Re: [Haskell-cafe] Re: instance Eq (a - b)
On Thu, 15 Apr 2010, Maciej Piechotka wrote: Are f 0 = 1 f n = f (n - 1) + f (n - 2) and g 0 = 1 g n | n 0 = g (n - 1) + g (n - 2) | n 0 = g (n + 2) - g (n + 1) The same (morally) function? Are: f x = 2*x and f x = undefined The same function Try using the (x == y) == (f x = g y) test yourself. -- Russell O'Connor http://r6.ca/ ``All talk about `theft,''' the general counsel of the American Graphophone Company wrote, ``is the merest claptrap, for there exists no property in ideas musical, literary or artistic, except as defined by statute.'' ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] cabal: other-modules
What is the purpose of the Other-Modules section in a cabal file? (I.e., can we drop it?) If it's just the set of dependencies of the Exported-Modules, then a reasonable build system should be able to figure this out on its own. The current situation is that I have to manage this list manually (or is there some tool?) and if I forget to name some other-module, then cabal install happily builds and installs (!) the package anyway, but I'm getting linker errors when using it. This is a nuisance, to say the least. J.W. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: instance Eq (a - b)
On Wed, 14 Apr 2010, Ashley Yakeley wrote: On 2010-04-14 14:58, Ashley Yakeley wrote: On 2010-04-14 13:59, rocon...@theorem.ca wrote: There is some notion of value, let's call it proper value, such that bottom is not one. In other words bottom is not a proper value. Define a proper value to be a value x such that x == x. So neither undefined nor (0.0/0.0) are proper values In fact proper values are not just subsets of values but are also quotients. thus (-0.0) and 0.0 denote the same proper value even though they are represented by different Haskell values. The trouble is, there are functions that can distinguish -0.0 and 0.0. Do we call them bad functions, or are the Eq instances for Float and Double broken? I'd call them disrespectful functions, or maybe nowadays I might call them improper functions. The good functions are respectful functions or proper functions. Proper functions are functions that are proper values i.e. f == f which is defined to mean that (x == y) == f x == f y (even if this isn't a decidable relation). Worse, this rules out values of types that are not Eq. Hmm, I guess I'm carrying all this over from the world of dependently typed programming where we have setoids and the like that admit equality relations that are not necessarily decidable. In Haskell only the decidable instances of equality manage to have a Eq instance. The other data types one has an (partial) equivalence relation in mind but it goes unwritten. But in my dependently typed world we don't have partial values so there are no bottoms to worry about; maybe these ideas don't carry over perfectly. -- Russell O'Connor http://r6.ca/ ``All talk about `theft,''' the general counsel of the American Graphophone Company wrote, ``is the merest claptrap, for there exists no property in ideas musical, literary or artistic, except as defined by statute.'' ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: Fwd: Re: Simple game: a monad for each player
Limestraël wrote: Okay, I start to understand better... Just, Heinrich, how would implement the mapMonad function in terms of the operational package? You just shown the signature. Ah, that has to be implemented by the library, the user cannot implement this. Internally, the code would be as Bertram suggests: mapMonad :: (Monad m1, Monad m2) = (forall a . m1 a - m2 a) - ProgramT instr m1 a - ProgramT instr m2 a mapMonad f (Lift m1) = Lift (f m1) mapMonad f (Bind m k) = Bind (mapMonad f m) (mapMonad f . k) mapMonad f (Instr i) = Instr i I was musing that every instance of MonadTrans should implement this function. Also note that there's a precondition on f , namely it has to respect the monad laws: f (m = k) = f m = f . k f return= return For instance, f :: Identity a - IO a f x = launchMissiles return (runIdentity x) violates this condition. Regards, Heinrich Apfelmus -- http://apfelmus.nfshost.com ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: instance Eq (a - b)
On Thu, 2010-04-15 at 03:53 -0400, rocon...@theorem.ca wrote: Hmm, I guess I'm carrying all this over from the world of dependently typed programming where we have setoids and the like that admit equality relations that are not necessarily decidable. In Haskell only the decidable instances of equality manage to have a Eq instance. The other data types one has an (partial) equivalence relation in mind but it goes unwritten. But in my dependently typed world we don't have partial values so there are no bottoms to worry about; maybe these ideas don't carry over perfectly. It's an interesting approach, though, since decided equality seems to capture the idea of full value fairly well. I'm currently thinking along the lines of a set V of Platonic values, while Haskell names are bound to expressions that attempt to calculate these values. At any given time during the calculation, an expression can be modelled as a subset of V. Initially, it's V, as calculation progresses it may become progressively smaller subsets of V. Saying a calculation is bottom is to make a prediction that cannot in general be decided. It's to say that the calculation will always be V. If it ever becomes not V, it's a partial value. If it ever becomes a singleton, it's a complete value. On the other hand, this approach may not help with strict vs. non-strict functions. -- Ashley Yakeley ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] GHC, odd concurrency space leak
Jason Dagit wrote:
On Wed, Apr 14, 2010 at 3:13 PM, Daniel Fischer
daniel.is.fisc...@web.de mailto:daniel.is.fisc...@web.de wrote:
Am Mittwoch 14 April 2010 23:49:43 schrieb Jason Dagit:
It will be interesting to hear what fixes this!
forever' m = do _ - m
forever' m
When I define that version of forever, the space leak goes away.
Not with optimisations.
Thanks for pointing that out. I forgot to say so in my email.
Here are two reduced versions of the original program:
snip
I find non-termination with a much simpler program than yours (GHC 6.12.1):
\begin{code}{-# OPTIONS -O1 #-}
import Control.Concurrent
import Control.Monad (forever)
main = do
putStrLn Main thread starting
forkIO $ do putStrLn Started thread
forever $ return ()
putStrLn Delaying
threadDelay (1 * 100)
putStrLn Delayed
\end{code}
If I compile that with ghc --make -threaded and run it, with -O1 or
-O2, it burns CPU and never terminates. With -O0 it terminates. So
looks like some optimisation is causing the problem.
I might guess it's something to do with the RTS and threadDelay that's
causing the problem. Delayed is never printed on my system, so it
seems like (even when run with +RTS -N2) the original thread is not ever
being rescheduled; perhaps the timeout queue isn't checked properly when
a thread is burning up the CPU like that, and optimisations are on?
Thanks,
Neil.
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Re: [Haskell-cafe] ANN: haskell-src-exts 1.9.0
Hi Niklas, I'm pleased to announce the release of haskell-src-exts-1.9.0! * On hackage: http://hackage.haskell.org/package/haskell-src-exts Any idea why the Haddock docs have not been generated for this version? There's also no built on available. Is it an issue with the server? Regards, Sean ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re[2]: [Haskell-cafe] GHC, odd concurrency space leak
Hello Neil, Thursday, April 15, 2010, 12:37:35 PM, you wrote: I find non-termination with a much simpler program than yours (GHC 6.12.1): forkIO $ do putStrLn Started thread forever $ return () ghc multithreading is actually cooperative: it switches only on memory allocation. since almost any haskell code allocates, there is no problem - it works like preemptive one. but sometimes this assumption fails - with optimization enabled, your code doesn't allocate so there are no chances for thread switching. replacing return () with threadDelay call solves the problem -- Best regards, Bulatmailto:bulat.zigans...@gmail.com ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Nomic game in Haskell
Yes indeed, Nomic couldn't be fully coded, only a subset of it could be. Rules that are outside of the box cannot be expressed, the goal is, to have the largest box possible! Your rule: * Players must stand when proposing new rules. couldn't be coded directly, of course, since the computer has no sensor to detect the position of player ;) But it could be indirectly. Your rule could be coded like that: Full rule tiltle: Players must stand when proposing new rules Code when filtering a proposed rule: A question is asked to all players except the author of the rule: Does Player X stood when he proposed this rule? A vast majority of Yes must be acknowlegded to accept the rule. On the other hand, if we choose not to interpret the rules, the program could just be a configuration management system for rules. It could be a web site that maintain active rules, allow player voting etc. Corentin. On 4/15/10, Brent Yorgey byor...@seas.upenn.edu wrote: On Wed, Apr 14, 2010 at 09:14:18PM +0200, Dupont Corentin wrote: Hello Café, do you know Nomic? It's a fabulous and strange game where you have the right to change the rules in the middle of the game! In fact, changing the rules is the goal of the game. Changing a rule is considered as a move. Of course even that could be changed! www.nomic.net I'm wondering if it could be possible to implement a Nomic (or an helper for the game) in Haskell. Haskell seems appropriate for that, since functions are first order objects, and Haskell is good at DSLs. I don't think you could actually implement Nomic in the way you describe, because any system you come up with will necessarily place restrictions on what sorts of rules you are able to represent. Much of the fun of Nomic lies in coming up with new rules that are completely outside the box. For example, how would you encode a rule like * Players must stand when proposing new rules. or * Rules which do not mention other rules shall remain in effect until such time as the mobile telephone of the Grand Counselor rings. You get the idea. However, implementing some sort of system for encoding certain types of rules, and checking that they are valid/consistent/etc. sounds like it could be a fun project from which you would probably learn a lot! Essentially, you would be designing a syntax for rules, and a type system for ensuring that rules are valid or used in valid ways. It wouldn't be Nomic, but it could be something fun. -Brent ___ 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] Re: Fwd: Re: Simple game: a monad for each player
Ok, but there is no function such as mapMonad in the operational package?
By the way, I noticed that ProgramT is not automatically made instance of
MonadIO when possible. It could be:
instance (MonadIO m) = MonadIO (ProgramT r m) where
liftIO = lift . liftIO
Is that intentional?
( In fact, I think it's a slip in the mtl package itself, since every
instance of MonadTrans can be declared instance of MonadIO:
instance (MonadTrans t, MonadIO m) = MonadIO (t m) where
liftIO = lift . liftIO
)
By the way, I finally managed to use operational to modify my TicTacToe
game.
(One shot, by the way, I had no bugs ^^. Very nice when it happens...)
Human player and AI are working. I'm currently fixing the Network player.
If you are interested, I could upload my code (it can be another example of
how to use the operational package).
In the end, I used a mix of your solution and my former one.
I have a Request datatype:
data Request a where
GetGrid :: Request Grid
TurnDone :: (Grid, Maybe GridResult) - Request ()
GetResult :: Request (Maybe GridResult)
(Grid is what you called Board, GridResult is a type which indicates if
someone wins or if there is a draw)
The game monad is PlayerMonadT, and is a newtype:
newtype PlayerMonadT m a = PMT (ProgramT Request m a)
deriving (Functor, Monad, MonadTrans)
I still have a datatype Player, which contains functions: (I tried to use
classes, but it was more complicated)
data Player m m' = Player {
-- | Gets the mark (Cross or Circle) of the player
plMark :: Mark,
-- | Called when the player must play
plTurn :: Grid - m Pos,
-- | Called when player tries to play at a forbidden position
plForbidden :: Pos - m (),
-- | Called when game has ended.
plGameOver :: GridResult - m (),
-- | Used to reach PlayerMonad in the monad stack
plLift :: forall a. PlayerMonadT m' a - m a,
-- | Used to run the monad stack the player runs in
plRun :: forall a. m a - PlayerMonadT m' a
}
*m* is the monad stack the player runs in. It must be able to run it, by
providing a plRun function.
*m'* is the top monad, which can't be run (IO for human, any monad for AI,
etc.)
The alteration done to this type is the addition of the plLift and plRun
functions. Those are the functions you, Heinrich, and Bertram told me about.
Then, *all* the players play according to this logic:
playerLogic :: (Monad m) = Player m m' - m ()
playerLogic pl = do
let toProg = plLift pl . PMT . singleton
grid - toProg GetGrid
pos - plTurn pl grid
case checkCell grid (plMark pl) pos of
Nothing - do-- The cell was already filled in
plForbidden pl pos -- We signal the error
playerLogic pl -- We start the turn again
Just newGridAndResult - do
-- The cell has been successfully marked, so we got
a new grid
toProg $ TurnDone newGridAndResult
-- At this point, the interpreter will switch to
the other player
mbResult - toProg $ GetResult
-- This player is back, and wants to know what's
new
case mbResult of
Nothing - playerLogic pl
Just res - plGameOver pl res
We can then run this function with the player custom stack thanks to the
runPlayer function:
runPlayer :: (Monad m) = Player m m' - PlayerMonadT m' ()
runPlayer pl = plRun pl $ playerLogic pl
And finally, the interpreter:
doGame :: (Monad m) = Grid - [PlayerMonadT m ()] - m Grid
doGame initGrid players =
mapM unwrap players = flip evalStateT (initGrid, Nothing) . eval
where
unwrap (PMT pl) = viewT pl
eval :: (Monad m) = [PromptT Request m ()] - StateT (Grid, Maybe
GridResult) m Grid
eval [] = liftM fst get
eval ((Return _) : pls) = eval pls
eval ((GetGrid := pl) : pls) = do
(grid, _) - get
p - lift . viewT $ pl grid
eval $ p : pls
eval ((TurnDone (newGrid, mbResult) := pl) : pls) = do
put (newGrid, mbResult)
p - lift . viewT $ pl ()
eval $ pls ++ [p]
eval ((GetResult := pl) : pls) = do
(_, mbResult) - get
p - lift . viewT $ pl mbResult
eval $ p : pls
The game can be launched by doing for example:
let pl1 = humanPlayer Cross
let pl2 = artificialPlayer Circle levelOfDifficulty
doGame blankGrid [runPlayer pl1, runPlayer pl2]
I did it!
2010/4/15 Heinrich Apfelmus apfel...@quantentunnel.de
Limestraël wrote:
Okay, I start to understand better...
Just, Heinrich, how would implement the mapMonad function in terms of the
operational package?
You just shown the signature.
Ah, that has to be implemented by the library, the user cannot implement
this. Internally, the code would be as Bertram suggests:
mapMonad :: (Monad m1, Monad m2)
= (forall a . m1 a - m2 a)
- ProgramT instr m1 a - ProgramT instr m2 a
mapMonad f (Lift m1) = Lift (f m1)
mapMonad f (Bind m k) = Bind (mapMonad f m) (mapMonad f . k)
mapMonad f (Instr i) = Instr i
I
Re: [Haskell-cafe] Can't install Criterion package on ghc ..
On 13.04.10 14:46, Mozhgan kabiri wrote:
I am trying to install Criterion package, but I keep getting an error
and I can't figure it out why it is like this !!
[...]
[8 of 9] Compiling Data.Vector.Algorithms.Intro (
Data/Vector/Algorithms/Intro.hs, dist/build/Data/Vector/Algorithms/Intro.o )
ghc: panic! (the 'impossible' happened)
(GHC version 6.10.4 for i386-unknown-linux):
idInfo co{v a9WB} [tv]
Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug
fwiw, the latest version of vector-algorithms (0.3.1) seems to build with ghc
6.10.4.
sk
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Re: [Haskell-cafe] ANN: haskell-src-exts 1.9.0
Sean Leather leat...@cs.uu.nl writes: I'm pleased to announce the release of haskell-src-exts-1.9.0! * On hackage: http://hackage.haskell.org/package/haskell-src-exts Any idea why the Haddock docs have not been generated for this version? There's also no built on available. Is it an issue with the server? Looks built to me... -- Ivan Lazar Miljenovic ivan.miljeno...@gmail.com IvanMiljenovic.wordpress.com ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] cabal: other-modules
Johannes Waldmann waldm...@imn.htwk-leipzig.de writes: What is the purpose of the Other-Modules section in a cabal file? (I.e., can we drop it?) Non-exported modules. If it's just the set of dependencies of the Exported-Modules, then a reasonable build system should be able to figure this out on its own. Explicit is better than implicit; this lets you have hidden modules that don't get shipped, auto-generated modules, etc. The current situation is that I have to manage this list manually (or is there some tool?) and if I forget to name some other-module, then cabal install happily builds and installs (!) the package anyway, but I'm getting linker errors when using it. Interesting; it normally complains when this occurs (for me at least); care to share the .cabal file to see which files it didn't complain about? -- Ivan Lazar Miljenovic ivan.miljeno...@gmail.com IvanMiljenovic.wordpress.com ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: True Random Numbers
Since they weren't mentioned in this thread, I'll point out that there are better sources of entropy than /dev/random, /dev/urandom, and the Windows API. For example, the two sites https://random.org/integers https://www.fourmilab.ch/hotbits/secure_generate.html both offer free random bits via a secure REST interface. Random.org is run by Mads Haahr of the School of Computer Science and Statistics at Trinity College, Dublin. They use background atmospheric radio noise to generate the entropy. Fourmilab is run by John Walker. He uses a source of radioactive decay (Ce 137) and a geiger counter to generate the entropy. Both sites have gone to some trouble in design and testing to ensure that their entropy is truly random. There are quotas on the number of bits you can retrieve per day for free at each of the sites. At random.org, you can purchase additional entropy at low cost. Regards, Yitz ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] ANN: haskell-src-exts 1.9.0
On Thu, Apr 15, 2010 at 12:00, Ivan Lazar Miljenovic ivan.miljeno...@gmail.com wrote: Sean Leather leat...@cs.uu.nl writes: I'm pleased to announce the release of haskell-src-exts-1.9.0! * On hackage: http://hackage.haskell.org/package/haskell-src-exts Any idea why the Haddock docs have not been generated for this version? There's also no built on available. Is it an issue with the server? Looks built to me... Hmm, now it does. Apparently, the server saw my email and responded nicely. http://hackage.haskell.org/packages/archive/haskell-src-exts/1.9.0/logs/success/ Thanks, Hackage! Sean ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] cabal: other-modules
On 15 Apr 2010, at 08:24, Johannes Waldmann wrote: What is the purpose of the Other-Modules section in a cabal file? (I.e., can we drop it?) If it's just the set of dependencies of the Exported-Modules, then a reasonable build system should be able to figure this out on its own. It is not used by the build system. It is used by 'cabal sdist' to build a distribution package that contains everything needed. If a file is not listed in the .cabal file, it will not end up in the tarball. Cabal has no dependency analysis to help discover un-listed modules. Regards, Malcolm ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] ANN: haskell-src-exts 1.9.0
Sean Leather leat...@cs.uu.nl writes: Hmm, now it does. Apparently, the server saw my email and responded nicely. Well, it takes half an hour or so... -- Ivan Lazar Miljenovic ivan.miljeno...@gmail.com IvanMiljenovic.wordpress.com ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Can't login to GHC trac
Am Donnerstag 15 April 2010 05:38:23 schrieb Jason Dagit: On Tue, Apr 13, 2010 at 3:47 AM, Erik de Castro Lopo mle...@mega-nerd.commle%2...@mega-nerd.com wrote: Daniel Fischer wrote: Am Dienstag 13 April 2010 09:29:18 schrieb Erik de Castro Lopo: Anyone else have the same problem? I have that problem with my hackage (Cabal/cabal-install) trac account (Firefox, SeaMonkey, Konqueror). It started when I forgot the password and had it mail a new one to me. Yep, thats when my problems started. Same here (with the GHC trac). I had to create a new account to get around it. Jason You might try again now, if you prefer your old username. Ian fixed something yesterday (I don't know whether it was a global fix or only the accounts with known problems) and it works again for me. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] ANN: haskell-src-exts 1.9.0
Hmm, now it does. Apparently, the server saw my email and responded nicely. Well, it takes half an hour or so... Yes, version 1.9.0 of haskell-src-exts was uploaded on Sun Apr 11 10:43:03 UTC 2010, but the ghc build is dated as modified on 15-Apr-2010 02:42 (in some unknown timezone) according the log http://hackage.haskell.org/packages/archive/haskell-src-exts/1.9.0/logs/success/. I believe that's longer than 30 minutes. Regards, Sean ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] What is the consensus about -fwarn-unused-do-bind ?
John Meacham schrieb: On Fri, Apr 09, 2010 at 09:07:29AM -0700, Bryan O'Sullivan wrote: On Fri, Apr 9, 2010 at 6:44 AM, Ivan Lazar Miljenovic ivan.miljeno...@gmail.com wrote: As of 6.12.1, the new -fwarn-unused-do-bind warning is activated with -Wall. This is based off a bug report by Neil Mitchell: http://hackage.haskell.org/trac/ghc/ticket/3263 . However, does it make sense for this to be turned on with -Wall? Personally, I find it to be tremendously noisy and unhelpful, and I always edit my .cabal files to turn it off. I think of it as a usability regression. I strongly agree. I do not even think it is bad style to ignore the result of a monad, depending on the particular monad used, it could be extremely common. If anything there should be a pragma one can attach to ceratin functions to warn if the result is unused, like 'mapM'. This would be similar to what gcc does, where you can specify an attribute saying a functions result should be used or the compiler should complain. The question is: Would people design libraries in a different way, if it is encouraged to respect monadic results? ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] ANN: haskell-src-exts 1.9.0
Sean Leather leat...@cs.uu.nl writes: Yes, version 1.9.0 of haskell-src-exts was uploaded on Sun Apr 11 10:43:03 UTC 2010, but the ghc build is dated as modified on 15-Apr-2010 02:42 (in some unknown timezone) according the log http://hackage.haskell.org/packages/archive/haskell-src-exts/1.9.0/logs/success/. I believe that's longer than 30 minutes. Interesting maybe there was some error on Hackage that stopped the builder from working... -- Ivan Lazar Miljenovic ivan.miljeno...@gmail.com IvanMiljenovic.wordpress.com ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: cabal: other-modules
What happened was this: 1. add some modules to a library (but forget to mention them in the cabal file), then (in the lib source dir, without cleaning/reconfiguring) cabal install --global (runs without complaint) 2. re-compile an application that uses the library (cabal configure cabal build): this gave undefined symbol errors (for things from the added modules) (with ghc-6.12.1 on i386 debian) I still don't see why this other-modules is needed. Ok, I understand the technical reason that cabal does not do dependency analysis but morally, it should? Best regards - J.W. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: cabal: other-modules
Hi, On Thu, Apr 15, 2010 at 14:40, Johannes Waldmann waldm...@imn.htwk-leipzig.de wrote: What happened was this: 1. add some modules to a library (but forget to mention them in the cabal file), then (in the lib source dir, without cleaning/reconfiguring) cabal install --global (runs without complaint) 2. re-compile an application that uses the library (cabal configure cabal build): this gave undefined symbol errors (for things from the added modules) Just to say that this has happened to me very often as well, on Windows. The first time it took me quite some time to realize what was going wrong... Cheers, Pedro ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: cabal: other-modules
Johannes Waldmann waldm...@imn.htwk-leipzig.de writes: What happened was this: I still don't see why this other-modules is needed. Ok, I understand the technical reason that cabal does not do dependency analysis but morally, it should? Why are people suddenly using the term morally when they mean why doesn't this do what I think it should? None of its definitions seem to match what you mean: http://wordnetweb.princeton.edu/perl/webwn?s=moral -- Ivan Lazar Miljenovic ivan.miljeno...@gmail.com IvanMiljenovic.wordpress.com ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] ANN: haskell-src-exts 1.9.0
On Thu, Apr 15, 2010 at 10:52:51AM +0200, Sean Leather wrote: Any idea why the Haddock docs have not been generated for this version? There's also no built on available. Is it an issue with the server? A glitch when I was switching the builds to use cabal install --dry-run. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] True Random Numbers
Christopher Done wrote: betterStdGen :: IO StdGen Here's what I have been using. It's a bit more complete. Of course, you can always use mkStdGen with it to get one of those if you want. (Yes, I often do that. StdGen is much maligned, but it's pretty good at what it's designed for.) Regards, Yitz module DevRandom where import System.IO import System.IO.Error import Foreign.Marshal.Alloc import Foreign.Storable import Foreign.Ptr data BlockingMode = Blocking | NonBlocking deriving (Eq, Show) -- Read data from the system random device. -- Return Nothing if there is currently not -- enough entropy in the system random device. devRandom :: Storable a = IO (Maybe a) devRandom = readDev /dev/random NonBlocking -- Read data from the system random device. -- If necessary, wait until there is -- enough entropy in the system random device. devRandomWait :: Storable a = IO a devRandomWait = readDev dev Blocking = maybe (devRandomError dev) return where dev = /dev/random -- Read data from the system random device. -- If there is currently not enough entropy -- in the system random device, use a lower -- quality source of randomness instead. devURandom :: Storable a = IO a devURandom = readDev dev NonBlocking = maybe (devRandomError dev) return where dev = /dev/urandom readDev :: Storable a = FilePath - BlockingMode - IO (Maybe a) readDev dev mode = do h - openFile dev ReadMode hSetBuffering h NoBuffering alloca $ getMaybe h undefined where getMaybe :: Storable a = Handle - a - Ptr a - IO (Maybe a) getMaybe h undef ptr = do let size = sizeOf undef n - case mode of Blocking- hGetBufh ptr size NonBlocking - hGetBufNonBlocking h ptr size if n size then return Nothing else fmap Just $ peek ptr devRandomError :: FilePath - IO a devRandomError p = ioError $ mkIOError illegalOperationErrorType Unable to read from the system random device Nothing (Just p) ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: instance Eq (a - b)
On 03:53 Thu 15 Apr , rocon...@theorem.ca wrote: On Wed, 14 Apr 2010, Ashley Yakeley wrote: On 2010-04-14 14:58, Ashley Yakeley wrote: On 2010-04-14 13:59, rocon...@theorem.ca wrote: There is some notion of value, let's call it proper value, such that bottom is not one. In other words bottom is not a proper value. Define a proper value to be a value x such that x == x. So neither undefined nor (0.0/0.0) are proper values In fact proper values are not just subsets of values but are also quotients. thus (-0.0) and 0.0 denote the same proper value even though they are represented by different Haskell values. The trouble is, there are functions that can distinguish -0.0 and 0.0. Do we call them bad functions, or are the Eq instances for Float and Double broken? I'd call them disrespectful functions, or maybe nowadays I might call them improper functions. The good functions are respectful functions or proper functions. snip from other post Try using the (x == y) == (f x = g y) test yourself. Your definitions seem very strange, because according to this, the functions f :: Double - Double f x = 1/x and g :: Double - Double g x = 1/x are not equal, since (-0.0 == 0.0) yet f (-0.0) /= g (0.0). -- Nick Bowler, Elliptic Technologies (http://www.elliptictech.com/) ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: cabal: other-modules
On Thu, Apr 15, 2010 at 1:49 PM, Ivan Lazar Miljenovic ivan.miljeno...@gmail.com wrote: Johannes Waldmann waldm...@imn.htwk-leipzig.de writes: What happened was this: I still don't see why this other-modules is needed. Ok, I understand the technical reason that cabal does not do dependency analysis but morally, it should? Why are people suddenly using the term morally when they mean why doesn't this do what I think it should? None of its definitions seem to match what you mean: http://wordnetweb.princeton.edu/perl/webwn?s=moral The proper use of words isn't dictated by what is found in small dictionaries but by the speakers of the language. Also I would caution against the judgement 'sudden' if you haven't done a corpus check: the recency illusion can be a real pain. 'Morally' seems just the perfect word for this occasion --- concerned with right or proper conduct. In this case, potential discrepancies between the files that cabal 'knows' about when issuing different commands; or the sense of deceit when it 'appears' to work only for faults to appear further down the line. I would guess this is just something we have to live with if cabal can't be expected to include its own parser dependency chaser. Documentation is always a good first step though :-) Cheers, D ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: cabal: other-modules
On Thu, Apr 15, 2010 at 10:45 AM, Dougal Stanton dou...@dougalstanton.net wrote: 'Morally' seems just the perfect word for this occasion --- concerned with right or proper conduct. In this case, potential discrepancies between the files that cabal 'knows' about when issuing different commands; or the sense of deceit when it 'appears' to work only for faults to appear further down the line. Beyond that, there are long established traditions in some parts of programming and mathematics for using ethical/moral terms to describe qualities that go beyond just technical requirements or correctness; this program should do the Right Thing, that bit of code is evil, and so on. Actually defining this moral sense is difficult, though, and it varies somewhat from one person to another, but there seems to be at least some common, shared understanding. It's about should and proper instead of is or must. Personally, I know I've written code that I'd feel guilty about even if it worked perfectly and no one else ever saw it--what else would you call that feeling? From another angle, here's an example of explicit moral terminology applied to mathematics: http://www.cheng.staff.shef.ac.uk/morality/ The mathematical sense there is slightly different from the programming sense, I think, but there seems to be some crossover. For instance, I've gotten the impression that something like a mathematical moral sense underlies much of the interest in programming language semantics, FRP, and dependently-typed languages, though I don't know if the people involved would necessarily call it that. - C. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: instance Eq (a - b)
On Apr 15, 2010, at 12:53 AM, rocon...@theorem.ca wrote: I'd call them disrespectful functions, or maybe nowadays I might call them improper functions. The good functions are respectful functions or proper functions. There's no need to put these into a different class. The IEEE defined this behavior in 1985, in order to help with rounding error. Floats and doubles are NOT a field, let alone an ordered field. 0.0 =/= -0.0 by design, for floats and doubles. 0.0 == -0.0 for integers, exact computable reals, etc. The problem isn't the functions, or the Eq instance. It's the semantics of the underlying data type -- or equivalently, expecting that floats and doubles form an ordered field. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Fwd: Re: Simple game: a monad for each player
There is the project.
I changed some little things with the player datatype. For flexibility sake,
it's stack has no longer to contain PlayerMonadT (I needed it for the net
player client)
The most interesting part (the one that deals with operational) is in
TicTacToe/Game.hs
This is not very, very clean (incomplete doc, for instance), but it'll do
the work.
By the way, the game.hs and client.hs are to be modified (it's the only way
to change the type of the players in the game)
2010/4/15 Limestraël limestr...@gmail.com
Ok, but there is no function such as mapMonad in the operational package?
By the way, I noticed that ProgramT is not automatically made instance of
MonadIO when possible. It could be:
instance (MonadIO m) = MonadIO (ProgramT r m) where
liftIO = lift . liftIO
Is that intentional?
( In fact, I think it's a slip in the mtl package itself, since every
instance of MonadTrans can be declared instance of MonadIO:
instance (MonadTrans t, MonadIO m) = MonadIO (t m) where
liftIO = lift . liftIO
)
By the way, I finally managed to use operational to modify my TicTacToe
game.
(One shot, by the way, I had no bugs ^^. Very nice when it happens...)
Human player and AI are working. I'm currently fixing the Network player.
If you are interested, I could upload my code (it can be another example of
how to use the operational package).
In the end, I used a mix of your solution and my former one.
I have a Request datatype:
data Request a where
GetGrid :: Request Grid
TurnDone :: (Grid, Maybe GridResult) - Request ()
GetResult :: Request (Maybe GridResult)
(Grid is what you called Board, GridResult is a type which indicates if
someone wins or if there is a draw)
The game monad is PlayerMonadT, and is a newtype:
newtype PlayerMonadT m a = PMT (ProgramT Request m a)
deriving (Functor, Monad, MonadTrans)
I still have a datatype Player, which contains functions: (I tried to use
classes, but it was more complicated)
data Player m m' = Player {
-- | Gets the mark (Cross or Circle) of the player
plMark :: Mark,
-- | Called when the player must play
plTurn :: Grid - m Pos,
-- | Called when player tries to play at a forbidden position
plForbidden :: Pos - m (),
-- | Called when game has ended.
plGameOver :: GridResult - m (),
-- | Used to reach PlayerMonad in the monad stack
plLift :: forall a. PlayerMonadT m' a - m a,
-- | Used to run the monad stack the player runs in
plRun :: forall a. m a - PlayerMonadT m' a
}
*m* is the monad stack the player runs in. It must be able to run it, by
providing a plRun function.
*m'* is the top monad, which can't be run (IO for human, any monad for AI,
etc.)
The alteration done to this type is the addition of the plLift and plRun
functions. Those are the functions you, Heinrich, and Bertram told me about.
Then, *all* the players play according to this logic:
playerLogic :: (Monad m) = Player m m' - m ()
playerLogic pl = do
let toProg = plLift pl . PMT . singleton
grid - toProg GetGrid
pos - plTurn pl grid
case checkCell grid (plMark pl) pos of
Nothing - do-- The cell was already filled in
plForbidden pl pos -- We signal the error
playerLogic pl -- We start the turn again
Just newGridAndResult - do
-- The cell has been successfully marked, so we
got a new grid
toProg $ TurnDone newGridAndResult
-- At this point, the interpreter will switch to
the other player
mbResult - toProg $ GetResult
-- This player is back, and wants to know what's
new
case mbResult of
Nothing - playerLogic pl
Just res - plGameOver pl res
We can then run this function with the player custom stack thanks to the
runPlayer function:
runPlayer :: (Monad m) = Player m m' - PlayerMonadT m' ()
runPlayer pl = plRun pl $ playerLogic pl
And finally, the interpreter:
doGame :: (Monad m) = Grid - [PlayerMonadT m ()] - m Grid
doGame initGrid players =
mapM unwrap players = flip evalStateT (initGrid, Nothing) . eval
where
unwrap (PMT pl) = viewT pl
eval :: (Monad m) = [PromptT Request m ()] - StateT (Grid, Maybe
GridResult) m Grid
eval [] = liftM fst get
eval ((Return _) : pls) = eval pls
eval ((GetGrid := pl) : pls) = do
(grid, _) - get
p - lift . viewT $ pl grid
eval $ p : pls
eval ((TurnDone (newGrid, mbResult) := pl) : pls) = do
put (newGrid, mbResult)
p - lift . viewT $ pl ()
eval $ pls ++ [p]
eval ((GetResult := pl) : pls) = do
(_, mbResult) - get
p - lift . viewT $ pl mbResult
eval $ p : pls
The game can be launched by doing for example:
let pl1 = humanPlayer Cross
let pl2 = artificialPlayer Circle levelOfDifficulty
doGame blankGrid [runPlayer pl1, runPlayer pl2]
I did it!
2010/4/15 Heinrich
[Haskell-cafe] Re: Fwd: Re: Simple game: a monad for each player
Limestraël wrote: I'd like to make it very accessible, so please don't hesitate to report any difficulties with finding and understanding documentation and examples! Then I think the name 'Prompt' may be misleading for those who doesn't know the MonadPrompt package. Maybe something like 'ProgramView' ? Very good point. I'll change that in a future version. Ok, but there is no function such as mapMonad in the operational package? No, not yet, but I'll probably add it, or at least its lesser cousin liftT :: Program instr a - ProgramT instr m a to a future version of the library. Still pondering. By the way, I noticed that ProgramT is not automatically made instance of MonadIO when possible. It could be: instance (MonadIO m) = MonadIO (ProgramT r m) where liftIO = lift . liftIO Is that intentional? Yes and no. I refrained from making instances for the mtl classes because I have not clearly thought about the design consequences yet. I think that monad transformers are not the last word on modular computational effects yet and I don't want to paint myself into a corner. For example, as you note, the MonadIO instance could be deduced automatically from the MonadTrans instance. Of course, if I make operational interoperable with the mtl , then I better adhere to its style even if I'm not entirely happy with it. By the way, I finally managed to use operational to modify my TicTacToe game. Yay! :D (One shot, by the way, I had no bugs ^^. Very nice when it happens...) Human player and AI are working. I'm currently fixing the Network player. If you are interested, I could upload my code (it can be another example of how to use the operational package). Sending me / uploading your TicTacToe code would be great! I probably won't use it verbatim, but try to simplify it a bit to turn it into another easy to understand example of how to use operational . Regards, Heinrich Apfelmus -- http://apfelmus.nfshost.com ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Automating injections: adding a type parameter
Hello everyone,
It's my very first post to this mailing list, though i read it for several
months.
I'm very interested in Swiertra's automatic injection technique [1].
http://www.cse.chalmers.se/~wouter//Publications/DataTypesALaCarte.pdfhttp://www.cse.chalmers.se/%7Ewouter//Publications/DataTypesALaCarte.pdf
http://www.cse.chalmers.se/~wouter//Misc/LaCarte.hshttp://www.cse.chalmers.se/%7Ewouter//Misc/LaCarte.hs
As a first exercise, i've tried to write an interpreter/transformer for
propositional logic, in the spirit of [2].
http://www.haskell.org/sitewiki/images/6/6a/TMR-Issue11.pdf
data LProp r = LProp String
instance Functor LProp where
fmap _ (LProp x) = LProp x
data LAnd r = LAnd r r
instance Functor LAnd where
fmap f (LAnd x y) = LAnd (f x) (f y)
Automatic injections are cool things to write helpers that work with any
type for formulae extending LProp with coproducts:
-- not very expressive, but it's not the point
type ConjLogicF = LProp :+: LAnd
type ConjLogic = Mu ConjLogicF
lprop :: (LProp :: f) = String - Mu f
lprop = \s - inject (LProp s)
land :: (LAnd :: f) = Mu f - Mu f - Mu f
land = \x y - inject (LAnd x y)
However, i'd like to parameterize the type of propositionnal variables for
the logic, that is, not only strings, but a given type parameter p. For
instance (that should make LProp' and LAnd' bifunctors i guess):
data LProp' p r = LProp' p
instance Functor (LProp' p) where
fmap _ (LProp' x) = LProp' x
data LAnd' p r = LAnd' r r
instance Functor (LAnd' p) where
fmap f (LAnd' x y) = LAnd' (f x) (f y)
type ConjLogicF' p = (LProp' p) :+: (LAnd' p)
type ConjLogic' p = Mu (ConjLogicF' p)
lprop' :: ((LProp' p) :: (f p)) = p - Mu (f p)
lprop' = \x - inject (LProp' x)
I'm stuck with the definition of the helper for LAnd'. I expect :
land' :: ((LAnd' p) :: (f p)) = Mu (f p) - Mu (f p) - Mu (f p)
land' = \x y - inject (LAnd' x y)
... but ghci 6.10.4 does not really like this definition...
Could not deduce (LAnd' p :: f p1)
from the context (LAnd' p1 :: f p1)
arising from a use of `inject' at PropSample.hs:128:16-33
Possible fix:
add (LAnd' p :: f p1) to the context of
the type signature for `land''
or add an instance declaration for (LAnd' p :: f p1)
In the expression: inject (LAnd' x y)
In the expression: \ x y - inject (LAnd' x y)
In the definition of `land'': land' = \ x y - inject (LAnd' x y)
Failed, modules loaded: none.
Does anybody have a clue for this problem ?
I don't really understand where is the trouble actually.
Cheers,
PS: haskellers rulez ;)
[1]
Swierstra, W.
Data types à la carte
J. Funct. Program.
Cambridge University Press, 2008, 18, 423-436
[2]
Knowles, K.
First-Order Logic à la Carte
The Monad.Reader, 2008, issue 11
--
Romuald THION
Docteur level 1.0 - Great master access control, +3 against half-dead
la vie, c'est comme un jeu mal foutu dont on ne connait pas les règles et
où il n'y a pas de sauvegardes
{-# OPTIONS -Wall #-}
{-# OPTIONS -fwarn-simple-patterns #-}
{-# OPTIONS -fwarn-tabs #-}
{-# OPTIONS -fwarn-incomplete-record-updates #-}
{-# OPTIONS -fwarn-monomorphism-restriction #-}
{-# LANGUAGE FlexibleContexts #-} -- no type variable in context
{-# LANGUAGE FlexibleInstances #-} -- type vars appears more than once in head
{-# LANGUAGE MultiParamTypeClasses #-}
{-# LANGUAGE GADTs #-} -- for Mu
{-# LANGUAGE TypeOperators #-} -- for :+: and ::
{-# LANGUAGE OverlappingInstances #-} -- for automatic injections
module Prop where
import Prelude
-- coproduct for (* - *)
data (f :+: g) a where
Inl :: (f a) - (f :+: g) a
Inr :: (g a) - (f :+: g) a
infixr 6 :+:
-- the coproduct of two functors is a functor
instance (Functor f, Functor g) = Functor (f :+: g) where
fmap f (Inl x) = Inl (fmap f x)
fmap f (Inr y) = Inr (fmap f y)
-- fixpoint
data Mu f where In {
out :: f (Mu f)
} :: Mu f
-- catamorphism
type Algebra f a = f a - a
cata :: Functor f = (Algebra f a) - (Mu f - a )
cata g = g . fmap (cata g) . out
-- Evaluation of an algebra
class Functor f = Eval f a where
evalAlgebra :: Algebra f a
-- Evaluation function
eval :: (Eval f a) = Mu f - a
eval = cata evalAlgebra
-- links between algebra of coproduct
instance (Eval f a, Eval g a) = Eval (f :+: g) a where
evalAlgebra (Inl x) = evalAlgebra x
evalAlgebra (Inr y) = evalAlgebra y
-- automatic injection
class (Functor sub, Functor sup) = sub :: sup where
inj :: sub a - sup a
instance (Functor f) = (::) f f where
inj = id
instance (Functor f, Functor g) = (::) f (f :+: g) where
inj = Inl
instance (Functor h, (::) f g) = (::) f (h :+: g) where
inj = Inr . inj
inject :: ((::) sub f) = sub (Mu f) - Mu f
inject = In . inj
data LProp r = LProp String
instance Functor LProp where
fmap _ (LProp x) = LProp x
instance
[Haskell-cafe] Building regex-posix for windows
I'm having trouble building regex-posix for Windows under MinGW because MinGW does not include regex.h. As far as I know Haskell Platform uses MinGW and it includes regex-posix. I'd like to build regex-posix by myself, like Haskell Platform does. I would appreciate it if someone suggests some resources about building regex-posix and other packages for windows. I’m also looking for Haskell Platform developer’s blog or something similar, where I can read about porting Haskell on Windows. Thanks. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: instance Eq (a - b)
On 2010-04-15 06:18, Nick Bowler wrote: Your definitions seem very strange, because according to this, the functions f :: Double - Double f x = 1/x and g :: Double - Double g x = 1/x are not equal, since (-0.0 == 0.0) yet f (-0.0) /= g (0.0). There's an impedance mismatch between the IEEE notion of equality (under which -0.0 == 0.0), and the Haskell notion of equality (where we'd want x == y to imply f x == f y). A Haskellish solution would be to implement Eq so that it compares the bits of the representations of Float and Double, thus -0.0 /= 0.0, NaN == NaN (if it's the same NaN). But this might surprise people expecting IEEE equality, which is probably almost everyone using Float or Double. -- Ashley Yakeley ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Automating injections: adding a type parameter
Am Donnerstag 15 April 2010 19:19:15 schrieb Romulus:
Hello everyone,
I'm stuck with the definition of the helper for LAnd'. I expect :
land' :: ((LAnd' p) :: (f p)) = Mu (f p) - Mu (f p) - Mu (f p)
land' = \x y - inject (LAnd' x y)
... but ghci 6.10.4 does not really like this definition...
Could not deduce (LAnd' p :: f p1)
from the context (LAnd' p1 :: f p1)
arising from a use of `inject' at PropSample.hs:128:16-33
Possible fix:
add (LAnd' p :: f p1) to the context of
the type signature for `land''
or add an instance declaration for (LAnd' p :: f p1)
In the expression: inject (LAnd' x y)
In the expression: \ x y - inject (LAnd' x y)
In the definition of `land'': land' = \ x y - inject (LAnd' x y)
Failed, modules loaded: none.
Does anybody have a clue for this problem ?
I don't really understand where is the trouble actually.
The expression (Land' x y) can have the type (Land' q (Mu (f p))) for all
q. But there's only an instance for the p used in Mu (f p) provided, so
Could not deduce (LAnd' p :: f p1)
from the context (LAnd' p1 :: f p1)
The solution is to tell the compiler that this expression should have the
type LAnd' p (Mu (f p)) for the f and p from the type signature, add
{-# LANGUAGE ScopedTypeVariables #-}
and modify land' to
land' :: forall f p. ((LAnd' p) :: (f p)) = Mu (f p) - Mu (f p) - Mu
(f p)
land' = \x y - inject (LAnd' x y :: LAnd' p (Mu (f p)))
to be greeted by
[1 of 1] Compiling Prop ( PropSample.hs, interpreted )
PropSample.hs:31:16:
Warning: Declaration of `In' uses deprecated syntax
Instead, use the form
In :: {out :: f (Mu f)} - Mu f
Ok, modules loaded: Prop.
*Prop
by 6.12.1 and
$ ghci-6.10.3 PropSample
GHCi, version 6.10.3: http://www.haskell.org/ghc/ :? for help
Loading package ghc-prim ... linking ... done.
Loading package integer ... linking ... done.
Loading package base ... linking ... done.
[1 of 1] Compiling Prop ( PropSample.hs, interpreted )
Ok, modules loaded: Prop.
*Prop
from the older GHC.
Cheers,
PS: haskellers rulez ;)
+1
[1]
Swierstra, W.
Data types à la carte
J. Funct. Program.
Cambridge University Press, 2008, 18, 423-436
[2]
Knowles, K.
First-Order Logic à la Carte
The Monad.Reader, 2008, issue 11
___
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Haskell-Cafe@haskell.org
http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Automating injections: adding a type parameter
Clear and concise answer.
Thank you.
On Thu, Apr 15, 2010 at 21:24, Daniel Fischer daniel.is.fisc...@web.dewrote:
Am Donnerstag 15 April 2010 19:19:15 schrieb Romulus:
Hello everyone,
I'm stuck with the definition of the helper for LAnd'. I expect :
land' :: ((LAnd' p) :: (f p)) = Mu (f p) - Mu (f p) - Mu (f p)
land' = \x y - inject (LAnd' x y)
... but ghci 6.10.4 does not really like this definition...
Could not deduce (LAnd' p :: f p1)
from the context (LAnd' p1 :: f p1)
arising from a use of `inject' at PropSample.hs:128:16-33
Possible fix:
add (LAnd' p :: f p1) to the context of
the type signature for `land''
or add an instance declaration for (LAnd' p :: f p1)
In the expression: inject (LAnd' x y)
In the expression: \ x y - inject (LAnd' x y)
In the definition of `land'': land' = \ x y - inject (LAnd' x y)
Failed, modules loaded: none.
Does anybody have a clue for this problem ?
I don't really understand where is the trouble actually.
The expression (Land' x y) can have the type (Land' q (Mu (f p))) for all
q. But there's only an instance for the p used in Mu (f p) provided, so
Could not deduce (LAnd' p :: f p1)
from the context (LAnd' p1 :: f p1)
The solution is to tell the compiler that this expression should have the
type LAnd' p (Mu (f p)) for the f and p from the type signature, add
{-# LANGUAGE ScopedTypeVariables #-}
and modify land' to
land' :: forall f p. ((LAnd' p) :: (f p)) = Mu (f p) - Mu (f p) - Mu
(f p)
land' = \x y - inject (LAnd' x y :: LAnd' p (Mu (f p)))
to be greeted by
[1 of 1] Compiling Prop ( PropSample.hs, interpreted )
PropSample.hs:31:16:
Warning: Declaration of `In' uses deprecated syntax
Instead, use the form
In :: {out :: f (Mu f)} - Mu f
Ok, modules loaded: Prop.
*Prop
by 6.12.1 and
$ ghci-6.10.3 PropSample
GHCi, version 6.10.3: http://www.haskell.org/ghc/ :? for help
Loading package ghc-prim ... linking ... done.
Loading package integer ... linking ... done.
Loading package base ... linking ... done.
[1 of 1] Compiling Prop ( PropSample.hs, interpreted )
Ok, modules loaded: Prop.
*Prop
from the older GHC.
Cheers,
PS: haskellers rulez ;)
+1
[1]
Swierstra, W.
Data types à la carte
J. Funct. Program.
Cambridge University Press, 2008, 18, 423-436
[2]
Knowles, K.
First-Order Logic à la Carte
The Monad.Reader, 2008, issue 11
--
Romuald THION
Docteur level 1.0 - Great master access control, +3 against half-dead
la vie, c'est comme un jeu mal foutu dont on ne connait pas les règles et
où il n'y a pas de sauvegardes
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Re: [Haskell-cafe] Nomic game in Haskell
Dupont asked: do you know Nomic? It's a fabulous and strange game where you have the right to change the rules in the middle of the game! I know nomic, but as has been pointed out, it's too wide-ranging to be captured in Haskell. So how about a game played in the Haskell type system where you get to play whatever type you like? Let's restrict ourselves to a total fragment of Haskell. Only allow structural recursion and that sort of thing. The 'board' is a Haskell type function. It'll look something like this: type Board a b c ... y z = ... with type variables a to z (no need to have precisely 26) and so that the right hand side is a type, not another type function. (A neutral third party will have to implement Board.) There are two players. They take turns where a turn consists of picking a concrete type to bind to precisely one previously unbound type variable. When there are no more legal moves left, player 1 now has to exhibit an element of the resulting type. If they succeed, they win, otherwise player 2 wins. Void is allowed. For example, consider type Board a b c d e f g = (Either a b, Either c d, Either e f, g) Player 1 must start by making g a type they know how to instantiate. Maybe g=Int. If not, then Player 2 chooses g=Void and they will never be able to make one of these 4-tuples. From now on, Player 2 has sente (to use go language) because Player 1 will always have to play in the same factor of the 4-tuple that Player 2 played in. Ultimately, however, Player 1 can force a win. -- Dan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Building regex-posix for windows
Hello You can build GNU's regex C-library with MinGW from source and this will give you regex.h and libregex.a / libregex.dll. I think I've only had the Haskell regex-posix package half-working doing this though; i.e. I could build and install regex-posix after I'd made and installed GNU regex, but when I tried to use (Haskell) packages that depended on (Haskell) regex-posix I got linker errors. As I could live without the dependent packages I never investigated further. Best wishes Stephen ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Building regex-posix for windows
2010/4/15 Станислав Черничкин schernich...@gmail.com I'm having trouble building regex-posix for Windows under MinGW because MinGW does not include regex.h. As far as I know Haskell Platform uses MinGW and it includes regex-posix. I'd like to build regex-posix by myself, like Haskell Platform does. I would appreciate it if someone suggests some resources about building regex-posix and other packages for windows. I'm also looking for Haskell Platform developer's blog or something similar, where I can read about porting Haskell on Windows. Thanks. I don't know the answer to your regex-posix question, but if you're looking for Haskell friendly blogs, try: http://planet.haskell.org Is it what you would have expected from a Haskell Platform Developer's blog? If not, what were you hoping to find? Thanks, Jason ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Building regex-posix for windows
Станислав Черничкин schernich...@gmail.com writes: I'm having trouble building regex-posix for Windows under MinGW because MinGW does not include regex.h. Which version of regex-posix is this? I think this might be a bug in regex-posix's .cabal file: the darcs repo seems to contain a regex.h which should probably be included and used on Windows. As far as I know Haskell Platform uses MinGW and it includes regex-posix. I'm not sure if it uses MinGW or Cygwin. -- Ivan Lazar Miljenovic ivan.miljeno...@gmail.com IvanMiljenovic.wordpress.com ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Building regex-posix for windows
Hi Ivan I believe that regex-posix (Haskell) is expecting regex.h to be the 'standard posix' header file. The versions of MinGW / MSys I'm using from around Christmas last year didn't ship with a Posix regex implementation, though this might have changed now. I seem to remember that GNU Posix was available as a package from the MinGW website, but there was some reason I choose to work from the GNU source tarball instead (what ever it was, I've now forgotten). Its certainly possible the original poster doesn't have a Posix regex implementation under MinGW either - I can't find the darcs repo to check, but I think MinGW would need more than a header file. Best wishes Stephen ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: Building regex-posix for windows
Hi, Станислав Черничкин schernichkin at gmail.com writes: I'm having trouble building regex-posix for Windows [...] See this thread: http://thread.gmane.org/gmane.comp.lang.haskell.libraries/12721 Basically, you need to checkout the darcs version which includes C sources for libregex and hack the .cabal file a bit. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Haskell web dev - ASP .NET analogue?
The state of Haskell web development is exciting and messy. We don't have a de facto way to do it like Rails or Django or ASP .NET, but we do have many imitations and ideas popping up. You can easily judge whether the community is happy with the state of web development by the number of new web frameworks coming out all the time. I'm wondering if there is a ASP .NET analogue for Haskell. ASP .NET manages compiled languages like C# well by compiling a given page when you run it, and also allowing you to build pages into DLLs and then link them in your project. I have used this development process for a year in a commercial business and quite like it. It's just really easy to develop. Often you make little mistakes on a given page, so you just edit one bit of code -- you don't want to have to run a command to reload this code yourself. I think that, with Hint, one could write a Haskell equivalent. The nice thing is you can test your Haskell code in GHCi and then save the page and load it in the browser and have it auto-recompile. As to how pages are generated I guess is up to whoever is using it. You have a kind of standard separation in ASP .NET: backend.vb: Sub submit(sender As Object, e As EventArgs) lbl1.Text=Your name is txt1.Text End Sub frontend.asp: form runat=server Enter your name: asp:TextBox id=txt1 runat=server / asp:Button OnClick=submit Text=Submit runat=server / pasp:Label id=lbl1 runat=server //p /form One could blatantly copy this model. And it's not a bad model. To start with anyway. It has the benefit that it's familiar to many web programmers, and, importantly, business practice/industry. My coworkers who only deal with HTML/CSS/JavaScript wouldn't care if backend.vb became backend.hs. I wrote an ecommerce site (http://productsforhair.co.uk/) a year ago in Haskell and used the Text.XHtml.Strict and hated it to be honest. It looks like a complete mess. Look at these two examples of using EDSLs to produce content. Messy and unmanageable. http://paste.lisp.org/display/97840 http://paste.lisp.org/system-server/show/lisppaste/web-server As much as I love EDSLs like html combinators, as soon as you get a nontrivial project with big complex elements it soon gets out of hand. BlazeHtml makes this a little nicer with its `do' syntax but it's still a problem. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: Nomic game in Haskell
On 2010-04-15 14:00, Dan Piponi wrote:
(A neutral third party will have to implement Board.)
data Three a b c where
{
MkThree :: Three () () ()
}
type Board a b c d e f g h i =
Either (Three a b c)
(Either (Three d e f)
(Either (Three g h i)
(Either (Three a d g)
(Either (Three b e h)
(Either (Three c f i)
(Either (Three a e i)
(Either (Three c e g)
)))
Player 2 wins, I think.
--
Ashley Yakeley
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[Haskell-cafe] auto-recompile (Re: Haskell web dev - ASP .NET analogue?)
Re the auto-recompiling part, here is one of my favourite tools. I have used it to auto-build happstack, yesod and hakyll apps/sites: # continuous integration - recompile and restart # whenever a module changes. sp is from searchpath.org, you might # need the patched version from http://joyful.com/repos/searchpath ci: sp --no-exts --no-default-map ghc --make -o app --make app.hs --run Also, you didn't ask for this but while I'm pasting.. here's a thorough darcs posthook, for doing something when a repo's content changes (add the below to _darcs/prefs/defaults): apply posthook make build apply run-posthook pull posthook make build pull run-posthook record posthook make build record run-posthook obliterate posthook make build obliterate run-posthook ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: Nomic game in Haskell
On Thu, Apr 15, 2010 at 4:58 PM, Ashley Yakeley ash...@semantic.org wrote: type Board a b c d e f g h i = Either (Three a b c) (Either (Three d e f) (Either (Three g h i) (Either (Three a d g) (Either (Three b e h) (Either (Three c f i) (Either (Three a e i) (Either (Three c e g) ))) In the service of readability we could also define: data X = X data O Though the victory conditions aren't precisely the usual ones. -- Dan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: Nomic game in Haskell
On 2010-04-15 17:39, Dan Piponi wrote: In the service of readability we could also define: data X = X data O In that case we'd want type Three a b c = (a,b,c) ...which is simpler than my GADT. -- Ashley Yakeley ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Why does the transformers/mtl 'Error' class exist?
Both the transformers[1] and mtl[2] define a class named 'Error', for use with MonadError and ErrorT. This class is required for the instance of Monad (and therefore MonadTrans, MonadIO, etc). However, I can't figure out why this class exists. Its presence means that instead of something like: - data NameError = ErrorFoo | ErrorBar validateName :: Monad m = Text - m (Either Error Text) validateName x = runErrorT $ do when (some condition) $ throwError ErrorFoo when (other condition) $ throwError ErrorBar return x - I have to define this, which is more verbose, no more useful, and adds a fake class to the Haddock docs (with a warning not to use it): - data Error = ErrorFoo | ErrorBar instance Error NameError where strMsg = error -- validateName ... - Is there any good reason why the 'Error' class can't just be removed? [1] http://hackage.haskell.org/packages/archive/transformers/0.2.0.0/doc/html/Control-Monad-Trans-Error.html [2] http://hackage.haskell.org/packages/archive/mtl/1.1.0.2/doc/html/Control-Monad-Error-Class.html ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Why does the transformers/mtl 'Error' class exist?
It's used in the implementation of fail for those monads.
class Monad m where
...
fail :: String - m a
fail = error -- default implementation
which is then used to desugar do-notation when pattern matching fails:
do
Left x - something
return x
=
something = \v - case v of { Left x - return x ; _ - fail
Pattern match failure ... }
You can argue about whether fail belongs in Monad (and many people
have), but that's why it is how it is.
-- ryan
On Thu, Apr 15, 2010 at 7:18 PM, John Millikin jmilli...@gmail.com wrote:
Both the transformers[1] and mtl[2] define a class named 'Error', for
use with MonadError and ErrorT. This class is required for the
instance of Monad (and therefore MonadTrans, MonadIO, etc). However, I
can't figure out why this class exists. Its presence means that
instead of something like:
-
data NameError = ErrorFoo | ErrorBar
validateName :: Monad m = Text - m (Either Error Text)
validateName x = runErrorT $ do
when (some condition) $ throwError ErrorFoo
when (other condition) $ throwError ErrorBar
return x
-
I have to define this, which is more verbose, no more useful, and adds
a fake class to the Haddock docs (with a warning not to use it):
-
data Error = ErrorFoo | ErrorBar
instance Error NameError where
strMsg = error
-- validateName ...
-
Is there any good reason why the 'Error' class can't just be removed?
[1]
http://hackage.haskell.org/packages/archive/transformers/0.2.0.0/doc/html/Control-Monad-Trans-Error.html
[2]
http://hackage.haskell.org/packages/archive/mtl/1.1.0.2/doc/html/Control-Monad-Error-Class.html
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[Haskell-cafe] what does the '~' mean ?
instance (BinaryDefer a, BinaryDefer b) = BinaryDefer (a,b) where
put (a,b) = put2 a b
get = get2 (,)
size x = let ~(a,b) = x in size a + size b
putFixed (a,b) = putFixed2 a b
getFixed = getFixed2 (,)
in `size` function, what does the `~` mean ?
Sincerely!
-
fac n = let { f = foldr (*) 1 [1..n] } in f
--
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