Re: [Haskell-cafe] Re: classes with types which are wrapped in
2010/1/27 Andrew U. Frank fr...@geoinfo.tuwien.ac.at:
{Snip]
dotoBfield :: (b - b) - X a b c - X a b c
dotoBfield op x = x { bfield = op (bfield x)}
and similar for A and C.
is there a better idiom to achieve the same effect?
can this be automated (for example, using generics)?
Hello Andrew
I use a family of variations on the S combinator (also known as
Starling). I wouldn't argue its a better idiom, but I find it
pleasantly regular.
Suppose I had a data type for source positions like Parsec:
data SrcPos = SrcPos {
src_line :: Int,
src_column :: Int,
src_tab_stop :: Int
}
Then update functions on the record follow this pattern
pstarn update-function (one-or more selection-function)
incrCol :: SrcPos - SrcPos
incrCol = pstar (\i s - s { src_column=i+1 }) src_column
incrTab :: SrcPos - SrcPos
incrTab = pstar2 (\i t s - s { src_column= (i+t) }) src_column src_tab_stop
incrLine :: SrcPos - SrcPos
incrLine = pstar (\i s - s { src_line =i+1, src_column=1 }) src_line
At the moment I call the function family 'pstar' for permutated
starlings, but in combinatory logic terms I don't think its strictly
true to consider them permutations so they really need a new name.
Here are the definitions, the order of arguments is changed from
starlings to allow them to be generalized to functors should I need
more generality:
pstar :: (a - r - ans)
- (r - a)
- r - ans
pstar f fa x = f (fa x) x
pstar2:: (a - b - r - ans)
- (r - a) - (r - b)
- r - ans
pstar2 f fa fb x = f (fa x) (fb x) x
pstar3:: (a - b - c - r - ans)
- (r - a) - (r - b) - (r - c)
- r - ans
pstar3 f fa fb fc x = f (fa x) (fb x) (fc x) x
pstar4:: (a - b - c - d - r - ans)
- (r - a) - (r - b) - (r - c) - (r - d)
- r - ans
pstar4 f fa fb fc fd x = f (fa x) (fb x) (fc x) (fd x) x
pstar5:: (a - b - c - d - e - r - ans)
- (r - a) - (r - b) - (r - c) - (r - d) - (r - e)
- r - ans
pstar5 f fa fb fc fd fe x = f (fa x) (fb x) (fc x) (fd x) (fe x) x
Best wishes
Stephen
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[Haskell-cafe] wxHaskell - using XRC files
Hi, I'm looking for documentation on using XRC files with wxHaskell. I finally managed to cabal-install wxHaskell last night alas sans docs. Günther BTW: I'm using wxFormBuilder, any other good tools out there? ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Map unionWith generalization
I need ideally some generalizations of unionWith and unionWithKey, for efficiency matters (i.e. avoiding conversions and traversing the maps more than once). I could use a modification of the code in Map.hs, but then the problem is that the module Map interface does not export the constructors of data Map. So suggestions are welcome. For example, in Map String Integer (sparse representation of monomials) compute the minimum value of all associative pairs with the same key (the gcd); if only one key is present, the absent should be treated as having value 0. So unionWith min xs ys will not work, because unionWith will always apply the identity to the remaining value when one key is missing, whereas it should be sent to 0. So here, one would want: (a - c) - (b - c) - (a - b - c) - Map k a - Map k b - Map k c where the two first functions are applied when the first or second key is missing. Hans ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] custom widgets
we used wx originally but switched to gtk. the great advantage is glade... which is very flexible and still you can add/change whatever you need to in gtk in your haskell code. we checked porting between linux (ubuntu) and windows (xp) and encountered no problems. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: wxHaskell - using XRC files
On Wed, 27 Jan 2010 11:09:06 +0100 Günther == Günther Schmidt gue.schm...@web.de wrote: Günther I'm looking for documentation on using XRC files with Günther wxHaskell. I'd like to find it too...so, far I've found only two samples: xrcmenu.xrc controls.xrc. Günther BTW: I'm using wxFormBuilder, any other good tools out there? Besides wxFormBuilder I played with DialogBlocks (eval version 'cause it's not free). Sincerely, Gour -- Gour | Hlapicina, Croatia | GPG key: F96FF5F6 signature.asc Description: PGP signature ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Map unionWith generalization
On Jan 27, 2010, at 5:53 AM, Hans Aberg wrote: I need ideally some generalizations of unionWith and unionWithKey, for efficiency matters (i.e. avoiding conversions and traversing the maps more than once). I could use a modification of the code in Map.hs, but then the problem is that the module Map interface does not export the constructors of data Map. So suggestions are welcome. For example, in Map String Integer (sparse representation of monomials) compute the minimum value of all associative pairs with the same key (the gcd); if only one key is present, the absent should be treated as having value 0. So unionWith min xs ys will not work, because unionWith will always apply the identity to the remaining value when one key is missing, whereas it should be sent to 0. So here, one would want: (a - c) - (b - c) - (a - b - c) - Map k a - Map k b - Map k c where the two first functions are applied when the first or second key is missing. Ah, the swiss army knife function on maps. This particular formulation works well for the application you describe above, where you're completely traversing both maps. The following really grubby variant can be used to implement asymptotically efficient variations of union, intersection, difference, etc., etc: swissArmy :: (Map k a - Map k c) --- Used to process submaps unique to the left map (Map k b - Map k c) --- Used to process submaps unique to the right map (a - b - Maybe c) - -- Used to process a single common entry Map k a - Map k b - Map k c Then your function appears to be: -- helper just2 :: (a - b - c) - a - b - Maybe c just2 f a b = Just (f a b) swissArmy (fmap (const 0)) (fmap (const 0)) (just2 gcd) Here are unionWith and intersectionWith: unionWith f = swissArmy id id (just2 f) intersectionWith = swissArmy (const empty) (const empty) (just2 f) differenceWith = swissArmy id (const empty) (\a b - Nothing) When throwing together tree-like data structures, I often start by writing this function; it handles most of the bulk operations I might want to do as one-liners. It's got a messy, ugly type signature, but it does everything you want as efficiently as you want.* -Jan-Willem Maessen * Actually, this is only true if you add the key as an argument to the third function, so that you can also encode unionWithKey etc! I've skipped that here. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: wxHaskell - using XRC files
Hello Gour, creating the .xrc files with WxFormBuilder isn't the problem, I'd need to see the .hs files where these resources are imported and used. Do you happen to know where to find those too? Günther Am 27.01.10 13:38, schrieb Gour: On Wed, 27 Jan 2010 11:09:06 +0100 Günther == Günther Schmidtgue.schm...@web.de wrote: Günther I'm looking for documentation on using XRC files with Günther wxHaskell. I'd like to find it too...so, far I've found only two samples: xrcmenu.xrc controls.xrc. Günther BTW: I'm using wxFormBuilder, any other good tools out there? Besides wxFormBuilder I played with DialogBlocks (eval version 'cause it's not free). Sincerely, Gour ___ 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] Re: wxHaskell - using XRC files
On Wed, 27 Jan 2010 14:56:28 +0100 Günther == Günther Schmidt gue.schm...@web.de wrote: Günther creating the .xrc files with WxFormBuilder isn't the problem, Günther I'd need to see the .hs files where these resources are Günther imported and used. Do you happen to know where to find those Günther too? I cannot remember where did I find them, but I'm sending 'em via email. Sincerely, Gour -- Gour | Hlapicina, Croatia | GPG key: F96FF5F6 signature.asc Description: PGP signature ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Map unionWith generalization
On 27 Jan 2010, at 14:56, Jan-Willem Maessen wrote: So here, one would want: (a - c) - (b - c) - (a - b - c) - Map k a - Map k b - Map k c where the two first functions are applied when the first or second key is missing. Ah, the swiss army knife function on maps. This particular formulation works well for the application you describe above, where you're completely traversing both maps. The following really grubby variant can be used to implement asymptotically efficient variations of union, intersection, difference, etc., etc: swissArmy :: (Map k a - Map k c) --- Used to process submaps unique to the left map (Map k b - Map k c) --- Used to process submaps unique to the right map (a - b - Maybe c) - -- Used to process a single common entry Map k a - Map k b - Map k c I'm not sure why you want to throw in functions between maps in the two first arguments. Then there is no requirement that single keys are preserved. But it is a good idea to have a Maybe so that one can remove keys on the fly. Then your function appears to be: -- helper just2 :: (a - b - c) - a - b - Maybe c just2 f a b = Just (f a b) swissArmy (fmap (const 0)) (fmap (const 0)) (just2 gcd) Here are unionWith and intersectionWith: unionWith f = swissArmy id id (just2 f) intersectionWith = swissArmy (const empty) (const empty) (just2 f) differenceWith = swissArmy id (const empty) (\a b - Nothing) When throwing together tree-like data structures, I often start by writing this function; it handles most of the bulk operations I might want to do as one-liners. It's got a messy, ugly type signature, but it does everything you want as efficiently as you want.* My guess is that is when you write things from scratch. I wanted to add these function on top of the module Data.Map, but then that seems not to be possible, as the constructors are not exported. I could make a copy of this file, and then make my own variation. Hans ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Supporting GHC 6.10 and 6.12 in HDBC-postgresql Setup.hs
The other HDBC problem I have is various dependencies relying on QC1. The next HP will ship with QC 2.1 (in coming weeks), so it might be a good time for people to start migrating, since that will be the only version of QC on many distros. I would strongly suggest moving to QC 2 for other reasons as well. It does substantially better at searching the random space, to the extent where several of my properties pass under QC 1 but fail under QC 2. It's a much better testing tool. Thanks, Neil ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: wxHaskell - using XRC files
Hi Guenther, Gour On Wed, 27 Jan 2010 13:38 +0100, Gour g...@gour-nitai.com wrote: On Wed, 27 Jan 2010 11:09:06 +0100 Günther == Günther Schmidt gue.schm...@web.de wrote: Günther I'm looking for documentation on using XRC files with Günther wxHaskell. I'd like to find it too...so, far I've found only two samples: xrcmenu.xrc controls.xrc. You have found just about all there is, I'm afraid. It's on my list for a Blog article, but as you may have realised, my list is quite long, and the rate of service rather slow. The basics are pretty straightforward if you have read and understood the wxWidgets documentation on XRC. - An XRC file needs to be loaded into a top level window. - The objects created when the XRC file is loaded can be made available to wxHaskell by name using the widgetRes functions (you will find most of them in Graphics.UI.WX.Controls) There are quite a few things to watch out for: - XRC is incompatible with Layout (the XRC contains its own sizers, and Layout creates sizers suitable for a given window layout) - You must load your control as a child of the window in which you loaded the XRC file - If you try to fetch a control whose name doesn't exist, or if you load a control by name as the wrong type of control, you will almost certainly crash irrecoverably (the crash is usually in the wxWidgets .DLL/.so/.dylib) - It is not really possible to control an XRC-based menu very well. As an example, I have never succeeded in disabling a menu option - I also have not succeeded in getting XRC to work with wxHaskell custom controls (and I've tried fairly hard). This is currently a show-stopper for me. I very much doubt that this will ever work without putting wxHaskell support into a GUI builder, since wxHaskell custom widgets do not look (to C++) quite the same as C++ custom widgets. The whole of the XRC support really needs a typesafe veneer over it (if you search the wxhaskell-devel archives, there was a proof of concept for doing this proposed about 8 months ago), and probably some wxHaskell-specific work in a GUI builder. I'll do my best to answer any specific questions you have. Best regards Jeremy Günther BTW: I'm using wxFormBuilder, any other good tools out there? Besides wxFormBuilder I played with DialogBlocks (eval version 'cause it's not free). Sincerely, Gour -- Gour | Hlapicina, Croatia | GPG key: F96FF5F6 -- Jeremy O'Donoghue jeremy.odonog...@gmail.com ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Supporting GHC 6.10 and 6.12 in HDBC-postgresql Setup.hs
Neil Mitchell wrote: The other HDBC problem I have is various dependencies relying on QC1. The next HP will ship with QC 2.1 (in coming weeks), so it might be a good time for people to start migrating, since that will be the only version of QC on many distros. I would strongly suggest moving to QC 2 for other reasons as well. It does substantially better at searching the random space, to the extent where several of my properties pass under QC 1 but fail under QC 2. It's a much better testing tool. I will be making that change once it gets into haskell-platform (and once I have the time). My more urgent problem, though, is maintaining Cabal compatibility with 6.10 and 6.12. -- John Thanks, Neil ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] scheduling an alarm
On Tue, 26 Jan 2010 22:41:44 -0800 Thomas DuBuisson thomas.dubuis...@gmail.com wrote: Brian Denheyer bri...@aracnet.com wrote: On Tue, 26 Jan 2010 10:54:03 -0800 Thomas DuBuisson thomas.dubuis...@gmail.com wrote: doEvent f usDelay = forkIO $ threadDelay usDelay doEvent f usDelay f Are you sure that's right ? It seems to be a memory-gobbling infinite loop... Infinite loop? yes, that is what you wanted. Memory gobbling? Why would you think that? Are you assuming no TCO and a full stack push on every function call? Haskell compilers don't work that way. Why would I think that ? I think that because the following code: import Control.Concurrent f = putStrLn foo doEvent f usDelay = do forkIO $ threadDelay usDelay doEvent f usDelay f _really_ _does_ start to consume all of the memory on my system, that's why. I don't know why, but that's what it does on my system. It's not obvious to me that it should do that. So maybe ghci is not doing TCO. 1) There are a million ways to do this - why does one working make you suspicious of another? You can always test the other - it does work so long as you fix the missing 'do'. The suspicious part, that was a joke. Having something that works is nice, making sure I understand it is better. I haven't used the Concurrent stuff before, so I'm just being tentative. 2) It strikes me as funny you suspect the first way when there is zero fundamental difference between that and the way you posted except that: a) My version maintains the correct delay. b) My version forks the doEvent call and runs the action in the older thread while yours forks the action thread and keeps the doEvent in the older thread. I suppose keeping the doEvent as the old thread is good so you can kill it with the original ThreadID that would be returned to the caller. Thanks for the explanation, as I said I'm a little fuzzy on what constitutes a thread, so the two versions will help. One interesting thing I noticed in the docs (which is not important for what I am trying to do, just interesting): There is no guarantee that the thread will be rescheduled promptly when the delay has expired, but the thread will never continue to run earlier than specified. I expect that this means promptly in the sense of not accurately, however I wonder what the upper bound on the (potential) delay is ? Some people miss the fact that threadDelay is a us value and an Int type - this limits the maximum delay to something like 35 minutes (assume a 32 bit Int) or even just 134 seconds if you go by Haskell 98 minimum of 27 bit Ints. Just making sure you realize this seeing as we are talking about delays in that order of magnitude. I advise the overly-complex but functional Control-Event package if you want longer delays. I did notice that the delay is in us. 35 minutes is plenty of time. I can always delay twice ;-) Thanks for pointing me to control event, that looks useful ! Brian ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Map unionWith generalization
On Jan 27, 2010, at 9:42 AM, Hans Aberg wrote: On 27 Jan 2010, at 14:56, Jan-Willem Maessen wrote: So here, one would want: (a - c) - (b - c) - (a - b - c) - Map k a - Map k b - Map k c where the two first functions are applied when the first or second key is missing. Ah, the swiss army knife function on maps. This particular formulation works well for the application you describe above, where you're completely traversing both maps. The following really grubby variant can be used to implement asymptotically efficient variations of union, intersection, difference, etc., etc: swissArmy :: (Map k a - Map k c) --- Used to process submaps unique to the left map (Map k b - Map k c) --- Used to process submaps unique to the right map (a - b - Maybe c) - -- Used to process a single common entry Map k a - Map k b - Map k c I'm not sure why you want to throw in functions between maps in the two first arguments. Then there is no requirement that single keys are preserved. But it is a good idea to have a Maybe so that one can remove keys on the fly. A good point. Technically, one should delimit the scope of the first two arguments: data KeyPreservingMapOperation k a b = AlwaysEmpty | Identity | MapMaybeWithKey (k - a - Maybe b) perform :: KeyPreservingMapOperation a b - Map k a - Map k b perform AlwaysEmpty = const empty perform Identity = id perform (MapMaybeWithKey f) = mapMaybeWithKey f When throwing together tree-like data structures, I often start by writing this function; it handles most of the bulk operations I might want to do as one-liners. It's got a messy, ugly type signature, but it does everything you want as efficiently as you want.* My guess is that is when you write things from scratch. Yes. On the other hand, I've repeatedly run into the same problem you're describing: a api that doesn't give me an efficient way to perform an operation I know to be very simple. If every map provided an operation like this one, then I can avoid writing my own library from scratch when I need it --- especially when from scratch means fork the code and add what I need. So, library implementors: think hard about your swiss army knife combinators. You end up with messy functions with gigantic signatures. On the other hand, you can often add a couple of judicious INLINE annotations and remove tons of code from the rest of your library. Then expose them, and mark them as the functions of last resort that they truly are. I bet there's even a fusion framework in here somewhere. -Jan___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Map unionWith generalization
On 27 Jan 2010, at 16:33, Jan-Willem Maessen wrote: I'm not sure why you want to throw in functions between maps in the two first arguments. Then there is no requirement that single keys are preserved. But it is a good idea to have a Maybe so that one can remove keys on the fly. A good point. Technically, one should delimit the scope of the first two arguments: data KeyPreservingMapOperation k a b = AlwaysEmpty | Identity | MapMaybeWithKey (k - a - Maybe b) perform :: KeyPreservingMapOperation a b - Map k a - Map k b perform AlwaysEmpty = const empty perform Identity = id perform (MapMaybeWithKey f) = mapMaybeWithKey f I'm thinking about (k - Maybe a - Maybe b - Maybe c) - Map k a - Map k b - Map k c The first two Maybe's tell if the keys are present, the last if one wants it in the resulting map. When throwing together tree-like data structures, I often start by writing this function; it handles most of the bulk operations I might want to do as one-liners. It's got a messy, ugly type signature, but it does everything you want as efficiently as you want.* My guess is that is when you write things from scratch. Yes. On the other hand, I've repeatedly run into the same problem you're describing: a api that doesn't give me an efficient way to perform an operation I know to be very simple. If every map provided an operation like this one, then I can avoid writing my own library from scratch when I need it --- especially when from scratch means fork the code and add what I need. So, library implementors: think hard about your swiss army knife combinators. You end up with messy functions with gigantic signatures. On the other hand, you can often add a couple of judicious INLINE annotations and remove tons of code from the rest of your library. Then expose them, and mark them as the functions of last resort that they truly are. One can transverse the product of keys. Then I'm thinking about (k1 - k2 - a - b - Maybe c - Maybe(k, c)) - Map k1 a - Map k2 b - Map k c The first Maybe tells if the key is already present; the second if one wants it inserted. The idea in both cases is to combine the modifying functions into one. This simplifies the interface. Hans ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] scheduling an alarm
On Wed, Jan 27, 2010 at 7:31 AM, Brian Denheyer bri...@aracnet.com wrote: On Tue, 26 Jan 2010 22:41:44 -0800 Thomas DuBuisson thomas.dubuis...@gmail.com wrote: Brian Denheyer bri...@aracnet.com wrote: On Tue, 26 Jan 2010 10:54:03 -0800 Thomas DuBuisson thomas.dubuis...@gmail.com wrote: doEvent f usDelay = forkIO $ threadDelay usDelay doEvent f usDelay f Are you sure that's right ? It seems to be a memory-gobbling infinite loop... Infinite loop? yes, that is what you wanted. Memory gobbling? Why would you think that? Are you assuming no TCO and a full stack push on every function call? Haskell compilers don't work that way. Why would I think that ? I think that because the following code: import Control.Concurrent f = putStrLn foo doEvent f usDelay = do forkIO $ threadDelay usDelay doEvent f usDelay f _really_ _does_ start to consume all of the memory on my system, that's why. I don't know why, but that's what it does on my system. It's not obvious to me that it should do that. So maybe ghci is not doing TCO. That would be a bug! I'm using GHC 6.12.1 i386 and both interpreted using GHCi CLI and compiled (even without optimization) there is no memory growth using either of the two versions. If you are using the latest GHC then consider filing a report at haskell.org/ghc 2) It strikes me as funny you suspect the first way when there is zero fundamental difference between that and the way you posted except that: a) My version maintains the correct delay. b) My version forks the doEvent call and runs the action in the older thread while yours forks the action thread and keeps the doEvent in the older thread. I suppose keeping the doEvent as the old thread is good so you can kill it with the original ThreadID that would be returned to the caller. Thanks for the explanation, as I said I'm a little fuzzy on what constitutes a thread, so the two versions will help. Well Concurrent Haskell has a version of green threads [1] which are scheduled (via the GHC RTS) on some number of OS threads (typically either 1 or equal to the number of cores on the machine). These light weight green threads are extremely cheap to create and destroy, costing a matter of 1K or less per thread, benchmarks can create/destory 100k threads in seconds. forkIO creates green threads while forkOS (which you generally should not use) creates OS threads. One interesting thing I noticed in the docs (which is not important for what I am trying to do, just interesting): There is no guarantee that the thread will be rescheduled promptly when the delay has expired, but the thread will never continue to run earlier than specified. Right, and this is the same as any commodity OS - you can delay for a certain amount of time and once the delay is up you will get rescheduled but the computer is likely busy with other processes/interrupts etc at the exact microsecond you are done. I think the GHC RTS schedules threads in 50us slices by default. Also, GHC uses (or used to use) allocation as a scheduling point so if you have long-running tight loops that don't allocate (and don't explicitly call 'yield') then this could be quite long. In practice I've only once had a problem (GTK GUI didn't update during a long computation - still not sure this was the reason). Cheers, Thomas [1] http://en.wikipedia.org/wiki/Green_threads ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Non-termination of type-checking
Dear Haskellers,
while trying to encode a paradox recently found in Coq if one has
impredicativity and adds injectivity of type constructors [1] I
stumbled on an apparent loop in the type checker when using GADTs,
Rank2Types and EmptyDataDecls.
{-# OPTIONS -XGADTs -XRank2Types -XEmptyDataDecls #-}
module Impred where
The identity type
data ID a = ID a
I is from (* - *) to *, we use a partial application of [ID] here.
data I f where
I1 :: I ID
The usual reification of type equality into a term.
data Equ a b where
Eqrefl :: Equ a a
The empty type
data False
This uses impredicativity: Rdef embeds a (* - *) - *
object into R x :: *.
data R x where
Rdef :: (forall a. Equ x (I a) - a x - False) - R x
r_eqv1 :: forall p. R (I p) - p (I p) - False
r_eqv1 (Rdef f) pip = f Eqrefl pip
r_eqv2 :: forall p. (p (I p) - False) - R (I p)
r_eqv2 f = Rdef (\ eq ax -
case eq of -- Uses injectivity of type
constructors
Eqrefl - f ax)
r_eqv_not_R_1 :: R (I R) - R (I R) - False
r_eqv_not_R_1 = r_eqv1
r_eqv_not_R_2 :: (R (I R) - False) - R (I R)
r_eqv_not_R_2 = r_eqv2
rir :: R (I R)
rir = r_eqv_not_R_2 (\ rir - r_eqv_not_R_1 rir rir)
Type checking seems to loop here with ghc-6.8.3, which is a
bit strange given the simplicity of the typing problem.
Maybe it triggers a constraint with something above?
-- Loops
-- absurd :: False
-- absurd = r_eqv_not_R_1 rir rir
[1]
http://thread.gmane.org/gmane.science.mathematics.logic.coq.club/4322/focus=1405
-- Matthieu
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[Haskell-cafe] ANNOUNCE: ThreadScope 0.1
I've just released ThreadScope version 0.1 on Hackage. Threadscope is a graphical utility for viewing profiling information about Haskell threads. It was written jointly with Simon Marlow and Donnie Jones. It uses Gtk2HS so it works under Windows and the L-word operating system although there seem to be problems making it work with OS-X (due to Gtk2Hs issues I think). $ cabal install threadscope You may need to do cabal update to update your packages list. On Windows operating systems you may need to issue the command from a shell that is running with administrative privileges. Resources: * Web page: http://research.microsoft.com/threadscope * Parallel Performance Tuning for Haskellhttp://research.microsoft.com/apps/pubs/default.aspx?id=80976 (paper at Haskell Symposium 2009) Please let me know if you have any problems. Also, please do let us know about your experience with ThreadScope and in particular about accounts of how you used ThreadScope to shed light on parallel performance bugs. If I get enough feedback I may collate the responses into an experience report or paper for ICFP or the Haskell Symposium. Thank you kindly. Enjoy! Cheers, Satnam Satnam Singh Microsoft 7 JJ Thomson Avenue Cambridge CB3 0FB United Kingdom Email: satn...@microsoft.commailto:satn...@microsoft.com UK tel: +44 1223 479905 Fax: +44 1223 479 999 UK mobile: +44 7979 648412 USA cell: 206 330 1580 USA tel: 206 219 9024 URL: http://research.microsoft.com/~satnams Live Messenger: sat...@raintown.orgmailto:sat...@raintown.org ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Determining application directory
Hi, I'm writing cross-platform application in Haskell which should be running under Windows and Linux. Under Linux configuration is stored in the /etc directory, and under Windows configuration is meant to be in the application directory. So, is there a way to get an application directory path under Windows? I remember that there is a way to do this using WinAPI, but how to do this Haskell? ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Determining application directory
Hi Matveev, You might be interested in the System.Directory module: http://hackage.haskell.org/packages/archive/directory/1.0.0.3/doc/html/System-Directory.html HTH, -chris On 27 jan 2010, at 18:06, Matveev Vladimir wrote: Hi, I'm writing cross-platform application in Haskell which should be running under Windows and Linux. Under Linux configuration is stored in the /etc directory, and under Windows configuration is meant to be in the application directory. So, is there a way to get an application directory path under Windows? I remember that there is a way to do this using WinAPI, but how to do this Haskell? ___ 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] Determining application directory
So, is there a way to get an application directory path under Windows? I remember that there is a way to do this using WinAPI, but how to do this Haskell? The System.Directory module has some methods to get specific directory names in an OS agnostic manner. The closest method that matches what you want is getAppUserDataDirectory which uses the windows API function SHGetFolderPath to get the folder for well known name. IIRC Windows supports a notion of Constant special item's and if getAppUserDataDirectory does not do what you want you can call SHGetFolderPath using the CSIDL you are interested in. The code to do so should be identical to the source for getAppUserDataDirectory CSIDL'a are listed here [1] Links. [1] http://msdn.microsoft.com/en-us/library/bb762494%28VS.85%29.a ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Determining application directory
Other responses have been great but if you are cabalizing you might also be interested in: http://neilmitchell.blogspot.com/2008/02/adding-data-files-using-cabal.html Cheers, Thomas On Wed, Jan 27, 2010 at 9:06 AM, Matveev Vladimir dpx.infin...@gmail.comwrote: Hi, I'm writing cross-platform application in Haskell which should be running under Windows and Linux. Under Linux configuration is stored in the /etc directory, and under Windows configuration is meant to be in the application directory. So, is there a way to get an application directory path under Windows? I remember that there is a way to do this using WinAPI, but how to do this Haskell? ___ 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] Determining application directory
Program directory is not system directory. So it doesn't have CSIDL. Program directory is the folder where executable file is located. I certainly remember that there is a way to get it without, for example, setting it in registry during install... On Wed, Jan 27, 2010 at 12:31:19PM -0500, Rahul Kapoor wrote: So, is there a way to get an application directory path under Windows? I remember that there is a way to do this using WinAPI, but how to do this Haskell? The System.Directory module has some methods to get specific directory names in an OS agnostic manner. The closest method that matches what you want is getAppUserDataDirectory which uses the windows API function SHGetFolderPath to get the folder for well known name. IIRC Windows supports a notion of Constant special item's and if getAppUserDataDirectory does not do what you want you can call SHGetFolderPath using the CSIDL you are interested in. The code to do so should be identical to the source for getAppUserDataDirectory CSIDL'a are listed here [1] Links. [1] http://msdn.microsoft.com/en-us/library/bb762494%28VS.85%29.a ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Determining application directory
Thanks, but my program will be distributed in self-made installer (on windows), though I'm using cabal and the sources are GPL-licensed. Just for users' convenience :) On Wed, Jan 27, 2010 at 09:42:45AM -0800, Thomas DuBuisson wrote: Other responses have been great but if you are cabalizing you might also be interested in: http://neilmitchell.blogspot.com/2008/02/adding-data-files-using-cabal.html Cheers, Thomas On Wed, Jan 27, 2010 at 9:06 AM, Matveev Vladimir dpx.infin...@gmail.comwrote: Hi, I'm writing cross-platform application in Haskell which should be running under Windows and Linux. Under Linux configuration is stored in the /etc directory, and under Windows configuration is meant to be in the application directory. So, is there a way to get an application directory path under Windows? I remember that there is a way to do this using WinAPI, but how to do this Haskell? ___ 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] Determining application directory
Oh yeah, it seems I found it. Solution is to use getModuleFileName and getModuleHandle functions from System.Win32.DLL. Thanks for attention :) ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Linguistic hair-splitting
Here's one for you to ponder. 7 is a number. 7 is an integer, and integers are numbers. 7 is not a field. 7 is an element of [at least one] field, but 7 itself is not a field. 7 is not a group. 7 is a member of the set of integers, but the set of integers is not a group either. The set of integers form a group when taken together with the addition operator. (And, actually, forms another, different, group when taken with the multiplication operator.) Now, here's the question: Is is correct to say that [3, 5, 8] is a monad? Is it correct to say that lists are a monad? Or would it be more correct to say that lists form a monad? ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Linguistic hair-splitting
Andrew Coppin wrote: 7 is a number. 7 is an integer, and integers are numbers. 7 is not a field. 7 is an element of [at least one] field, but 7 itself is not a field. 7 is not a group. Why not? It might be useful to use the notation '7' for the cyclic group with 7 elements. 7 is a member of the set of integers, but the set of integers is not a group either. The set of integers form a group when taken together with the addition operator. (And, actually, forms another, different, group when taken with the multiplication operator.) The integers endowed with the usual multiplication is not a group. (The only invertible elements of this monoid are 1 and -1.) Now, here's the question: Is is correct to say that [3, 5, 8] is a monad? In what sense would this be a monad? I don't quite get your question. Cheers, Jochem -- Jochem Berndsen | joc...@functor.nl ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Linguistic hair-splitting
The list type constructor ([] :: * - *) is a functor, and if you add the implementations of join/return (or just return and bind) those together make the monad. The value-level list [3,5,8] is just a list :) On Wed, Jan 27, 2010 at 1:30 PM, Andrew Coppin andrewcop...@btinternet.comwrote: Here's one for you to ponder. 7 is a number. 7 is an integer, and integers are numbers. 7 is not a field. 7 is an element of [at least one] field, but 7 itself is not a field. 7 is not a group. 7 is a member of the set of integers, but the set of integers is not a group either. The set of integers form a group when taken together with the addition operator. (And, actually, forms another, different, group when taken with the multiplication operator.) Now, here's the question: Is is correct to say that [3, 5, 8] is a monad? Is it correct to say that lists are a monad? Or would it be more correct to say that lists form a monad? ___ 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] Determining application directory
Am Mittwoch, den 27.01.2010, 21:19 +0300 schrieb Vladimir Matveev: Oh yeah, it seems I found it. Solution is to use getModuleFileName and getModuleHandle functions from System.Win32.DLL. Thanks for attention :) You can also use the (portable) package 'directory' from Hackage (http://hackage.haskell.org/package/directory). ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Linguistic hair-splitting
On Wed, Jan 27, 2010 at 11:39 AM, Jochem Berndsen joc...@functor.nl wrote: Now, here's the question: Is is correct to say that [3, 5, 8] is a monad? In what sense would this be a monad? I don't quite get your question. I think the question is this: if m is a monad, then what do you call a thing of type m Int, or m Whatever. Luke ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Linguistic hair-splitting
Luke Palmer wrote: On Wed, Jan 27, 2010 at 11:39 AM, Jochem Berndsen joc...@functor.nl wrote: Now, here's the question: Is is correct to say that [3, 5, 8] is a monad? In what sense would this be a monad? I don't quite get your question. I think the question is this: if m is a monad, then what do you call a thing of type m Int, or m Whatever. Ah yes, I see. It's probably the most common to call this a monadic value or monadic action. As Daniel pointed out, the type constructor itself is called a monad (e.g., Maybe). Jochem -- Jochem Berndsen | joc...@functor.nl ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Map unionWith generalization
On Jan 27, 2010, at 10:54 AM, Hans Aberg wrote: On 27 Jan 2010, at 16:33, Jan-Willem Maessen wrote: I'm not sure why you want to throw in functions between maps in the two first arguments. Then there is no requirement that single keys are preserved. But it is a good idea to have a Maybe so that one can remove keys on the fly. A good point. Technically, one should delimit the scope of the first two arguments: data KeyPreservingMapOperation k a b = AlwaysEmpty | Identity | MapMaybeWithKey (k - a - Maybe b) perform :: KeyPreservingMapOperation a b - Map k a - Map k b perform AlwaysEmpty = const empty perform Identity = id perform (MapMaybeWithKey f) = mapMaybeWithKey f I'm thinking about (k - Maybe a - Maybe b - Maybe c) - Map k a - Map k b - Map k c The first two Maybe's tell if the keys are present, the last if one wants it in the resulting map. That has the same behavior semantically, but it's no more efficient than performing a unionWith followed by a filter. For example, consider implementing: xs `intersection` singleton k v in this way. With the function given, the complexity is necessarily O(size xs): we must traverse every key/value pair in xs. By contrast, by aggregating the operations on keys that exist only in a single map, we can write functions like intersection with the desired complexity (which is O(log (size xs)) in this case). Yes. On the other hand, I've repeatedly run into the same problem you're describing: a api that doesn't give me an efficient way to perform an operation I know to be very simple. If every map provided an operation like this one, then I can avoid writing my own library from scratch when I need it --- especially when from scratch means fork the code and add what I need. So, library implementors: think hard about your swiss army knife combinators. You end up with messy functions with gigantic signatures. On the other hand, you can often add a couple of judicious INLINE annotations and remove tons of code from the rest of your library. Then expose them, and mark them as the functions of last resort that they truly are. One can transverse the product of keys. Then I'm thinking about (k1 - k2 - a - b - Maybe c - Maybe(k, c)) - Map k1 a - Map k2 b - Map k c The first Maybe tells if the key is already present; the second if one wants it inserted. Traversing cross products is a very different operation from zipping in the key space. Again I wouldn't want to mistakenly substitute one for the other! But in this case I think you'll find that you're already well served by the functions that already exist---adding this function doesn't enable you to do anything more efficiently (at least in a big-O sense). The idea in both cases is to combine the modifying functions into one. This simplifies the interface. Understood, and with a sufficiently smart compiler we might analyze the behavior of the function and do the right thing with the single-function interface in both cases. I have yet to encounter a compiler that is both smart and reliable on this count. That is why I've found it necessary to expose these kinds of functions. -Jan Hans ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Map unionWith generalization
On 27 Jan 2010, at 21:29, Jan-Willem Maessen wrote: I'm thinking about (k - Maybe a - Maybe b - Maybe c) - Map k a - Map k b - Map k c The first two Maybe's tell if the keys are present, the last if one wants it in the resulting map. That has the same behavior semantically, but it's no more efficient than performing a unionWith followed by a filter. It would not be the complexity, but the constant factor, by not having to transverse it twice. I'm not sure how it works in a functional language, and the trees must be rebalanced, too. For example, consider implementing: xs `intersection` singleton k v in this way. With the function given, the complexity is necessarily O(size xs): we must traverse every key/value pair in xs. By contrast, by aggregating the operations on keys that exist only in a single map, we can write functions like intersection with the desired complexity (which is O(log (size xs)) in this case). That is a good point. One can transverse the product of keys. Then I'm thinking about (k1 - k2 - a - b - Maybe c - Maybe(k, c)) - Map k1 a - Map k2 b - Map k c The first Maybe tells if the key is already present; the second if one wants it inserted. Traversing cross products is a very different operation from zipping in the key space. Again I wouldn't want to mistakenly substitute one for the other! For the first one, think of sums of sparse matrices or polynomials, and the second, products. But in this case I think you'll find that you're already well served by the functions that already exist---adding this function doesn't enable you to do anything more efficiently (at least in a big-O sense). Yes, I can't implements (-) directly; it must be a combination of (+) and negate, and the 0 must be filtered out in an extra pass. And for gcd of monomials, it is now a combination of lcm, (*) and (/), instead of a single pass. Unfortunately, these operations are used a lot, so getting a smaller constant factor is important. The idea in both cases is to combine the modifying functions into one. This simplifies the interface. Understood, and with a sufficiently smart compiler we might analyze the behavior of the function and do the right thing with the single- function interface in both cases. I have yet to encounter a compiler that is both smart and reliable on this count. That is why I've found it necessary to expose these kinds of functions. By your example above, there may be a conflict between a general, simple interface, and implementing things like intersections. Hans ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Linguistic hair-splitting
Hi On 27 Jan 2010, at 20:14, Luke Palmer lrpal...@gmail.com wrote: On Wed, Jan 27, 2010 at 11:39 AM, Jochem Berndsen joc...@functor.nl wrote: Now, here's the question: Is is correct to say that [3, 5, 8] is a monad? In what sense would this be a monad? I don't quite get your question. I think the question is this: if m is a monad, then what do you call a thing of type m Int, or m Whatever. It has been known to call such things 'computations', as opposed to 'values', and even to separate the categories of types and expressions which deliver the two. I think that's a useful separation: I wish return (embedding values in computations) were silent, and thunk (embedding computations in values) made more noise. Cheers Conor Luke ___ 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] Linguistic hair-splitting
Am Mittwoch 27 Januar 2010 22:50:35 schrieb Conor McBride: It has been known to call such things 'computations', as opposed to 'values', and even to separate the categories of types and expressions which deliver the two. As usual, that only works part of the time. [1,4,15,3,7] is not a computation, it's a list of numbers. A plain and simple everyday value. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Non-termination of type-checking
The compiler doesn't loop for me with GHC6.10.4; I think GADTs still
had some bugs in GHC6.8.
That said, this is pretty scary. Here's a simplified version that
shows this paradox with just a single GADT and no other extensions.
No use of fix or recursion anywhere!
{-# LANGUAGE GADTs #-}
module Contr where
newtype I f = I (f ())
data R o a where R :: (a (I a) - o) - R o (I a)
run :: R o (I (R o)) - R o (I (R o)) - o
run x (R f) = f x
rir :: (R o) (I (R o))
rir = R (\x - run x x)
absurd :: a
absurd = run rir rir
-- ryan
On Wed, Jan 27, 2010 at 8:27 AM, Matthieu Sozeau mat...@mattam.org wrote:
Dear Haskellers,
while trying to encode a paradox recently found in Coq if one has
impredicativity and adds injectivity of type constructors [1] I
stumbled on an apparent loop in the type checker when using GADTs,
Rank2Types and EmptyDataDecls.
{-# OPTIONS -XGADTs -XRank2Types -XEmptyDataDecls #-}
module Impred where
The identity type
data ID a = ID a
I is from (* - *) to *, we use a partial application of [ID] here.
data I f where
I1 :: I ID
The usual reification of type equality into a term.
data Equ a b where
Eqrefl :: Equ a a
The empty type
data False
This uses impredicativity: Rdef embeds a (* - *) - *
object into R x :: *.
data R x where
Rdef :: (forall a. Equ x (I a) - a x - False) - R x
r_eqv1 :: forall p. R (I p) - p (I p) - False
r_eqv1 (Rdef f) pip = f Eqrefl pip
r_eqv2 :: forall p. (p (I p) - False) - R (I p)
r_eqv2 f = Rdef (\ eq ax -
case eq of -- Uses injectivity of type constructors
Eqrefl - f ax)
r_eqv_not_R_1 :: R (I R) - R (I R) - False
r_eqv_not_R_1 = r_eqv1
r_eqv_not_R_2 :: (R (I R) - False) - R (I R)
r_eqv_not_R_2 = r_eqv2
rir :: R (I R)
rir = r_eqv_not_R_2 (\ rir - r_eqv_not_R_1 rir rir)
Type checking seems to loop here with ghc-6.8.3, which is a
bit strange given the simplicity of the typing problem.
Maybe it triggers a constraint with something above?
-- Loops
-- absurd :: False
-- absurd = r_eqv_not_R_1 rir rir
[1]
http://thread.gmane.org/gmane.science.mathematics.logic.coq.club/4322/focus=1405
-- Matthieu
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Re: [Haskell-cafe] Non-termination of type-checking
Ryan Ingram wrote:
The compiler doesn't loop for me with GHC6.10.4; I think GADTs still
had some bugs in GHC6.8.
That said, this is pretty scary. Here's a simplified version that
shows this paradox with just a single GADT and no other extensions.
No use of fix or recursion anywhere!
{-# LANGUAGE GADTs #-}
module Contr where
newtype I f = I (f ())
data R o a where R :: (a (I a) - o) - R o (I a)
run :: R o (I (R o)) - R o (I (R o)) - o
run x (R f) = f x
rir :: (R o) (I (R o))
rir = R (\x - run x x)
absurd :: a
absurd = run rir rir
I think that's essentially the same as this:
data Fix a = Fix { unFix :: Fix a - a }
run :: Fix a - Fix a - a
run x f = unFix f x
rir :: Fix a
rir = Fix (\x - run x x)
absurd :: a
absurd = run rir rir
Non-positive recursive occurrences in type definitions provide various
ways to encode the Y-combinator in a typed lambda calculus, without the
need for any recursive let primitive. Haskell allows such non-positive
occurrences, but for strong normalisation, languages like Coq must
disallow them.
If you change data to newtype in the above, the GHC 6.10.4 compiler
(but not GHCi) will loop. I think this is just a case of the infelicity
documented here:
http://www.haskell.org/ghc/docs/latest/html/users_guide/bugs.html
Regards,
Matthew
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Re: [Haskell-cafe] Linguistic hair-splitting
On 27 Jan 2010, at 22:02, Daniel Fischer daniel.is.fisc...@web.de wrote: Am Mittwoch 27 Januar 2010 22:50:35 schrieb Conor McBride: It has been known to call such things 'computations', as opposed to 'values', and even to separate the categories of types and expressions which deliver the two. As usual, that only works part of the time. [1,4,15,3,7] is not a computation, it's a list of numbers. A plain and simple everyday value. Yes, the separation is not clear in Haskell. (I consider this unfortunate.) I was thinking of Paul Levy's call-by-push-value calculus, where the distinction is clear, but perhaps not as fluid as one might like. Int list values and nondeterministic int computations are conceptually different, even if they have isomorphic representations. Identifying their types has its downsides. Cheers Conor ___ 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] ANNOUNCE: ThreadScope 0.1
On Wed, Jan 27, 2010 at 8:51 AM, Satnam Singh satn...@microsoft.com wrote: I’ve just released ThreadScope version 0.1 on Hackage. Threadscope is a graphical utility for viewing profiling information about Haskell threads. It was written jointly with Simon Marlow and Donnie Jones. It uses Gtk2HS so it works under Windows and the L-word operating system although there seem to be problems making it work with OS-X (due to Gtk2Hs issues I think). This is great news! ThreadScope was very useful when I was debugging threading issues in the new I/O manager [1] Bryan and I have been working on. I managed to get it to work on OS X after building gtk2hs from source. Once I got it to build the only problem I had is that it crashes when I try to save to an image file. Cheers, Johan 1. http://github.com/tibbe/event ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Map unionWith generalization
Hans Aberg wrote: For example, in Map String Integer (sparse representation of monomials) compute the minimum value of all associative pairs with the same key (the gcd); if only one key is present, the absent should be treated as having value 0. So unionWith min xs ys will not work, because unionWith will always apply the identity to the remaining value when one key is missing, whereas it should be sent to 0. If missing keys represent 0, then wouldn't this work? intersectionWith min xs ys Twan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Linguistic hair-splitting
On Jan 27, 2010, at 4:57 PM, Conor McBride wrote: Yes, the separation is not clear in Haskell. (I consider this unfortunate.) I was thinking of Paul Levy's call-by-push-value calculus, where the distinction is clear, but perhaps not as fluid as one might like. What, exactly, is the supposed difference between a value and a computation? Please remember that computations can and very often do return computations as results. Please remember that in order for a function to be computed for a value, binding and computation must occur. And that for every value computed, a computation must occur, even if it is just under identity the identity function. Let's not forget that there's a monad for every one-argument (id est, monadic) function, and vice-versa. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] ghc-core 0.5 build fails
Hi all, ghc-core.hs:263:13: Not in scope: data constructor `C.ExitException' Looks like this comes from the base control.exception ? When I go to the web page for control.exception, there is no exitexception. My reading of the hackage entry for ghc-core makes me think that I've got the correct version of everything. ghc is 6.10.4 Brian Creating dist/build/ghc-core (and its parents) Creating dist/build/ghc-core/ghc-core-tmp (and its parents) /usr/bin/ghc -o dist/build/ghc-core/ghc-core --make -hide-all-packages -i -idist/build/ghc-core/ghc-core-tmp -i. -idist/build/autogen -Idist/build/autogen -Idist/build/ghc-core/ghc-core-tmp -optP-include -optPdist/build/autogen/cabal_macros.h -odir dist/build/ghc-core/ghc-core-tmp -hidir dist/build/ghc-core/ghc-core-tmp -stubdir dist/build/ghc-core/ghc-core-tmp -package base-4.1.0.0 -package colorize-haskell-1.0.0 -package directory-1.0.0.3 -package filepath-1.1.0.2 -package pcre-light-0.3.1 -package process-1.0.1.1 -O -Wall -XPatternGuards ./ghc-core.hs ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] ghc-core 0.5 build fails
briand: Hi all, ghc-core.hs:263:13: Not in scope: data constructor `C.ExitException' Looks like this comes from the base control.exception ? When I go to the web page for control.exception, there is no exitexception. My reading of the hackage entry for ghc-core makes me think that I've got the correct version of everything. ghc is 6.10.4 Thanks for the report. ghc-core 0.5.1 was released today, so cabal update; cabal install ghc-core and you should be fine. Cheers, Don ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] ghc-core 0.5 build fails
Don Stewart d...@galois.com writes: Thanks for the report. ghc-core 0.5.1 was released today, so cabal update; cabal install ghc-core and you should be fine. Even though I told you about this problem (your overly loose base constraint) four months ago? -- 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
