Re: [Haskell-cafe] Poll: Do you want a mascot?
Yes On 23/11/11 19:11, heathmatlock wrote: Question: Do you want a mascot? Answers: Yes No -- This is an attempt to figure out if this idea is going anywhere. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe -- PMatos ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Cairo and Haskell
Hi, I would like to use Haskell to generate automatically a poster. I guess that would be using Cairo so I can have a 2d canvas to draw in and maybe even preview before exporting to PDF. However, I can't find any documentation on Cairo with Haskell or any code examples related to what I want to do. Any suggestions? Cheers, -- PMatos ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Cairo and Haskell
Thanks I will take a look at those. On 15/04/11 15:12, Robert Wills wrote: Have a look at http://hackage.haskell.org/package/diagrams and http://hackage.haskell.org/package/Hieroglyph ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Cairo and Haskell
On 15/04/11 15:19, Chris Smith wrote: To answer my own email, yes, PDF support is there. Great, I assume it would also allow me to preview it on a GTK canvas, right? -- PMatos ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Cairo and Haskell
On 15/04/11 16:13, John Obbele wrote: bash $ mkdir /tmp/uncabal cd /tmp/uncabal bash $ cabal unpack cairo bash $ cd /tmp/uncabal/cairo-*/demo bash $ runghc StarAndRing.hs The gtk2hs bindings are generaly pretty dumb and just mimic the original C behaviour. So the best source of documentation is the original cairo website: http://cairographics.org/documentation/ Awesome, just tried it and it worked! Will start off based on that! :) -- PMatos ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Installing agda through cabal
Hi all, I am trying to install agda through cabal but I get this: $ cabal install alex Resolving dependencies... [1 of 1] Compiling Main ( /tmp/alex-2.3.116333/alex-2.3.1/Setup.lhs, /tmp/alex-2.3.116333/alex-2.3.1/dist/setup/Main.o ) /tmp/alex-2.3.116333/alex-2.3.1/Setup.lhs:6:51: Warning: In the use of `buildVerbose' (imported from Distribution.Simple.Setup): Deprecated: Use buildVerbosity instead /tmp/alex-2.3.116333/alex-2.3.1/Setup.lhs:7:51: Warning: In the use of `defaultUserHooks' (imported from Distribution.Simple): Deprecated: Use simpleUserHooks or autoconfUserHooks, unless you need Cabal-1.2 compatibility in which case you must stick with defaultUserHooks Linking /tmp/alex-2.3.116333/alex-2.3.1/dist/setup/setup ... Warning: defaultUserHooks in Setup script is deprecated. Configuring alex-2.3.1... Preprocessing executables for alex-2.3.1... Building alex-2.3.1... [ 1 of 16] Compiling Set ( src/Set.hs, dist/build/alex/alex-tmp/Set.o ) [ 2 of 16] Compiling DFS ( src/DFS.hs, dist/build/alex/alex-tmp/DFS.o ) [ 3 of 16] Compiling Sort ( src/Sort.hs, dist/build/alex/alex-tmp/Sort.o ) [ 4 of 16] Compiling CharSet ( src/CharSet.hs, dist/build/alex/alex-tmp/CharSet.o ) [ 5 of 16] Compiling Map ( src/Map.hs, dist/build/alex/alex-tmp/Map.o ) [ 6 of 16] Compiling Paths_alex ( dist/build/autogen/Paths_alex.hs, dist/build/alex/alex-tmp/Paths_alex.o ) [ 7 of 16] Compiling Util ( src/Util.hs, dist/build/alex/alex-tmp/Util.o ) [ 8 of 16] Compiling AbsSyn ( src/AbsSyn.hs, dist/build/alex/alex-tmp/AbsSyn.o ) [ 9 of 16] Compiling ParseMonad ( src/ParseMonad.hs, dist/build/alex/alex-tmp/ParseMonad.o ) [10 of 16] Compiling Scan ( dist/build/alex/alex-tmp/Scan.hs, dist/build/alex/alex-tmp/Scan.o ) [11 of 16] Compiling Output ( src/Output.hs, dist/build/alex/alex-tmp/Output.o ) [12 of 16] Compiling Info ( src/Info.hs, dist/build/alex/alex-tmp/Info.o ) [13 of 16] Compiling NFA ( src/NFA.hs, dist/build/alex/alex-tmp/NFA.o ) [14 of 16] Compiling DFA ( src/DFA.hs, dist/build/alex/alex-tmp/DFA.o ) [15 of 16] Compiling Parser ( dist/build/alex/alex-tmp/Parser.hs, dist/build/alex/alex-tmp/Parser.o ) [16 of 16] Compiling Main ( src/Main.hs, dist/build/alex/alex-tmp/Main.o ) Linking dist/build/alex/alex ... Installing executable(s) in /home/pmatos/.cabal/bin pma...@drserver ~ $ cabal install agda Resolving dependencies... Configuring Agda-2.2.2... cabal: alex version =2.0.1 3 is required but it could not be found. cabal: Error: some packages failed to install: Agda-2.2.2 failed during the configure step. The exception was: exit: ExitFailure 1 As you can see, I had just finished installing alex 2.3.1, so why does cabal still request alex =2.0.1 3? Cheers, Paulo Matos ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Installing agda through cabal
On Fri, 2009-06-19 at 15:35 -0500, Jake McArthur wrote: Paulo J. Matos wrote: As you can see, I had just finished installing alex 2.3.1, so why does cabal still request alex =2.0.1 3? Probably you don't have alex in your PATH. - Jake Shouldn't cabal make sure the library it installs are in PATH? or at least, they are in the PATH of the apps built by cabal itself? Cheers, Paulo Matos ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Installing agda through cabal
On Fri, 2009-06-19 at 23:35 +0200, Max Rabkin wrote: On Fri, Jun 19, 2009 at 11:20 PM, Paulo J. Matospocma...@gmail.com wrote: Shouldn't cabal make sure the library it installs are in PATH? This would require modifying the path (since there may be no writable location on the existing path). But the PATH is set by a combination of several programs written in Turing-complete languages (shell script), and those programs themselves are in unknown locations (depending on the shell in use). or at least, they are in the PATH of the apps built by cabal itself? This is a possibility. But surely you're one day going to want to run your cabal-installed programs yourself (there are some pretty handy ones), so the easiest thing is to extend your path. You're right. Added .cabal/bin to path and everything is ok. It might be a good idea for cabal-install to warn that its bin directory is not in your path when you install an executable. Yep, might be an interesting idea for warning. :) --Max ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Verifying Haskell Programs
On Mon, Feb 2, 2009 at 10:04 PM, Don Stewart d...@galois.com wrote: pocmatos: Hi all, Much is talked that Haskell, since it is purely functional is easier to be verified. However, most of the research I have seen in software verification (either through model checking or theorem proving) targets C/C++ or subsets of these. What's the state of the art of automatically verifying properties of programs written in Haskell? State of the art is translating subsets of Haskell to Isabelle, and verifying them. Using model checkers to verify subsets, or extracting Haskell from Agda or Coq. Any references to publications related to this? -- Don -- Paulo Jorge Matos - pocmatos at gmail.com Webpage: http://www.personal.soton.ac.uk/pocm ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Verifying Haskell Programs
On Tue, Feb 3, 2009 at 12:28 AM, Don Stewart d...@galois.com wrote: dbueno: On Mon, Feb 2, 2009 at 15:04, Don Stewart d...@galois.com wrote: pocmatos: Hi all, Much is talked that Haskell, since it is purely functional is easier to be verified. However, most of the research I have seen in software verification (either through model checking or theorem proving) targets C/C++ or subsets of these. What's the state of the art of automatically verifying properties of programs written in Haskell? State of the art is translating subsets of Haskell to Isabelle, and verifying them. Using model checkers to verify subsets, or extracting Haskell from Agda or Coq. Don, can you give some pointers to literature on this, if any? That is, any documentation of a verification effort of Haskell code with Isabelle, model checkers, or Coq? (It's not that I don't believe you -- I'd be really interested to read it!) All on haskell.org, http://haskell.org/haskellwiki/Research_papers/Testing_and_correctness#Verifying_Haskell_programs And there's been work since I put that list together. Opps, sorry, missed this message. Should read everything before replying! :) -- Don -- Paulo Jorge Matos - pocmatos at gmail.com Webpage: http://www.personal.soton.ac.uk/pocm ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Verifying Haskell Programs
Hi all, Much is talked that Haskell, since it is purely functional is easier to be verified. However, most of the research I have seen in software verification (either through model checking or theorem proving) targets C/C++ or subsets of these. What's the state of the art of automatically verifying properties of programs written in Haskell? Cheers, -- Paulo Jorge Matos - pocmatos at gmail.com Webpage: http://www.personal.soton.ac.uk/pocm ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] IO () and IO [()]
Hello all, I find it funny that IO () is different from IO [()]. For example, if I define a function to output some lines with mapT, I would do: outputLines :: Int - IO () outputLines i = mapM (putStrLn . show) (take i $ iterate ((+) 1) 1) However, this is in fact outputLines :: Int - IO [()] I would like to know if in fact there's any difference in practice between (), [()], i.e. if in practice the difference matters. My first guess is that this is just a consequence of the Haskell type system and so that everything fits this really needs to be like this. Because mapM :: (Monad m) = (a - m b) - [a] - m [b] So I guess that it makes sense that you get IO [()] instead of IO (), and adding an exception just to say that [()] == () isn't good. By the way, as a consequence can you possibly get IO (()) or IO ([()]) and are these all different from each other? Cheers, -- Paulo Jorge Matos - pocm at soton.ac.uk http://www.personal.soton.ac.uk/pocm PhD Student @ ECS University of Southampton, UK Sponsor ECS runners - Action against Hunger: http://www.justgiving.com/ecsrunslikethewind ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: Internships at GHC HQ
On Jan 25, 2008 11:40 AM, Simon Peyton-Jones [EMAIL PROTECTED] wrote: Would you be interested in working at Microsoft Research for three months? If so, you might want to think about applying for an internship. Simon and I are looking for interns, starting in summer 2008. Lots of background info here: http://hackage.haskell.org/trac/ghc/wiki/Internships including a bunch of possible projects, although you may also have ideas of your own. Hello Simon, I wonder if there is any interest by the part of Microsoft and the Haskell community in a software model checker using SAT-based techniques for Haskell. There's have been in the last few year a couple of approaches on this for C by several people, including some Microsoft people. Cheers, Paulo Matos But the bottom line is - apply by end Feb 2008 for this round - tell one of us that you have done so (None of this is restricted to Haskell stuff. You can apply to work at any Microsoft Research lab, on any topic. But there are a lot of applicants, so you are more likely to be successful if you are fairly specific about who at MSR you'd like to work with and why, and contact that person to say that you've applied.) Simon ___ Glasgow-haskell-users mailing list [EMAIL PROTECTED] http://www.haskell.org/mailman/listinfo/glasgow-haskell-users -- Paulo Jorge Matos - pocm at soton.ac.uk http://www.personal.soton.ac.uk/pocm PhD Student @ ECS University of Southampton, UK ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Comments on reading two ints off Bytestring
On Dec 23, 2007 12:44 PM, Isaac Dupree [EMAIL PROTECTED] wrote: -- this should work too parseHeader3 :: BS.ByteString - Maybe (Int, Int) --note accurate type signature, which helps us use Maybe failure-monad, --although losing your separate error messages Oh gee, I just noticed that my type sig is in fact not correct. How come GHC doesn't complain? parseHeader3 bs = do (x, rest) - BS.readInt $ BS.dropWhile (not . isDigit) bs (y, _) - BS.readInt $ BS.dropWhile (not . isDigit) rest return (x, y) What happens then if the first BS.readInt return Nothing??? --or to be clearer without syntactic sugar, that is parseHeader3 bs = (BS.readInt $ BS.dropWhile (not . isDigit) bs) = \(x, rest) - (BS.readInt $ BS.dropWhile (not . isDigit) rest) = \(y, _) - return (x, y) Isaac Paulo J. Matos wrote: On Dec 23, 2007 12:32 PM, Paulo J. Matos [EMAIL PROTECTED] wrote: Hello all, It is either too difficult to get two integers of a bytestring, in which case something should be done to ease the process or I should learn much more Haskell. I guess the latter is the correct guess. I have a bytestring containing two naturals. I was to get them as efficiently as possible. Here's my code: Just tried a better one, what do you think of this: parseHeader2 :: BS.ByteString - (Int, Int) parseHeader2 bs = case (BS.readInt $ BS.dropWhile (not . isDigit) bs) of Nothing - error Couldn't find first natural. Just (x, rest) - case (BS.readInt $ BS.dropWhile (not . isDigit) rest) of Nothing - error Couldn't find second natural. Just (y, _) - (x, y) parseHeader :: BS.ByteString - (Int, Int) parseHeader bs = let first = BS.readInt $ BS.dropWhile (not . isDigit) bs in if(isNothing first) then error Couldn't find first natural. else let second = BS.readInt $ BS.dropWhile (not . isDigit) $ snd $ fromJust first in if(isNothing second) then error Couldn't find second natural. else (fst $ fromJust first, fst $ fromJust second) This seems to work: parseHeader $ BS.pack hello 252 359 (252,359) Is there a better way? Cheers, -- Paulo Jorge Matos - pocm at soton.ac.uk http://www.personal.soton.ac.uk/pocm PhD Student @ ECS University of Southampton, UK -- Paulo Jorge Matos - pocm at soton.ac.uk http://www.personal.soton.ac.uk/pocm PhD Student @ ECS University of Southampton, UK ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Comments on reading two ints off Bytestring
On Dec 24, 2007 11:55 AM, Paulo J. Matos [EMAIL PROTECTED] wrote: On Dec 23, 2007 12:44 PM, Isaac Dupree [EMAIL PROTECTED] wrote: -- this should work too parseHeader3 :: BS.ByteString - Maybe (Int, Int) --note accurate type signature, which helps us use Maybe failure-monad, --although losing your separate error messages Oh gee, I just noticed that my type sig is in fact not correct. How come GHC doesn't complain? parseHeader3 bs = do (x, rest) - BS.readInt $ BS.dropWhile (not . isDigit) bs (y, _) - BS.readInt $ BS.dropWhile (not . isDigit) rest return (x, y) What happens then if the first BS.readInt return Nothing??? Ok, got it, I'm not returning a maybe. That's it then. Still, the first question remains... what happens to (x, rest) if BS.readInt returns Nothing. -- Paulo Jorge Matos - pocm at soton.ac.uk http://www.personal.soton.ac.uk/pocm PhD Student @ ECS University of Southampton, UK ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Comments on reading two ints off Bytestring
Hello all, It is either too difficult to get two integers of a bytestring, in which case something should be done to ease the process or I should learn much more Haskell. I guess the latter is the correct guess. I have a bytestring containing two naturals. I was to get them as efficiently as possible. Here's my code: parseHeader :: BS.ByteString - (Int, Int) parseHeader bs = let first = BS.readInt $ BS.dropWhile (not . isDigit) bs in if(isNothing first) then error Couldn't find first natural. else let second = BS.readInt $ BS.dropWhile (not . isDigit) $ snd $ fromJust first in if(isNothing second) then error Couldn't find second natural. else (fst $ fromJust first, fst $ fromJust second) This seems to work: parseHeader $ BS.pack hello 252 359 (252,359) Is there a better way? Cheers, -- Paulo Jorge Matos - pocm at soton.ac.uk http://www.personal.soton.ac.uk/pocm PhD Student @ ECS University of Southampton, UK ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: Comments on reading two ints off Bytestring
On Dec 23, 2007 12:32 PM, Paulo J. Matos [EMAIL PROTECTED] wrote: Hello all, It is either too difficult to get two integers of a bytestring, in which case something should be done to ease the process or I should learn much more Haskell. I guess the latter is the correct guess. I have a bytestring containing two naturals. I was to get them as efficiently as possible. Here's my code: Just tried a better one, what do you think of this: parseHeader2 :: BS.ByteString - (Int, Int) parseHeader2 bs = case (BS.readInt $ BS.dropWhile (not . isDigit) bs) of Nothing - error Couldn't find first natural. Just (x, rest) - case (BS.readInt $ BS.dropWhile (not . isDigit) rest) of Nothing - error Couldn't find second natural. Just (y, _) - (x, y) parseHeader :: BS.ByteString - (Int, Int) parseHeader bs = let first = BS.readInt $ BS.dropWhile (not . isDigit) bs in if(isNothing first) then error Couldn't find first natural. else let second = BS.readInt $ BS.dropWhile (not . isDigit) $ snd $ fromJust first in if(isNothing second) then error Couldn't find second natural. else (fst $ fromJust first, fst $ fromJust second) This seems to work: parseHeader $ BS.pack hello 252 359 (252,359) Is there a better way? Cheers, -- Paulo Jorge Matos - pocm at soton.ac.uk http://www.personal.soton.ac.uk/pocm PhD Student @ ECS University of Southampton, UK -- Paulo Jorge Matos - pocm at soton.ac.uk http://www.personal.soton.ac.uk/pocm PhD Student @ ECS University of Southampton, UK ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Quickcheck generator for arrays of integers
Hello all, I using an IArray to represent a matrix. I'm trying to write some properties checks with Quickcheck. Quickcheck lacks instance generators for arrays of ints for example, is there anything I can use out there or should I define it myself? (I'm asking because it seems to be something that other people already did) Cheers, -- Paulo Jorge Matos - pocm at soton.ac.uk http://www.personal.soton.ac.uk/pocm PhD Student @ ECS University of Southampton, UK ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] I'm translating All about Monads to Chinese
On Dec 3, 2007 12:39 PM, Albert Lee [EMAIL PROTECTED] wrote: I have been confussed by monad for a long time. and I can't stand for it any more. so I start to translate the tutorial All About Monads to my mother language Chinese. My English is not good enough, so this work is only for my own study~ I know there are some other Chinese fellow in this list, wish it would be helpful. I will work for one chapter everyday. Let me just add that it was (after reading several other tutorials) All About Monads that enlightened me about them. :) the address is: http://www.kamang.net ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe -- Paulo Jorge Matos - pocm at soton.ac.uk http://www.personal.soton.ac.uk/pocm PhD Student @ ECS University of Southampton, UK ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: Why is this strict in its arguments?
I'm glad that my initial post generated such an interesting discussion but I'm still not understanding why the first version of findAllPath seems to be computing the whole list even when I just request the head, while the second one doesn't. I thought that this was denominated by findAllPath is strict in its arguments but it seems that I haven't used the right terminology to explain what I really wanted to understand. -- Paulo Jorge Matos - pocm at soton.ac.uk http://www.personal.soton.ac.uk/pocm PhD Student @ ECS University of Southampton, UK ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Why is this strict in its arguments?
On Dec 5, 2007 1:51 PM, Luke Palmer [EMAIL PROTECTED] wrote: On Dec 4, 2007 9:41 PM, Paulo J. Matos [EMAIL PROTECTED] wrote: Hello all, As you might have possibly read in some previous blog posts: http://users.ecs.soton.ac.uk/pocm06r/fpsig/?p=10 http://users.ecs.soton.ac.uk/pocm06r/fpsig/?p=11 we (the FPSIG group) defined: data BTree a = Leaf a | Branch (BTree a) a (BTree a) and a function that returns a list of all the paths (which are lists of node values) where each path element makes the predicate true. findAllPath :: (a - Bool) - (BTree a) - Maybe [[a]] findAllPath pred (Leaf l) | pred l = Just [[l]] | otherwise = Nothing findAllPath pred (Branch lf r rt) | pred r = let lfpaths = findAllPath pred lf rtpaths = findAllPath pred rt in if isNothing lfpaths isNothing rtpaths then Nothing else if isNothing lfpaths then Just (map (r:) $ fromJust rtpaths) else if isNothing rtpaths then Just (map (r:) $ fromJust lfpaths) else Just (map (r:) $ fromJust rtpaths ++ fromJust lfpaths) | otherwise = Nothing I don't think this evaluates the whole tree every time, but it certainly evaluates more than it needs to. It has to do with an extra check. Here's a very operational description: First note that if findAllPath returns Nothing, then it has evaluated the tree down to the contour where all the preds are false. Let's suppose that this is the best possible case, where there is a path down the left side of the tree with no backtracking where all nodes are true. findAllPath pred (Leaf l) = Just [[l]] Now: if isNothing lfpaths ... -- false already, lfpaths is a Just, go to else branch else if isNothing lfpaths ... -- false again, go to else branch else if isNothing rtpaths ... To check this, you have to evaluate rtpaths down to its false contour before you can proceed. You didn't need to do this. Instead, writing the last else as: else Just (map (r:) $ fromJust lfpaths ++ fromMaybe [] rtpaths) Will get you behavior -- I think -- equivalent to the original. Except for that it will return paths in leftmost order rather than rightmost. But changing the order of some of those checks will get you back the original rightmost behavior and lazy semantics. Left as an exercise for the OP :-) Oh, ok! :) I think I got it now! Thank you! Cheers, Paulo Matos Luke Later on we noticed that this could be simply written as: findAllPath :: (a - Bool) - (BTree a) - [[a]] findAllPath pred = g where g (Leaf l) | pred l = [[l]] g (Branch lf r rt) | pred r = map (r:) $ (findAllPath pred lf) ++ (findAllPath pred rt) g _ = [] without even using maybe. However, 2 questions remained: 1 - why is the first version strict in its arguments? 2 - if it really is strict in its arguments, is there any automated way to know when a function is strict in its arguments? Cheers, -- Paulo Jorge Matos - pocm at soton.ac.uk http://www.personal.soton.ac.uk/pocm PhD Student @ ECS University of Southampton, UK ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe -- Paulo Jorge Matos - pocm at soton.ac.uk http://www.personal.soton.ac.uk/pocm PhD Student @ ECS University of Southampton, UK ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Why is this strict in its arguments?
On Dec 5, 2007 1:43 PM, Benja Fallenstein [EMAIL PROTECTED] wrote: Hi Paolo, On Dec 5, 2007 2:09 PM, Paulo J. Matos [EMAIL PROTECTED] wrote: I'm glad that my initial post generated such an interesting discussion but I'm still not understanding why the first version of findAllPath seems to be computing the whole list even when I just request the head, while the second one doesn't. Because the function starts its work with if isNothing lfpaths isNothing rtpaths then Nothing else ... which forces the evaluation of 'lfpaths' and 'rtpaths' to see whether they are Just or Nothing, which recursively forces the evaluation of findAllPath for the whole tree. Oh, but lfpaths is not nothing so that means that isNothing rtpaths shouldn't be evaluated, right? Hope this helps, - Benja -- Paulo Jorge Matos - pocm at soton.ac.uk http://www.personal.soton.ac.uk/pocm PhD Student @ ECS University of Southampton, UK ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Why is this strict in its arguments?
On Dec 4, 2007 10:00 PM, Neil Mitchell [EMAIL PROTECTED] wrote: Hi findAllPath :: (a - Bool) - (BTree a) - [[a]] findAllPath pred = g where g (Leaf l) | pred l = [[l]] g (Branch lf r rt) | pred r = map (r:) $ (findAllPath pred lf) ++ (findAllPath pred rt) g _ = [] without even using maybe. However, 2 questions remained: 1 - why is the first version strict in its arguments? Because in all call paths findAllPath will call g with its second argument. g will always evaluate (by pattern matching on) its value argument. Wait! You're analyzing my second function and you're saying that it is strict in its arguments? Gee, that's bad. I questioned about the first one. The second seems to be definitely lazy because I can use it on such big trees like I showed. How come I can do this computation if like you said the function is strict? 2 - if it really is strict in its arguments, is there any automated way to know when a function is strict in its arguments? Yes, strictness analysis is a very well studied subject - http://haskell.org/haskellwiki/Research_papers/Compilation#Strictness . Essentially, an argument is strict if passing _|_ for that value results in _|_. So to take your example, evaluating: findAllPath a _|_ g _|_ _|_ Since g tests what value _|_ has, we get bottom. Thanks Neil -- Paulo Jorge Matos - pocm at soton.ac.uk http://www.personal.soton.ac.uk/pocm PhD Student @ ECS University of Southampton, UK ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Why is this strict in its arguments?
On Dec 5, 2007 10:44 AM, Jules Bean [EMAIL PROTECTED] wrote: Paulo J. Matos wrote: Hello all, Hi. findAllPath :: (a - Bool) - (BTree a) - Maybe [[a]] findAllPath pred (Leaf l) | pred l = Just [[l]] | otherwise = Nothing findAllPath pred (Branch lf r rt) | pred r = let lfpaths = findAllPath pred lf rtpaths = findAllPath pred rt in if isNothing lfpaths isNothing rtpaths then Nothing else if isNothing lfpaths then Just (map (r:) $ fromJust rtpaths) else if isNothing rtpaths then Just (map (r:) $ fromJust lfpaths) else Just (map (r:) $ fromJust rtpaths ++ fromJust lfpaths) | otherwise = Nothing Ignoring the fact that you found a better way to write this entirely, a style point. Use of isNothing and fromJust and a cascade of ifs is generally a poor sign, much better to use case: findAllPath pred (Branch lf r rt) | pred r = case (findAllPath pred lf,findAllPath pred rt) of (Nothing,Nothing) - Nothing (Nothing,Just rtpaths) - Just (map (r:) rtpaths) (Just lfpaths,Nothing) - Just (map (r:) lfpaths) (Just lfpaths,Just rtpaths) - Just (map (r:) $ rtpaths ++ lfpaths) | otherwise = Nothing the general pattern is : replace isNothing with a case match on Nothing, replace fromJust with a case match on Just, don't be afraid to case two expressions at once. Hope someone finds that useful, Thanks, Although I think that the general thread diverged from my initial question, here it is again, why is this terrible function (I know it is ugly) evaluating all of the resulting list when I just request the head? (at seems from my experiments that's what it seems to be doing). BTW, I thought that the problem of evaluating all of the resulting list when I just request the head was related to argument strictness but from the other mails, I think I was wrong. :) Jules -- Paulo Jorge Matos - pocm at soton.ac.uk http://www.personal.soton.ac.uk/pocm PhD Student @ ECS University of Southampton, UK ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Why is this strict in its arguments?
On Dec 5, 2007 12:16 AM, Aaron Denney [EMAIL PROTECTED] wrote: On 2007-12-04, Paulo J. Matos [EMAIL PROTECTED] wrote: Hello all, As you might have possibly read in some previous blog posts: http://users.ecs.soton.ac.uk/pocm06r/fpsig/?p=10 http://users.ecs.soton.ac.uk/pocm06r/fpsig/?p=11 we (the FPSIG group) defined: data BTree a = Leaf a | Branch (BTree a) a (BTree a) Totally avoiding your question, but I'm curious as to why you deliberately exclude empty trees. Come to think of it, how can you represent a tree with two elements? Good question. I think we were just trying to define a tree in the meeting and everyone agreed on this representation. Wouldn't data BTree a = Empty | Branch (BTree a) a (BTree a) be better? Possibly :) I think that at the time nobody really cared about empty trees! But for a really application we would have had to define them probably. Now thinking about it, it seems like defining lists without Null, strange, isn't it? -- Aaron Denney -- ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe -- Paulo Jorge Matos - pocm at soton.ac.uk http://www.personal.soton.ac.uk/pocm PhD Student @ ECS University of Southampton, UK ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Why is this strict in its arguments?
Hello all, As you might have possibly read in some previous blog posts: http://users.ecs.soton.ac.uk/pocm06r/fpsig/?p=10 http://users.ecs.soton.ac.uk/pocm06r/fpsig/?p=11 we (the FPSIG group) defined: data BTree a = Leaf a | Branch (BTree a) a (BTree a) and a function that returns a list of all the paths (which are lists of node values) where each path element makes the predicate true. findAllPath :: (a - Bool) - (BTree a) - Maybe [[a]] findAllPath pred (Leaf l) | pred l = Just [[l]] | otherwise = Nothing findAllPath pred (Branch lf r rt) | pred r = let lfpaths = findAllPath pred lf rtpaths = findAllPath pred rt in if isNothing lfpaths isNothing rtpaths then Nothing else if isNothing lfpaths then Just (map (r:) $ fromJust rtpaths) else if isNothing rtpaths then Just (map (r:) $ fromJust lfpaths) else Just (map (r:) $ fromJust rtpaths ++ fromJust lfpaths) | otherwise = Nothing Later on we noticed that this could be simply written as: findAllPath :: (a - Bool) - (BTree a) - [[a]] findAllPath pred = g where g (Leaf l) | pred l = [[l]] g (Branch lf r rt) | pred r = map (r:) $ (findAllPath pred lf) ++ (findAllPath pred rt) g _ = [] without even using maybe. However, 2 questions remained: 1 - why is the first version strict in its arguments? 2 - if it really is strict in its arguments, is there any automated way to know when a function is strict in its arguments? Cheers, -- Paulo Jorge Matos - pocm at soton.ac.uk http://www.personal.soton.ac.uk/pocm PhD Student @ ECS University of Southampton, UK ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Haskell code in Wordpress
Thanks all for your suggestions. On Nov 23, 2007 10:31 PM, Duncan Coutts [EMAIL PROTECTED] wrote: On Fri, 2007-11-23 at 20:22 +, Paulo J. Matos wrote: Hi all, I'm curious about the best way to typeset haskell code in a wordpress blog. Using blockquote removes all indentation. :-( For the Gtk2Hs website I used a program (partly derived from hscolour) to highlight and adds links to documentation. It generates xhtml which one can just paste in. See the hello world example on this page: http://haskell.org/gtk2hs/documentation/ The program is here: http://darcs.haskell.org/gtk2hs/docs/tools/AddLinks.hs Duncan -- Paulo Jorge Matos - pocm at soton.ac.uk http://www.personal.soton.ac.uk/pocm PhD Student @ ECS University of Southampton, UK ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Haskell code in Wordpress
Hi all, I'm curious about the best way to typeset haskell code in a wordpress blog. Using blockquote removes all indentation. :-( Cheers, -- Paulo Jorge Matos - pocm at soton.ac.uk http://www.personal.soton.ac.uk/pocm PhD Student @ ECS University of Southampton, UK ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Why can't Haskell be faster?
On 01/11/2007, Simon Peyton-Jones [EMAIL PROTECTED] wrote: Yes, that's right. We'll be doing a lot more work on the code generator in the rest of this year and 2008. Here we includes Norman Ramsey and John Dias, as well as past interns Michael Adams and Ben Lippmeier, so we have real muscle! That's very good to know. I wonder where could I read more about current state of the art on Haskell compilation techniques and about the implementation of ghc in general? Is there a book on it or maybe some group of papers that would aid me to understand it? Cheers, Paulo Matos Simon | I don't think the register allocater is being rewritten so much as it is | being written: | | From talking to Ben, who rewrote the register allocator over the | summer, he said that the new graph based register allocator is pretty | good. The thing that is holding it back is the CPS conversion bit, | which was also being rewritten over the summer, but didn't get | finished. I think these are both things which are likely to be done | for 6.10. | | Thanks | | Neil | ___ | Haskell-Cafe mailing list | Haskell-Cafe@haskell.org | http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe -- Paulo Jorge Matos - pocm at soton.ac.uk http://www.personal.soton.ac.uk/pocm PhD Student @ ECS University of Southampton, UK ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Why can't Haskell be faster?
Hello all, I, along with some friends, have been looking to Haskell lately. I'm very happy with Haskell as a language, however, a friend sent me the link: http://shootout.alioth.debian.org/gp4/ which enables you compare several language implementations. Haskell seems to lag behind of Clean. From what I've seen of Clean it seems almost like Haskell. It even distributes a Haskell-Clean translator so the obvious question is, why is Haskell slower? Being similar languages and being GHC a very good compiler, can't it get at least as fast as Clean? What am I missing here? (I wrote this mail assuming the results from the URL are trustworthy). Cheers, -- Paulo Jorge Matos - pocm at soton.ac.uk http://www.personal.soton.ac.uk/pocm PhD Student @ ECS University of Southampton, UK ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Why can't Haskell be faster?
On 31/10/2007, Peter Hercek [EMAIL PROTECTED] wrote: Add to that better unbox / box annotations, this may make even bigger difference than the strictness stuff because it allows you to avoid a lot of indirect references do data. Anyway, if Haskell would do some kind of whole program analyzes and transformations it probably can mitigate all the problems to a certain degree. So, I might assert that it is not a problem of the Haskell language itself, it is a problem with the compiler. Which means that with enough effort it would be possible for the compiler to generate compiled code with performance as good as Clean. So the slowness of Haskell (compared to Clean) is consequence of its type system. OK, I'll stop, I did not write Clean nor Haskell optimizers or stuff like that :-D type system? Why is that? Shouldn't type system in fact speed up the generated code, since it will know all types at compile time? Peter. Peter Hercek wrote: I'm curious what experts think too. So far I just guess it is because of clean type system getting better hints for optimizations: * it is easy to mark stuff strict (even in function signatures etc), so it is possible to save on unnecessary CAF creations * uniqueness types allow to do in-place modifications (instead of creating a copy of an object on heap and modifying the copy), so you save GC time and also improve cache hit performance Peter. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe -- Paulo Jorge Matos - pocm at soton.ac.uk http://www.personal.soton.ac.uk/pocm PhD Student @ ECS University of Southampton, UK ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Fast Paced Haskell Tutorial
Hello all, I'm interested in a freely available fast paced haskell tutorial. By fast paced, I means I want something that goes through basic in a very fast pace, presents a couple of examples and then talks about more advanced features. A set of tutorials would be also good. References to these kind of tutorials would be great. Cheers, -- Paulo Jorge Matos - pocm at soton.ac.uk http://www.personal.soton.ac.uk/pocm PhD Student @ ECS University of Southampton, UK ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Using haskell with emacs
Thank you all for your references and tips, I'll be using them. :-) On 06/08/2007, Jules Bean [EMAIL PROTECTED] wrote: Thomas Schilling wrote: On 6 aug 2007, at 22.11, Paulo J. Matos wrote: If you're used to Slime+Paredit, then there isn't something really comparable, but you get some basic interactive programming with the standard key-bindings: (But paredit does work in haskell-mode, and I find it useful...) Jules -- Paulo Jorge Matos - pocm at soton.ac.uk http://www.personal.soton.ac.uk/pocm PhD Student @ ECS University of Southampton, UK ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Using haskell with emacs
Hi all, I'm starting to learn haskell by my own, being currently mostly a Common Lisp, Scheme, C++ programmer... I've got the haskell emacs mode but can't find a manual. Moreover, I've found some keybindings on the net but nothing that allows me to start an interpreter in emacs and send definitions, one by one to the interpreter. Is this possible? Is there any good reference of the emacs keybindings for haskell mode? Cheers, -- Paulo Jorge Matos - pocm at soton.ac.uk http://www.personal.soton.ac.uk/pocm PhD Student @ ECS University of Southampton, UK ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
