- Haskell-Cafe - Haskell.org

HUnit
by Matt Roberts 03 Feb '06

03 Feb '06

I am in love with HUnit and QuickCheck. However, I am missing one important functionality I want to call a command line program that will search all the .hs files I have in a particular directory, pull out all HUnit test (based on what they are called, or perhaps their type signature) and run them all. I have done a bit of a search and can't find anything like this, am I going to have to write it myself? Matt

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Known Unknowns
by Chris Kuklewicz 03 Feb '06

03 Feb '06

There is a new combined benchmark, "partial sums" that subsumes several earlier benchmarks and runs 9 different numerical calculations: http://haskell.org/hawiki/PartialSumsEntry I took the Clean entry and, since there were so many recursive computations, I made compute and altCompute higher order functions. No speed optimization work has been done yet, but it seems really fast. A new http://haskell.org/hawiki/KnucleotideEntry has been accepted, replacing the one with the memory leak. The speed is also better, but still poor, due to Data.Hashtable. GHC 6.6.x should eventually help. Also on the topic of poor speed: http://haskell.org/hawiki/NbodyEntry At the bottom of the page is Einar's really cool existing entry (open mutable records). At the top of the page is best effort to replace it, but it runs at almost the same speed. Which is very much slower (10x) than other entries, such as OCaml. It is odd that small scale numerics, such as the partial-sums functions, can be made fast but not medium scale numerics like the n-body integration. There are 5 fixed mass parameters and 30 variables (5*3 positions + 5*3 velocities). Addition, Subtraction, Multiplication, Division. And we can't get it going nearly as fast as it ought to run. Note: The garbage collector is not a factor (%GC time 0.9%). Like the Hashtable glitch, if this were part of real program then a small bit of c-code could be attached via FFI. Are there little known Haskell idioms for doing math? Do we have to write a recursive function with 30 separate parameters? Do we have to peek and poke unboxed doubles? Is there an undocumented -funleash-fortran parameter? Will this be fixable in Haskell' ("Haskell-Prime")?

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Number 1, at least for now
by dons＠cse.unsw.edu.au 03 Feb '06

03 Feb '06

Haskell is now ranked number 1 on the Great Language Shootout! http://shootout.alioth.debian.org/gp4/benchmark.php?test=all&lang=all Hooray :) -- Don

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Re: [Haskell-cafe] EclipseFP (Haskell IDE) 0.9.1 released
by dagit＠eecs.oregonstate.edu 02 Feb '06

02 Feb '06

Quoting Thiago Arrais <thiago.arrais(a)gmail.com>: > 2006/2/1, Graham Klyne <GK(a)ninebynine.org>: > > [I should say that I haven't yet actually tried this software, though I'd > like > > to do so when I get some time.] > > I really hope you find the time to do so. We would be glad to be > hearing from you again. I haven't found time (yet) to look at your new version, but I tried out the stable version from about a week ago and played with it a bit. I might as well tell you what I found then and why I'm unable to use EclipseFP at this time. > At some point of the wave, the integrated environments appear. They > come, as the name says, to integrate the previous tools in an easy to > use and productive environment. Not that the previous tools were hard > to use or counter-productive, it is just that by integrating them much > time is saved from the details and the programmer can spend more time > on the creative and useful things only he can do. I think it's important to keep this aspect, the ramping up and the integration. Particularly, I'm against tools that want to do things their way. I'd much rather have the tool automate the tools I already have instead of creating a new mechanism. For example, I'd rather have the IDE work with my makefiles than ignore them and use some builtin make system. I need to be able to separate from the IDE whenever it becomes cumbersome or when I want to share the code. > > So is there a compelling feature in this Eclipse plugin that isn't easily > > achieved using simpler tools? > > When we write an Eclipse plugin, we get a lot of things for free. Just > to cite one, there is already CVS integration support within every > Eclipse installation, which includes a very neat diff viewer. Adding > support for other version control systems isn't very hard. There are > plugins, for example, for Darcs and Subversion too. I was trying the Darcs plugin in conjunction with EclipseFP as my first attempt at using eclispe. I found that waiting for eclipse to "autobuild" everything in _darcs was a waste of time and just plain silly. Hopefully, there is a way to avoid this excessive building and still use autobuild. I couldn't find it. > Another very nice feature of the Eclipse platform is the refactoring > support. Wouldn't you like to refactor your Haskell code as easily as > selecting some context-menu item? Not to mention code assistance and > 'go to declaration support' (click a module/function/whatever > reference and open its corresponding declaration). This has saved me a > lot of time when browsing code. This is the reason I sought out EclipseFP. I want to automate as much of the refactoring as I can while making it safe. But now let me turn to the reasons I'm not using it anymore. Some of the reasons have to do with eclipse itself (I think), some are related to the very nice plugin you have created, and some are related to the darcs plugin. Some of my problems may even be fixed in the announced version, but I haven't had a chance to check. I wanted to use EclipseFP to help with darcs development. The first problem I encountered was that darcs has a makefile which is growing in complexity. Some files are compiled with this flag, others with that flag. I couldn't figure out how to import the make rules. I did find a way to set the compilation options, but they were per project instead of per file as near as I could tell. I would a makefile import to be automated and to watch the makefile for changes. One direction would be fine for now, but ultimately I would want it to let me change build settings in Eclipse and have it mirrored in the makefile. Does eclipse have a makefile plugin? I also had a problem with autobuild building too much as noted above. I also couldn't figure out a way to ask eclipse to delegate to make for building. The next problem I encountered was the parser was not forgiving enough to parse the darcs source code, as a result everything was colored as a comment. Every file that contained "#include", "#define" or similar threw a lexical error. The code is meant to be run through ghc with the -cpp flag turned on. Is it possible to use ghc-api for parsing the code? I also noticed that when you click on an error so that eclipse will take you to the place of the error, it often took me to lines that were perfectly fine, in fact, I think it was often the wrong file. The first time I created a "Hello, World" project in win32 eclipseFP gave some odd errors that I didn't write down. I haven't seen that error since so I can't make a bug report, but it was certainly confusing. It was to the effect that ghc had crashed while generating the project. After I got that error, I stop using eclipse in windows and switched to OSX. I had some other problems, but don't think they were related enough to list them here. In the end, it was a horrible first experience with eclipse and I'm not looking forward to ever using eclipse again. On the other hand, I want some sort of IDE for Haskell to help automate certain things, like refactoring. I'm a long time fan of emacs, but the more I use emacs the more I see that it may never handle certain things well. For example, using regexp to do syntax highlighting is quick and easy it's also the source of many of the problems with using emacs for coding in Haskell. The indentation is off, block uncomment is not the inverse of block comment, if you use a string like "{-" it throws off the highlighting until a matching -} is found and so on. My advice would be to download the darcs source code and try to use darcs with EclipseFP. You'll see first hand some things that could use some fix'n :) And I think I could stand to use eclipse to test out your changes if you need a tester, but I doubt I'd have much more time to spare than testing. > Of course, you need to write the code to tell the platform about your > language. That's what the EclipseFP team is trying to do. Yes, and I'm very happy to see someone doing this. I wish you the best of luck and when the problems I encountered are fixed I will try eclipse again. Hopefully my rantings will be helpful to you and not make you lose hope :) I really want see you succeed. Thanks, Jason

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RE: [Haskell-cafe] Number 1, at least for now
by Simon Peyton-Jones 02 Feb '06

02 Feb '06

| > though, I think this is a great oprotunity to improve ghc's optimizer. | | Huh, that would be the best thing with the whole shootout endeavour.. Yes indeed. One thing that would be really helpful, as a first step, would be to identify a bunch of concrete examples that GHC "should" have optimised, or perhaps "could" have optimised, and attach them to the GHC wiki somewhere. One place would be here http://haskell.org/haskellwiki/Performance or perhaps somewhere on the developers wiki, or as a task. http://hackage.haskell.org/trac/ghc I'm not promising that anything will happen fast (unless someone else does it!) but it's always much more likely to happen if there's a specific place that advertises low-hanging performance fruit. This is closely related to the "advice to programmers" that Don circulated yesterday, in which he explained how he optimised one particular case. But not quite the same. Simon

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SCC accounting
by Andrew Pimlott 02 Feb '06

02 Feb '06

We've been trying to track down a memory leak, and by adding SCC annotations, pinned it down to a very brief expression. Unfortunately, the expression is just a variable! We even looked at the generated core: (case ([Soutei.Term Logic.BodyVar] -> (...) -> Logic.Frame -> Logic.QState -> FBackTrackT.Stream m_aYsk Logic.QState) lookup_aYPK pred_aXVH ctxIdx_aYpI of wild_B1 { Data.Maybe.Nothing -> GHC.Err.patError ... Data.Maybe.Just x_aXVL -> __scc {pqzifoozq Assertions} x_aXVL }); Note the __scc annotation just before x_aXVL at the end of the expression. Yet in the time and allocation profile, this SCC is charged for a lot of time and allocations in the "individual" column; individual inherited COST CENTRE no. entries %time %alloc %time %alloc pq.foo' 466 50001 8.0 12.1 8.0 13.2 and in the heap profile, it is a major memory leak. The Haskell code looks like predQuery pred = case lookup pred ctxIdx of Just f -> {-# SCC "pq.foo'" #-} f Note that f is a function, which we expect to be expensive when it is called. However, that should be charged to the definition of the function, right? We tried pretty hard to reproduce this in a small test case, but never succeeded. Always, the cost was accounted to the definition of the function in the intuitive way. We're using ghc 6.4.1 and compiling without optimization. Can any ghc hacker suggest how this could happen, or give us any hints on what to try next? Andrew [1] http://haskell.org/ghc/docs/latest/html/users_guide/profiling.html

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unary pattern matching
by John Meacham 01 Feb '06

01 Feb '06

I have often wanted a shorthand syntax for testing if a value matches a given pattern. I want to implement such an extension for jhc but can't decide an appropriate syntax so I thought I'd ask the group. basically I want something like /Left (Just _)/ expands to \x -> case x of Left (Just _) -> True _ -> False so you can do things like when (/Just _/ x) $ putStrLn "x is something" or map /Left (Foo _ 'x')/ xs to get a list of booleans saying whether the xs match or not. however, the '/' syntax clearly doesn't work, nor would anything that conflicts with normal haskell syntax. does anyone have any better ideas? John -- John Meacham - ⑆repetae.net⑆john⑈

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RE: [Haskell-cafe] Known Unknowns
by Simon Peyton-Jones 01 Feb '06

01 Feb '06

| Here's a brief introduction. I intend to write up (on the performance page on | the wiki) a list of things we've done to improve the shootout entries. Yes, do put what you wrote before on the Wiki. (The performance-advice page seems to have vanished but it should be on the user-documentation wiki somewhere. I'm sure we'll find it.) | Multiple calls to sin. Hmm :/ And similar for cos, as well as k*k. Not sure | why GHC isn't removing these (SimonM?), so let's do that by hand GHC doesn't do full CSE. It'd be a relatively easy pass for someone to add, but it can cause space leaks. And it can replace two strictly-evaluated calls with one lazy thunk: let { x = case e of ....; y = case e of .... } in ... ==> let { v = e; x = case v of ...; y = case v of ... } in ... Instead GHC does "opportunistic CSE". If you have let x = e in .... let y = e in .... then it'll discard the duplicate binding. But that's very weak. I've added this to the GHC FAQ Simon

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point-free simplification algoritm.
by Nuno Pinto 01 Feb '06

01 Feb '06

Since it's my first post, hi all! I have been reading this for some days but only now i decided to write something. I am researching a to build a computer assisted simplification algorithm used to simplify pointfree expression.. Example. If i give the program: fst . snd . id . id it will return: fst . snd. it wil also show all steps it made to reach that goal. to do this we must have the laws (such as f. id = f) that help us doing this defined. the program uses a datatype such as: data ExpTree v c = Var v | Term c [ExpTree] exp :: Exp Char PF exp = Term Comp [Term Comp [Term Fst [], Term Comp [Term Snd [], Term Id []]], Term Id []] I have previously defined the catamorphism, hylo and anamorphism for this data type, so recursion is insured. I have also implemented a generic calculador that, given a list of functions will try to aply them and returns the best simplification aswell as the steps made to reach it. I am now trying to implement such functions in a "decent" way, but i am however interested in the theory behind all this. I am looking for algorithms that will help me efficiently simplify the expression to the fullest. I am also interested in knowing what zygomorphisms and paramorphisms are? and how can u build a gcata?? (a cata for all datatypes). I head about "proof-by-exhaustion" and "four color theorem" beeing used to make mathematical proves such as this ones, but i have never seen any example of such and would like to see it, if possible, in haskell.. If anyone can help me find what im looking for, a decent mathematical proofing algoritm.. or just tell me what it is that im looking for :P. or even contribute with any ideas, it would be very much aprecciated. :) TY, and Hi all :D :) and have fun coding haskell :) _________________________________________________________________ Don't just search. Find. Check out the new MSN Search! http://search.msn.click-url.com/go/onm00200636ave/direct/01/

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Correct usage of MonadError, ErrorT?
by Daniel 31 Jan '06

31 Jan '06

Hi, I've got some functions in MonadError with different Error types. I would like to map errors of one Error type onto the other Error type. It seems that the only facility for doing this is mapErrorT, but that seems to force me to work in ErrorT rather than any old instance of MonadError. Am I barking up the wrong tree trying to keep the functions generalised over MonadError? Is there some other paradigm I should use for passing errors across system layers in haskell? I would like to do something like the following, but I don't know how to achieve the 'mapError errMap' part of g. instance Error Int where strMsg s = 0 f :: (MonadError Int m, MonadIO m) => Int -> m String f 0 = do liftIO $ putStrLn "The int is 0, that'll be an error." throwError (-27) f i = do liftIO $ putStrLn ("The int is " ++ show i ++ ", we'll do the division.") return $ show (100 `div` i) g :: (MonadError String m, MonadIO m) => Int -> m String g i = do liftIO $ putStrLn ("Will try to divide by " ++ show i) mapError errMap (f i) h :: (MonadIO m) => Int -> m String h i = (runErrorT (g i)) >>= either (\e -> return ("had an error: " ++ e)) return Thanks Daniel

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