Re: [Haskell-cafe] IO (Either a Error) question
Brandon S. Allbery KF8NH wrote: It's not a call, it's a definition as shown above. The simpler translation is: x - y becomes y = \x - (note incomplete expression; the next line must complete it) and the refutable pattern match takes place in the lambda binding. But because of the whole fail thing, instead of letting pattern match failure be caught by the lambda binding it gets handled specially beforehand, which is especially silly when in most cases fail is defined to do the same thing as the lambda binding would. I'm suggesting (as is David, I think) that a saner definition would let the lambda binding randle refutable patterns, and for something like Maybe (=) can decide how to deal with it in the usual way. Otherwise you're either using a default fail that duplicates the lambda binding, or if you want custom handling (as with Maybe and Either that propagate Nothing/Left _ respectively) you end up reimplementing part of (=) as fail, which is just dumb. +1. I've never understood what exactly the goal of 'fail'-able patterns was. It's a *solution* to the problem of pattern matching, but what is the *goal* of allowing pattern matching in the first place? What semantics is the solution trying to capture? The vast majority of code I've written or seen uses plain variables as the binding pattern, in which case the definition of (=) should handle issues like this. And in the cases where we want more than just a plain variable, we usually want to handle the exceptional branch on a case-by-case basis, so the pattern gets boiled out of the - syntax anyways. The only examples I can think of where we'd want 'fail'-able patterns are entirely pedagogical (and are insignificantly altered by not using 'fail'-able patterns). I can't think of any real code where it would actually help with clarity. -- Live well, ~wren ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Haskell and the Software design process
Rafael Cunha de Almeida wrote: I don't think that safeSecondElement is worse than secondElement. I think it's better for the program to crash right away when you try to do something that doesn't make sense. Getting the secondElement of a list with one or less elements doesn't make sense, so you are definetely doing something wrong if you expected the list to have two elements, but it doesn't. It's best that the program crashes there, than propagate the error and crash somewhere else or, worse, not crash at all and give a wrong answer. There are two different issues at stake here, one is reactive and the other is proactive. You're responding to the reactive question: how do I deal with unexpected errors when they arise? But those who argue against partial functions are usually responding to the proactive question: how do I prevent unexpected errors from arising in the first place? By allowing partial functions we allow for the introduction of unexpected errors, which then forces us to handle the reactive question of what to do when those errors show up. But if partial functions are avoided, then there are no unexpected errors (of that sort) which could ever show up. We already have to deal with bottom, that's a fact of life for general-purpose programming. But partial functions allow us to introduce bottom in new ways. When we have bottom meaning just non-termination, then we have a good idea about how we should treat it. But once we start introducing other bottoms for things like non-exhaustive pattern matching or recoverable exceptions, then it's no longer clear what exactly bottom means. This in turn makes it hard to know whether the semantics of the program match the semantics we want. In particular, I'm a fan of semantics which say my program will not crash. Sure, crashing is better than silently corrupting everything; but not crashing is better than crashing. -- Live well, ~wren ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: How efficient is read?
PEM In fact, the time you'd spend writing read instances would not PEM compare to the half hour required to learn parsec. maybe the wiki could be updated to give more clues for a newcomer. http://www.haskell.org/haskellwiki/Parsec in particular : - link 1 points to the parsec site, with an almost 10 years old documentation, for a previous major release - link 3 is broken The rest of the page is a bit terse as well. I'm really wondering what one should start reading to learn how to parse a stream in haskell. -- Paul ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Haskell and the Software design process
Gregory Crosswhite wrote: Yes, but I think that it is also important to distinguish between cases where an error is expected to be able to occur at runtime, and cases where an error could only occur at runtime *if the programmer screwed up*. Well sure, but how can you demonstrate that you (the programmer) haven't screwed up? That's the point that I'm most interested in. Certainly there is a difference between exceptional behavior at runtime (e.g., due to malformed inputs) vs programming errors. We can't stop the former without broadening the scope of the typesystem to include runtime inputs; but we can, at least idealistically, stop the latter. While complex invariants require full dependent types to capture, there are a surprising number of invariants that Haskell's type system can already capture (even without GADTs!). If you structure your code to preserve and rely on the invariant that a given list has at least two elements, then it makes sense to call secondElement because if the list doesn't have two elements then you screwed up. Furthermore, there is no way to recover from such an error because you don't necessarily know where the invariant was broken because if you did you would have expected the possibility and already fixed it. If you're structuring your code with that invariant, then why aren't you using the correct type? data AtLeastTwo a = ALT a a [a] If your response is that you use too many of the standard list functions, then write a module with ALT versions (because evidently you need one). If your response is that you convert between lists and ALT too often, then you probably need to restructure the code. At the very least you should be using a newtype and smart constructors, so that you can actually prove your invariant whenever necessary: newtype AtLeastTwo a = Hidden_ALT [a] altEnd :: a - a - AtLeastTwo a altCons :: a - AtLeastTwo a - AtLeastTwo a altList :: a - a - [a] - AtLeastTwo a fromList :: [a] - Maybe (AtLeastTwo a) toList :: AtLeastTwo a - [a] Without smart constructors or an ADT to enforce your invariants, why should you be convinced that you (the programmer) haven't messed up? The cheap and easy access to ADTs is one of the greatest benefits of Haskell over mainstream languages, don't fear them. -- Live well, ~wren ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] How efficient is read?
In fact, the time you'd spend writing read instances would not compare to the half hour required to learn parsec. And your parser will be efficient (at least, according to the guys from the parser team ;-) I agree that Read is likely to be inefficient, but the more important aspect is that it gives you no useful error message if the parse fails. Parser combinators are really rather easy to learn and use, and tend to give decent error reports when something goes wrong. In fact, if you just want Read-like functionality for a set of Haskell datatypes, use polyparse: the DrIFT tool can derive polyparse's Text.Parse class (the equivalent of Read) for you, so you do not even need to write the parser yourself! I would caution against using Parsec if your dataset is large. Parsec does not return anything until it has seen the entire input, so can use a huge amount of memory. The other day someone was observing on haskell-cafe that parsing a 9Mb XML file using a Parsec-based parser required 7Gb of memory, compared with 1.3Gb for a strict polyparse- based parser (still too much), and the happy conclusion was that the lazy polyparse variant uses a neglible amount by comparison. (Declaration of interest: I wrote polyparse.) Regards, Malcolm ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] How efficient is read?
Malcolm Wallace malcolm.wall...@cs.york.ac.uk writes: (Declaration of interest: I wrote polyparse.) For which I, for one, am grateful! (So, when are you going to release an updated version with a fixed definition of discard for the lazy parser? :p) -- Ivan Lazar Miljenovic ivan.miljeno...@gmail.com IvanMiljenovic.wordpress.com ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Would it be evil to add deriving Typeable to newtype Q?
Mike Dillon wrote: begin Ivan Lazar Miljenovic quotation: I take it you haven't had the legal problems that DrIFT had when it used to be called Derive? http://www.dcs.gla.ac.uk/~nww/Derive/History.html Looks like they stopped selling it in June 2007, at least in the UK: http://education.ti.com/educationportal/sites/UK/productDetail/uk_derive6.html The other link I found redirected to a page that didn't mention Derive™ at all. I can confirm that Derive, as a commercial product, no longer exists. [This comes from discussions with one of the original developers of Derive, as well as a developer at TI who worked on Derive until TI changed their computer algebra strategy]. Jacques ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] IO (Either a Error) question
On Sun, May 9, 2010 at 7:27 AM, wren ng thornton w...@freegeek.org wrote: The only examples I can think of where we'd want 'fail'-able patterns are entirely pedagogical (and are insignificantly altered by not using 'fail'-able patterns). I can't think of any real code where it would actually help with clarity. You're not a fan of e.g. catMaybes xs = [x | Just x - xs] or the do-notation form: catMaybes xs = do Just x - xs return x then? (I actually prefer foldr (maybe id (:)) [] but that's probably just me :) ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: How efficient is read?
On 9 May 2010 08:45, Paul R paul.r...@gmail.com wrote: [SNIP] http://www.haskell.org/haskellwiki/Parsec in particular : - link 1 points to the parsec site, with an almost 10 years old documentation, for a previous major release - link 3 is broken The rest of the page is a bit terse as well. I'm really wondering what one should start reading to learn how to parse a stream in haskell. Hi Paul The 10 year old documentation is very good though - for my taste, Parsec 2.0 is the best documented Haskell lib I've seen. If you want to parse a stream, you don't want Parsec as produces as it isn't an online parser - online meaning 'streaming' i.e. it can produce some results during the 'work' rather than a single result at the end. From the descriptions on Hackage, Parsimony and uu-parsinglib sound like better candidates; similarly one of the Polyparse modules provides an online parser. If you want to learn how to write a streaming parser, pick one of those - start work and post back to this list if/when you have problems. Remember that a non-streaming parser is simpler than a streaming one: you might want to write a version that works on short input first and your result type has to support streaming (probably best if it is a list). Also for any parser, but especially an online one you'll have to be careful to use backtracking sparingly. Best wishes Stephen ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: How efficient is read?
Stephen Tetley stephen.tet...@gmail.com writes: The 10 year old documentation is very good though - for my taste, Parsec 2.0 is the best documented Haskell lib I've seen. But does it help with Parsec-3? If you want to parse a stream, you don't want Parsec as produces as it isn't an online parser - online meaning 'streaming' i.e. it can produce some results during the 'work' rather than a single result at the end. I thought this was one of the new features in Parsec-3... -- Ivan Lazar Miljenovic ivan.miljeno...@gmail.com IvanMiljenovic.wordpress.com ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: How efficient is read?
On 9 May 2010 11:42, Ivan Lazar Miljenovic ivan.miljeno...@gmail.com wrote: If you want to parse a stream, you don't want Parsec ___ as it isn't an online parser - online meaning 'streaming' i.e. it can produce some results during the 'work' rather than a single result at the end. I thought this was one of the new features in Parsec-3... Hi Ivan Possibly? If so, maybe the authors ought to mention it in the cabal.file / package description. I know it can use bytestrings which have efficiency advantages over String, but that doesn't make it online. Best wishes Stephen ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: How efficient is read?
Stephen Tetley stephen.tet...@gmail.com writes: On 9 May 2010 11:42, Ivan Lazar Miljenovic ivan.miljeno...@gmail.com wrote: If you want to parse a stream, you don't want Parsec ___ as it isn't an online parser - online meaning 'streaming' i.e. it can produce some results during the 'work' rather than a single result at the end. I thought this was one of the new features in Parsec-3... Possibly? If so, maybe the authors ought to mention it in the cabal.file / package description. I know it can use bytestrings which have efficiency advantages over String, but that doesn't make it online. Well, RWH talks about Parsecs' input stream, so maybe I'm just confusing the terms: http://book.realworldhaskell.org/read/using-parsec.html -- Ivan Lazar Miljenovic ivan.miljeno...@gmail.com IvanMiljenovic.wordpress.com ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] mixing map and mapM ?
Pierre-Etienne Meunier wrote: This way : do times-mapM PF.getFileStatus filenames = return.(map PF.modificationTime) Or also : do times-mapM (PF.getFileStatus = (return.(PF.modificationTime))) filenames let sorted=... I do not know exactly how ghc compiles the IO monad, but it seems to me that the latter would allocate a little less. FWIW, (a = (return . f)) == (liftM f a) ~= (fmap f a) Where available, the fmap version is the most efficient. The liftM function can be less efficient since it's defined generically (namely with the bind/return definition above), whereas fmap can take advantage of knowing the specific monad it's working on. But then, not everyone defines Functor instances for their monads... -- Live well, ~wren ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: nun.haskell.org http services down?
Jason Dagit wrote: The last time I noticed it was down I made the following observations... I hope you find this info useful. That is indeed very useful. I had noticed a few times that the apache processes had not exhausted memory when the problem occurred - though usually they do exhaust memory. Your detective work is strong evidence that the memory problem is probably just another side effect of the real problem. Right now, we are in the process of moving c.h.o to a server with a more recent OS and more hardware capacity. That will take a little while, so in the meantime we are trying to use the available time most effectively by focusing mostly on server upgrade. We are hoping to keep the old server limping along in the meantime with band-aids like periodic restarts of apache. However, your work shows that this problem may not just go away by itself with the upgrade. Thanks for your help in further tracking down this problem. Let us know (possibly off list) if you have any more ideas. Regards, Yitz ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] IO (Either a Error) question
On May 9, 2010, at 06:18 , Ben Millwood wrote: On Sun, May 9, 2010 at 7:27 AM, wren ng thornton w...@freegeek.org wrote: The only examples I can think of where we'd want 'fail'-able patterns are entirely pedagogical (and are insignificantly altered by not using 'fail'-able patterns). I can't think of any real code where it would actually help with clarity. You're not a fan of e.g. catMaybes xs = [x | Just x - xs] I've always had the feeling that if I need catMaybes, I haven't thought through the data representation (or possibly manipulation) fully. -- brandon s. allbery [solaris,freebsd,perl,pugs,haskell] allb...@kf8nh.com system administrator [openafs,heimdal,too many hats] allb...@ece.cmu.edu electrical and computer engineering, carnegie mellon universityKF8NH PGP.sig Description: This is a digitally signed message part ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: How efficient is read?
On May 9, 2010, at 06:53 , Ivan Lazar Miljenovic wrote: Stephen Tetley stephen.tet...@gmail.com writes: On 9 May 2010 11:42, Ivan Lazar Miljenovic ivan.miljeno...@gmail.com wrote: If you want to parse a stream, you don't want Parsec ___ as it isn't an online parser - online meaning 'streaming' i.e. it can produce some results during the 'work' rather than a single result at the end. I thought this was one of the new features in Parsec-3... Possibly? If so, maybe the authors ought to mention it in the cabal.file / package description. I know it can use bytestrings which have efficiency advantages over String, but that doesn't make it online. Well, RWH talks about Parsecs' input stream, so maybe I'm just confusing the terms: http://book.realworldhaskell.org/read/using-parsec.html Hm. I'd understand that as referring to the fact that Parsec 3 can use arbitrary input types instead of [Char], not to streams as in stream fusion or lazy processing. -- brandon s. allbery [solaris,freebsd,perl,pugs,haskell] allb...@kf8nh.com system administrator [openafs,heimdal,too many hats] allb...@ece.cmu.edu electrical and computer engineering, carnegie mellon universityKF8NH PGP.sig Description: This is a digitally signed message part ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] mixing map and mapM ?
On May 9, 2010, at 07:18 , wren ng thornton wrote: Where available, the fmap version is the most efficient. The liftM function can be less efficient since it's defined generically (namely with the bind/return definition above), whereas fmap can take advantage of knowing the specific monad it's working on. But then, not everyone defines Functor instances for their monads... Arguably that deserves a bug report, as logically a Monad is an Applicative is a Functor (or read is a as subset of for pedantry). -- brandon s. allbery [solaris,freebsd,perl,pugs,haskell] allb...@kf8nh.com system administrator [openafs,heimdal,too many hats] allb...@ece.cmu.edu electrical and computer engineering, carnegie mellon universityKF8NH PGP.sig Description: This is a digitally signed message part ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] IO (Either a Error) question
Brandon S. Allbery KF8NH allb...@ece.cmu.edu writes: I've always had the feeling that if I need catMaybes, I haven't thought through the data representation (or possibly manipulation) fully. I've used catMaybes in several places: for example, in SourceGraph only interesting analyses are reported (e.g. if there's only one connected component, then don't bother mentioning it, as the big point is when your module has more than one component); I indicate this by having each separate analysis function returning a Maybe value and then applying catMaybes. -- Ivan Lazar Miljenovic ivan.miljeno...@gmail.com IvanMiljenovic.wordpress.com ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: Frama-C
On Sun, May 9, 2010 at 12:54 AM, Lee Pike leep...@gmail.com wrote: Tom, Have you used any of these tools? They're pretty cool. I'd be interested to hear you opinion. http://frama-c.com/ Not yet. We were considering using them for a C security-analysis, but rolled-our-own stuff in Haskell. Do you guys support ACSL or something similar? One major short comings of Frama-C is its inability to prove a formula false. As such, the tool will not return any counter examples to help with debugging. I'll ask around Galois if there's been any experience with it. Did anyone respond to your post about a Haskell interface? Negative. I'm looking into writing a bit of OCaml to dump out the Cil+ACSL stuff, which I can then read with Haskell. One thing I really like about Frama-C is its use of multiple solvers. Some work better than others, and it's very easy to see this in the gWhy GUI, as well as overall proof coverage. It would be nice to have a Haskell library where we could stream in a bunch of proof obligations and it would farm it out to different solvers, possibly running on different machines. It could also keep track of which obligations have proved true or false, so it doesn't wast time running the obligation on other solvers -- gWhy doesn't currently do this. You kind of alluded to these benefits when you recommended using SMT-LIB instead of Yices for AFV, but I didn't appreciated it until now. -Tom ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] How efficient is read?
On Sun, May 9, 2010 at 3:36 AM, Malcolm Wallace (Declaration of interest: I wrote polyparse.) Yes, I used polyparse in the VCD library. It rocks! I'll check out the DrIFT tool. Thanks. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: How efficient is read?
On 9 May 2010 13:25, Brandon S. Allbery KF8NH allb...@ece.cmu.edu wrote: [SNIP] Hm. I'd understand that as referring to the fact that Parsec 3 can use arbitrary input types instead of [Char], not to streams as in stream fusion or lazy processing. Hi Brandon Yes - that's my impression too. There is a package for Parsec iteratee package on Hackage that would presumably support for streaming (thats to say online, or synonymously - 'piecemeal' / lazy processing). However unless I could find a tutorial, I'd go with Polyparse or uu-parsinglib (Doaitse Swierstra has a tech report that gives a very detailed guide to uu-parsinglib). Best wishes Stephen ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] polyvariadic function for Applicative instances
Hi, Is it possible to have a function accept variable number of arguments, such that 'f' can be instantiated to different concrete types as f :: Applicative a = (e1 - f) - a e1 - A f f g a = pure g * a f :: Applicative a = (e1 - e2 - f) - a e1 - a e2 - A f f g a b = pure g * a * b Thanks, Xiao-Yong -- Jc/*__o/* X\ * (__ Y*/\ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Chicago Haskell Users Group Meeting Tuesday, May 11, 7PM
Hello Chicago People! The Chicago Haskell Users Group will be meeting this Tuesday, May 11, at 7PM at The Grafton. Say goodbye to Tom Tobin (our founder), and hello to Haskell world domination! The Grafton is in Lincoln Square next to the Old Town School of Folk Music, close to the Western stop on the Brown line. We will be wishing Tom Tobin goodbye as he prepares to head back to New York. Leon Smith is possibly doing a presentation on concurrency and/or circular programming. And we will have open discussion on Haskell and non-Haskell related topics. Ideally we will be sitting in the back on the couches near the fireplace, subject to availability (alas, we can't reserve them). The Grafton has free wi-fi, and great Irish food, beer, and drinks. Stay until 9PM and hear a variety of musicians playing rare and original folk music songs. http://www.thegrafton.com/ Also, be sure to join our brand new facebook group, http://www.facebook.com/group.php?gid=119966508024820 And google discussion group: http://groups.google.com/group/haskell-chicago Thanks! - jeremy ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Haskell and the Software design process
On May 9, 2010, at 1:04 AM, wren ng thornton wrote: If you're structuring your code with that invariant, then why aren't you using the correct type? I do try to use the type system as much as possible to enforce constraints. However. it is not always so simple as making sure that a list always has two elements; you might be working with some kind of complicated data structure such that if you see that it satisfies some property then if you preserved the invariant correctly then you know that a given list must have at least two elements. If your response is that you use too many of the standard list functions, then write a module with ALT versions (because evidently you need one) While, again, I do agree that it is smart to use the type system as much as possible to enforce constraints in order to avoid refutable pattern matches, I would argue that when you start creating duplicates of entire pre-existing modules towards this end then the cure may be starting to become worse that the disease. Cheers, Greg ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: Set Operations In Haskell's Type System
On May 9, 4:46 am, wren ng thornton w...@freegeek.org wrote: John Creighton wrote: On May 6, 4:30 am, Bartek Ćwikłowski paczesi...@gmail.com wrote: 2010/5/6 John Creighton johns2...@gmail.com: a isa d if their exists a b and c such that the following conditions hold: a isa subset of b, b isa c c is a subset of d This definition doesn't make sense - it's recursive, but there's no base case, unless this is some kind of co-recursion. Are you sure that subset isn't what you really want? With subset you can already ask questions such as is tabby cat an animal?. If so, my code (from hpaste) already has this (iirc isDescendentOf ). When I succeed in implementing it I'll show you the result. Anyway, some perspective (perhaps), I once asked, what is the difference between a subset and an element of a set: http://www.n-n-a.com/science/about33342-0-asc-0.html And it's truly an interesting question. Too bad it didn't get a better discussion going (from what I read of it). Though the link Peter_Smith posted looks interesting. note 1) Okay I'm aware some will argue my definitions here and if it helps I could choose new words, the only question really is, is the relationship isa which I described a useful abstraction. I think the key issue comes down to what you want to do with it. I'm not entirely sure what the intended reading is for isa subset of, but I'll assume you mean the same as is a subset of[1]. One apparent side effect of the definition above is that it collapses the hierarchy. That is, with traditional predicates for testing element and subset membership, we really do construct a hierarchy. If A `elem` B and B `elem` C, it does not follow that A `elem` C (and similar examples). But with your definition it seems like there isn't that sort of stratification going on. If the requirements are A `subset` B, B `elem` C, and C `subset` D--- well we can set C=D, and now: A `elem` D = A `subset` B B `elem` D. Depending on the ontology you're trying to construct, that may be perfectly fine, but it's certainly a nonstandard definition for elements and subsets. I don't know if this mathematical object has been worked on before, but it's not a hierarchy of sets. [1] My other, equivalent, guess would be you mean A isa (powerset B) but avoided that notation because it looks strange. -- Live well, ~wren ___ Haskell-Cafe mailing list haskell-c...@haskell.orghttp://www.haskell.org/mailman/listinfo/haskell-cafe -- You received this message because you are subscribed to the Google Groups Haskell-cafe group. To post to this group, send email to haskell-c...@googlegroups.com. To unsubscribe from this group, send email to haskell-cafe+unsubscr...@googlegroups.com. For more options, visit this group athttp://groups.google.com/group/haskell-cafe?hl=en. Keep in mind that my recent definition of is a a isa d if their exists a b and c such that the following conditions hold: a isa subset of b, b isa c c is a subset of d is distinct from the question I asked a long time ago of the difference between a set and an element. The question I asked a long time ago is largely philosophical but can have axiomatic consequences in set theory. Ignoring the philosophical meanings behind a set, both the operations of subset and element of, define a partial order. The subset relationship seems to define things that are more similar then the element of relationship. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] polyvariadic function for Applicative instances
hello, Is it possible to have a function accept variable number of arguments, such that 'f' can be instantiated to different concrete types as f :: Applicative a = (e1 - f) - a e1 - A f f g a = pure g * a f :: Applicative a = (e1 - e2 - f) - a e1 - a e2 - A f f g a b = pure g * a * b f is just a left fold over the list of arguments. I've written about such things here: http://paczesiowa.blogspot.com/2010/03/generalized-zipwithn.html regards, Bartek Ćwikłowski ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] FRP demos and tutorials page
Haskell Cafe'rs, My student and I (sometimes it's difficult to determine who is who) have struggled to understand Reactive for several months and thanks to some initial help from the Reactive list (thanks Paul C) have been able to write some demos and tutorials. Apologies for posting this to the Haskell Cafe, instead of the FRP list but we wanted to make our efforts available to a wider audience, and the experts there are the choir. We have created are a set of demos and tutorials for FRP (Conal reactive). It consists of four demos: the simple furnace, the human controlled furnace, the hybrid robot sim, and the FRP robot sim. The furnace demos both consist of a thermostat like application, in which a furnace heats up and cools down in attempt maintain a constant temperature. In the simple furnace, the goal temperature is a fixed constant, while in the human controlled furnace, the user can control the goal temperature. The robot sim demos both consist of a 3D simulation in which a robot follows the walls of an arena using a simple control algorithm. The hybrid robot sim consists of two programs, one with FRP that simulates the robot, and one GLUT program that reads piped date from the first program to display the 3D view. The FRP robot sim is a single program that simulates the same robot scenario as the first, but uses reactive GLUT and FRP to do the whole demo in reactive style. We attempted to but as much documentation in the programs as possible, as well as give an overview on the webpage about the functions we used. Please note that both of us are rather new to Haskell, and so, we may have used poor programming practices in these tutorials and demos. If you have any suggestions about them, please feel free to write to us. Website: http://www.formicite.com/dopage.php?frp/frp.html Thanks, Tom and Tony ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Why cannot ghc find a existng module ?
%pacman -Q|grep xmonad xmonad 0.9.1-4 xmonad-contrib 0.9.1-2 %%xmonad --recompile Error detected while loading xmonad configuration file: /home/sw2wolf/.xmonad/xmonad.hs xmonad.hs:20:7: Could not find module `XMonad.Layout.LayoutHints': Use -v to see a list of the files searched for. %ghc-pkg list|grep xmonad xmonad-0.9.1 xmonad-contrib-0.9.1 %pacman -Ql xmonad-contrib|grep LayoutHints xmonad-contrib /usr/lib/ghc-6.12.1/site-local/xmonad-contrib-0.9.1/XMonad/Layout/LayoutHints.hi Sincerely! - e^(π⋅i) + 1 = 0 -- View this message in context: http://old.nabble.com/Why-cannot-ghc-find-a-existng-module---tp28507704p28507704.html Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Why cannot ghc find a existng module ?
Does ghc-pkg check complain? Is the version of GHC being used the same one that was used to build xmonad-contrib? What does ghc-pkg field xmonad-contrib exposed-modules | grep LayoutHints say? On 10 May 2010 14:59, zaxis z_a...@163.com wrote: %pacman -Q|grep xmonad xmonad 0.9.1-4 xmonad-contrib 0.9.1-2 %%xmonad --recompile Error detected while loading xmonad configuration file: /home/sw2wolf/.xmonad/xmonad.hs xmonad.hs:20:7: Could not find module `XMonad.Layout.LayoutHints': Use -v to see a list of the files searched for. %ghc-pkg list|grep xmonad xmonad-0.9.1 xmonad-contrib-0.9.1 %pacman -Ql xmonad-contrib|grep LayoutHints xmonad-contrib /usr/lib/ghc-6.12.1/site-local/xmonad-contrib-0.9.1/XMonad/Layout/LayoutHints.hi Sincerely! - e^(π⋅i) + 1 = 0 -- View this message in context: http://old.nabble.com/Why-cannot-ghc-find-a-existng-module---tp28507704p28507704.html Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe -- Ivan Lazar Miljenovic ivan.miljeno...@gmail.com IvanMiljenovic.wordpress.com ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Why cannot ghc find a existng module ?
There is no any complain by ghc-pkg. %ghc-pkg field xmonad-contrib exposed-modules | grep LayoutHints XMonad.Layout.LayoutCombinators XMonad.Layout.LayoutHints Ivan Lazar Miljenovic wrote: Does ghc-pkg check complain? Is the version of GHC being used the same one that was used to build xmonad-contrib? What does ghc-pkg field xmonad-contrib exposed-modules | grep LayoutHints say? On 10 May 2010 14:59, zaxis z_a...@163.com wrote: %pacman -Q|grep xmonad xmonad 0.9.1-4 xmonad-contrib 0.9.1-2 %%xmonad --recompile Error detected while loading xmonad configuration file: /home/sw2wolf/.xmonad/xmonad.hs xmonad.hs:20:7: Could not find module `XMonad.Layout.LayoutHints': Use -v to see a list of the files searched for. %ghc-pkg list|grep xmonad xmonad-0.9.1 xmonad-contrib-0.9.1 %pacman -Ql xmonad-contrib|grep LayoutHints xmonad-contrib /usr/lib/ghc-6.12.1/site-local/xmonad-contrib-0.9.1/XMonad/Layout/LayoutHints.hi Sincerely! - e^(π⋅i) + 1 = 0 -- View this message in context: http://old.nabble.com/Why-cannot-ghc-find-a-existng-module---tp28507704p28507704.html Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe -- Ivan Lazar Miljenovic ivan.miljeno...@gmail.com IvanMiljenovic.wordpress.com ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe - e^(π⋅i) + 1 = 0 -- View this message in context: http://old.nabble.com/Why-cannot-ghc-find-a-existng-module---tp28507704p28507747.html Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Why cannot ghc find a existng module ?
(Note that this really should be on the xmonad mailing list, but anyway...).
On 10 May 2010 15:09, zaxis z_a...@163.com wrote:
There is no any complain by ghc-pkg.
%ghc-pkg field xmonad-contrib exposed-modules | grep LayoutHints
XMonad.Layout.LayoutCombinators XMonad.Layout.LayoutHints
Try rm ~/.xmonad/xmonad.{hi,o} and then xmonad --recompile again.
--
Ivan Lazar Miljenovic
ivan.miljeno...@gmail.com
IvanMiljenovic.wordpress.com
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Re: [Haskell-cafe] Why cannot ghc find a existng module ?
%rm ~/.xmonad/xmonad.{hi,o}
%ls ~/.xmonad
history xmonad-i386-linux* xmonad.errors xmonad.hs
%xmonad --recompile
Error detected while loading xmonad configuration file:
/home/sw2wolf/.xmonad/xmonad.hs
xmonad.hs:20:7:
Could not find module `XMonad.Layout.LayoutHints':
Use -v to see a list of the files searched for.
Please check the file for errors.
Ivan Lazar Miljenovic wrote:
(Note that this really should be on the xmonad mailing list, but
anyway...).
On 10 May 2010 15:09, zaxis z_a...@163.com wrote:
There is no any complain by ghc-pkg.
%ghc-pkg field xmonad-contrib exposed-modules | grep LayoutHints
XMonad.Layout.LayoutCombinators XMonad.Layout.LayoutHints
Try rm ~/.xmonad/xmonad.{hi,o} and then xmonad --recompile again.
--
Ivan Lazar Miljenovic
ivan.miljeno...@gmail.com
IvanMiljenovic.wordpress.com
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-
e^(π⋅i) + 1 = 0
--
View this message in context:
http://old.nabble.com/Why-cannot-ghc-find-a-existng-module---tp28507704p28507878.html
Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com.
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Re: [Haskell-cafe] Why cannot ghc find a existng module ?
I suggest you either go on #xmonad and ask the people there, or send
an email to the xmonad mailing list with your config attached.
On 10 May 2010 15:37, zaxis z_a...@163.com wrote:
%rm ~/.xmonad/xmonad.{hi,o}
%ls ~/.xmonad
history xmonad-i386-linux* xmonad.errors xmonad.hs
%xmonad --recompile
Error detected while loading xmonad configuration file:
/home/sw2wolf/.xmonad/xmonad.hs
xmonad.hs:20:7:
Could not find module `XMonad.Layout.LayoutHints':
Use -v to see a list of the files searched for.
Please check the file for errors.
Ivan Lazar Miljenovic wrote:
(Note that this really should be on the xmonad mailing list, but
anyway...).
On 10 May 2010 15:09, zaxis z_a...@163.com wrote:
There is no any complain by ghc-pkg.
%ghc-pkg field xmonad-contrib exposed-modules | grep LayoutHints
XMonad.Layout.LayoutCombinators XMonad.Layout.LayoutHints
Try rm ~/.xmonad/xmonad.{hi,o} and then xmonad --recompile again.
--
Ivan Lazar Miljenovic
ivan.miljeno...@gmail.com
IvanMiljenovic.wordpress.com
___
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-
e^(π⋅i) + 1 = 0
--
View this message in context:
http://old.nabble.com/Why-cannot-ghc-find-a-existng-module---tp28507704p28507878.html
Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com.
___
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--
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ivan.miljeno...@gmail.com
IvanMiljenovic.wordpress.com
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