-1.1\ghc-6.6.1/libHSPlot-1.1.a(View.o)(.text+0x20c9):fake: undefined reference to `Plotzm1zi1_GraphicsziPlotziUtilOp_zlzhzhzg_closure' C:\Program Files\Haskell\Plot-1.1\ghc-6.6.1/libHSPlot-1.1.a(View.o)(.text+0x21fc):fake: undefined reference to `Plotzm1zi1_GraphicsziPlotziUtilOp_zhzh_closure' C:\Program Files\Haskell\Plot-1.1\ghc-6.6.1/libHSPlot-1.1.a(View.o)(.text+0x22f0):fake: undefined reference to `Plotzm1zi1_GraphicsziPlotziUtilOp_zhzh_closure' C:\Program Files\Haskell\Plot-1.1\ghc-6.6.1/libHSPlot-1.1.a(View.o)(.text+0x2400):fake: undefined reference to `Plotzm1zi1_GraphicsziPlotziUtilOp_zhzh_closure' C:\Program Files\Haskell\Plot-1.1\ghc-6.6.1/libHSPlot-1.1.a(View.o)(.text+0x2e83):fake: undefined reference to `Plotzm1zi1_GraphicsziPlotziUtilOp_zlzhzhzg_closure' C:\Program Files\Haskell\Plot-1.1\ghc-6.6.1/libHSPlot-1.1.a(View.o)(.text+0x2f74):fake: undefined reference to `Plotzm1zi1_GraphicsziPlotziUtilOp_zhzh_closure' C:\Program Files\Haskell\Plot-1.1\ghc-6.6.1/libHSPlot-1.1.a(View.o)(.text+0x305c):fake: undefined reference to `Plotzm1zi1_GraphicsziPlotziUtilOp_zhzh_closure' C:\Program Files\Haskell\Plot-1.1\ghc-6.6.1/libHSPlot-1.1.a(View.o)(.text+0x37f9):fake: undefined reference to `Plotzm1zi1_GraphicsziPlotziUtilOp_zlzhzhzg_closure' C:\Program Files\Haskell\Plot-1.1\ghc-6.6.1/libHSPlot-1.1.a(View.o)(.text+0x3954):fake: undefined reference to `Plotzm1zi1_GraphicsziPlotziUtilOp_zhzh_closure' C:\Program Files\Haskell\Plot-1.1\ghc-6.6.1/libHSPlot-1.1.a(View.o)(.text+0x3a60):fake: undefined reference to `Plotzm1zi1_GraphicsziPlotziUtilOp_zhzh_closure' C:\Program Files\Haskell\Plot-1.1\ghc-6.6.1/libHSPlot-1.1.a(View.o)(.text+0x3b88):fake: undefined reference to `Plotzm1zi1_GraphicsziPlotziUtilOp_zhzh_closure' C:\Program Files\Haskell\Plot-1.1\ghc-6.6.1/libHSPlot-1.1.a(View.o)(.text+0x3dec):fake: undefined reference to `Plotzm1zi1_GraphicsziPlotziUtilOp_zhzh_closure' C:\Program Files\Haskell\Plot-1.1\ghc-6.6.1/libHSPlot-1.1.a(View.o)(.text+0x3ebc):fake: undefined reference to `Plotzm1zi1_GraphicsziPlotziUtilOp_zhzh_closure' C:\Program Files\Haskell\Plot-1.1\ghc-6.6.1/libHSPlot-1.1.a(View.o)(.text+0x402a):fake: undefined reference to `Plotzm1zi1_GraphicsziPlotziUtilOp_zlzhzhzg_closure' C:\Program Files\Haskell\Plot-1.1\ghc-6.6.1/libHSPlot-1.1.a(View.o)(.text+0x43c1):fake: undefined reference to `Plotzm1zi1_GraphicsziPlotziUtilOp_zlzhzhzg_closure' C:\Program Files\Haskell\Plot-1.1\ghc-6.6.1/libHSPlot-1.1.a(View.o)(.text+0x45f2):fake: undefined reference to `Plotzm1zi1_GraphicsziPlotziUtilOp_zlzhzhzg_closure' C:\Program Files\Haskell\Plot-1.1\ghc-6.6.1/libHSPlot-1.1.a(View.o)(.text+0x4975):fake: undefined reference to `Plotzm1zi1_GraphicsziPlotziUtilOp_zlzhzhzg_closure' C:\Program Files\Haskell\Plot-1.1\ghc-6.6.1/libHSPlot-1.1.a(View.o)(.text+0x4c5a):fake: undefined reference to `Plotzm1zi1_GraphicsziPlotziUtilOp_zlzhzhzg_closure' C:\Program Files\Haskell\Plot-1.1\ghc-6.6.1/libHSPlot-1.1.a(View.o)(.text+0x4efe):fake: more undefined references to `Plotzm1zi1_GraphicsziPlotziUtilOp_zlzhzhzg_closure' follow C:\Program Files\Haskell\Plot-1.1\ghc-6.6.1/libHSPlot-1.1.a(View.o)(.text+0x5b0a):fake: undefined reference to `Plotzm1zi1_GraphicsziPlotziCallback_Reshape_con_info' C:\Program Files\Haskell\Plot-1.1\ghc-6.6.1/libHSPlot-1.1.a(View.o)(.text+0x5b38):fake: undefined reference to `Plotzm1zi1_GraphicsziPlotziCallback_Motion_con_info' C:\Program Files\Haskell\Plot-1.1\ghc-6.6.1/libHSPlot-1.1.a(View.o)(.text+0x5b65):fake: undefined reference to `Plotzm1zi1_GraphicsziPlotziCallback_KeyMouse_con_info' C:\Program Files\Haskell\Plot-1.1\ghc-6.6.1/libHSPlot-1.1.a(View.o)(.rodata+0x130):fake : undefined reference to `Plotzm1zi1_GraphicsziPlotziUtilOp_zhzh_closure' C:\Program Files\Haskell\Plot-1.1\ghc-6.6.1/libHSPlot-1.1.a(View.o)(.rodata+0x134):fake : undefined reference to `Plotzm1zi1_GraphicsziPlotziUtilOp_zlzhzhzg_closure' C:\Program Files\Haskell\Plot-1.1\ghc-6.6.1/libHSPlot-1.1.a(View.o)(.rodata+0x144):fake : undefined reference to `Plotzm1zi1_GraphicsziPlotziUtilOp_zhzh_closure' C:\Program Files\Haskell\Plot-1.1\ghc-6.6.1/libHSPlot-1.1.a(View.o)(.rodata+0x148):fake : undefined reference to `Plotzm1zi1_GraphicsziPlotziUtilOp_zlzhzhzg_closure' C:\Program Files\Haskell\Plot-1.1\ghc-6.6.1/libHSPlot-1.1.a(View.o)(.rodata+0x170):fake : undefined reference to `Plotzm1zi1_GraphicsziPlotziUtilOp_zhzh_closure' C:\Program Files\Haskell\Plot-1.1\ghc-6.6.1/libHSPlot-1.1.a(View.o)(.rodata+0x174):fake : undefined reference to `Plotzm1zi1_GraphicsziPlotziUtilOp_zlzhzhzg_closure' C:\Program Files\Haskell\Plot-1.1\ghc-6.6.1/libHSPlot-1.1.a(View.o)(.rodata+0x1a4):fake : undefined reference to `Plotzm1zi1_GraphicsziPlotziUtilOp_zhzh_closure' C:\Program Files\Haskell\Plot-1.1\ghc-6.6.1/libHSPlot-1.1.a(View.o)(.rodata+0x1a8):fake : undefined reference to `Plotzm1zi1_GraphicsziPlotziUtilOp_zlzhzhzg_closure' C:\Program Files\Haskell\Plot-1.1\ghc-6.6.1/libHSPlot-1.1.a(Render.o)(.text+0x1e2b):fak e: undefined reference to `Plotzm1zi1_GraphicsziPlotziTexture_cacheTexture_closure' C:\Program Files\Haskell\Plot-1.1\ghc-6.6.1/libHSPlot-1.1.a(Render.o)(.text+0x2146):fak e: undefined reference to `Plotzm1zi1_GraphicsziPlotziRaster_withRasterCoords_closure' C:\Program Files\Haskell\Plot-1.1\ghc-6.6.1/libHSPlot-1.1.a(Render.o)(.text+0x2484):fak e: undefined reference to `Plotzm1zi1_GraphicsziPlotziRaster_withRasterCoords_closure' C:\Program Files\Haskell\Plot-1.1\ghc-6.6.1/libHSPlot-1.1.a(Render.o)(.rodata+0xc0):fak e: undefined reference to `Plotzm1zi1_GraphicsziPlotziRaster_withRasterCoords_closure' C:\Program Files\Haskell\Plot-1.1\ghc-6.6.1/libHSPlot-1.1.a(Render.o)(.rodata+0xc4):fak e: undefined reference to `Plotzm1zi1_GraphicsziPlotziTexture_cacheTexture_closure' C:\Program Files\Haskell\Plot-1.1\ghc-6.6.1/libHSPlot-1.1.a(Animate.o)(.text+0x322):fak e: undefined reference to `Plotzm1zi1_GraphicsziPlotziUtilOp_zlzhzhzg_closure' C:\Program Files\Haskell\Plot-1.1\ghc-6.6.1/libHSPlot-1.1.a(Animate.o)(.text+0x511):fak e: undefined reference to `Plotzm1zi1_GraphicsziPlotziUtilOp_zlzhzhzg_closure' C:\Program Files\Haskell\Plot-1.1\ghc-6.6.1/libHSPlot-1.1.a(Animate.o)(.text+0x75c):fak e: undefined reference to `Plotzm1zi1_GraphicsziPlotziUtilOp_zhzh_closure' C:\Program Files\Haskell\Plot-1.1\ghc-6.6.1/libHSPlot-1.1.a(Animate.o)(.text+0x838):fak e: undefined reference to `Plotzm1zi1_GraphicsziPlotziUtilOp_zhzh_closure' C:\Program Files\Haskell\Plot-1.1\ghc-6.6.1/libHSPlot-1.1.a(Animate.o)(.text+0x908):fak e: undefined reference to `Plotzm1zi1_GraphicsziPlotziUtilOp_zhzh_closure' C:\Program Files\Haskell\Plot-1.1\ghc-6.6.1/libHSPlot-1.1.a(Animate.o)(.text+0x1111):fa ke: undefined reference to `Plotzm1zi1_GraphicsziPlotziUtilOp_zlzhzhzg_closure' C:\Program Files\Haskell\Plot-1.1\ghc-6.6.1/libHSPlot-1.1.a(Animate.o)(.text+0x1220):fa ke: undefined reference to `Plotzm1zi1_GraphicsziPlotziUtilOp_zhzh_closure' C:\Program Files\Haskell\Plot-1.1\ghc-6.6.1/libHSPlot-1.1.a(Animate.o)(.text+0x151a):fa ke: undefined reference to `Plotzm1zi1_GraphicsziPlotziUtilOp_zlzhzhzg_closure' C:\Program Files\Haskell\Plot-1.1\ghc-6.6.1/libHSPlot-1.1.a(Animate.o)(.text+0x16bc):fa ke: undefined reference to `Plotzm1zi1_GraphicsziPlotziCallback_KeyMouse_con_info' C:\Program Files\Haskell\Plot-1.1\ghc-6.6.1/libHSPlot-1.1.a(Animate.o)(.text+0x17bd):fa ke: undefined reference to `Plotzm1zi1_GraphicsziPlotziUtilOp_zlzhzhzg_closure' C:\Program Files\Haskell\Plot-1.1\ghc-6.6.1/libHSPlot-1.1.a(Animate.o)(.text+0x18b4):fa ke: undefined reference to `Plotzm1zi1_GraphicsziPlotziUtilOp_zhzh_closure' C:\Program Files\Haskell\Plot-1.1\ghc-6.6.1/libHSPlot-1.1.a(Animate.o)(.text+0x1a24):fa ke: undefined reference to `Plotzm1zi1_GraphicsziPlotziUtilOp_zhzh_closure' C:\Program Files\Haskell\Plot-1.1\ghc-6.6.1/libHSPlot-1.1.a(Animate.o)(.rodata+0x28):fa ke: undefined reference to `Plotzm1zi1_GraphicsziPlotziUtilOp_zhzh_closure' C:\Program Files\Haskell\Plot-1.1\ghc-6.6.1/libHSPlot-1.1.a(Animate.o)(.rodata+0x2c):fa ke: undefined reference to `Plotzm1zi1_GraphicsziPlotziUtilOp_zlzhzhzg_closure' C:\Program Files\Haskell\Plot-1.1\ghc-6.6.1/libHSPlot-1.1.a(Animate.o)(.rodata+0x98):fa ke: undefined reference to `Plotzm1zi1_GraphicsziPlotziUtilOp_zlzhzhzg_closure' C:\Program Files\Haskell\Plot-1.1\ghc-6.6.1/libHSPlot-1.1.a(Animate.o)(.rodata+0xac):fa ke: undefined reference to `Plotzm1zi1_GraphicsziPlotziUtilOp_zhzh_closure' C:\Program Files\Haskell\Plot-1.1\ghc-6.6.1/libHSPlot-1.1.a(Animate.o)(.rodata+0xb0):fa ke: undefined reference to `Plotzm1zi1_GraphicsziPlotziUtilOp_zlzhzhzg_closure' C:\Program Files\Haskell\Plot-1.1\ghc-6.6.1/libHSPlot-1.1.a(Display.o)(.text+0x766):fak e: undefined reference to `Plotzm1zi1_GraphicsziPlotziDump_dumpFragmentState_closure' C:\Program Files\Haskell\Plot-1.1\ghc-6.6.1/libHSPlot-1.1.a(Display.o)(.text+0x76d):fak e: undefined reference to `Plotzm1zi1_GraphicsziPlotziDump_dumpFramebufferState_closure' C:\Program Files\Haskell\Plot-1.1\ghc-6.6.1/libHSPlot-1.1.a(Display.o)(.text+0x7d7):fak e: undefined reference to `Plotzm1zi1_GraphicsziPlotziDump_dumpGlutState_closure' C:\Program Files\Haskell\Plot-1.1\ghc-6.6.1/libHSPlot-1.1.a(Display.o)(.rodata+0xa4):fa ke: undefined reference to `Plotzm1zi1_GraphicsziPlotziDump_dumpGlutState_closure' C:\Program Files\Haskell\Plot-1.1\ghc-6.6.1/libHSPlot-1.1.a(Display.o)(.rodata+0xa8):fa ke: undefined reference to `Plotzm1zi1_GraphicsziPlotziDump_dumpFramebufferState_closure' C:\Program Files\Haskell\Plot-1.1\ghc-6.6.1/libHSPlot-1.1.a(Display.o)(.rodata+0xac):fa ke: undefined reference to `Plotzm1zi1_GraphicsziPlotziDump_dumpFragmentState_closure' collect2: ld returned 1 exit status

2 2

Remember the future
by Andrew Coppin 25 Aug '07

25 Aug '07

I've seen comments in various places that monads allow you to "borrow things from the future". That sounds completely absurd to me... can anybody explain?

8 12

Re: [Haskell-cafe] Style
by Marc A. Ziegert 25 Aug '07

25 Aug '07

whops... i did check it, but that was a copypaste mistake. buggy: > tm_parallelizable_v1 = \n -> sum . takeWhile (>0) $ map (div n) fives > where fives = iterate (*5) 1 should be: > tm_parallelizable_v1 = \n -> sum . takeWhile (>0) $ map (div n) fives > where fives = iterate (*5) 5 - marc Am Freitag, 24. August 2007 schrieben Sie: > Hi Marc > > First off, thanks for your reply. > >> tm_parallelizable_v1 = \n -> sum . takeWhile (>0) $ map (div n) fives > >> where fives = iterate (*5) 1 > Did you check this one? IMHO I think it's producing the 'wrong' answer. > > *Main> tm_parallelizable_v1 100 > 124 > (0.00 secs, 0 bytes) > > *Main> tm 100 > 24 > (0.00 secs, 0 bytes) > > If comparing the result to the other variants is accepted as a sort > of proof. ;-) > > But calculating the number of trailing zero's of n! is a matter of > counting powers of five in the factorized n!: f.e.: > > 10! = 1 2 3 2^2 5 2*3 7 2^3 3^2 2*5 > --> 5^2 --> picking up enough powers of 2 --> (2*5)^2 = 100 > > So you will have to correct your 'fives' to f.e. > > fives = tail $ iterate (*5) 1 > > > > Regards > > > @@i > > >

1 0

Help using CGIT
by Rich Neswold 25 Aug '07

25 Aug '07

Hello! I've been having a tough time trying to use the CGI monad transformer (CGIT). Hopefully someone can show me my misstep(s). I have a CGI script that's evolving. Early on, it needed a single database access. Now it's doing two accesses (and it looks like I'll be adding more.) Rather than making a connection for each access, the script needs to connect once. To do this, I want to combine the CGI monad with the Reader monad. This version compiles cleanly: > module AppMonad (App (..), runApp) > where > > import Control.Exception (bracket) > import Control.Monad.Reader > import Network.CGI.Monad > import Network.CGI.Protocol > import System.IO (stdin, stdout) > import Database.HSQL.PostgreSQL > > newtype App a = App (ReaderT Connection (CGIT IO) a) > deriving (Monad, MonadIO, MonadReader Connection) > > runApp :: App CGIResult -> IO () > runApp (App a) = > bracket (connect "host" "dbname" "user" "password") > disconnect > (\c -> do { env <- getCGIVars > ; hRunCGI env stdin stdout (runCGIT (runReaderT a c)) > ; return () } ) Unfortunately, when another module tries to actually use the monad, I get warnings about "No instance for (MonadCGI App)". I tried making an instance: > instance MonadCGI App where > cgiAddHeader = ? > cgiGet = ? But I don't know how to define these functions. I tried various 'lift'ing combinations, but couldn't come up with a solution that would compile. I'm also disappointed that I had to break apart 'runCGI' (by cut-and-pasting its source) because I couldn't make it believe my monad looked enough like MonadCGI. My previous experiment with monad transformers was successful. It didn't use CGIT, however, so the 'run*' functions were simpler. Does anyone have an example of using CGIT (I didn't find any from Google)? Shouldn't I be able to use 'runCGI' with my monad? CGIT users shouldn't be required to re-implement 'runCGI", right? Any help or ideas is appreciated! -- Rich JID: rich(a)neswold.homeunix.net AIM: rnezzy

3 4

Re: [Haskell-cafe] Re: Graph reduction [Was: Where is StackOverflow on the Wiki?]
by Andrew Coppin 25 Aug '07

25 Aug '07

Shiqi Cao wrote: > Check out this > > http://www.cas.mcmaster.ca/~kahl/HOPS/ > <http://www.cas.mcmaster.ca/%7Ekahl/HOPS/> > Heh. I was thinking about trying to build something *exactly like* this... OOC, how the heck did they make it work through a "document interface"? Surely that's impossible?

1 0

IO inside CGI
by Adrian Neumann 24 Aug '07

24 Aug '07

-----BEGIN PGP SIGNED MESSAGE----- Hash: RIPEMD160 I'm toying around with web programming in Haskell. I'm trying to write a script which GETs an id and returns a couple of random numbers. Something like this: cgiMain :: CGI CGIResult cgiMain = do inp <- getInput "id" let gen = parse inp output $ take 10 (randoms gen) parse :: Maybe String-> StdGen parse (Just x) = read x parse Nothing = undefined Now I'd like to get a new StdGen, in case no id was supplied to the script. cgiMain :: CGI CGIResult cgiMain = do inp <- getInput "id" gen <- parse inp output $ take 10 (randoms gen) parse :: Maybe String-> IO StdGen parse (Just x) = return $ read x parse Nothing = getStdGen Obviously this doesn't work because I'm trying to do IO inside CGI (right?). Is there some incantation I can perform to make this possible? Like gen <- arcaneMagic parse inp As you probably have noticed I don't know very much about monads, all I did until now was reading or writing some files. Thanks in advance -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.7 (MingW32) Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org iD8DBQFGzudU11V8mqIQMRsRA33RAJ9buZDHgz/eXi8Jw9OBwbTErDccRgCfbGrr 1WXiGHmxlTBe01E409yJyv8= =XSDj -----END PGP SIGNATURE-----

3 2

2D game graphics library for Haskell?
by Ben Lippmeier 24 Aug '07

24 Aug '07

Hi Peter, The OpenGL/GLUT bindings support all the things you would want, but it's a bit too much pain for first year students. For the last couple of years at the ANU (Australian National University, Canberra) we've been using a front end library that I wrote which is similar to SOE/HGL but with support for images, animation, alpha blending and some other things. I think the real trick is hiding enough of the OpenGL/GLUT internals to make it suitable for first year students, while at the same time exposing enough functionality so they don't feel constrained by what they can do with the library. Usually we think of the project we want the students to do, then supply most of the infrastructure via the library - leaving the students to fill in the 'fun' stuff. There is the added benefit that the OpenGL/GLUT bindings (and hence our library also) compiles out of the box on both Linux and Windows. We use linux machines at uni for the student labs, but students have been able to take their code home and get it running on their home Windows PC's without much difficulty. You can get our library (with examples) from my homepage at http://cs.anu.edu.au/people/Ben.Lippmeier/ I've also got a simple asteroids game which I wrote with an extended version of it. There is a playable version, but unfortunately it's on my home machine that is now packed in storage while I'm at MSR, Cambridge. I'm getting back to Canberra late October so if you're still interested I can dig it out and send you a copy then. Cheers, Ben. From: haskell-cafe-bounces(a)haskell.org [mailto:haskell-cafe-bounces@haskell.org] On Behalf Of peterv Sent: 24 August 2007 11:32 To: haskell-cafe(a)haskell.org Subject: [Haskell-cafe] 2D game graphics library for Haskell? I'm currently playing around with SOE to make some simple interactive math exercises for students. This worked fine, although I could have done this much faster using C# (which I know very well), but since I'm addicted to Haskell now, I used the latter language ;) Furthermore, I hope that one day, I will know enough Haskell to learn it to the students, because I feel that functional programming should not be given in the last bachelor or master years, since most software engineering students then know OO programming extremely well and have a horrible time with FP (I currently did not meet anyone in my sector of game development that liked FP, and many of those people had a masters degree and some were PhDs) Anyway, SOE is great for learning Haskell, but it lacks a couple of fundamental functions to make it really attractive, like: - Support for images - Support for rendering to an "offscreen graphics surface" and reading the pixels from that surface (for pixel-wise collision detection) - Support for detecting non-ASCII key presses (cursor keys, etc) - Support for joysticks Concurrent Clean seems to have a nice 2D game library and PLT/DrScheme also has nice support for basic 2D graphics, but somehow I feel Haskell is more mature and more elegant. So before digging into "advanced" APIs (like GTK itself, which I know nothing about, I'm a Win32 GDI/XNA/WPF expert), I should ask the question if something similar exists? It has to be as simple as SOE. Would it be possible to extend the GTK SOE with support for the features mentioned above? Is this insanely difficult for someone like me who knows a lot about Win32 but little Haskell? Thanks, Peter Verswyvelen No virus found in this outgoing message. Checked by AVG Free Edition. Version: 7.5.484 / Virus Database: 269.12.4/969 - Release Date: 23/08/2007 16:04

1 0

newbie : multi-parameter type classes
by Thomas Girod 24 Aug '07

24 Aug '07

Hi there. I'm trying to define a generic graph type here and don't understand on one error I get. Here I come. module Graph where class (Eq n, Eq e) => Topo a n e where empty :: a nodes :: a -> [n] edges :: a -> [e] data Node n = Node n deriving (Eq,Show) data Edge n e = Edge e (Node n) (Node n) deriving (Show) instance (Eq e) => Eq (Edge n e) where (Edge e1 _ _) == (Edge e2 _ _) = e1 == e2 data Graph n e = Graph [Node n] [Edge n e] deriving (Eq,Show) instance (Eq n, Eq e) => Topo (Graph n e) (Node n) (Edge n e) where empty = Graph [] [] nodes (Graph ns _) = ns edges (Graph _ es) = es My class Topo (for topography) is supposed to give the basic interface any graph should have. My instance is Topo (Graph n e) (Node n) (Edge n e), so the infered types of the functions should be : empty :: Graph n e nodes :: Graph n e -> [Nodes n] edges :: Graph n e -> [Edge n e] right ? When I load the code in GHCi, no errors. But then : *Graph> let g = Graph [Node 0, Node 1] [] *Graph> nodes g <interactive>:1:0: No instance for (Topo (Graph Integer e1) n e) arising from use of `nodes' at <interactive>:1:0-6 Possible fix: add an instance declaration for (Topo (Graph Integer e1) n e) In the expression: nodes g In the definition of `it': it = nodes g *Graph> And I don't understand this. How can he search for an instance of Topo (Graph integer e1) n e) ? regards, Thomas

3 3

Re: [Haskell] Issue about use of WinHugs
by Neil Mitchell 24 Aug '07

24 Aug '07

Hi > I'm new to WinHugs, what's wrong with isUpper of my WinHugs? Nothing. The book/tutorial you are going from is out of date. Before using the isUpper/isLower functions you first have to type ":load Char": Hugs> :load Char Hugs> filter isUpper "ABCDEfgh" "ABCDE" The ":load Char" loads the Char module into scope, which provides the isUpper function. The haskell@ mailing list is mainly for announcements, so I've sent this email to haskell-cafe@ - which is the right place for questions like this. Thanks Neil

1 0

latest cabal conflict?
by Luc TAESCH 24 Aug '07

24 Aug '07

when trying to build the latest cabal from darcs, I got luc@haserv:~/src/cabinstall/cabal$ runghc Setup.lhs configure Distribution/Simple.hs:110:7: Could not find module `System.FilePath': it was found in multiple packages: filepath-1.0 FilePath-0.11 luc@haserv:~/src/cabinstall/cabal$ sound like a conflict , i still have ghc 6.6, not 6.6.1. what should I do ? hide FilePath-0.11 in Distribution/Simple.hs imports ? ( and for all othe files? any way to just have FilePath out of the way via a Cabal statement? thks

2 1

Haddock: documenting parameters of functional arguments
by Henning Thielemann 24 Aug '07

24 Aug '07

I like to write documentation comments like fix :: ( a {- ^ local argument -} -> a {- ^ local output -} ) -> a {- ^ global output -} but Haddock doesn't allow it. Or is there a trick to get it work?

2 1

Newbie question: Where is StackOverflow on the Wiki?
by Peter Verswyvelen 24 Aug '07

24 Aug '07

When reading an article about tail recursion (http://themechanicalbride.blogspot.com/2007/04/haskell-for-c-3-programmers. html) I came across the follow statements: "If you can write a non-recursive function that uses the colon syntax it is probably better than a tail recursive one that doesn't. This is because Haskell's lazy evaluation enabled you to use the non-tail recursive version on an infinite stream without getting a stack overflow. " and ""Unfortunately", laziness "gets in the way". While transforming non-tail-recursive code to a tail-recursive form is important and useful for functional programming in general, dealing with laziness requires a little more care, and often "non-tail-recursive" versions are preferrable. flatten is an example of this, the first version is better in many ways. While I don't believe it happens in this case, oftentimes naively writing code "tail-recursively" in Haskell will actually -make- it overflow the stack. Another (actual) benefit of the first version of flatten is that it will work on infinite lists. http://www.haskell.org/hawiki/StackOverflow gives a simple example and some explanation." Unfortunately I can't find the StackOverflow page anymore. Now if I understand this correctly, this just means that when writing something like: foo n = if n<0 then [] else n : foo (n-1) bar n = aux 0 [] where aux i xs = if i>n then xs else aux (i+1) (i:xs) that foo is more efficient than bar because lazy evaluation of foo just puts the delayed computation in the "cdr" of the list, while lazy evaluation of bar has to keep track of all aux calls (the "closures") which gives much more overhead, maybe even stack overflow? Something like that? Thanks, Peter

9 14

Re: [Haskell-cafe] Re: Newbie question: Where is StackOverflow on the Wiki?
by Peter Verswyvelen 24 Aug '07

24 Aug '07

I think DrScheme does that for Scheme. So a must have for Haskell! Maybe could be added to the Helium project? >----- Oorspronkelijk bericht ----- >Van: apfelmus [mailto:apfelmus@quantentunnel.de] >Verzonden: donderdag, augustus 23, 2007 08:00 PM >Aan: haskell-cafe(a)haskell.org >Onderwerp: [Haskell-cafe] Re: Newbie question: Where is StackOverflow on the Wiki? > >Neil Mitchell wrote: >>>> sum (enum 1 10) => >>>> sum' 0 (enum 1 10) => >>>> ... >>>> >>>> sum' 36 (9 : enum (9+1) 10) => >>>> (sum' $! (36+9)) (enum (9+1) 10) => >>>> sum' 45 (enum (9+1) 10) => >>>> sum' 45 [] => >>>> 45 >>>> >>>> (I need to find some way to automate making these trails :) ) >>> Yes! We'd need such an automatic tool for the wikibook, too. >> >> The problem is that Haskell is ridiculously complex, and the "small >> step" interpretation is much harder than you'd think. For example, sum >> may well be defined as foldl' (+) 0, which is a CAF, so gets reduced >> once. The 0 won't actually be a 0, but will be fromInteger 0, which >> will correspond to looking up an item in the dictionary and applying >> it. Dictionaries especially make the "simple" interpretation >> completely wrong. >> >> It's easy to do informally, but once you start being more precise, its >> very complex. > >Yeah, the precise details may vary, even :) But for teaching, an >automatic tool that does graph reduction would be great. I don't mind if >it's sloppy (directly apply definitions & pattern matching VS everything >is a lambda abstraction) and only does simply typed lambda calculus (no >type applications, no type classes). > >Regards, >apfelmus > >_______________________________________________ >Haskell-Cafe mailing list >Haskell-Cafe(a)haskell.org >http://www.haskell.org/mailman/listinfo/haskell-cafe > >

1 0

help understanding lazy evaluation
by Xavier Noria 24 Aug '07

24 Aug '07

I am learning Haskell with "Programming in Haskell" (an excellent book BTW). I have background in several languages but none of them has lazy evaluation. By now I am getting along with the intuitive idea that things are not evaluated until needed, but there's an example I don't understand (which means the intuitive idea needs some revision :-). We have factors(), defined on page 39 like this[*]: factors :: Int -> [Int] factors n = [x | x <- [1..n], n `mod` x == 0] and we base prime() on it this way: prime :: Int -> Bool prime n = factors n == [1, n] Now, the books says prime does not necessarily compute all of the factors of n because of lazy evaluation. Meaning that if n is composite as soon as some non-trivial divisor appears we halt computation and return False. My vague intuition said "we either need factors or we don't, we do because we need to perform the test, so we compute it". That's wrong, so a posteriori the explanation must be something like this: 1. someone knows we want factor() to perform an equality test 2. someone knows an equality test between lists is False as soon as we have a mismatch, left to right 3. thus, instead of evaluating factors completely we are going to build sublists of the result and perform the tests on those ones against [1, n]. That's a lot of *context* about that particular evaluation of factors, in particular step puzzles me. Can anyone explain how lazy evaluation fits there? I suspect the key is the implementation of == together with the fact that list comprehensions are lazy themselves, is that right? -- fxn [*] Which notation do you use for functions in text? is f() ok?

11 11

Ann: Gtk2Hs Tutorial Port
by Hans van Thiel 23 Aug '07

23 Aug '07

Hello All, I've already announced this on the Gtk2Hs users' list, but for those who are not using Gtk2Hs at the moment, but who might be interested: I've started a port of the Gtk+2.0 tutorial by Tony Gail and Ian Main and the first part is available on: http://darcs.haskell.org/gtk2hs/docs/tutorial/Tutorial_Port/ The chapters are: Contents and Copyright Notice chap1.html Getting Started chap3.html Packing Widgets chap4.html Packing Demonstration Program chap5a.html Packing Using Tables chap5b.html The Button Widget chap6.html Adjustments, Scale and Range chap7.html All examples are also available as .hs files. For a beginner, working through these should be sufficient, so that he/she can carry on with the original C based tutorial. The correlation between the examples and the Gtk2Hs API is (mostly) straightforward. But I'm working on the other widgets in the Gtk+2.0 tutorial too (might take a while). Currently available on my own web site (but no .hs files): Labels chap8.html Arrows and Tooltips chap9.html http://j-van-thiel.speedlinq.nl/gtk2hs/chap8.html http://j-van-thiel.speedlinq.nl/gtk2hs/chap9.html New additions will be listed in chap1.html As said, probably the second part of the port is not really needed, as the Gtk2Hs API documentation maps (mostly) very clearly onto the C functions. Note 1: I'm not a Gtk2Hs expert, but I'm journaling my own learning experience. The code works, but feel free to comment. Someone has kindly promised to review this version, so it will certainly be improved later on. Note 2: the Gtk+2.0 tutorial has not been updated since 2002 (if the copyright notice is to be trusted) and does not cover everything. The same applies to the port. Moreover, advanced widgets like Tree List are large and complicated and will not be treated at all. Note 3: This tutorial, and in particular the 'Getting Started' chapter, replaces the old 'Getting Started' page, which has been removed. Many Thanks, Hans van Thiel

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Tackling IO (the correct way)
by Dave Tapley 23 Aug '07

23 Aug '07

Hi again all, I could do with some design pointers for a project I'm working on combining Haskell with a robot. My situation is: I read sensor data from the robot lazily a line at a time, as soon as a line is read in my code sends out a response down a pipe. Implemented in this fashion: > mapM_ (updateFunction myIORef) fromRobot ::IO () > fromRobot :: String > updateFunction :: IORef -> String -> IO () Now I wish to update a HOpenGL window synchronously with this. To establish this I make a new HOpenGL window & return an IORef (IO ()) which holds the actions to draw my graphics. In this fashion: > myIORef <- makeWindow --- Above code --- > mainLoop This can be passed to updateFunction as shown above so every time it processes a new line from the robot is can update the graphics via the IORef. Because neither 'mapM_ (updateFunction myIORef) fromRobot' nor 'mainLoop' terminate I've been using 'forkIO' to split one off. This way the lazy evaluation keeps running and then window keeps updating itself. This works, sort of. I have problems because the my HOpenGL code also has magic to allow you to change the point of view using the keyboard. But when I do I get this after a while: LOCK SET! Previous intel_span.c:210 Current: intel_batchbuffer.c:63 Can anyone suggest how to resolve this "two functions which never terminate but both share IORefs" problem? Many thanks, Dave

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Using Collections: ElemsView and KeysView
by Benjamin Franksen 23 Aug '07

23 Aug '07

Hi I am using collections-0.3 and need to perform some operations on keys resp. values of a map. In the concrete implementations there are functions like 'elems' and 'keys' but there is no such thing in Data.Collections. Instead there are the types 'ElemsView' and 'KeysView' and functions 'withElems' and 'withKeys', but I have not the slightest idea how they are supposed to be used, there is very sparse documentation and no examples. I'd be glad for any hints. Cheers Ben

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Haskell vs GC'd imperative languages, threading, parallelizeability (is that a word? :-D )
by Hugh Perkins 23 Aug '07

23 Aug '07

Haskell vs GC'd imperative languages =========================== On 8/10/07, Thomas Conway <drtomc(a)gmail.com> wrote: > > > Well, C++ is not really competitive with Haskell, because C++ does not > have > > a GC, and it's trivial to corrupt the stack/heap. > > Beg to differ. I offer the following proof by contradiction. :-) > > In my current job, I had a version-1 implementation in Python which > had severe performance problems, and was not amenable to concurrency > (The Python interpreter has a global lock, so you can only execute > python bytecodes from one thread at a time. :-(). The natural > alternative implementation language was C++, but I argued successfully > that a Haskell implementation would be significantly easier to make > concurrent. > > Well, Python is comparable to Haskell to the extent that it has a GC. OTOH it is interpreted, and, well, slow. It's also got a Big Lock around the core system libraries. Trying to avoid naming it by name, because there's a lot of elitism against using mainstream languages that are used by "stupid people", but the fastest imperative GC'd language that I know of is C#. Even the opensource mono version is wickedly fast. The Microsoft version shaves another 20% off execution speed or so. See, I get the feeling that a lot of people are using Haskell not because they compared it to C# and found it better ,but because they compared it to: - C -> Haskell is easier - C++ -> Haskell is easier - Python -> Haskell is faster C# -> fast and easy ;-) Threading ======= I'm not trolling, despite strong appearances to the contrary ;-) My primary objective/goal is to find a way to make threading easy. Thread management today is like memory management in the early 90s. We kindof had tools (new, delete in C++ for example) to do it. At some point we started to use things like Smart Pointers to make it easier, but none of it really worked. Issues such as circular referential loops caused this not to work very well. At some point, someone came out with the idea of a garbage collector, which is really very simple once you know: all it does is walk the graph of variables, starting with those we know are definitely used, and delete all those objects that didnt get walked on. Simple, easy, magic. We should do the same thing for threads. Threading is going to become a major issue soon, maybe not tomorrow, but there is a GPL'd Niagara 2 out with 64 threads (I think?), so the time is now. Haskell solves a huge issue with threads, which is locking, which is a total PITA in imperative languages, it's of the same order of magnitude of problem as eliminating memory leaks, without deleting something twice etc, used to be in pre-GC C++. Nevertheless, one cannot be interested in threads without being interested in performance. There's no point in running a program in 1024 threads, if the single-core C# version runs faster than that, and often it does! Parallelizeability ============ Now, I did have kindof a shootout thread with Don and Sebastien, calculating prime numbers, where Don managed to get to within an order of magnitude of C# performance (I think he got to about 70-80% of C# performance, cool!) -> BUT, and its a big but ;-), as far as I can tell, he did that by sacrificing the Haskell ability to be easily parallelized; his solution was essentially imperative.

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#haskell irc channel reaches 400 users
by dons＠cse.unsw.edu.au 23 Aug '07

23 Aug '07

A small announcement :) 5 1/2 years after its inception, under the guiding hand of Shae Erisson (aka shapr), the #haskell IRC channel[1] on freenode has finally reached 400 users! To chart the growth, we can note that the channel was founded in late 2001, and had slow growth till 2006, reaching 200 users in January of that year. Since then growth in the user base has been far more rapid, reaching 300 users in Dec 2006, and 400 users now, in August 2007. This puts the channel at around the 13th largest community of the 5500 freenode channels. For comparision, a sample of the state of the other language communities: #php 485 #perl 472 ##c++ 457 ##c 445 #python 430 #ruby-lang 420 > #haskell 411 #lisp 246 ##java 236 ##javascript 226 #perl6 144 #scheme 139 #erlang 118 #lua 105 #ocaml 58 You can see the growth of the channel over here: http://www.cse.unsw.edu.au/~dons/irc If you've not dropped by the channel yet, feel free to come and chat, and toss around some lambdas! :) Cheers, Don 1. http://www.haskell.org/haskellwiki/IRC_channel

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-f flag to runghc broken, or is it just me? (because trying switch elegantly between ghc 6.6 and ghc 6.7)
by Thomas Hartman 23 Aug '07

23 Aug '07

I'm doing a lot of switching between ghc 6.6 and ghc 6.7 on the same computer. I install modules using $ runghc Setup.hs configure etc. I would like to specify which version of ghc should be getting the package installed via the f flag to runghc $ :~/personal/PersonalRepos/pharchive/learning/haskell/UnixTools/arghandling>runghc runghc: syntax: runghc [-f GHCPATH] [GHC-ARGS] FILE ARG... but this appears to be broken. $ :~/personal/PersonalRepos/pharchive/learning/haskell/UnixTools/arghandling>runghc arghandling-nice.hs arghandling-nice.hs: args length does not equal 3. args: : [] usage example: $ runghc arghandling-nice.hs firstarg secondarg thirdarg without the flag works but $ :~/personal/PersonalRepos/pharchive/learning/haskell/UnixTools/arghandling>runghc -f /usr/local/bin/ghc-6.6.1 arghandling-nice.hs does nothing. $ :~/personal/PersonalRepos/pharchive/learning/haskell/UnixTools/arghandling>ls -l /usr/local/bin/ghc-6.6.1 -rwxr-xr-x 1 root root 151 2007-06-16 20:22 /usr/local/bin/ghc-6.6.1 In general I don't like using runghc because it doesn't appear to be documented anywhere except that (incorrect?) usage message. Is there a way to do a package install just using ghc -e? (Sure I could compile, but it helps me sometimes if I can not, a la runghc.) At any rate I couldn't figure out how to pass arguments to main via ghc -e. $ :~/personal/PersonalRepos/pharchive/learning/haskell/UnixTools/arghandling>cat arghandling-nice.hs import System main = do args <- getArgs let usagemsg = "usage example: $ runghc arghandling-nice.hs firstarg secondarg thirdarg" case args of [first,second,third] -> process first second third _ -> error $ "args length does not equal 3. args: : " ++ ( show args ) ++ "\n" ++ usagemsg process a b c = print $ unwords [a,b,c] Thanks for anybody who can help me out with this. Thomas. --- This e-mail may contain confidential and/or privileged information. If you are not the intended recipient (or have received this e-mail in error) please notify the sender immediately and destroy this e-mail. Any unauthorized copying, disclosure or distribution of the material in this e-mail is strictly forbidden.

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Parsing binary data.
by Peter Cai 22 Aug '07

22 Aug '07

Hi all, Recently I am considering doing part of my job using Haskell. My duty is writing a network server which talks to another server through a binary based private protocol. As the old version of this component is written in C, it's very natural that this protocol is base on C structure definitions, which are, unfortunately, very complicated. And the worse is that every field in every structure must be converted to Network Endian. As I am a newbie to Haskell, I am not sure how to handle this problem with less work. Do you have any ideas about this problem? Thanks in advance! -- There is No CODE That is More Flexible Than NO Code!

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Impredicativity confusion
by Gleb Alexeyev 22 Aug '07

22 Aug '07

Hello Cafe! Is there some reason why definition of 'boom' in the code below won't compile? Is it documented somewhere? Thanks. {-# OPTIONS_GHC -fglasgow-exts #-} data Foo a foo :: Foo a -> a -> Bool foo = undefined newtype A = A (forall a. a->a) ok = foo f (A id) where f = undefined :: Foo A type B = forall a. a->a boom = foo f (id :: B) where f = undefined :: Foo B

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Generic data constructor in pattern?
by Peter Verswyvelen 22 Aug '07

22 Aug '07

Consider the following example code: data Vector = V Float Float data Matrix = M Vector Vector liftV1 f (V x y) = V (f x) (f y) liftV2 f (V x1 y1) (V x2 y2) = V (f x1 x2) (f y1 y2) liftM1 f (M x y) = M (f x) (f y) liftM2 f (M x1 y1) (M x2 y2) = M (f x1 x2) (f y1 y2) Both pairs of lift functions have almost identical implementations. Can I merge these somehow? I know data constructors are first class values and are not types, but if I want to merge these lift functions I have to write something like lift1 f (d x y) = d (f x) (f y) lift2 f (d x1 y1) (d x2 y2) = d (f x1 x2) (f y1 y2) But this does not work, as the pattern matcher does not seem to like this. Thanks, Peter Verswyvelen PS: Of course I could define a single type like: data Pair a = P a a type Vector = Pair Float type Matrix = Pair Vector lift1 f (P x y) = P (f x) (f y) lift2 f (P x1 y1) (P x2 y2) = P (f x1 x2) (f y1 y2) But that's beside the question :)

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