Re: [Haskell-cafe] Parsec bug, or...?
I could not resist this. The code import Text.ParserCombinators.UU.Parsing pCommand [] = pure [] pCommand xxs@(x:xs) = ((:) $ pSym x * pCommand xs) `opt` xxs pCommands = amb . foldr (|) pFail . map pCommand $ [banana, chocolate, frito, fromage] t :: String - ([String], [Error Char Char Int]) t input = parse ( (,) $ pCommands * pEnd) (listToStr input) gives the following results: *Main t ([banana,chocolate,frito,fromage],[]) *Main t b ([banana],[]) *Main t fr ([frito,fromage],[]) *Main t x ([banana,chocolate,frito,fromage],[ The token 'x'was not consumed by the parsing process.]) *Main t frox ([fromage],[ The token 'x'was not consumed by the parsing process.]) *Main t frx ([frito,fromage],[ The token 'x'was not consumed by the parsing process.]) *Main I think it is less clumsy and far less confusing than the Parsec code. Note that the function amb tells that its parameter parser can be ambiguous Doaitse On 13 okt 2009, at 17:10, Uwe Hollerbach wrote: On 10/12/09, Martijn van Steenbergen mart...@van.steenbergen.nl wrote: Brandon S. Allbery KF8NH wrote: My fix would be to have myPrefixOf require the prefix be terminated in whatever way is appropriate (end of input, white space, operator?) instead of simply accepting as soon as it gets a prefix match regardless of what follows. Maybe you can use notFollowedBy for this. HTH, Martijn. Yes, I've looked at that and am thinking about it. I'm not quite certain it's needed in my real program... I seem to have convinced myself that if I actually specify a proper set of unique prefixes, ie, set the required lengths for both frito and fromage to 3 in the test program, I won't get into this situation. Assuming I haven't committed another brain-fart there, that would be sufficient; presumably, in a real program one would want to actually specify the unique prefix, rather than a non-unique pre-prefix. It seems to work fine in my real program, anyway. Uwe ___ 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
Re: [Haskell-cafe] Exponential complexity of type checking (Was: Type-level naturals multiplication)
You can help ghci out a bit with type synonyms: type T a = (a, a) type T2 a = T (T a) type T4 a = T2 (T2 a) type T8 a = T4 (T4 a) type T16 a = T8 (T8 a) f0 :: a - T a f1 :: a - T2 a f2 :: a - T4 a f3 :: a - T8 a f4 :: a - T16 a f0 x = (x,x) f1 = f0 . f0 f2 = f1 . f1 f3 = f2 . f2 f4 = f3 . f3 f5 = f4 . f4 With newtypes I can probably abstract even more. (newtype X a b = X (a (a b)) Inferring the type of f5 also stops my machine in its tracks. But I *was* able to infer the type of (f4 . f4). :t (f4 . f4) (f4 . f4) :: a - T16 (T16 a) :t f5 -- buy new computer Even when you only specify a type for f0 in terms of T you'll get more readable types: :t f3 f3 :: a - T (T (T (T (T (T (T (T a))) But the amount of computation required seems the same. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Exponential complexity of type checking (Was: Type-level naturals multiplication)
On Wednesday 14 October 2009 5:25:10 am Roel van Dijk wrote:
With newtypes I can probably abstract even more. (newtype X a b = X (a (a
b))
In fact, with GHC extensions, you don't need newtypes:
{-# LANGUAGE LiberalTypeSynonyms #-}
type T a = (a,a)
type X f a = f (f a)
f0 :: a - T a
f0 x = (x,x)
f1 :: a - X T a
f1 = f0 . f0
f2 :: a - X (X T) a
f2 = f1 . f1
f3 :: a - X (X (X T)) a
f3 = f2 . f2
f4 :: a - X (X (X (X T))) a
f4 = f3 . f3
Inferring the type of f5 also stops my machine in its tracks. But I
*was* able to infer the type of (f4 . f4).
:t (f4 . f4)
(f4 . f4) :: a - T16 (T16 a)
:t f5
Yeah. Asking for the type of 'f4 . f4' doesn't seem to expand the synonyms,
while checking f5 does for some reason. I'm perplexed that having f5 defined
in the file doesn't trigger the explosion unless you declare a type (even in
terms of X and T) or ask for its type at the prompt.
-- Dan
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Re: [Haskell-cafe] Exponential complexity of type checking (Was: Type-level naturals multiplication)
On Wed, Oct 14, 2009 at 11:53 AM, Dan Doel dan.d...@gmail.com wrote:
In fact, with GHC extensions, you don't need newtypes:
{-# LANGUAGE LiberalTypeSynonyms #-}
Ah, I completely forgot about that language extension. Thanks!
Yeah. Asking for the type of 'f4 . f4' doesn't seem to expand the synonyms,
while checking f5 does for some reason. I'm perplexed that having f5 defined
in the file doesn't trigger the explosion unless you declare a type (even in
terms of X and T) or ask for its type at the prompt.
If you declare a type for f5 then ghci must check if that type is
correct, which triggers the explosion. If you don't declare a type
then it won't infer the type until necessary. Basically, ghci is lazy
:-)
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[Haskell-cafe] ANN: fp-southwales, the South Wales Functional Programming User Group
Dear friends, It is my pleasure to announce the formation of fp-southwales, a user group for anybody interested in functional programming in the area of south Wales, UK. We're based out of Swansea University's Computer Science department, where there are a few of us using Haskell for our research, but we welcome anyone who wants to join in, from academia or industry, from Swansea, or Cardiff, or indeed anywhere in south Wales. As the name of the group also suggests, we're interested in all aspects of functional programming, not just Haskell, although we expect that to be a central topic, for now at least. We exist online as a google group: http://groups.google.com/group/fp-southwales The first point of business is: hello, what shall we do, and when shall we do it? :-) http://groups.google.com/group/fp-southwales/browse_thread/thread/ddb2d352a14896d8 All welcome! -Andy ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Exponential complexity of type checking (Was: Type-level naturals multiplication)
On Wednesday 14 October 2009 6:15:11 am Roel van Dijk wrote: If you declare a type for f5 then ghci must check if that type is correct, which triggers the explosion. If you don't declare a type then it won't infer the type until necessary. Basically, ghci is lazy Well, that may be the explanation, but it's a bit more convoluted than I'd have initially thought. For instance, if I write: e = head () it fails immediately with a type error, so clearly it must be doing some level of checking immediately. However, it only needs to check 'head' and '()' to notice that they're incompatible, so I suppose it may not need to compute the type of e (were it well-typed). But then, adding: f6 = f5 . f5 produces no more delay than before. Nor does: g = snd . f5 So ghci is able to verify that f5 can be instantiated to the forms a - b and b - c in the first case, and that it is of the form a - (b,c) in the second case, without blowing up. However, either of: e = f5 () e' () = f5 () does blow up, so it must be verifying more than the fact that f5 is of the form a - b, where a can be instantiated to (), which is odd if it's smart enough to only compute the portion of the type necessary to verify that applications can be well typed. -- Dan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Fuzzy Logic / Linguistic Variables
So i was reading Programming Game AI by Example by Mat Buckland (http://www.ai-junkie.com/books/toc_pgaibe.html) and decided to rewrite his chapter on Fuzzy logic in haskell (from C++). My initial impression: its one of those scenarios where OOP grossly over complicates things Heres an example taken from the book: An agent needs to decide what weapon to use based on his distance from the target and the amount of ammo each has. The result is in the desirability domain (0-100). http://code.haskell.org/~hexpuem/fuzzyLogic/AI/Logic/Fuzzy/Example.hs An excerpt: weapons = [ Weapon RocketLauncher 9 rocketLauncher, Weapon ShotGun 13 shotgun, Weapon AssaultRifle 120 assaultRifle, Weapon SniperRifle 7 sniperRifle, Weapon Knife 1 knife ] chooseWeapon dist = maximum ratings where ratings = [ (f dist ammo, n) | Weapon n ammo f - weapons ] shotgun :: Double - Double - Double shotgun dist ammo = unfuzz desireDom $ rules (fuzz distDom dist) (fuzz ammoDom ammo) where rules :: Fuzzy Distances - Fuzzy Ammo - FL Desirability rules distance ammo = do distance `is` SniperSuited = Pointless distance `is` Far = Undesirable distance `is` Medium = Undesirable distance `is` Melee= Undesirable (distance `fairly` Near) (ammo `fairly` High) = VeryDesirable (distance `fairly` Near) (ammo `fairly` Good) = Desirable (distance `fairly` Near) (ammo `is` Low) = Undesirable Full code at http://code.haskell.org/~hexpuem/fuzzyLogic/. Suggestions welcome - maybe it'd be useful to upload to hackage at some point. It only supports triangle, shoulder, and singleton memberships at the moment. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Reverse dependencies in Hackage
Nice, thank you for the great work. Browsing the reverse dependencies of popular packages like bytestring http://bifunctor.homelinux.net/~roel/cgi-bin/hackage-scripts/revdeps/bytestring-0.9.1.5 can be improved a bit. 1) Can you please sort the reverse dependent package names? That makes it easier to find packages with certain names. 2) I found the columns Direct and Indirect confusing until i found out that they show the number of reverse dependencies for those packages themselves and are not related to direct/indirect dependencies of the current package. I don't think it is necessary to provide those data here and i would be in favor of reducing the information overload by leaving those data to each package detail page. 3) Can you try to print the reverse packages horizontally instead of vertically in tables? Browsing two long tables of direct/indirect reverse dpependencies like for bytestring makes it tedious to get an overview. Besides that, i am quite happy. Thanks, Lenny___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: Reverse dependencies in Hackage
On Wed, Oct 14, 2009 at 3:24 PM, hask...@kudling.de hask...@kudling.de wrote: Nice, thank you for the great work. Browsing the reverse dependencies of popular packages like bytestring http://bifunctor.homelinux.net/~roel/cgi-bin/hackage-scripts/revdeps/bytestring-0.9.1.5 can be improved a bit. You should try base ;-) 1) Can you please sort the reverse dependent package names? That makes it easier to find packages with certain names. 2) I found the columns Direct and Indirect confusing until i found out that they show the number of reverse dependencies for those packages themselves and are not related to direct/indirect dependencies of the current package. I don't think it is necessary to provide those data here and i would be in favor of reducing the information overload by leaving those data to each package detail page. I'll respond to 1 and 2 since they are related. Right now the packages are sorted by their total reverse-dependency count. The idea is that this gives an idea of the relative importance of a package (in the closed system of the hackage packet database). However, sorting by name makes just as much sense. Sorting by reverse-dependency count is useful if you want to know which are the most important reverse dependencies. Sorting by name is useful if you want to find out if a specific package is a reverse dependency. Ideally I would like to support both. Maybe a bit of JavaScript could be used to sort the table client-side. Something like this: http://www.kryogenix.org/code/browser/sorttable/ 3) Can you try to print the reverse packages horizontally instead of vertically in tables? Browsing two long tables of direct/indirect reverse dpependencies like for bytestring makes it tedious to get an overview. That would make sense if I wouldn't also show the reverse-dependencies of the reverse-dependencies. But I still think that information is usefull. Another option would be to have the two tables side-by-side. But that might be a bit to much for a modestly sized monitor. Again, I wonder what could be achieved with a little JavaScript in this area. Thank you for the constructive criticism, Roel ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: Parsec bug, or...?
My fix would be to parse as many letters as possible many1 alpha (that's longest match) and then check the result with isPrefixOf for all your alternatives (and return the alternative that matches first). Cheers Christian Martijn van Steenbergen wrote: Brandon S. Allbery KF8NH wrote: My fix would be to have myPrefixOf require the prefix be terminated in whatever way is appropriate (end of input, white space, operator?) instead of simply accepting as soon as it gets a prefix match regardless of what follows. Maybe you can use notFollowedBy for this. HTH, Martijn. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Setting environment variables on Windows
On Friday 09 October 2009 07:07:21 pm Duncan Coutts wrote: On Fri, 2009-10-09 at 17:37 +0200, Sönke Hahn wrote: Hi! I need to set an environment variable from Haskell and i would like to do that cross-platform. There is System.Posix.Env.setEnv, which does exactly, what i want on Linux. There is the module System.Environment, which seems to be cross-platform, but it does not contain functions to manipulate the environment (, just to inspect it). At first glance, I didn't find anything relevant in the sub-modules of System.Win32. Note that often it is enough to set environment variables for the programs that you invoke, rather than for your own process. If that's enough then you can do it via the System.Process.createProcess action. Duncan Thanks for the suggestion. In my case, that would be a workaround. Maybe still better than writing a .bat-file for the same purpose. Sönke ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Setting environment variables on Windows
On Friday 09 October 2009 07:19:30 pm Peter Verswyvelen wrote: Mmm, that seems like a shortcoming. Well, you could just wrap the C functions yourself, like this (two possibilities, no error checking yet, quick hack): http://hpaste.org/fastcgi/hpaste.fcgi/view?id=10565#a10565 Note that using SetEnvironmentVariable does not seem to be compatible with getEnv, but calling _putenv does work. Both solutions seem to work on my system. Using c_putenv doesn't require linking additional libraries in my case, so i'm going with that. You've been very helpful, thank you very much. So I guess someone should add this setEnv wrapper to the System.Environment module? Ticket? Once i figure out, how to implement functions differently for linux and windows, i'll write a ticket with an example module based on your suggestion. Again, many thanks, Sönke On Fri, Oct 9, 2009 at 5:37 PM, Sönke Hahn sh...@cs.tu-berlin.de wrote: Hi! I need to set an environment variable from Haskell and i would like to do that cross-platform. There is System.Posix.Env.setEnv, which does exactly, what i want on Linux. There is the module System.Environment, which seems to be cross-platform, but it does not contain functions to manipulate the environment (, just to inspect it). At first glance, I didn't find anything relevant in the sub-modules of System.Win32. Is this just not implemented? How could i implement it myself? Grateful for any comment, Sönke ___ 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
[Haskell-cafe] example of PortMidi use
Can someone give me an example of Sound.PortMidi use? I'm having trouble. This program has bugs---makes sound only intermittently, and seems to have set up some kind of loop that is sending midi messages continuously even after terminating the program: import Sound.PortMidi import Foreign.C msgs = [ (0::CULong,PMMsg 0x9c 0x40 0x40) , (500, PMMsg 0x8c 0x40 0x40) , (1000, PMMsg 0x9c 0x41 0x40) , (1500, PMMsg 0x8c 0x41 0x40) ] main = do let deviceId = 12 initialize = print getDeviceInfo deviceId = print startTime - time let evts = map (\(t,msg) - PMEvent msg (t+startTime)) msgs result - openOutput deviceId 10 case result of Right err - putStrLn (After open: ++ show err) Left stream - do result - writeEvents stream evts putStrLn (After write: ++ show result) close stream return () terminate = print ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] GHC devs
Random question of the day: How many developers are working on GHC? I had always *assumed* that there was something like a hundred core developers, with a much larger number of people casually testing and occasionally submitting the odd patch or two. However, I watched a video of a talk the other day (no, I don't remember which one) and it made me reconsider this view. Somebody muttered something like GHC is really too big now for just 3 developers to manage, which makes it sound as if there are only 3 active developers... Surely that can't be correct. (There would never be any releases, for one thing...) Does anybody know anything concrete about this? ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Monotype error
Dear café,
{-# LANGUAGE Rank2Types #-}
{-# LANGUAGE ImpredicativeTypes #-}
type Void = forall a. a
newtype Mono a = Mono { runMono :: [Void] }
beep :: Mono a - Mono a
beep (Mono vs) = Mono (map undefined vs)
Compiling this with GHC results in:
Monotype.hs:9:28:
Cannot match a monotype with `Void'
Expected type: Void
Inferred type: a
What does this error mean and why does the code not compile?
Thanks!
Martijn.
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Re: [Haskell-cafe] GHC devs
I think the contributors page on GHC's wiki contains relevant information: http://hackage.haskell.org/trac/ghc/wiki/Contributors ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] GHC devs
Hello Andrew, Wednesday, October 14, 2009, 10:28:45 PM, you wrote: I had always *assumed* that there was something like a hundred core developers only 10 and only in binary system :))) Simon Peyton-Jones works on front-end, i.e compiling Haskell down to simple core language, and Simon Marlow does back-end i.e. compiling this to actual machine code and dealing with idiosyncrasies of all target systems. and Ian Lynagh is Build engineer maintaining releases, bug tracking and so on there are dozens of people doing interesting things with GHC and some of them are even going to main tree. and there are interns that implements some rather small and isolated parts of GHC. and dozen or so of people porting GHC to their environment, building packages and so on -- Best regards, Bulatmailto:bulat.zigans...@gmail.com ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re:
On Wed, Oct 14, 2009 at 7:33 AM, o...@okmij.org wrote:
Martin Sulzmann wrote:
Undecidable instances means that there exists a program for which
there's
an infinite reduction sequence.
I believe this may be too strong of a statement. There exists patently
terminating type families that still require undecidable
instances in GHC.
Sorry, I wasn't precise enough.
I didn't mean to say that *every* program which requires undecidable
instance won't terminate.
Rather, take any of the properties which imply decidability. Then,
there *exists* a program which satisfies the negated property and this
program won't terminate.
As you show, for specific cases we can argue that undecidable instances
are decidable. You can even argue that the Add/Mult example is decidable,
assuming we never generate loopy type constraints.
-Martin
Here is an example:
{-# LANGUAGE TypeFamilies #-}
type family I x :: *
type instance I x = x
type family B x :: *
type instance B x = I x
GHC 6.8.3 complaints:
Application is no smaller than the instance head
in the type family application: I x
(Use -fallow-undecidable-instances to permit this)
In the type synonym instance declaration for `B'
But there cannot possibly be any diverging reduction sequence here, can it?
The type family I is the identity, and the type family B is its
alias. There is no recursion. The fact that type families are open is
not relevant here: our type families I and B are effectively closed,
because one cannot define any more instance for I and B (or risk
overlap, which is rightfully not supported for type families).
The reason GHC complains is because it checks termination
instance-by-instance. To see the termination in the above program, one
should consider instances I and B together. Then we will see that I
does not refer to B, so there are no loops. But this global
termination check -- for a set of instances -- is beyond the
abilities of GHC. This is arguably the right decision: after all, GHCi
is not a full-blown theorem prover.
Thus there are perfectly decidable type programs that require
undecidable instances. Indeed, there is no reason to be afraid of that
extension.
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Re: [Haskell-cafe] example of PortMidi use
On Wed, 14 Oct 2009, Michael Mossey wrote: Can someone give me an example of Sound.PortMidi use? I'm having trouble. This program has bugs---makes sound only intermittently, and seems to have set up some kind of loop that is sending midi messages continuously even after terminating the program: You may also try http://lists.lurk.org/mailman/listinfo/haskell-art (haskell-...@lists.lurk.org). ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] GHC devs
bulat.ziganshin: Hello Andrew, Wednesday, October 14, 2009, 10:28:45 PM, you wrote: I had always *assumed* that there was something like a hundred core developers only 10 and only in binary system :))) Simon Peyton-Jones works on front-end, i.e compiling Haskell down to simple core language, and Simon Marlow does back-end i.e. compiling this to actual machine code and dealing with idiosyncrasies of all target systems. and Ian Lynagh is Build engineer maintaining releases, bug tracking and so on there are dozens of people doing interesting things with GHC and some of them are even going to main tree. and there are interns that implements some rather small and isolated parts of GHC. and dozen or so of people porting GHC to their environment, building packages and so on About 1000 people have worked on libraries on Hackage. That's about two orders of magnitude more than work on GHC. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Why does replicateM (10^6) $ return 0 produce output in the IO monad, but overflow the maybe monad?
-- Why does replicateM (10^6) $ return 0 produce output in the IO monad, but overflow the maybe monad? iterateNTimes i f x = foldr (.) id (replicate i f) $ x tntIO :: IO Int -- same as replicateM (10^6) $ return 0, same as sequence . replicate (10^6) $ return 0 tntIO = return . head = (iterateNTimes (10^6) (mcons . return $ 0) (return [])) -- produces output tntMb :: Maybe Int -- overflows tntMb = return . head = (iterateNTimes (10^6) (mcons . return $ 0) (return [])) -- stack overflow -- equivalently: mcons m ms = (:) $ m * ms mcons m ms = ap (liftM (:) m) $ ms I guess the maybe version builds up a huge chain of unevaluated thunks somewhere, that's usually the reason. But specifically where and why, and why doesn't IO do the same thing? Equivalent, with 3 element list: (mcons $ return $ 0 ) $ (mcons $ return $ 0) $ (mcons $ return $ 0) $ (return []) (ap . liftM (:) . return $ 0 ) $ (ap . liftM (:) . return $ 0) $ (ap . liftM (:) . return $ 0) $ (return []) (ap $ liftM (:) $ return $ 0 ) $ (ap $ liftM (:) $ return $ 0) $ (ap $ liftM (:) $ return $ 0) $ (return []) t. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] GHC core packages: same core?
Dimitry, I *believe* ext-core will match that document, but I'm not sure of the exact status. Tim Chevalier has done a lot of great work maintaining the external core stuff and I think he is actively using the extcore library, so *that* should almost certainly match GHC's output. It's great to hear that you are interested in writing an alternative backend! I think LHC is also using ext-core to build a backend, so this seems like a viable approach. All the best, Max 2009/10/13 Dimitry Golubovsky golubov...@gmail.com: Max, Thanks for the explanation. So, the extcore library is expected to match the spec in http://www.haskell.org/ghc/docs/6.10.4/html/ext-core/core.pdf and the core itself can be produced with -fext-core, correct? I think it might be interesting for people working on alternative backends (inlcuding myself). On Tue, Oct 13, 2009 at 4:53 PM, Max Bolingbroke batterseapo...@hotmail.com wrote: [skip] extcore is a library that parses external Core, which is an alternative format intended to be stable and hence a suitable target for consumption by non-GHC tooling. You can have GHC output external core instead of machine code / C. I don't believe this is widely used yet. -- Dimitry Golubovsky Anywhere on the Web ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] GHC core packages: same core?
On Wed, Oct 14, 2009 at 10:28 PM, Max Bolingbroke batterseapo...@hotmail.com wrote: Dimitry, I *believe* ext-core will match that document, but I'm not sure of the exact status. Tim Chevalier has done a lot of great work maintaining the external core stuff and I think he is actively using the extcore library, so *that* should almost certainly match GHC's output. It's great to hear that you are interested in writing an alternative backend! I think LHC is also using ext-core to build a backend, so this seems like a viable approach. LHC is using a different external core parser. -- Cheers, Lemmih ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] GHC devs
Don Stewart wrote: bulat.ziganshin: Hello Andrew, Wednesday, October 14, 2009, 10:28:45 PM, you wrote: I had always *assumed* that there was something like a hundred core developers only 10 and only in binary system :))) About 1000 people have worked on libraries on Hackage. That's about two orders of magnitude more than work on GHC. Sure. But libraries are more or less self-contained, generally. GHC is one giant system of closely interacting components, so it (presumably?) takes about two orders of magnitude more cooperation to work on it. ;-) Still, if there are only 10 core people actively working on it... well that explains why the wishlist is always so much longer than the feature list. (Not that GHC doesn't already _have_ some pretty cool features, mind you...) Does anybody actually get paid to develop GHC? Or is this all people working on it in their spare time? It would seem like pushing such a huge piece of software forward at anything more than glacial pace would require quite a lot of manpower (which I guess is why I assumed there were a lot of people working on it). For that matter, who pays for the servers which host the code repos and so forth? ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re[2]: [Haskell-cafe] GHC devs
Hello Andrew, Thursday, October 15, 2009, 12:54:37 AM, you wrote: Does anybody actually get paid to develop GHC? Or is this all people SPJ, SM and Ian are paid by MS Research. Other people involved in core development are mainly scientists (afaik) -- Best regards, Bulatmailto:bulat.zigans...@gmail.com ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] newtype deriving Alternative
Hello café, I've never written an Alternative instance for a newtype yet that doesn't look like this: instance Alternative T where empty = T empty T x | T y = T (x | y) Why does newtype deriving not work for Alternative? (It works fine for Monoid.) Thanks, Martijn. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Sharing Subexpressions: Memoization of Fibonacci sequence
Hallo Daniel, can you explain the difference between a pattern binding and a function binding? I haven't heard about these two terms so far. And furthermore: Why does the memoization only happen with pattern binding? Best regards, Simon -- View this message in context: http://www.nabble.com/Sharing-Subexpressions%3A-Memoization-of-Fibonacci-sequence-tp25861134p25899401.html Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Monotype error
* Martijn van Steenbergen mart...@van.steenbergen.nl [2009-10-14
20:35:06+0200]
Dear café,
{-# LANGUAGE Rank2Types #-}
{-# LANGUAGE ImpredicativeTypes #-}
type Void = forall a. a
newtype Mono a = Mono { runMono :: [Void] }
beep :: Mono a - Mono a
beep (Mono vs) = Mono (map undefined vs)
Compiling this with GHC results in:
Monotype.hs:9:28:
Cannot match a monotype with `Void'
Expected type: Void
Inferred type: a
What does this error mean and why does the code not compile?
It works if you annotate the type of undefined:
beep (Mono vs) = Mono (map (undefined :: Void - Void) vs)
--
Roman I. Cheplyaka :: http://ro-che.info/
Don't let school get in the way of your education. - Mark Twain
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Re: [Haskell-cafe] newtype deriving Alternative
Works for me on GHC6.10.4:
{-# LANGUAGE GeneralizedNewtypeDeriving #-}
module NewtypeDerive where
import Control.Applicative
newtype Foo f a = Foo (f a) deriving (Functor, Applicative, Alternative)
newtype Bar a = Bar [a] deriving (Functor, Applicative, Alternative)
-- ryan
On Wed, Oct 14, 2009 at 2:16 PM, Martijn van Steenbergen
mart...@van.steenbergen.nl wrote:
Hello café,
I've never written an Alternative instance for a newtype yet that doesn't
look like this:
instance Alternative T where
empty = T empty
T x | T y = T (x | y)
Why does newtype deriving not work for Alternative? (It works fine for
Monoid.)
Thanks,
Martijn.
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Re: [Haskell-cafe] newtype deriving Alternative
You guys are right. I was being silly. Thanks. :-) Ryan Ingram wrote: Works for me on GHC6.10.4: ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Setting environment variables on Windows
On Wednesday 14 October 2009 04:50:56 pm Sönke Hahn wrote: On Friday 09 October 2009 07:19:30 pm Peter Verswyvelen wrote: Mmm, that seems like a shortcoming. Well, you could just wrap the C functions yourself, like this (two possibilities, no error checking yet, quick hack): http://hpaste.org/fastcgi/hpaste.fcgi/view?id=10565#a10565 Note that using SetEnvironmentVariable does not seem to be compatible with getEnv, but calling _putenv does work. Both solutions seem to work on my system. Using c_putenv doesn't require linking additional libraries in my case, so i'm going with that. You've been very helpful, thank you very much. So I guess someone should add this setEnv wrapper to the System.Environment module? Ticket? Once i figure out, how to implement functions differently for linux and windows, i'll write a ticket with an example module based on your suggestion. Here's the ticket: http://hackage.haskell.org/trac/ghc/ticket/3587 Again, many thanks, Sönke On Fri, Oct 9, 2009 at 5:37 PM, Sönke Hahn sh...@cs.tu-berlin.de wrote: Hi! I need to set an environment variable from Haskell and i would like to do that cross-platform. There is System.Posix.Env.setEnv, which does exactly, what i want on Linux. There is the module System.Environment, which seems to be cross-platform, but it does not contain functions to manipulate the environment (, just to inspect it). At first glance, I didn't find anything relevant in the sub-modules of System.Win32. Is this just not implemented? How could i implement it myself? Grateful for any comment, Sönke ___ 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 ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] newtype deriving Alternative
It doesn't work for this one:
newtype Split a = Split { runSplit :: [Either a (Char, Split a) ]}
But my handwritten instance remains identical.
Groetjes,
Martijn.
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Re: [Haskell-cafe] Sharing Subexpressions: Memoization of Fibonacci sequence
Am Mittwoch 14 Oktober 2009 23:30:05 schrieb SimonK77: Hallo Daniel, can you explain the difference between a pattern binding and a function binding? I haven't heard about these two terms so far. The formal specification is at http://haskell.org/onlinereport/decls.html#sect4.4.3 A function binding is a binding where the function name and at least one parameter (pattern) appear to the left of '=', while in a pattern binding only bound patterns appear on the left. -- function bindings fun x = expression -- binds fun x \/ y = expr' -- binds (\/) -- pattern bindings func = \x - expression -- binds func var = expr -- binds var (v1,v2) = express-- binds v1 and v2 (a0:a1:tl) -- binds a0, a1 and tl | even v1 = exp1 | otherwise = exp2 The first three are *simple* pattern bindings. And furthermore: Why does the memoization only happen with pattern binding? I don't know all the details either, but the point is that names bound by a (simple) pattern binding are constant applicative forms (http://www.haskell.org/haskellwiki/CAF) which can be shared by all uses (if they have a monomorphic type, cf. also http://www.haskell.org/haskellwiki/Monomorphism_Restriction and http://haskell.org/onlinereport/decls.html#sect4.5.5), while names bound by a function binding aren't shared across computations (I think it is generally undecidable how much could be shared and anyway it would be too complicated for the compiler to investigate that - too little gain for too much effort). So with function-bound fbfib :: Int - Integer fbfib k = let fib 0 = 0 fib 1 = 1 fib n = fbfib (n-2) + fbfib (n-1) in (map fib [0 ..] !! k) fb2fib :: Int - Integer fb2fib k = let fib 0 = 0 fib 1 = 1 fib n = fb2fib (n-2) + fb2fib (n-1) flst = map fib [0 .. ] in (flst !! k) nothing is shared, each (recursive) call to fb(2)fib creates a new list of Fibonacci values (in principle, different arguments could require very different code-paths, so we don't even bother to let the compiler look for the few cases where it could determine sharing would be beneficial). With pattern-bound functions, it's harder to know when sharing will happen. It depends on the form of the RHS and where things that might be shared are bound. In memoized_fib :: Int - Integer memoized_fib = let fib 0 = 0 fib 1 = 1 fib n = memoized_fib (n-2) + memoized_fib (n-1) in (map fib [0 ..] !!) the list of Fibonacci numbers is shared, even though it hasn't been given a name (In general, give entities you want to be shared a name of their own to increase the chance of them being really shared). If you define the function with a simple pattern binding which has a lambda-expression on the right hand side, it depends on whether things are bound within the lambda-scope or outside. In plfib :: Int - Integer plfib = \k - let fib 0 = 0 fib 1 = 1 fib n = plfib (n-2) + plfib (n-1) in (map fib [0 ..] !! k) the things which could be shared are bound inside the lambda-expression, therefore they aren't shared (they could potentially depend on the lambda-bound variable[s], here k). Lifting the binding of fib outside the lambda pblfib :: Int - Integer pblfib = let fib 0 = 0 fib 1 = 1 fib n = pblfib (n-2) + pblfib (n-1) in \k - (map fib [0 ..] !! k) doesn't help - of course, the list in which we index is still inside the lambda. Give it a name and hoist it outside the lambda: peblfib :: Int - Integer peblfib = let fib 0 = 0 fib 1 = 1 fib n = peblfib (n-2) + peblfib (n-1) flst = map fib [0 .. ] in \k - (flst !! k) Now flst is a CAF which can be shared, and indeed it is: *MFib peblfib 40 102334155 (0.00 secs, 0 bytes) Best regards, Simon Hope this gets you started, Daniel ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Fuzzy Logic / Linguistic Variables
I didn't read the book, but your code seems very elegant, more than I even thought possible. I've never programmed with fuzzy logic before, but I can understand your code - it reads naturally. Fernando Henrique Sanches On Wed, Oct 14, 2009 at 9:59 AM, Neal Alexander relapse@gmx.com wrote: So i was reading Programming Game AI by Example by Mat Buckland ( http://www.ai-junkie.com/books/toc_pgaibe.html) and decided to rewrite his chapter on Fuzzy logic in haskell (from C++). My initial impression: its one of those scenarios where OOP grossly over complicates things Heres an example taken from the book: An agent needs to decide what weapon to use based on his distance from the target and the amount of ammo each has. The result is in the desirability domain (0-100). http://code.haskell.org/~hexpuem/fuzzyLogic/AI/Logic/Fuzzy/Example.hshttp://code.haskell.org/%7Ehexpuem/fuzzyLogic/AI/Logic/Fuzzy/Example.hs An excerpt: weapons = [ Weapon RocketLauncher 9 rocketLauncher, Weapon ShotGun 13 shotgun, Weapon AssaultRifle 120 assaultRifle, Weapon SniperRifle 7 sniperRifle, Weapon Knife 1 knife ] chooseWeapon dist = maximum ratings where ratings = [ (f dist ammo, n) | Weapon n ammo f - weapons ] shotgun :: Double - Double - Double shotgun dist ammo = unfuzz desireDom $ rules (fuzz distDom dist) (fuzz ammoDom ammo) where rules :: Fuzzy Distances - Fuzzy Ammo - FL Desirability rules distance ammo = do distance `is` SniperSuited = Pointless distance `is` Far = Undesirable distance `is` Medium = Undesirable distance `is` Melee= Undesirable (distance `fairly` Near) (ammo `fairly` High) = VeryDesirable (distance `fairly` Near) (ammo `fairly` Good) = Desirable (distance `fairly` Near) (ammo `is` Low) = Undesirable Full code at http://code.haskell.org/~hexpuem/fuzzyLogic/http://code.haskell.org/%7Ehexpuem/fuzzyLogic/ . Suggestions welcome - maybe it'd be useful to upload to hackage at some point. It only supports triangle, shoulder, and singleton memberships at the moment. ___ 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
Re: [Haskell-cafe] GHC devs
bulat.ziganshin: Hello Andrew, Thursday, October 15, 2009, 12:54:37 AM, you wrote: Does anybody actually get paid to develop GHC? Or is this all people SPJ, SM and Ian are paid by MS Research. Other people involved in core development are mainly scientists (afaik) Besides MSR and the university groups, the IHG funds Well-Typed to do development, as well. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] newtype deriving Alternative
Martijn van Steenbergen wrote:
It doesn't work for this one:
newtype Split a = Split { runSplit :: [Either a (Char, Split a) ]}
But my handwritten instance remains identical.
The instance has the form [], not the form [Either _ (Char, Split _)].
Since they don't match exactly, it won't give you an instance
automagically. It could have been the case that you intended some other
instance besides []'s. All generalized newtype deriving does is derive
instances for newtypes that wrap exactly what the instance is defined over.
- Jake
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