[Haskell-cafe] Re: Is there anyone out there who can translate C# generics into Haskell?
Jonathan Cast [EMAIL PROTECTED] wrote:
On 4 Jan 2008, at 2:00 AM, Nicholls, Mark wrote:
You may be right...but learning is not an atomic thingwherever I
start I will get strange things happening.
The best place to start learning Haskell is with the simplest type
features, not the most complicated. And it's the simplest features
that are most unlike OO.
Yes, Haskell will be `strange'. But if you think you're `the
intersection' between Haskell and OO, you'll think things are
familiar, and you'll be surprised when they turn out to be
different. I'd concentrate on watching out for differences --- but
then I can't imagine how finding `familiar' ideas would help.
just a sec...
things like
data State = State
{ winSize :: IORef Size
, t :: IORef Int
, fps :: IORef Float
, showFPS :: IORef Bool
, showHelp :: IORef Bool
, grabMouse :: IORef Bool
, mousePos :: IORef (Maybe Position)
, mouseDelta :: IORef Position
, viewRot :: IORef Vec3
, angle':: IORef GLfloat
, ballPos :: IORef Vec2
, ballVel :: IORef Vec2
}
makeState :: IO State
makeState = do
size - newIORef $ Size 0 0
t' - newIORef 0
fps' - newIORef 0
sfps - newIORef False
gm - newIORef False
mp - newIORef Nothing
md - newIORef $ Position 0 0
sh - newIORef False
v - newIORef (0, 0, 0)
a - newIORef 0
bp - newIORef (0, 0)
bv - newIORef (0.002, 0.002)
{ winSize = size
, t = t', fps = fps'
, showFPS = sfps, showHelp = sh
, grabMouse = gm, mousePos = mp, mouseDelta = md
, viewRot = v, angle' = a
, ballPos = bp, ballVel = bv
}
and
keyboard state (Char 'f') Down_ _ = showFPS state $~ not
modRot :: State - View - IO ()
modRot state (dx,dy,dz) = do
(x, y, z) - get $ viewRot state
viewRot state $= (x + dx, y + dy, z + dz)
postRedisplay Nothing
come to mind.
But then this has more to do with Monads than with classes. IO, in
particular, and GL and GLUT, which are state machines and
thus predestined for OOP.
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[Haskell-cafe] Am I blind?
Don Stewart wrote: --- Haskell Weekly News Issue 68 - January 05, 2008 --- Announcements GHC 6.8.2. The GHC Team [2]announced the release of GHC 6.8.2, featuring optimisation improvements, improvements to ghci and fixes to standalone deriving. I've searched all over the place, and I can't find this information actually announced anywhere except on the GHC homepage itself. And yet, I've seen emails bouncing around that appear to be replies to the announcement email. But I can't find the actual announcement email anywhere. Am I going mad? ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] US Homeland Security program language security risks
Galchin Vasili wrote: Hello, https://buildsecurityin.us-cert.gov/daisy/bsi/articles/knowledge/coding/295.html I stumbled across this page. It seems that Haskell and other strongly typed functional languages like Ml/OCaml will fare much, much better, e.g. buffer overrun. Thoughts . comments. Human kind has yet to design a programming language which eliminates all possible bugs. ;-) ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Concurrency questions
Just a couple of things I was wondering about... 1. Is there some way to assign a priority to Haskell threads? (The behaviour I'd like is that high priority threads always run first, and low priority threads potentially never run at all unless there's an available processor which is completely idle.) 2. I have a situation where I have a thread generating some data and putting it into a mutable array, and another thread trying to read that data. Is there a way I can make the reader thread block if it tries to read a cell that hasn't been computed yet, but not introduce too much overhead for cells that have been filled in? 3. Would it be hard to make it so that the number of real threads (the RTS +N flag) could be adjusted at runtime? ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Am I blind?
I've searched all over the place, and I can't find this information actually announced anywhere except on the GHC homepage itself. And yet, I've seen emails bouncing around that appear to be replies to the announcement email. But I can't find the actual announcement email anywhere. Am I going mad? It was on just the Haskell rather than Haskell-cafe mailing list. http://www.mail-archive.com/[EMAIL PROTECTED]/msg20759.html regards allan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Am I blind?
Allan Clark wrote: I've searched all over the place, and I can't find this information actually announced anywhere except on the GHC homepage itself. And yet, I've seen emails bouncing around that appear to be replies to the announcement email. But I can't find the actual announcement email anywhere. Am I going mad? It was on just the Haskell rather than Haskell-cafe mailing list. http://www.mail-archive.com/[EMAIL PROTECTED]/msg20759.html You're quite right - there it is - and yet I still can't find this through Gname. [Even though I now know what date to look at.] Odd... ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Concurrency questions
On Jan 6, 2008 9:30 AM, Andrew Coppin [EMAIL PROTECTED] wrote: 2. I have a situation where I have a thread generating some data and putting it into a mutable array, and another thread trying to read that data. Is there a way I can make the reader thread block if it tries to read a cell that hasn't been computed yet, but not introduce too much overhead for cells that have been filled in? If your thread fills the array linearly, you could maintain a variable shared by those threads that say the last cell computed, and have the read thread check that before reading. I think this wouldn't create too much overhead, although it seems like there must be something cleverer somewhere. -- Felipe. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: Concurrency questions
Andrew Coppin [EMAIL PROTECTED] wrote: 2. I have a situation where I have a thread generating some data and putting it into a mutable array, and another thread trying to read that data. Is there a way I can make the reader thread block if it tries to read a cell that hasn't been computed yet, but not introduce too much overhead for cells that have been filled in? This http://www.haskell.org/ghc/docs/latest/html/libraries/stm/Control-Concurrent-STM-TChan.html could be what you're looking for. -- (c) this sig last receiving data processing entity. Inspect headers for past copyright information. All rights reserved. Unauthorised copying, hiring, renting, public performance and/or broadcasting of this signature prohibited. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Concurrency questions
Felipe Lessa wrote: On Jan 6, 2008 9:30 AM, Andrew Coppin [EMAIL PROTECTED] wrote: 2. I have a situation where I have a thread generating some data and putting it into a mutable array, and another thread trying to read that data. Is there a way I can make the reader thread block if it tries to read a cell that hasn't been computed yet, but not introduce too much overhead for cells that have been filled in? If your thread fills the array linearly, you could maintain a variable shared by those threads that say the last cell computed, and have the read thread check that before reading. I think this wouldn't create too much overhead, although it seems like there must be something cleverer somewhere. That's just it - it fills the array in a fairly random order. (The *scanning* is, however, in linear order.) It's not a big problem - I can wait for the entire array to be filled, and then scan it. But I'd like to do both in parallel if there's a reasonably easy way to do it. I suppose an array of MVars would do it, but 1. How big is an MVar? 2. You have to take the data out of an MVar to read it. In other words, only 1 thread can read an MVar at once [by design]. This isn't truly a problem in the current case, but it's irritating in principle that I can't make it so that once the cell is written, multiple threads can read it simultaneously... ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Basic question concerning the category Hask (was: concerning data constructors)
I wrote: What goes wrong with finite coproducts? The obvious thing to do would be to take the disjoint union of the sets representing the types, identifying the copies of _|_. Jonathan Cast wrote: This isn't a coproduct. If we have f x = 1 and g y = 2, then there should exist a function h such that h . Left = f and h . Right = g... But by your rule, Left undefined = Right undefined... Which is a contradiction... OK, thanks. Unless, of course, your require your functions to be strict --- then both f and g above become illegal, and repairing them removes the problem. You don't have to make them illegal - just not part of your notion of coproduct. That is an entirely category-theoretic concept, since Empty is bi-universal, and a morphism is strict iff the diagram f A --- B \ ^ v/ Empty commutes. However, the coproduct you get is the one I suggested, namely Either !A !B, not the one we usually use. What is the lifted version you are referring to? Take the ordinary disjoint union, and then add a new _|_ element, distinct from both existing copies of _|_ (which are still distinct from each other). Of course, Haskell makes things even worse by lifting the product and exponential objects, OK, what goes wrong there, and what is the lifting? Again, in Haskell, (_|_, _|_) /= _|_. The difference is in the function f (x, y) = 1 which gives f undefined = undefined but f (undefined, undefined) = 1. Unfortunately, this means that (alpha, beta) has an extra _|_ element (_|_, _|_), so it's not the categorical product (which would lack such an element for the same reason as above). This is partly an implementation issue --- compiling pattern matching without introducing such a lifting requires a parallel implementation --- and partly a semantic issue --- data introduces a single level of lifting, every time it is used, and every constructor is completely lazy. Functions have the same issue --- in the presence of seq, undefined / = const undefined. Extensionality is a key part of the definition of all of these constructions. The categorical rules are designed to require, in concrete categories, that the range of the two injections into a coproduct form a partition of the coproduct, the surjective pairing law (fst x, snd x) = x holds, and the eta reduction law (\ x - f x) = f holds. Haskell flaunts all three; while some categories have few enough morphisms to get away with this (at least some times), Hask is not one of them. jcc ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Wikipedia on first-class object
On Fri, 2007-12-28 at 17:54 -0600, Jonathan Cast wrote: Programming languages are generally classified into three groups, imperative, functional, and logical. The difference is in the style of programming encouraged (or mandated, for older languages) by the language. Usually the divide is imperative v. declarative with the four major paradigms (procedural, OO and logic, FP respectively) being subgroups of those divisions. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Quanta. Was: Wikipedia on first-class object
On Sun, 2007-12-30 at 12:27 +0100, [EMAIL PROTECTED] wrote: [...] I don't understand your point. We know what swimming is: floating and moving autonomously. Thinking is different, since our thinking is (at least for some of us) conscious, and we have no idea what is the conscience. For goodness sake, I have *REALLY* the impression that those guys who speak about computability of the Universe, have the mentality of 18 century thinkers for whom the world was simple and mechanistic. Or even the mentality of people contemporary of Democritus, for whom everything reduced to some dance of atoms. Or a wave function for the Universe... ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Basic question concerning the category Hask (was: concerning data constructors)
On Wed, 2008-01-02 at 15:49 +0200, Yitzchak Gale wrote: [...] Some people are worried that this version of Hask is missing certain nice properties that one would like to have. For example, it was recently claimed on this list that tuples are not products in that category. (Or some such. I would be interested to see a demonstration of that.) Johnathan has given such a demonstration (and it has been demonstrated many times on this list since it's creation, it's well-known). I am not impressed by those complaints. As usual in category theory, you define corresponding notions in Hask, and prove that they are preserved under the appropriate functors. That should always be easy. And if ever it is not, then you have discovered an interesting non-trivial consequence of laziness that deserves study. You are right not to be impressed by such complaints, but you misrepresent people's views on this by saying that the worry about such problems. As you say (people say), these properties [that Hask is cartesian closed to start] would be nice to have and are very convenient to assume which is often safe enough. Certainly computer scientists of a categorical bent have developed (weaker) notions to use; namely, monoidal, pre-monoidal, Freyd, and/or kappa categories and no doubt others. Using these, however, removes some of the allure of using a categorical approach. Also, there is a Haskell-specific problem at the very get-go. The most obvious choice for the categorical composition operator assuming the obvious choice for the arrows and objects does not work, it does not satisfy the laws of a category assuming the = used in them is observational equality. Namely, id . f /= f /= f . id for all functions f, in particular, it fails when f = undefined. This can easily be fixed by making the categorical (.) strict in both arguments and there is no formal problem with it being different from Haskell's (.), but it certainly is not intuitively appealing. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Basic question concerning the category Hask (was: concerning data constructors)
(sorry, I hit the send button) What is the lifted version you are referring to? Take the ordinary disjoint union, and then add a new _|_ element, distinct from both existing copies of _|_ (which are still distinct from each other). Now why is that not the category-theoretic coproduct? h . Left = f and h . Right = g both for _|_ and for finite elements of the types. And it looks universal to me. Of course, Haskell makes things even worse by lifting the product and exponential objects, OK, what goes wrong there, and what is the lifting? Again, in Haskell, (_|_, _|_) /= _|_. The difference is in the function f (x, y) = 1 which gives f undefined = undefined but f (undefined, undefined) = 1. I don't get that one. Given any f and g, we define h x = (f x, g x). Why do we not have fst . h = f and snd . h = g, both in Hask and StrictHask? fst and snd are strict. Unfortunately, this means that (alpha, beta) has an extra _|_ element (_|_, _|_), so it's not the categorical product (which would lack such an element for the same reason as above). The reason you can't adjoin an extra element to (A,B) in, say, Set, is that you would have nowhere to map it under fst and snd. But here that is not a problem, _|_ goes to _|_ under both. This is partly an implementation issue --- compiling pattern matching without introducing such a lifting requires a parallel implementation That's interesting. So given a future platform where parallelizing is much cheaper than it is today, we could conceivably have a totally lazy version of Haskell. I wonder what it would be like to program in that environment, what new problems would arise and what new techniques would solve them. Sounds like a nice research topic. Who is working on it? --- and partly a semantic issue --- data introduces a single level of lifting, every time it is used, and every constructor is completely lazy. Unless you use bangs. So both options are available, and that essentially is what defines Haskell as being a non-strict language. Functions have the same issue --- in the presence of seq, undefined / = const undefined. Right. I am becoming increasingly convinced that the seq issue is a red herring. Extensionality is a key part of the definition of all of these constructions. The categorical rules are designed to require, in concrete categories, that the range of the two injections into a coproduct form a partition of the coproduct, the surjective pairing law (fst x, snd x) = x holds, and the eta reduction law (\ x - f x) = f holds. Haskell flaunts all three; while some categories have few enough morphisms to get away with this (at least some times), Hask is not one of them. That interpretation is not something that is essential in the notion of category, only in certain specific examples of categories that you know. Product and coproduct in any given category - whether they exist, what they are like if they exist, and what alternative constructions exist if they do not - reflect the nature of the structure that the category is modeling. I am interested in understanding the category Hask that represents what Haskell really is like as a programming language. Not under some semantic mapping that includes non-computable functions, and that forgets some of the interesting structure that comes from laziness (though that is undoubtably also very interesting). -Yitz ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] US Homeland Security program language security risks
Hi, Andrew Coppin wrote: Galchin Vasili wrote: Hello, https://buildsecurityin.us-cert.gov/daisy/bsi/articles/knowledge/coding/295.html I stumbled across this page. It seems that Haskell and other strongly typed functional languages like Ml/OCaml will fare much, much better, e.g. buffer overrun. Thoughts . comments. Human kind has yet to design a programming language which eliminates all possible bugs. ;-) And we never will. See http://en.wikipedia.org/wiki/Halting_problem . Greetings, Mads ___ 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] US Homeland Security program language security risks
Am Sonntag, 6. Januar 2008 14:27 schrieb Mads Lindstrøm:
Hi,
Andrew Coppin wrote:
Galchin Vasili wrote:
Hello,
https://buildsecurityin.us-cert.gov/daisy/bsi/articles/knowledge/coding
/295.html
I stumbled across this page. It seems that Haskell and other strongly
typed functional languages like Ml/OCaml will fare much, much better,
e.g. buffer overrun. Thoughts . comments.
Human kind has yet to design a programming language which eliminates all
possible bugs. ;-)
And we never will. See http://en.wikipedia.org/wiki/Halting_problem .
Greetings,
Mads
Just because I don't know:
what bugs would be possible in a language having only the instruction
return ()
(';' for imperative programmers)?
Cheers,
Daniel
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Re: [Haskell-cafe] US Homeland Security program language security risks
Mads Lindstrøm wrote: Hi, Andrew Coppin wrote: Human kind has yet to design a programming language which eliminates all possible bugs. ;-) And we never will. Quite so. How can a machine possibly tell whether a given behaviour is a bug or an intended behaviour? This is impossible. ;-) ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] US Homeland Security program language security risks
Daniel Fischer wrote: Just because I don't know: what bugs would be possible in a language having only the instruction return () Bug #1: You cannot write any nontrivial programs. ;-) ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: US Homeland Security program language security risks
Daniel Fischer [EMAIL PROTECTED] wrote:
Just because I don't know:
what bugs would be possible in a language having only the instruction
return ()
(';' for imperative programmers)?
/me waves meaningful with his hand.
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Re: [Haskell-cafe] Basic question concerning the category Hask (was: concerning data constructors)
I wrote: ...it was recently claimed on this list that tuples are not products in that category. Derek Elkins wrote: Johnathan has given such a demonstration (and it has been demonstrated many times on this list since it's creation, it's well-known). We're still working on it. I've not been convinced yet. Sorry about my thickness. Perhaps this should be on a nice wiki page somewhere. I tried to convince David House to put it in the Wikibook chapter, but he is right, that needs to simpler. There is some discussion on the talk page for that chapter, but no one spells out the details there, either. You are right not to be impressed by such complaints, but you misrepresent people's views on this by saying that they worry about such problems. Sorry, I hope I am not misrepresenting anyone. I just notice that people make assumptions about a so-called category Hask, derive various conclusions, then mention that they are not really true. Perhaps it is only me who is worried. As you say (people say), these properties [that Hask is cartesian closed to start] would be nice to have and are very convenient to assume which is often safe enough. I'd like to understand better what is true, so that I can understand what is safe. Certainly computer scientists of a categorical bent have developed (weaker) notions to use; namely, monoidal, pre-monoidal, Freyd, and/or kappa categories and no doubt others. Using these, however, removes some of the allure of using a categorical approach. It would be nice to distill out of that the basics that are needed to get the properties that we need for day-to-day work in Haskell. Also, there is a Haskell-specific problem at the very get-go. The most obvious choice for the categorical composition operator assuming the obvious choice for the arrows and objects does not work... ...This can easily be fixed by making the categorical (.) strict in both arguments and there is no formal problem with it being different from Haskell's (.), but it certainly is not intuitively appealing. I'm not sure it's so bad. First of all, not only is it not a formal problem, it's also not really a practical problem - there will rarely if ever be any difference between the two when applied in real programs. My opinion is that there would not be any problem with using that version as (.) in the Prelude. Even if we never do, at least we should then use (.!) when we state the so-called Monad laws. It bothers me that Haskell's so-called monads really aren't. That is bound to cause problems. And it would be so easy to fix in most cases - just require monad bind to be strict on the second parameter. Thanks, Yitz ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: US Homeland Security program language security risks
Mads Lindstrøm wrote: Andrew Coppin wrote: Human kind has yet to design a programming language which eliminates all possible bugs. ;-) And we never will. See http://en.wikipedia.org/wiki/Halting_problem . If you limit usage of general recursion (and rather favor structural recursion) then you can mitigate the halting problem. But there always will be specification bugs (when one implenetes something else than what was needed). Peter. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] US Homeland Security program language security risks
Am Sonntag, 6. Januar 2008 15:18 schrieb Andrew Coppin: Daniel Fischer wrote: Just because I don't know: what bugs would be possible in a language having only the instruction return () Bug #1: You cannot write any nontrivial programs. ;-) That's not a bug, that's a feature. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: US Homeland Security program language security risks
Daniel Fischer [EMAIL PROTECTED] wrote: Am Sonntag, 6. Januar 2008 15:18 schrieb Andrew Coppin: Daniel Fischer wrote: Just because I don't know: what bugs would be possible in a language having only the instruction return () Bug #1: You cannot write any nontrivial programs. ;-) That's not a bug, that's a feature. That's an interesting task: Design a non-touring complete, restricted language in which every expression is decidable, without making the language unusable for usual programming problems. -- (c) this sig last receiving data processing entity. Inspect headers for past copyright information. All rights reserved. Unauthorised copying, hiring, renting, public performance and/or broadcasting of this signature prohibited. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: US Homeland Security program blahBlah...
Peter Hercek writes: Andrew Coppin wrote: Human kind has yet to design a programming language which eliminates all possible bugs. ;-) ...you can mitigate the halting problem. But there always will be specification bugs (when one implenetes something else than what was needed). Look, you are descending an infinite ramp to conceptual hell, the hell of triviality. Now, you will discuss what is needed, and from FP we get into politics! But, if it is something you need... Read then the passage of Earthsea of Ursula LeGuin. There is something about a language in which YOU COULD NOT LIE. It was the ancient tongue of dragons. Now we see why the dragons are extinct... They were incompatible with the Democracy, AND with Computing Technology... Jerzy Karczmarczuk ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: US Homeland Security program language security risks
Achim Schneider wrote: That's an interesting task: Design a non-touring complete, restricted language in which every expression is decidable, without making the language unusable for usual programming problems. Have a look about dependently typed languages like Epigram: http://www.e-pig.org/ Regards, apfelmus ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: US Homeland Security program language security risks
Am Sonntag, 6. Januar 2008 15:54 schrieb Achim Schneider: Daniel Fischer [EMAIL PROTECTED] wrote: Am Sonntag, 6. Januar 2008 15:18 schrieb Andrew Coppin: Daniel Fischer wrote: Just because I don't know: what bugs would be possible in a language having only the instruction return () Bug #1: You cannot write any nontrivial programs. ;-) That's not a bug, that's a feature. That's an interesting task: Design a non-touring complete, restricted language in which every expression is decidable, without making the language unusable for usual programming problems. I'm not a logician, but didn't Gödel prove that you couldn't express the (full) arithmetic of natural numbers in such a language? Of course it might be possible to express a sufficiently interesting part of it, but I should be surprised. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: US Homeland Security program language security risks
On Sun, 06 Jan 2008 17:19:31 +0200, Daniel Fischer [EMAIL PROTECTED] wrote: Am Sonntag, 6. Januar 2008 15:54 schrieb Achim Schneider: Daniel Fischer [EMAIL PROTECTED] wrote: Am Sonntag, 6. Januar 2008 15:18 schrieb Andrew Coppin: Daniel Fischer wrote: Just because I don't know: what bugs would be possible in a language having only the instruction return () Bug #1: You cannot write any nontrivial programs. ;-) That's not a bug, that's a feature. That's an interesting task: Design a non-touring complete, restricted language in which every expression is decidable, without making the language unusable for usual programming problems. I'm not a logician, but didn't Gödel prove that you couldn't express the (full) arithmetic of natural numbers in such a language? Of course it might be possible to express a sufficiently interesting part of it, but I should be surprised. Neither do I, but if you have non turing algorithms, maybe you could do it. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: Basic question concerning the category Hask (was: concerning data constructors)
Yitzchak Gale wrote: I wrote: ...it was recently claimed on this list that tuples are not products in that category. I've not been convinced yet. I'm going to try convince you :) The crucial problem of Haskell's product is that (_|_,_|_) ≠ _|_ but that the two projections fst :: (A,B) - A snd :: (A,B) - B cannot distinguish between both values. But if (,) were a categorial product, fst and snd would completely determine it. We would have the universal property that for every f :: C - A g :: C - B there is a _unique_ morphism f g :: C - (A,B) subject to f = fst . (f g) g = snd . (f g) In other words, there is a unique function () :: forall c . (c - A) - (c - B) - (c - (A,B)) f g = \c - (f c, g c) In the particular case of C=(A,B), f=fst and g=snd , the identity function is such a morphism which means fst snd = id due to uniqueness. But id _|_ ≠ id (_|_,_|_) while clearly (fst snd) _|_ = (fst snd) (_|_,_|_) Derek Elkins wrote: Also, there is a Haskell-specific problem at the very get-go. The most obvious choice for the categorical composition operator assuming the obvious choice for the arrows and objects does not work... ...This can easily be fixed by making the categorical (.) strict in both arguments and there is no formal problem with it being different from Haskell's (.), but it certainly is not intuitively appealing. Note that the problem with (.) is seq's fault (pun intended :) Otherwise, it would be impossible to distinguish _|_ from its eta-expansion \x._|_ . Regards, apfelmus ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: US Homeland Security program language security risks
On Sun, 2008-01-06 at 16:19 +0100, Daniel Fischer wrote: Am Sonntag, 6. Januar 2008 15:54 schrieb Achim Schneider: Daniel Fischer [EMAIL PROTECTED] wrote: Am Sonntag, 6. Januar 2008 15:18 schrieb Andrew Coppin: Daniel Fischer wrote: Just because I don't know: what bugs would be possible in a language having only the instruction return () Bug #1: You cannot write any nontrivial programs. ;-) That's not a bug, that's a feature. That's an interesting task: Design a non-touring complete, restricted language in which every expression is decidable, without making the language unusable for usual programming problems. I'm not a logician, but didn't Gödel prove that you couldn't express the (full) arithmetic of natural numbers in such a language? Of course it might be possible to express a sufficiently interesting part of it, but I should be surprised. What Goedel meant by arithmetic is a bit more than one usually associates with the term. One person mentioned Epigram. Most theorem provers and most? (of the few) dependently typed programming languages would fit Achim's criterion depending on the range of usable and usual. Coq, for example, is likely to be capable of formalizing just about anything you'd want. Of course, there is one class of programming problem that we can already say can't be handled; namely implementing interpreters (for Turing complete languages). We can formalize analyses, make compilers, prove the compilers correct with respect to a semantics, and even prove that a -description- of an interpreter correctly implements the semantics, but we can't actually -run- the interpreter. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: US Homeland Security program language security risks
On 2008.01.06 15:54:00 +0100, Achim Schneider [EMAIL PROTECTED] scribbled 0.6K characters: Daniel Fischer [EMAIL PROTECTED] wrote: Am Sonntag, 6. Januar 2008 15:18 schrieb Andrew Coppin: Daniel Fischer wrote: Just because I don't know: what bugs would be possible in a language having only the instruction return () Bug #1: You cannot write any nontrivial programs. ;-) That's not a bug, that's a feature. That's an interesting task: Design a non-touring complete, restricted language in which every expression is decidable, without making the language unusable for usual programming problems. Total functional programming, yay: http://lambda-the-ultimate.org/node/2003. -- gwern $ Majic shaped Grove infrastructure Spoke BOSS mercur SEIDM BX pgpvu78AlgsIx.pgp Description: PGP signature ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Basic question concerning the category Hask (was: concerning data constructors)
Take the ordinary disjoint union, and then add a new _|_ element, distinct from both existing copies of _|_ (which are still distinct from each other). Now why is that not the category-theoretic coproduct? h . Left = f and h . Right = g both for _|_ and for finite elements of the types. And it looks universal to me. Yeah, but there could be more functions from Either X Y to Z than pairs of functions from X to Z and from Y to Z. For example, if z :: Z, then you have two functions h1 and h2 such that h1 . Left = const z and h1 . Right = const z and the same holds for h2. Namely, h1 = const z h2 = either (const z) (const z) This functions are different : h1 (_|_) = z while h2 (_|_) = (_|_). And if Either X Y was a category-theoretic coproduct, then the function from Either X Y to Z would be UNIQUELY determined by it's restrictions to X and Y. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Wikipedia on first-class object
On 6 Jan 2008, at 3:02 AM, Derek Elkins wrote: On Fri, 2007-12-28 at 17:54 -0600, Jonathan Cast wrote: Programming languages are generally classified into three groups, imperative, functional, and logical. The difference is in the style of programming encouraged (or mandated, for older languages) by the language. Usually the divide is imperative v. declarative with the four major paradigms (procedural, OO and logic, FP respectively) being subgroups of those divisions. And your explanation of this classification is? I find the term `declarative' to be almost completely meaningless. jcc ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Is there anyone out there who can translate C# generics into Haskell?
On 6 Jan 2008, at 2:13 AM, Achim Schneider wrote: Jonathan Cast [EMAIL PROTECTED] wrote: On 4 Jan 2008, at 2:00 AM, Nicholls, Mark wrote: You may be right...but learning is not an atomic thingwherever I start I will get strange things happening. The best place to start learning Haskell is with the simplest type features, not the most complicated. And it's the simplest features that are most unlike OO. Yes, Haskell will be `strange'. But if you think you're `the intersection' between Haskell and OO, you'll think things are familiar, and you'll be surprised when they turn out to be different. I'd concentrate on watching out for differences --- but then I can't imagine how finding `familiar' ideas would help. just a sec... things like C++ translated into Haskell come to mind. But then this has more to do with Monads than with classes. IO, in particular, and GL and GLUT, which are state machines and thus predestined for OOP. Your example is very unintuitive and unidiomatic Haskell. The reference to GL makes me think this is for a `low-level' binding to an imperative library, no? Those are scarcely good places to learn Haskell. jcc ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Basic question concerning the category Hask (was: concerning data constructors)
On 6 Jan 2008, at 3:55 AM, Yitzchak Gale wrote: I wrote: What goes wrong with finite coproducts? The obvious thing to do would be to take the disjoint union of the sets representing the types, identifying the copies of _|_. Jonathan Cast wrote: This isn't a coproduct. If we have f x = 1 and g y = 2, then there should exist a function h such that h . Left = f and h . Right = g... But by your rule, Left undefined = Right undefined... Which is a contradiction... OK, thanks. Unless, of course, your require your functions to be strict --- then both f and g above become illegal, and repairing them removes the problem. You don't have to make them illegal - just not part of your notion of coproduct. We're talking past each other --- what is the distinction you are making? jcc ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Basic question concerning the category Hask (was: concerning data constructors)
On 6 Jan 2008, at 5:32 AM, Yitzchak Gale wrote: (sorry, I hit the send button) What is the lifted version you are referring to? Take the ordinary disjoint union, and then add a new _|_ element, distinct from both existing copies of _|_ (which are still distinct from each other). Now why is that not the category-theoretic coproduct? h . Left = f and h . Right = g both for _|_ and for finite elements of the types. And it looks universal to me. Not quite. The only requirement for h _|_ is that it be = f x for all x and = g y for all y. If f x = 1 = g y for all x, y, then both h _|_ = _|_ and h _|_ = 1 are arrows of the category. So the universal property still fails. Of course, Haskell makes things even worse by lifting the product and exponential objects, OK, what goes wrong there, and what is the lifting? Again, in Haskell, (_|_, _|_) /= _|_. The difference is in the function f (x, y) = 1 which gives f undefined = undefined but f (undefined, undefined) = 1. I don't get that one. Given any f and g, we define h x = (f x, g x). Why do we not have fst . h = f and snd . h = g, both in Hask and StrictHask? fst and snd are strict. Again, if f and g are both strict, we have a choice for h _|_ --- either h _|_ = _|_ or h _|_ = (_|_, _|_) will work (fst . h = f and snd . h = g), but again these are different morphisms. Unfortunately, this means that (alpha, beta) has an extra _|_ element (_|_, _|_), so it's not the categorical product (which would lack such an element for the same reason as above). The reason you can't adjoin an extra element to (A,B) in, say, Set, is that you would have nowhere to map it under fst and snd. But here that is not a problem, _|_ goes to _|_ under both. This is partly an implementation issue --- compiling pattern matching without introducing such a lifting requires a parallel implementation That's interesting. So given a future platform where parallelizing is much cheaper than it is today, we could conceivably have a totally lazy version of Haskell. I wonder what it would be like to program in that environment, what new problems would arise and what new techniques would solve them. Sounds like a nice research topic. Who is working on it? --- and partly a semantic issue --- data introduces a single level of lifting, every time it is used, and every constructor is completely lazy. Unless you use bangs. So both options are available, and that essentially is what defines Haskell as being a non-strict language. (!alpha, !beta) isn't a categorical product, either. snd (undefined, 1) = undefined with this type. Functions have the same issue --- in the presence of seq, undefined / = const undefined. Right. I am becoming increasingly convinced that the seq issue is a red herring. Care to give an explanation? Extensionality is a key part of the definition of all of these constructions. The categorical rules are designed to require, in concrete categories, that the range of the two injections into a coproduct form a partition of the coproduct, the surjective pairing law (fst x, snd x) = x holds, and the eta reduction law (\ x - f x) = f holds. Haskell flaunts all three; while some categories have few enough morphisms to get away with this (at least some times), Hask is not one of them. That interpretation is not something that is essential in the notion of category, only in certain specific examples of categories that you know. I understand category theory. I also know that the definitions used are chosen to get Set `right', which means extensionality in that case, and are then extended uniformly across all categories. This has the effect of requiring similar constructions to those in Set in other concrete categories. Product and coproduct in any given category - whether they exist, what they are like if they exist, and what alternative constructions exist if they do not - reflect the nature of the structure that the category is modeling. I understand that. I'm not sure you do. I am interested in understanding the category Hask that represents what Haskell really is like as a programming language. Good luck. Not under some semantic mapping that includes non-computable functions, and that forgets some of the interesting structure that comes from laziness (though that is undoubtably also very interesting). Bear in mind in your quest, that at the end of it you'll most likely conclude, like everyone else, that good old equational reasoning is sound for the programs you actually right at least 90% of the time (with appropriate induction principles), and complete for at least 90% of what you want to right, and go back to using it exclusively for real programming. jcc ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Newbie question related to list evaluation
Hi, I am new to functional and lazy programming languages ( that's correct, my life has been pretty pathetic so far) and am not able to understand GHC's behaviour for a particular function. Can someone help me please? I am trying to write a function which would compare two strings (from reverse) and return the position of first mismatch. This is part of the right-to-left scan of bayer-moore algorithm.. and it is essential for me to do it from reverse. Since my goal is to learn haskell, I am not using Data.ByteString. My function is as follows: matchReverse :: String - String -Int-(Bool,Int) matchReverse [] [] pos = (True,pos) matchReverse _ [] pos = (False,pos) matchReverse [] _ pos = (False,pos) matchReverse (x:xs) (y:ys) pos = let (matched,pos) = matchReverse xs ys (pos +1) in if matched then ((x==y),pos) else (False,pos) The behaviour I expected in four scenarios is as below: 1.matchReverse kapilash kapilash 0 --should return (True,0) 2.matchReverse kapilash kapilast 0 --should return (False,8) 3.matchReverse str1 str2 0 --should return (False,0) 4.matchReverse str1 str1 0 --should return (True,0) where str1 and str2 are defined as below: str1 = replicate 1000 'a' str2 = 'b':(replicate 999 'a') what confounds me is that it is able to identify the first element of the tuple in ALL the cases. Invoking fst on the each of the four calls instantly returns the expected value.(even for the cases 3 and 4 where, there are thousand elements) But it seems to go into an infinite loop while calculating the 'snd' of the tuple. Even for strings containing just one element each. can someone throw some light on this please? Why does it go into an infinite loop? Many thanks Kapilash -- I drink I am thunk. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Newbie question related to list evaluation
You have used the name 'pos' twice, for both the parameter and the returned value of the recursive call. The reason this results in an infinite loop is that in code like let x = x + 1 Haskell treats both xs to be references to the same thing, so evaluates: x = x + 1 = (x + 1) + 1 = ((x + 1) + 1) + 1 ... which results in the infinite loop. On 06/01/2008, Sai Hemanth K [EMAIL PROTECTED] wrote: Hi, I am new to functional and lazy programming languages ( that's correct, my life has been pretty pathetic so far) and am not able to understand GHC's behaviour for a particular function. Can someone help me please? I am trying to write a function which would compare two strings (from reverse) and return the position of first mismatch. This is part of the right-to-left scan of bayer-moore algorithm.. and it is essential for me to do it from reverse. Since my goal is to learn haskell, I am not using Data.ByteString. My function is as follows: matchReverse :: String - String -Int-(Bool,Int) matchReverse [] [] pos = (True,pos) matchReverse _ [] pos = (False,pos) matchReverse [] _ pos = (False,pos) matchReverse (x:xs) (y:ys) pos = let (matched,pos) = matchReverse xs ys (pos +1) in if matched then ((x==y),pos) else (False,pos) The behaviour I expected in four scenarios is as below: 1.matchReverse kapilash kapilash 0 --should return (True,0) 2.matchReverse kapilash kapilast 0 --should return (False,8) 3.matchReverse str1 str2 0 --should return (False,0) 4.matchReverse str1 str1 0 --should return (True,0) where str1 and str2 are defined as below: str1 = replicate 1000 'a' str2 = 'b':(replicate 999 'a') what confounds me is that it is able to identify the first element of the tuple in ALL the cases. Invoking fst on the each of the four calls instantly returns the expected value.(even for the cases 3 and 4 where, there are thousand elements) But it seems to go into an infinite loop while calculating the 'snd' of the tuple. Even for strings containing just one element each. can someone throw some light on this please? Why does it go into an infinite loop? Many thanks Kapilash -- I drink I am thunk. ___ 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] Newbie question related to list evaluation
On 6 Jan 2008, at 10:34 AM, Sai Hemanth K wrote: Hi, I am new to functional and lazy programming languages ( that's correct, my life has been pretty pathetic so far) and am not able to understand GHC's behaviour for a particular function. Can someone help me please? I am trying to write a function which would compare two strings (from reverse) and return the position of first mismatch. This is part of the right-to-left scan of bayer-moore algorithm.. and it is essential for me to do it from reverse. Since my goal is to learn haskell, I am not using Data.ByteString. My function is as follows: matchReverse :: String - String -Int-(Bool,Int) matchReverse [] [] pos = (True,pos) matchReverse _ [] pos = (False,pos) matchReverse [] _ pos = (False,pos) matchReverse (x:xs) (y:ys) pos = let (matched,pos) = matchReverse xs ys (pos +1) in if matched then ((x==y),pos) else (False,pos) let is always recursive in Haskell, so this is a recursive definition of pos. To break the recursion, use matchReverse (x:xs) (y:ys) pos = let (matched, pos') = matchReverse xs ys (pos + 1) in if matched then ((x==y), pos') else (False, pos') The behaviour I expected in four scenarios is as below: 1.matchReverse kapilash kapilash 0 --should return (True,0) 2.matchReverse kapilash kapilast 0 --should return (False,8) 3.matchReverse str1 str2 0 --should return (False,0) 4.matchReverse str1 str1 0 --should return (True,0) where str1 and str2 are defined as below: str1 = replicate 1000 'a' str2 = 'b':(replicate 999 'a') what confounds me is that it is able to identify the first element of the tuple in ALL the cases. Invoking fst on the each of the four calls instantly returns the expected value.(even for the cases 3 and 4 where, there are thousand elements) But it seems to go into an infinite loop while calculating the 'snd' of the tuple. Even for strings containing just one element each. can someone throw some light on this please? Why does it go into an infinite loop? Many thanks Kapilash -- I drink I am thunk. ___ 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] Newbie question related to list evaluation
On Jan 6, 2008 4:40 PM, Jonathan Cast [EMAIL PROTECTED] wrote: let is always recursive in Haskell, so this is a recursive definition of pos. To break the recursion, use matchReverse (x:xs) (y:ys) pos = let (matched, pos') = matchReverse xs ys (pos + 1) in if matched then ((x==y), pos') else (False, pos') Actually, I think he meant matchReverse (x:xs) (y:ys) pos = let (matched, pos') = matchReverse xs ys (pos + 1) in if matched then ((x==y), pos) else (False, pos') As as side note, GHC's flag -Wall would have warned about creating a variable with a name already in scope. -- Felipe. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Newbie question related to list evaluation
AAh! Thanks a ton! Hemanth K On Jan 7, 2008 12:10 AM, Rodrigo Queiro [EMAIL PROTECTED] wrote: You have used the name 'pos' twice, for both the parameter and the returned value of the recursive call. The reason this results in an infinite loop is that in code like let x = x + 1 Haskell treats both xs to be references to the same thing, so evaluates: x = x + 1 = (x + 1) + 1 = ((x + 1) + 1) + 1 ... which results in the infinite loop. On 06/01/2008, Sai Hemanth K [EMAIL PROTECTED] wrote: Hi, I am new to functional and lazy programming languages ( that's correct, my life has been pretty pathetic so far) and am not able to understand GHC's behaviour for a particular function. Can someone help me please? I am trying to write a function which would compare two strings (from reverse) and return the position of first mismatch. This is part of the right-to-left scan of bayer-moore algorithm.. and it is essential for me to do it from reverse. Since my goal is to learn haskell, I am not using Data.ByteString. My function is as follows: matchReverse :: String - String -Int-(Bool,Int) matchReverse [] [] pos = (True,pos) matchReverse _ [] pos = (False,pos) matchReverse [] _ pos = (False,pos) matchReverse (x:xs) (y:ys) pos = let (matched,pos) = matchReverse xs ys (pos +1) in if matched then ((x==y),pos) else (False,pos) The behaviour I expected in four scenarios is as below: 1.matchReverse kapilash kapilash 0 --should return (True,0) 2.matchReverse kapilash kapilast 0 --should return (False,8) 3.matchReverse str1 str2 0 --should return (False,0) 4.matchReverse str1 str1 0 --should return (True,0) where str1 and str2 are defined as below: str1 = replicate 1000 'a' str2 = 'b':(replicate 999 'a') what confounds me is that it is able to identify the first element of the tuple in ALL the cases. Invoking fst on the each of the four calls instantly returns the expected value.(even for the cases 3 and 4 where, there are thousand elements) But it seems to go into an infinite loop while calculating the 'snd' of the tuple. Even for strings containing just one element each. can someone throw some light on this please? Why does it go into an infinite loop? Many thanks Kapilash -- I drink I am thunk. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe -- I drink I am thunk. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: Is there anyone out there who can translate C# generics into Haskell?
Jonathan Cast [EMAIL PROTECTED] wrote: On 6 Jan 2008, at 2:13 AM, Achim Schneider wrote: Jonathan Cast [EMAIL PROTECTED] wrote: On 4 Jan 2008, at 2:00 AM, Nicholls, Mark wrote: You may be right...but learning is not an atomic thingwherever I start I will get strange things happening. The best place to start learning Haskell is with the simplest type features, not the most complicated. And it's the simplest features that are most unlike OO. Yes, Haskell will be `strange'. But if you think you're `the intersection' between Haskell and OO, you'll think things are familiar, and you'll be surprised when they turn out to be different. I'd concentrate on watching out for differences --- but then I can't imagine how finding `familiar' ideas would help. just a sec... things like C++ translated into Haskell come to mind. But then this has more to do with Monads than with classes. IO, in particular, and GL and GLUT, which are state machines and thus predestined for OOP. Your example is very unintuitive and unidiomatic Haskell. The reference to GL makes me think this is for a `low-level' binding to an imperative library, no? Those are scarcely good places to learn Haskell. Well, I learnt a lot, knowing GL quite well already and seeing how easy everything fit together and how easy it was to abstract things away, like stuffing a bunch of IO actions consisting of GL primitives into a map, automatically generating and managing display-lists... I don't speak C++, btw, just C and Java. You can't just take years of programming experience and then start again with calculating Fibonacci numbers, just this time implemented functionally... There's always this creepy feeling that you understand everything, although you didn't understand a thing. Shivers run down my spine when I think about how let amb = 0.2 ambm = 0.2 spec = 0.7 preservingMatrix $ do materialDiffuse FrontAndBack $= Color4 ambm ambm ambm 0.3 materialSpecular FrontAndBack $= Color4 spec spec spec 0.7 materialShininess FrontAndBack $= 50 border 30 40 (depth * 10) 0.01 True looks like in C. or, for that matter, what atrocious code gcc generates if you parametrise calls to vertex3f with functions. -- (c) this sig last receiving data processing entity. Inspect headers for past copyright information. All rights reserved. Unauthorised copying, hiring, renting, public performance and/or broadcasting of this signature prohibited. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: US Homeland Security program language security risks
That's an interesting task: Design a non-touring complete, restricted language in which every expression is decidable, without making the language unusable for usual programming problems. Well, I did something like that a few years ago - it was a sort of assembler language, allowing the programmer to, say, sort an array, but not to calculate Akkerman function. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Newbie question related to list evaluation
Felipe Lessa wrote: As as side note, GHC's flag -Wall would have warned about creating a variable with a name already in scope. *makes a mental note* I've created bugs like this far too many times... ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Quanta. Was: Wikipedia on first-class object
Derek Elkins [EMAIL PROTECTED] writes: I don't understand your point. We know what swimming is: floating and moving autonomously. You're the first one I've heard who would use the term 'swimming' for ships. (And to be pedantic, wouldn't you say that fish swim, except when they float?) The point - stolen from Dennet, I think -- is that it is not terribly relevant wheter machines can think or just, you know, float and move autonomously, forever voyaging through dark seas... For goodness sake, I have *REALLY* the impression that those guys who speak about computability of the Universe, Who is speaking about computability of the universe? This looks like a straw man to me. have the mentality of 18 century thinkers for whom the world was simple and mechanistic. Or even the mentality of people contemporary of Democritus, for whom everything reduced to some dance of atoms. Or a wave function for the Universe... So - your counterclaim is that something complex and mystic and incomprehensible cannot arise from the simple, tangible and understood? Perhaps my views are *so* 1980s, but not 18th century, I think. Why is it that we cannot design roads so that we avoid traffic jams? Don't we understand cars and asphalt? Quantum effects in the combustion engine, perhaps? More seriously, perhaps quantum enters into the equation in how the brain works, perhaps it is even necessary for thought. However, I get worried it's just another mystical mantra, a gratuitous factor that, lacking any theory about how and what it does, adds nothing to help understanding the issue. -k -- If I haven't seen further, it is by standing in the footprints of giants ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: Basic question concerning the category Hask (was: concerning data constructors)
Jonathan Cast jonathanccast at fastmail.fm writes: Extensionality is a key part of the definition of all of these constructions. The categorical rules are designed to require, in concrete categories, that the range of the two injections into a coproduct form a partition of the coproduct, the surjective pairing law (fst x, snd x) = x holds, and the eta reduction law (\ x - f x) = f holds. Haskell flaunts all three; while some categories have few enough morphisms to get away with this (at least some times), Hask is not one of them. That interpretation is not something that is essential in the notion of category, only in certain specific examples of categories that you know. I understand category theory. I also know that the definitions used are chosen to get Set `right', which means extensionality in that case, and are then extended uniformly across all categories. This has the effect of requiring similar constructions to those in Set in other concrete categories. Referring to my copy of Sheaves in Geometry and Logic, Moerdijk and Mac Lane state that in 1963 Lawvere embarked on the daring project of a purely categorical foundation of all mathematics. Did he fail? I'm probably misunderstanding what you are saying here but I didn't think you needed sets to define categories; in fact Set is a topos which has far more structure than a category. Can you be clearer what you mean by extensionality in this context? And how it relates to Set? On a broader note, I'm pleased that this discussion is taking place and I wish someone would actually write a wiki page on why Haskell isn't a nicely behaved category and what problems this causes / doesn't cause. I wish I had time. Dominic. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Quanta. Was: Wikipedia on first-class object
On Jan 6, 2008, at 15:02 , Ketil Malde wrote: More seriously, perhaps quantum enters into the equation in how the brain works, perhaps it is even necessary for thought. However, I get worried it's just another mystical mantra, a gratuitous factor that, lacking any theory about how and what it does, adds nothing to help understanding the issue. I should not get into these off-topic things... but the viewpoint that worries you is only espoused by people looking for excuses to apply their favorite mystical mantra. Quantum effects are well defined, but nonintuitive (for example, particles tunneling through a barrier). -- brandon s. allbery [solaris,freebsd,perl,pugs,haskell] [EMAIL PROTECTED] system administrator [openafs,heimdal,too many hats] [EMAIL PROTECTED] electrical and computer engineering, carnegie mellon universityKF8NH ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: Re: US Homeland Security program language security risks
Miguel Mitrofanov wrote: That's an interesting task: Design a non-touring complete, restricted language in which every expression is decidable, without making the language unusable for usual programming problems. Well, I did something like that a few years ago - it was a sort of assembler language, allowing the programmer to, say, sort an array, but not to calculate Akkerman function. P. Wadler, in his famous paper Theorems for free!, writes on page 2: Indeed, every recursive function that can be proved total in second order Peano arithmetic can be written as a term in the Girard/Reynolds calculus [...]. This includes, for instancs, Ackerman's function [...], but excludes interpreters for most languages (including the Girard/Reynolds calculus itself). BTW, another name for the Girard/Reynolds calculus is (pure) polymorphic lambda calculus; and yes, it is strongly normalizing. (Wadler cites some papers to support the above claim.) It seems there is quite a lot of interesting stuff that can be done in a language where every expression is guaranteed to terminate. Cheers Ben ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Basic question concerning the category Hask (was: concerning data constructors)
On 6 Jan 2008, at 12:27 PM, Dominic Steinitz wrote: Jonathan Cast jonathanccast at fastmail.fm writes: Extensionality is a key part of the definition of all of these constructions. The categorical rules are designed to require, in concrete categories, that the range of the two injections into a coproduct form a partition of the coproduct, the surjective pairing law (fst x, snd x) = x holds, and the eta reduction law (\ x - f x) = f holds. Haskell flaunts all three; while some categories have few enough morphisms to get away with this (at least some times), Hask is not one of them. That interpretation is not something that is essential in the notion of category, only in certain specific examples of categories that you know. I understand category theory. I also know that the definitions used are chosen to get Set `right', which means extensionality in that case, and are then extended uniformly across all categories. This has the effect of requiring similar constructions to those in Set in other concrete categories. Referring to my copy of Sheaves in Geometry and Logic, Moerdijk and Mac Lane state that in 1963 Lawvere embarked on the daring project of a purely categorical foundation of all mathematics. Did he fail? I'm probably misunderstanding what you are saying here but I didn't think you needed sets to define categories; Right. But category theory is nevertheless `backward compatible' with set theory, in the sense that the category theoretic constructions in a category satisfying ZFC will be the same constructions we are familiar with already. The category-theoretic definitions, when specialized to Set, are precise (up to natural isomorphism) definitions of the pre-existing concepts of cartesian products, functions, etc. in Set. Or, to put it another way, the category-theoretic definitions are generalizations of those pre- existing concepts to other categories. Hask has a structure that is Set-like enough that these concepts generalize very little when moving to Hask. in fact Set is a topos which has far more structure than a category. Can you be clearer what you mean by extensionality in this context? By `extensionality' I mean the equalities which follow from using standard set-theoretic definitions for functions, products, coproducts, etc. --- surjective pairing, eta-contraction, etc. My understanding is that, in fact, the category-theoretic definitions are designed to capture those equations in diagrams that can be used as definitions in arbitrary categories. It's possible to view those definitions, then, as more fundamental descriptions of the concepts than what they generalize, but the fact that they are generalizations of the ideas from Set shows up in categories similar to Set (and Hask is certainly more similar to Set than, say, Vec). jcc ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: Concurrency questions
Andrew Coppin wrote: Felipe Lessa wrote: On Jan 6, 2008 9:30 AM, Andrew Coppin [EMAIL PROTECTED] wrote: 2. I have a situation where I have a thread generating some data and putting it into a mutable array, and another thread trying to read that data. Is there a way I can make the reader thread block if it tries to read a cell that hasn't been computed yet, but not introduce too much overhead for cells that have been filled in? I am fairly sure that this is not possible with an MVar that contains the whole array. You could, however, keep the information about which elements have already been initialized in a separate data structure, for instance a set of indices (using e.g. Data.IntSet) If your thread fills the array linearly, you could maintain a variable shared by those threads that say the last cell computed, and have the read thread check that before reading. I think this wouldn't create too much overhead, although it seems like there must be something cleverer somewhere. That's just it - it fills the array in a fairly random order. (The *scanning* is, however, in linear order.) It's not a big problem - I can wait for the entire array to be filled, and then scan it. But I'd like to do both in parallel if there's a reasonably easy way to do it. I suppose an array of MVars would do it, but 1. How big is an MVar? 2. You have to take the data out of an MVar to read it. In other words, only 1 thread can read an MVar at once [by design]. This isn't truly a problem in the current case, but it's irritating in principle that I can't make it so that once the cell is written, multiple threads can read it simultaneously... I first thought that Control.Concurrent.SampleVar would be your solution but nope, reading it still makes it empty. Have you tried STM and TVar? (I mean, an array of TVars). Cheers Ben ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Wikipedia on first-class object
On Sun, 2008-01-06 at 09:45 -0800, Jonathan Cast wrote: On 6 Jan 2008, at 3:02 AM, Derek Elkins wrote: On Fri, 2007-12-28 at 17:54 -0600, Jonathan Cast wrote: Programming languages are generally classified into three groups, imperative, functional, and logical. The difference is in the style of programming encouraged (or mandated, for older languages) by the language. Usually the divide is imperative v. declarative with the four major paradigms (procedural, OO and logic, FP respectively) being subgroups of those divisions. And your explanation of this classification is? I find the term `declarative' to be almost completely meaningless. I was originally thinking of having the final sentence: There are no clear, accepted meanings for any of these terms. Many people find any, perhaps all, of the terms: functional, object oriented, imperative to be almost completely meaningless. Mostly the terms have no prescriptive meaning, but rather are defined by example. At any rate, I wasn't and didn't explain anything as that was not my intention. I was merely pointing out that your usage is against the norms and in a way similar in its disconcertingness to saying, American politics is classified into three groups, conservatives, Democrats and libertarians. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Wikipedia on first-class object
Derek Elkins writes: Jonathan Cast wrote: I find the term `declarative' to be almost completely meaningless. I was originally thinking of having the final sentence: There are no clear, accepted meanings for any of these terms. Clear, no. Accepted, yes. Let Jonathan Cast repeat that statement to people who organise conferences on Declarative Programming, or those who assembled: http://en.wikipedia.org/wiki/Declarative_programming http://burks.brighton.ac.uk/burks/foldoc/90/29.htm (or http://foldoc.org/foldoc.cgi?declarative+language) I can't see what is the purpose of all your argument... Jerzy Karczmarczuk ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: Quanta. Was: Wikipedia on first-class object
Brandon S. Allbery KF8NH wrote: On Jan 6, 2008, at 15:02 , Ketil Malde wrote: More seriously, perhaps quantum enters into the equation in how the brain works, perhaps it is even necessary for thought. However, I get worried it's just another mystical mantra, a gratuitous factor that, lacking any theory about how and what it does, adds nothing to help understanding the issue. The brain, being real, is best modeled by a final theory that physicists have not yet (noticed) written down. how the brain works appears to be though electro- and bio- chemistry, which are best modeled/described right now by quantum mechanics. There are observable quantum correlations that cannot be described by a classical theory. So long as the processes you care about (e.g. whatever the hell consciousness is) do not use these non-classical correlations then you can create a simplified model that avoids the complexity of quantum theory. I should not get into these off-topic things... but the viewpoint that worries you is only espoused by people looking for excuses to apply their favorite mystical mantra. Quantum effects are well defined, but nonintuitive (for example, particles tunneling through a barrier). Right. Even if there are some quantum correlations that are used in the brain, then you just use a more complicated mathematical model. Nothing mystical/spooky/special about it. Final note: Quantum tunneling is only surprising if you insist on thinking about particles or photons meeting some kind of impenetrable wall (made of what?). All real barriers are made of forces exerted by other particles. So the whole idea of a barrier is flawed in this regime. -- Chris ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Wikipedia on first-class object
On Sun, 2008-01-06 at 22:31 +0100, [EMAIL PROTECTED] wrote: Derek Elkins writes: Jonathan Cast wrote: I find the term `declarative' to be almost completely meaningless. I was originally thinking of having the final sentence: There are no clear, accepted meanings for any of these terms. Clear, no. Accepted, yes. That was a conjunction: clear AND accepted. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Wikipedia on first-class object
On 6 Jan 2008, at 1:31 PM, [EMAIL PROTECTED] wrote: Derek Elkins writes: Jonathan Cast wrote: I find the term `declarative' to be almost completely meaningless. I was originally thinking of having the final sentence: There are no clear, accepted meanings for any of these terms. Clear, no. Accepted, yes. Let Jonathan Cast repeat that statement to people who organise conferences on Declarative Programming, or those who assembled: http://en.wikipedia.org/wiki/Declarative_programming http://burks.brighton.ac.uk/burks/foldoc/90/29.htm (or http://foldoc.org/foldoc.cgi?declarative+language) To quote your last citation: declarative language: Any relational language or functional language. Yes, the term `declarative' means something in the sense that we can tell whether any given language is declarative or not, so I should have been more clear. To wit, I do not believe the term `declarative' has any single referent, even in the sense that the term `functional' has any single referent. I find the only similarity between Haskell and Prolog to be that neither is imperative. I can't see what is the purpose of all your argument... Granted. jcc ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Wikipedia on first-class object
On 6 Jan 2008, at 12:13 PM, Derek Elkins wrote: On Sun, 2008-01-06 at 09:45 -0800, Jonathan Cast wrote: On 6 Jan 2008, at 3:02 AM, Derek Elkins wrote: On Fri, 2007-12-28 at 17:54 -0600, Jonathan Cast wrote: Programming languages are generally classified into three groups, imperative, functional, and logical. NB: I will stipulate that most people consider imperative vs. declarative to be a further hierarchy above this division. I will even stipulate that most people consider the procedural vs. OO distinction other than a distraction :) So I should have said: programming languages may be classified into three groups, ... --- where the groups themselves are generally agreed to exist, to be mutually exclusive, and to capture the vast majority of programming languages. The difference is in the style of programming encouraged (or mandated, for older languages) by the language. Usually the divide is imperative v. declarative with the four major paradigms (procedural, OO and logic, FP respectively) being subgroups of those divisions. And your explanation of this classification is? I find the term `declarative' to be almost completely meaningless. I was originally thinking of having the final sentence: There are no clear, accepted meanings for any of these terms. Many people find any, perhaps all, of the terms: functional, object oriented, imperative to be almost completely meaningless. Mostly the terms have no prescriptive meaning, but rather are defined by example. I was trying to work within this framework. Most languages support both imperative and functional paradigms, these days; but there are patterns which are awkward in some languages and natural in others. That is what I consider the main distinction. But, while there are patterns that are natural in all (at least structured) imperative languages and no or few non-imperative ones (like while loops), I don't know of any patterns that are natural in all declarative languages. At any rate, I wasn't and didn't explain anything as that was not my intention. I was merely pointing out that your usage is against the norms As a statistical statement, this may be true. and in a way similar in its disconcertingness to saying, American politics is classified into three groups, conservatives, Democrats and libertarians. Or like saying American politics is classified into three groups, statists, Rothbardians, and Randians :) jcc ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: Quanta. Was: Wikipedia on first-class object
ChrisK [EMAIL PROTECTED] wrote: how the brain works appears to be though electro- and bio- chemistry, which are best modeled/described right now by quantum mechanics. Erm... There is this story about some military (US afair) training a neural net to detect tanks in images, I can't find the link right now. It worked, with amazing 100% accuracy. Then they threw another batch of images at the net. It worked, with devastating 50% accuracy. It turned out that in the first batch, all the pictures with tanks on them were shot in sunny weather, all the pictures without tanks were shot with cloudy sky. It's kind of claiming to understand every single program that ever has been written and ever will be written just because one understands touring-complete language X in detail. Or me claiming that I understand more than say 40% of what Jonathan says, although I do understand English. -- (c) this sig last receiving data processing entity. Inspect headers for past copyright information. All rights reserved. Unauthorised copying, hiring, renting, public performance and/or broadcasting of this signature prohibited. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Wikipedia on first-class object
On Sun, 2008-01-06 at 13:48 -0800, Jonathan Cast wrote: On 6 Jan 2008, at 1:31 PM, [EMAIL PROTECTED] wrote: Derek Elkins writes: Jonathan Cast wrote: I find the term `declarative' to be almost completely meaningless. I was originally thinking of having the final sentence: There are no clear, accepted meanings for any of these terms. Clear, no. Accepted, yes. Let Jonathan Cast repeat that statement to people who organise conferences on Declarative Programming, or those who assembled: http://en.wikipedia.org/wiki/Declarative_programming http://burks.brighton.ac.uk/burks/foldoc/90/29.htm (or http://foldoc.org/foldoc.cgi?declarative+language) To quote your last citation: declarative language: Any relational language or functional language. Yes, the term `declarative' means something in the sense that we can tell whether any given language is declarative or not, so I should have been more clear. To wit, I do not believe the term `declarative' has any single referent, even in the sense that the term `functional' has any single referent. I find the only similarity between Haskell and Prolog to be that neither is imperative. Indeed, you've discovered it. The definition of declarative is often not imperative. (Or vice versa, where, as I said earlier, these are primarily defined by example rather than some predicate.) ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Wikipedia on first-class object
Derek Elkins writes: Jonathan Cast wrote: I find the only similarity between Haskell and Prolog to be that neither is imperative. Indeed, you've discovered it. The definition of declarative is often not imperative. I disagree. Practically. (I won't discuss doctrinal matter nor linguistic hairsplitting). The relational syntax of Prolog is more universal than the functional notation, since you have logic variables and logical-non-determinism, and - thus - the possibility of making predicates where the roles of input and output parameters are not pre-assigned, - - but there is a *strong* (meaning important) functional layer within, and plenty of Prolog algorithms are expressed similarly in Lisp or in Haskell. Many non-deterministic ones have natural translation into the List monad. Some circular definitions using laziness are related to ones with non-instantiated logical variables. If you don't want to see similarities, you won't. But I assure you that I have profited enormously from tha *affinities* between functional and logic approaches, and you won't convince me that declarative is without substance. Jerzy Karczmarczuk ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Implicit parameters and Arrows/Yampa?
If I understand it correctly, implicit parameters in Haskell allow you to pass values to functions with explicitly adding a parameter to each of the functions being called (I appologize for my imperative terminology here. How would I say this correctly? Being evaluated?) The arrows always use tuples to group the input and output parameters, like: foo :: SF (Int,Int,Int) (Int,Int) foo = proc (x,y,z) - do p - cat - (x,y) q - dog - z returnA - (p,q) where cat = proc (x,y) - returnA - (x+y) dog = proc z - returnA - 10*z Suppose I don't want to explicitly pass the x and y parameters to the cat (and deeper) arrows, but make them implicit. I guess that would be impossible? I mean, I can't use implicit parameters language extension to make the arrow input parameters implicit? Thanks, Peter ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
RE: [Haskell-cafe] Wikipedia on first-class object
Jerzy wrote: The relational syntax of Prolog is more universal than the functional notation, since you have logic variables and logical-non-determinism, and Isn't this just because mathematically, a function *is* a relation, but not vice versa? A relation being just a subset of a Cartesian product of sets, while a function being a special kind of relation for which each element in the domain has exactly one image? So relations are inherently much more universal than functions, but they are not that practical to work with (for a computer and/or human?). Gee, I should not talk about math here, as you category theory guys know a thousand times more math than I do ;-) Cheers, Peter ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] GHC's dynamic linker and Windows
I recently tried the latest version of HS-PLUGINS, and it gave an error on Windows. After a bit of Googling it seemed Conal Elliot had the same problem. I reported this problem to the author. This is also (one of) the reason why I could not get YI running on Windows. Now, according to the documentation, HS-PLUGINS seems to be mainly a handy wrapper around GHC's dynamic linker and compiler. Suppose I would use GHC's dynamic linker, interpreter and compiler directly (aha GHC as a library); does this work on Windows, or are there known problems with these? Thanks, Peter ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Wikipedia on first-class object
Peter Verswyvelen writes: Jerzy wrote: The relational syntax of Prolog is more universal than the functional notation, since you have logic variables and logical-non-determinism, and Isn't this just because mathematically, a function *is* a relation, but not vice versa? A relation being just a subset of a Cartesian product of sets, while a function being a special kind of relation for which each element in the domain has exactly one image? So relations are inherently much more universal than functions, but they are not that practical to work with (for a computer and/or human?). You are right. Yes, functions are subsets of relations, and the affinity between logical and functional programming is all but accidental. But relations ARE PRACTICAL! Prolog, Mercury, etc. use them. Leda, Life ... Combined paradigms are not so exotic. Gee, I should not talk about math here, as you category theory guys know a thousand times more math than I do ;-) On the contrary, you should. Tell what is interesting for you. Don't let hairsplitters monopolize the discussion of mathematical side of Haskell. I am sick seeing that 75% of true deep discussion turns around ... sorry for the swearword - ... bottom. Jerzy Karczmarczuk ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Wikipedia on first-class object
On Sun, 2008-01-06 at 23:28 +0100, [EMAIL PROTECTED] wrote: Derek Elkins writes: Jonathan Cast wrote: I find the only similarity between Haskell and Prolog to be that neither is imperative. Indeed, you've discovered it. The definition of declarative is often not imperative. I disagree. Practically. (I won't discuss doctrinal matter nor linguistic hairsplitting). I wasn't being that serious there, though oftentimes declarative -is- used in a way that is mostly meaningless or as a buzzword. One thing I will stand by, however, is that the consensus is that declarative and imperative are meant to be exhaustive and ideally disjoint (though where to draw the line is tricky), and thus in that sense, declarative is not imperative (and, as I said originally though you elided it, vice versa.) The relational syntax of Prolog is more universal than the functional notation, since you have logic variables and logical-non-determinism, and - thus - the possibility of making predicates where the roles of input and output parameters are not pre-assigned, - - but there is a *strong* (meaning important) functional layer within, and plenty of Prolog algorithms are expressed similarly in Lisp or in Haskell. Many non-deterministic ones have natural translation into the List monad. Some circular definitions using laziness are related to ones with non-instantiated logical variables. If you don't want to see similarities, you won't. But I assure you that I have profited enormously from tha *affinities* between functional and logic approaches, and you won't convince me that declarative is without substance. declarative is often used in a way where HTML, XML and such are declarative languages. At any rate, also in the elided part of my reply, was the statement that imperative/declarative are often defined by example, and the above is just such a case (unless you have a clear definition of functional and logical). This simply defines declarative to mean functional+logical making declarative a pure name devoid of any descriptive power. To make this email constructive, however, I will propose a slightly less fuzzy criterion: namely a declarative language is one that, via the Curry-Howard correspondence(s), corresponds strongly with (a relatively standard) logic. This arguably can be used to give some oomph to the usage of the term declarative rather than it being just a name, though I'll not bother. This recovers the fact that functional and logic languages are declarative and gives a -specific- similarity. It agrees fairly well with the ordering more declarative than determined by consensus. Finally, it points the way to allowing other languages rather than not (functional or logical) = not declarative. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Implicit parameters and Arrows/Yampa?
On Sun, 2008-01-06 at 23:44 +0100, Peter Verswyvelen wrote: If I understand it correctly, implicit parameters in Haskell allow you to pass values to functions with explicitly adding a parameter to each of the functions being “called” (I appologize for my imperative terminology here. How would I say this correctly? Being “evaluated”?) No one is going to get upset if you use call, but if you'd like, the more technical term in this context is applied, instead of call f passing x, we would say apply f to x. The arrows always use tuples to group the input and output parameters, like: foo :: SF (Int,Int,Int) (Int,Int) foo = proc (x,y,z) - do p - cat - (x,y) q - dog - z returnA - (p,q) where cat = proc (x,y) - returnA - (x+y) dog = proc z - returnA - 10*z Suppose I don’t want to explicitly pass the x and y parameters to the cat (and deeper) arrows, but make them implicit. I guess that would be impossible? I mean, I can’t use implicit parameters language extension to make the arrow input parameters implicit? Implicit parameters add an extra argument to a function conceptually. What you need is to add an argument to SF which implicit parameters don't know how to do since SF is just some data structure. One way to deal with this is the way you deal with the same problem in Haskell without implicit parameters. (I never use implicit parameters). In that case you would use the Reader monad (transformer). Similarly, you can use an equivalent Reader/Environment arrow transformer. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] ANN: A triple of new packages for talking to the outside world
Over the Xmas break I made some headway on writing an RPC package
since many of the ideas that I want to play with involve such a thing
as a basic building block. However, some might find some of the
spin-off packages that I wrote along the way useful.
* binary-strict:
This is mostly a cut-n-paste job from the excellent binary package
which provides Data.Binary.Strict.Get - a monad which is a drop in
replacement for Get, but which parses strict ByteStrings and returns
an Either, thus one can parse binary data without triggering an
exception on failure.
* codec-libevent:
This parses the tagging IDL files introduced in libevent[1]
1.4.0-beta and later and can generate the Haskell code for them. These
are platform-independent structs (in the C sense) and libevent
provides the complementary C infrastructure for them. You should be
able to understand almost everything these is to know about them from
a quick example:
struct msg {
string from_name = 1;
string to_name = 2;
optional struct[kill] attack = 3;
array struct[run] run = 4;
}
[1] http://monkey.org/~provos/libevent/
* control-timeout:
This module provides simple timeouts - e.g. actions which occur after
a given number of seconds and which can be canceled. It does it in a
not-totally-stupid fashion so that you don't need to worry about
setting hundreds of them.
AGL
--
Adam Langley [EMAIL PROTECTED]
http://www.imperialviolet.org 650-283-9641
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[Haskell-cafe] Re: Wikipedia on first-class object
On 2008-01-06, Jonathan Cast [EMAIL PROTECTED] wrote: To wit, I do not believe the term `declarative' has any single referent, even in the sense that the term `functional' has any single referent. I find the only similarity between Haskell and Prolog to be that neither is imperative. Have you tried comparing Prolog to GHC's multiparameter type-classes? -- Aaron Denney -- ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: Quanta. Was: Wikipedia on first-class object
On 2008-01-06, ChrisK [EMAIL PROTECTED] wrote: Brandon S. Allbery KF8NH wrote: On Jan 6, 2008, at 15:02 , Ketil Malde wrote: More seriously, perhaps quantum enters into the equation in how the brain works, perhaps it is even necessary for thought. However, I get worried it's just another mystical mantra, a gratuitous factor that, lacking any theory about how and what it does, adds nothing to help understanding the issue. The brain, being real, is best modeled by a final theory that physicists have not yet (noticed) written down. how the brain works appears to be though electro- and bio- chemistry, which are best modeled/described right now by quantum mechanics. Quantum mechanics models these, but for most domains it's a substrate that is unnecessary -- modeling at the level of chemistry works. There are observable quantum correlations that cannot be described by a classical theory. Not in the brain. It's *way* too warm and squishy. So long as the processes you care about (e.g. whatever the hell consciousness is) do not use these non-classical correlations then you can create a simplified model that avoids the complexity of quantum theory. Right. -- Aaron Denney -- ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Wikipedia on first-class object
On 6 Jan 2008, at 4:00 PM, Aaron Denney wrote: On 2008-01-06, Jonathan Cast [EMAIL PROTECTED] wrote: To wit, I do not believe the term `declarative' has any single referent, even in the sense that the term `functional' has any single referent. I find the only similarity between Haskell and Prolog to be that neither is imperative. Have you tried comparing Prolog to GHC's multiparameter type-classes? Well, they both express relations, they both stand in opposition to more basically functional approaches, and they are interpreted at entirely different points in the program's lifetime. So I guess you could find lots of points of comparison. Similarity? I'm still not convinced. jcc ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Software Tools in Haskell
On 2007.12.12 12:51:58 -0600, Tommy M McGuire [EMAIL PROTECTED] scribbled 2.7K characters: Gwern Branwen wrote: Some of those really look like they could be simpler, like 'copy' - couldn't that simply be 'main = interact (id)'? Have you seen http://haskell.org/haskellwiki/Simple_Unix_tools? For example, 'charcount' could be a lot simpler - 'charcount = showln . length' would work, wouldn't it, for the core logic, and the whole thing might look like: main = do (print . showln . length) = getContents Similarly wordcount could be a lot shorter, like 'wc_l = showln . length . lines' (showln is a convenience function: showln a = show a ++ \n) Yes, that's absolutely true, and I am adding a section showing implementations based on interact as soon as I send this message. The reason I didn't do so before is that I was trying to (to an extent) preserve the structure of the original implementations, which means using an imperative style. Yes, I'm looking at it now. Pretty nice. Strangely, I have considerably more confidence in the imperative-ish Haskell code than I do in the imperative Pascal code, in spite of the fact that they are essentially the same. Probably this is due to the referential transparency that monadic IO preserves and that does not even enter into the picture in traditional Pascal. For example, the pseudo-nroff implementation has a giant, horrible block of a record (containing the state taken directly from KP) that is threaded through the program, but I am tolerably happy with it because I know that is the *only* state going through the program. Further, while interact could probably handle all of the filter-style programs (and if I understand correctly, could also work for the main loop of the interactive editor) If your editor is referentially transparent, I think. Something like ed or sed could be done, as long as you didn't implement any of the IO stuff (like ! for ed). and a similar function could handle the later file-reading programs, I do not see how to generalize that to the out-of-core sort program. Well, for out-of-core sort, someone several many months back posted a very neat solution using ByteStrings which iirc had performance as competitive as GNU sort's out-of-core sort [much searching later] Ah! Here we go: [Haskell-cafe] External Sort and unsafeInterleaveIO http://www.haskell.org/pipermail/haskell-cafe/2007-July/029156.html. I at least found it interesting. (Plus, interact is scary. :-D ) It's not scary! It's neat! I... I want to provide a one-liner for 'detab', but it looks impressively monstrous and I'm not sure I understand it. If you think that's bad :-) detab is one of the programs I do not like. I kept the direct translation approach up through that, but I think it really hides the simplicity there; detab copies its input to its output replacing tabs with 1-8 spaces, based on where the tab occurs in a line. The only interesting state dealt with is the count of characters on each line, but that gets hidden, not emphasized. On the other hand, I'm not looking for one-liners; I really want clarity as opposed to cleverness. Well, one-liners generally can be expanded to 2 or 3 lines if you want to add descriptive variable names. Better to start with a short version and expand it where unclear than have a long unclear one in the first place, right? One final comment: as regards run-length encoding, there's a really neat way to do it. I wrote a little article on how to do it a while ago, so I guess I'll just paste it in here. :) That *is* neat. -- Tommy M. McGuire Thanks. It took a while to write, but I never really found any place to put it up for other people to read. -- gwern GSM Submarine E. 510 ddnp building y friends RDI JCET pgpHvlS1RIXiQ.pgp Description: PGP signature ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] map/reduce example
Just going back to this, the channel issue may be solved by the
strict-concurrency package (strict Chans and MVars), and the general
problem of distributing arrays seems to be solved more thoroughly
by the data parallel array library (map, fold, scanl, filter, zip et
al), not just map and reduce?
It takes care of the problem of forking gang threads, distributing work,
and does so with a pure interface.
-- Don
bulat.ziganshin:
Hello Haskell-Cafe,
i've written small program which demonstrates how map/reduce may be
implemented in Haskell. it counts amount of words in file, splitting
it into 64kb blocks processed by two threads. their results are
combined by another two threads. how it may be made better? in
particular, is it strict in values send over channels?
{-# LANGUAGE BangPatterns #-}
import Control.Concurrent
import Control.Concurrent.Chan
import Control.Monad
import Data.IORef
import Data.ByteString.Char8 as B hiding (length)
import System.Environment
import System.IO
main = do
(file:_) - getArgs
h - openBinaryFile file ReadMode
map- newChan
reduce - newChan
result - newChan
replicateM_ 2 (forkIO$ mapThread map reduce)
replicateM_ 2 (forkIO$ reduceThread reduce result)
jobs - new 0
untilM (hIsEOF h) $ do
str - B.hGet h 65536
writeChan map str
jobs += 1
jobs' - val jobs
writeChan reduce (0,-jobs')
res - readChan result
print res
mapThread map reduce =
forever $ do
str - readChan map
let !sum = length (B.words str)
writeChan reduce (sum,1)
reduceThread reduce result =
forever $ do
(sum1,n1) - readChan reduce
(sum2,n2) - readChan reduce
let (!sum,!n) = (sum1+sum2,n1+n2)
case n of
0 - writeChan result sum
_ - writeChan reduce (sum,n)
untilM cond action = do
deny - cond
unless deny $ do
action
untilM cond action
forever action = action forever action
infixl 0 =:, +=
new = newIORef
val = readIORef
a=:b = writeIORef a b
a+=b = modifyIORef a (\a-a+b)
--
Best regards,
Bulat mailto:[EMAIL PROTECTED]
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Re: [Haskell-cafe] what does @ mean?.....
On Fri, 2007-12-28 at 09:51 -0700, Luke Palmer wrote: On Dec 28, 2007 9:35 AM, Jules Bean [EMAIL PROTECTED] wrote: In particular, adding sharing can stop something being GCed, which can convert an algorithm which runs in linear time and constant space to one which runs in linear space (and therefore, perhaps, quadratic time). I've heard of this before, but can you give an example? I don't know why they were so modest. Run the following two programs in the Haskell implementation of your choice 1) powerset [] = [[]] powerset (x:xs) = powerset xs ++ map (x:) (powerset xs) 2) powerset [] = [[]] powerset (x:xs) = xss ++ map (x:) xss where xss = powerset xs Compare it on programs such as length (powerset [1..n]) for n in the range of 20-30. Make sure you aren't doing anything important when you use the second version for larger inputs. These two programs are an extreme case of trading space for time, and an extreme case of why common subexpression elimination can be a massive pessimization. In this particular case, there is an exponential increase in the size of the live-set. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] reifying is-a
Hi, all! I guess what I am about to ask is currently impossible, but as you haskellers always manage to amaze me here it goes. Given two type classes A t and B t, I'd like to derive (two) different A t instances depending exactly on whether t is an instance of B. In other words, is it possible to define a type-level function/class IsB t f such that: IsB t HTrue = (B t) exists IsB t HFalse = otherwise? If not, is this wish intrisically pointless? Thanks in advance. Cheers, Jorge M. Pelizzoni ICMC - Universidade de São Paulo ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] PHP/code generation libraries?
jgbailey: I'm working on a project which would generate a PHP data-access layer from a Haskell model. I'm wondering what libraries might be already be available for generating PHP or other types of code. The pretty-printing library is one option. Any other suggestions? i only know of pretty printers/parsers for C. not php. -- Don ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] ANN: A triple of new packages for talking to the outside world
Adam Langley wrote: This is mostly a cut-n-paste job from the excellent binary package which provides Data.Binary.Strict.Get - a monad which is a drop in replacement for Get, but which parses strict ByteStrings and returns an Either, Ooh, nice. We could really do with an incremental version, too, which could be spoonfed chunks of bytes, and dole out values as deserialisation completes. Passing back a Left String is in some sense not much of an improvement over calling error, as if I merely doesn't have enough bytes accumulated yet, I can't restart parsing from the point the bytes ran out. Any chance you'd like to hand back a continuation instead? b ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Quanta. Was: Wikipedia on first-class object
Achim Schneider wrote: There is this story about some military (US afair) training a neural net to detect tanks in images, I can't find the link right now. It worked, with amazing 100% accuracy. Then they threw another batch of images at the net. It worked, with devastating 50% accuracy. Indeed. This is not the sort of thing you want to get wrong. http://blog.wired.com/defense/2007/10/robot-cannon-ki.html b ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
