Re: [Haskell-cafe] Blocking IO FIFOs
From Jason Dusek jason.du...@gmail.com, ... If I could somehow arrange to detect EOF when /tmp/exitpipe is closed, then I might as well redirect 1 and 2 to FIFOs and wait for them to EOF, collecting the output. However, all of my experiments suggest that there is simply no way in Haskell to detect the closing of the write end of a FIFO. With `openFileBlocking', one can detect when a FIFO is *opened*; but not when it is closed. It looks to me like our colleague in another followup may have it working in an example. I have run into some trouble myself, with an example program demonstrating the approach I proposed. With a pre-existing named pipe, that I would just keep using, for whatever reason it worked the first time, failed the second, and so forth, working every other time. If the test program created the named pipe, it failed every time. There are probably reasons for all this, but I haven't looked very hard. That was using withFile. If I use POSIX I/O, it works fine. So it looks to me like there is indeed a way in Haskell to detect a closed FIFO, it just may not be Haskell I/O without a lot more work ironing out the possible causes of failure. I believe that doesn't need to be a problem for you, though, because 1) your application is by nature exclusive to POSIX platforms, and 2) you need the named pipe only to detect command process exit, and you can still apply Haskell I/O to the more interesting data that accumulates in the command output disk file. And there may be an answer for my problems with Haskell I/O. Could be as simple as using openFileBlocking, which apparently isn't supported in the ghc I'm using. Could have something to do with the fine points of named pipes - for example, I believe you're supposed to open them O_RDWR in situations you'd think would call for O_READONLY. (Though the latter worked for me with POSIX I/O.) While I'm here ... I share the concern expressed in an earlier followup about the outputs from bash in runInteractiveProcess. This looks like a feature of runInteractiveProcess that makes it intrinsically something like a code smell. input-only and output-only processes are commonly used and fairly tractable, where input-output processes are unusual and and fragile, so it's an unfortunate convenience. I think the idea is that you'd use createProcess specifying only the input redirection. Donn ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Blocking IO FIFOs
2012/10/21 Donn Cave d...@avvanta.com: From Jason Dusek jason.du...@gmail.com: If I could somehow arrange to detect EOF when /tmp/exitpipe is closed, then I might as well redirect 1 and 2 to FIFOs and wait for them to EOF, collecting the output. However, all of my experiments suggest that there is simply no way in Haskell to detect the closing of the write end of a FIFO. With `openFileBlocking', one can detect when a FIFO is *opened*; but not when it is closed. [...] If I use POSIX I/O, it works fine. So it looks to me like there is indeed a way in Haskell to detect a closed FIFO, it just may not be Haskell I/O without a lot more work ironing out the possible causes of failure. Sadly, I can not do Posix IO on handles or read a ByteString from a Posix FD. 2) you need the named pipe only to detect command process exit, and you can still apply Haskell I/O to the more interesting data that accumulates in the command output disk file. Writing data to disk for communicating with other processes is not a good pattern, I think. And there may be an answer for my problems with Haskell I/O. Could be as simple as using openFileBlocking, which apparently isn't supported in the ghc I'm using. Could have something to do with the fine points of named pipes - for example, I believe you're supposed to open them O_RDWR in situations you'd think would call for O_READONLY. (Though the latter worked for me with POSIX I/O.) It is okay to open it O_READONLY if blocking when there is no writer is acceptable. For this application, it is. While I'm here ... I share the concern expressed in an earlier followup about the outputs from bash in runInteractiveProcess. This looks like a feature of runInteractiveProcess that makes it intrinsically something like a code smell. input-only and output-only processes are commonly used and fairly tractable, where input-output processes are unusual and and fragile, so it's an unfortunate convenience. I think the idea is that you'd use createProcess specifying only the input redirection. I am averse to adding just in case code that may not do anything; too much system level code attains an air of mystery this way. -- Jason Dusek pgp // solidsnack // C1EBC57DC55144F35460C8DF1FD4C6C1FED18A2B ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] How do I specify language literals in hsparql?
If the raw SPARQL is rdfs:label D (programming language)@en, what would the hsparql http://hackage.haskell.org/package/hsparql syntax be? The docshttps://github.com/robstewart57/hsparql/blob/master/tests/DBPedia.hs don't include any language literal examples. -- Cheers, Andrew Pennebaker www.yellosoft.us ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Blocking IO FIFOs
On Sun, Oct 21, 2012 at 1:25 PM, Jason Dusek jason.du...@gmail.com wrote: Sadly, I can not do Posix IO on handles or read a ByteString from a Posix FD. Try the unix-bytestring package. G -- Gregory Collins g...@gregorycollins.net ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] serialize an unknown type
Nobody on this one? Here is a simplified version: data Event a where InputChoice :: a - Event a How to serialize/deserialize this? Cheers, Corentin On Sat, Oct 20, 2012 at 10:49 PM, Corentin Dupont corentin.dup...@gmail.com wrote: Hi the list! I have a simple question, how can I serialize/deserialize a structure like this: data InputChoice c deriving Typeable data Event a where InputChoice :: (Eq c, Show c) = [c] - c - Event (InputChoice c) (...) I'd like that the values of type c get serialized to a String... That's the easy part, but for deserializing, oops! Cheers, Corentin ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] serialize an unknown type
On Sun, Oct 21, 2012 at 12:39 PM, Corentin Dupont corentin.dup...@gmail.com wrote: Nobody on this one? Here is a simplified version: data Event a where InputChoice :: a - Event a How to serialize/deserialize this? How were you expecting to serialize/deserialize a function? -- brandon s allbery kf8nh sine nomine associates allber...@gmail.com ballb...@sinenomine.net unix/linux, openafs, kerberos, infrastructure http://sinenomine.net ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] serialize an unknown type
Seems like nobody really understands what is it that you want to accomplish or what your problem is. Отправлено с iPhone 21.10.2012, в 20:39, Corentin Dupont corentin.dup...@gmail.com написал(а): Nobody on this one? Here is a simplified version: data Event a where InputChoice :: a - Event a How to serialize/deserialize this? Cheers, Corentin On Sat, Oct 20, 2012 at 10:49 PM, Corentin Dupont corentin.dup...@gmail.com wrote: Hi the list! I have a simple question, how can I serialize/deserialize a structure like this: data InputChoice c deriving Typeable data Event a where InputChoice :: (Eq c, Show c) = [c] - c - Event (InputChoice c) (...) I'd like that the values of type c get serialized to a String... That's the easy part, but for deserializing, oops! Cheers, Corentin ___ 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] serialize an unknown type
Hi, Sorry if it was not enough explicit. I want to write functions like this: serialize :: (Show a) = Event a - IO () deserialize :: (Read a) = IO () - Event a The functions would write and read the data in a file, storing/retrieving also the type a I suppose... BR, C On Sun, Oct 21, 2012 at 7:03 PM, MigMit miguelim...@yandex.ru wrote: Seems like nobody really understands what is it that you want to accomplish or what your problem is. Отправлено с iPhone 21.10.2012, в 20:39, Corentin Dupont corentin.dup...@gmail.com написал(а): Nobody on this one? Here is a simplified version: data Event a where InputChoice :: a - Event a How to serialize/deserialize this? Cheers, Corentin On Sat, Oct 20, 2012 at 10:49 PM, Corentin Dupont corentin.dup...@gmail.com wrote: Hi the list! I have a simple question, how can I serialize/deserialize a structure like this: data InputChoice c deriving Typeable data Event a where InputChoice :: (Eq c, Show c) = [c] - c - Event (InputChoice c) (...) I'd like that the values of type c get serialized to a String... That's the easy part, but for deserializing, oops! Cheers, Corentin ___ 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] serialize an unknown type
On Sun, Oct 21, 2012 at 07:20:10PM +0200, Corentin Dupont wrote: Hi, Sorry if it was not enough explicit. I want to write functions like this: serialize :: (Show a) = Event a - IO () deserialize :: (Read a) = IO () - Event a The functions would write and read the data in a file, storing/retrieving also the type a I suppose... Can't you simply, when defining the type event, add a deriving (Show, Read)? Then the standard (but slow) read/show serialisation would work for you. If you're asking to de-serialise an unknown type (i.e. you don't know what type it should restore a-priori, but you want to do that based on the contents of the file), things become a little more complex. Unless you can further restrict the type 'a', really complex. Maybe stating your actual problem, rather than the implementation question, would be better? regards, iustin ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] How do I specify language literals in hsparql?
On Sun, Oct 21, 2012 at 10:41 AM, Andrew Pennebaker andrew.penneba...@gmail.com wrote: If the raw SPARQL is rdfs:label D (programming language)@en, what would the hsparql syntax be? The docs don't include any language literal examples. Have you emailed the maintainer of the package? Not all package authors subscribe to high-traffic lists like haskell-cafe. Antoine -- Cheers, Andrew Pennebaker www.yellosoft.us ___ 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] serialize an unknown type
Hi Iustin, yes I want to deserialize an unknown type based on the content of the file (in this example). Let's say I can reduce the spectum of types to: Strings, all the types in Enum, Ints. Is it possible? My real problem is that on my web interface I want to use web routes to allow a user to pass an Event back to the engine. The problem is that it seems that web-routes only accepts Strings (or some known types) to be passed on the web route, whereas I need to pass random types. On Sun, Oct 21, 2012 at 8:00 PM, Iustin Pop iu...@k1024.org wrote: On Sun, Oct 21, 2012 at 07:20:10PM +0200, Corentin Dupont wrote: Hi, Sorry if it was not enough explicit. I want to write functions like this: serialize :: (Show a) = Event a - IO () deserialize :: (Read a) = IO () - Event a The functions would write and read the data in a file, storing/retrieving also the type a I suppose... Can't you simply, when defining the type event, add a deriving (Show, Read)? Then the standard (but slow) read/show serialisation would work for you. If you're asking to de-serialise an unknown type (i.e. you don't know what type it should restore a-priori, but you want to do that based on the contents of the file), things become a little more complex. Unless you can further restrict the type 'a', really complex. Maybe stating your actual problem, rather than the implementation question, would be better? regards, iustin ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] serialize an unknown type
Oh, now I've got it. First of all, functions of type IO () - Event a are impossible (unless you resort to tricks with unsafePerformIO, which is not what you want to deal with right now). You've probably meant something like IO (Event a) (at least, that is the type of function which would read Event a from file or input stream or something else external). Secondly, functions (and values) with parametric types, like IO (Event a) require you to provide the type a in your code. They won't take it from somewhere magically. You can take a look at the read function in Prelude for example. If you really want to store the type information and read it back, you should do it yourself, inventing some representation for your type, writing it to disk, reading back and parsing it. And you can't do that for all types in existence, so you'll need to do that for some specific types (and no, instances of Typeable aren't what you want). And you'll have to deal with type system, which won't allow you to just say hey, let that be whatever type it happens to be, I don't care; you'd have to wrap this into one existentially quantified type (or GADT). Keep in mind that this is not very Haskell-y. First of all, try to analyse, what this a in Event a could be. What are the limits here? And don't say there aren't any, because if you don't know anything about the type, you can't do anything with it. So, maybe you would end up with a finite set of types — this would simplify matters a lot. Or maybe you'd find out that there are inifinitely many types of events — but they can be somehow generated with a finite number of constructors — that would be quite simple as well. So, what is the bigger picture here? On Oct 21, 2012, at 9:20 PM, Corentin Dupont corentin.dup...@gmail.com wrote: Hi, Sorry if it was not enough explicit. I want to write functions like this: serialize :: (Show a) = Event a - IO () deserialize :: (Read a) = IO () - Event a The functions would write and read the data in a file, storing/retrieving also the type a I suppose... BR, C On Sun, Oct 21, 2012 at 7:03 PM, MigMit miguelim...@yandex.ru wrote: Seems like nobody really understands what is it that you want to accomplish or what your problem is. Отправлено с iPhone 21.10.2012, в 20:39, Corentin Dupont corentin.dup...@gmail.com написал(а): Nobody on this one? Here is a simplified version: data Event a where InputChoice :: a - Event a How to serialize/deserialize this? Cheers, Corentin On Sat, Oct 20, 2012 at 10:49 PM, Corentin Dupont corentin.dup...@gmail.com wrote: Hi the list! I have a simple question, how can I serialize/deserialize a structure like this: data InputChoice c deriving Typeable data Event a where InputChoice :: (Eq c, Show c) = [c] - c - Event (InputChoice c) (...) I'd like that the values of type c get serialized to a String... That's the easy part, but for deserializing, oops! Cheers, Corentin ___ 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] serialize an unknown type
You can include the type in the serialized string. When recovering you can read the type and use to look for the appropriate deserializer in a lookup table where you have registered the deserializer. I use this trick in the IDynamic package,. that serializes-deserializes dynamic types: http://hackage.haskell.org/package/IDynamic-0.1 2012/10/20 Corentin Dupont corentin.dup...@gmail.com Hi the list! I have a simple question, how can I serialize/deserialize a structure like this: data InputChoice c deriving Typeable data Event a where InputChoice :: (Eq c, Show c) = [c] - c - Event (InputChoice c) (...) I'd like that the values of type c get serialized to a String... That's the easy part, but for deserializing, oops! Cheers, Corentin ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe -- Alberto. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] serialize an unknown type
On Sun, Oct 21, 2012 at 08:11:50PM +0200, Corentin Dupont wrote: Hi Iustin, yes I want to deserialize an unknown type based on the content of the file (in this example). Let's say I can reduce the spectum of types to: Strings, all the types in Enum, Ints. Is it possible? Maybe :) I don't know how to do all the types in enum. For Strings, Ints and Float, you could have something like: serialise a pair instead of just the type, and decode: data Event = EventString String | EventInt Int | EventFloat Float … (kind, val) - read in_data return $ case kind of string - EventString val int - EventInt (read val) float - EventFloat (read val) But this is only for a very few specific types. My real problem is that on my web interface I want to use web routes to allow a user to pass an Event back to the engine. The problem is that it seems that web-routes only accepts Strings (or some known types) to be passed on the web route, whereas I need to pass random types. Are you sure you need to pass random types? Can't you define a (large) set of known types, for example? regards, iustin On Sun, Oct 21, 2012 at 8:00 PM, Iustin Pop iu...@k1024.org wrote: On Sun, Oct 21, 2012 at 07:20:10PM +0200, Corentin Dupont wrote: Hi, Sorry if it was not enough explicit. I want to write functions like this: serialize :: (Show a) = Event a - IO () deserialize :: (Read a) = IO () - Event a The functions would write and read the data in a file, storing/retrieving also the type a I suppose... Can't you simply, when defining the type event, add a deriving (Show, Read)? Then the standard (but slow) read/show serialisation would work for you. If you're asking to de-serialise an unknown type (i.e. you don't know what type it should restore a-priori, but you want to do that based on the contents of the file), things become a little more complex. Unless you can further restrict the type 'a', really complex. Maybe stating your actual problem, rather than the implementation question, would be better? regards, iustin ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] serialize an unknown type
On Sun, Oct 21, 2012 at 8:42 PM, MigMit miguelim...@yandex.ru wrote: Oh, now I've got it. First of all, functions of type IO () - Event a are impossible (unless you resort to tricks with unsafePerformIO, which is not what you want to deal with right now). You've probably meant something like IO (Event a) (at least, that is the type of function which would read Event a from file or input stream or something else external). Yes, sorry, that's what I meant. Secondly, functions (and values) with parametric types, like IO (Event a) require you to provide the type a in your code. They won't take it from somewhere magically. You can take a look at the read function in Prelude for example. If you really want to store the type information and read it back, you should do it yourself, inventing some representation for your type, writing it to disk, reading back and parsing it. And you can't do that for all types in existence, so you'll need to do that for some specific types (and no, instances of Typeable aren't what you want). And you'll have to deal with type system, which won't allow you to just say hey, let that be whatever type it happens to be, I don't care; you'd have to wrap this into one existentially quantified type (or GADT). Keep in mind that this is not very Haskell-y. First of all, try to analyse, what this a in Event a could be. What are the limits here? And don't say there aren't any, because if you don't know anything about the type, you can't do anything with it. So, maybe you would end up with a finite set of types -- this would simplify matters a lot. Or maybe you'd find out that there are inifinitely many types of events -- but they can be somehow generated with a finite number of constructors -- that would be quite simple as well. So, what is the bigger picture here? In my application, the user can define the a. That's what makes it difficult. For example, the user can define a new enumerate and submit it to the program (it will be interpreted by hint): data Choice = You | Me | Them | Everybody deriving (Enum, Typeable, Show, Eq, Bounded) So, the list of types is not known in advance. I could ask my user to make his new type an instance of a class as suggested by Alberto... On Oct 21, 2012, at 9:20 PM, Corentin Dupont corentin.dup...@gmail.com wrote: Hi, Sorry if it was not enough explicit. I want to write functions like this: serialize :: (Show a) = Event a - IO () deserialize :: (Read a) = IO () - Event a The functions would write and read the data in a file, storing/retrieving also the type a I suppose... BR, C On Sun, Oct 21, 2012 at 7:03 PM, MigMit miguelim...@yandex.ru wrote: Seems like nobody really understands what is it that you want to accomplish or what your problem is. Отправлено с iPhone 21.10.2012, в 20:39, Corentin Dupont corentin.dup...@gmail.com написал(а): Nobody on this one? Here is a simplified version: data Event a where InputChoice :: a - Event a How to serialize/deserialize this? Cheers, Corentin On Sat, Oct 20, 2012 at 10:49 PM, Corentin Dupont corentin.dup...@gmail.com wrote: Hi the list! I have a simple question, how can I serialize/deserialize a structure like this: data InputChoice c deriving Typeable data Event a where InputChoice :: (Eq c, Show c) = [c] - c - Event (InputChoice c) (...) I'd like that the values of type c get serialized to a String... That's the easy part, but for deserializing, oops! Cheers, Corentin ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] ANN: hledger 0.19
I'm pleased to announce the release of hledger 0.19! This release has just two visible changes: a much faster balance command, and support for the latest GHC and libs. (A hledger-web update will follow.) hledger is a command-line tool and haskell library for tracking financial transactions, which are stored in a human-readable plain text format. In addition to reporting, it can also help you record new transactions, or convert CSV data from your bank. Add-on packages include hledger-web, a web interface. hledger is inspired by and compatible with John Wiegley's Ledger. For more, see http://hledger.org . Install it: cabal update; cabal install hledger . For installation help, see http://hledger.org/MANUAL.html#installing . Or, sponsor a ready-to-run binary for your platform: http://hledger.org/DOWNLOAD.html . Release notes: hledger, hledger-lib: support GHC 7.6 and latest cmdargs, haskeline, split balance report no longer has an O(n^2) slowdown with large numbers of accounts, and is generally more speedy. Benchmark on a 2010 macbook: +---++--+--++ | || hledger-0.18 | hledger-0.19 | ledger | +===++==+==++ | -f data/100x100x10.journal balance|| 0.21 | 0.07 | 0.09 | | -f data/1000x1000x10.journal balance||10.13 | 0.47 | 0.62 | | -f data/1000x1x10.journal balance||40.67 | 0.67 | 1.01 | | -f data/1x1000x10.journal balance||15.01 | 3.22 | 2.36 | | -f data/1x1000x10.journal balance aa || 4.77 | 4.40 | 2.33 | +---++--+--++ build version is set with CPP instead of cabal-file-th Release contributors: Simon Michael, Sergei Trofimovich Release stats: 106 days, 21 commits, 1 end-user fix, 0 end-user features since last release Project stats: 222 unit functional tests, 7740 lines of code including hledger-web, 21 committers___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Solving integer equations in Haskell
On Oct 17, 2012, at 3:35 AM, Justin Paston-Cooper paston.coo...@gmail.com wrote: Thanks for all the informative replies. SBV seems the simplest solution right now, and speed isn't too much of an issue here. Anything under 20 seconds per solution should be bearable. I'm happy to announce the SMT based linear equation solver library: http://hackage.haskell.org/package/linearEqSolver You can use it get solutions over Integers only, or over Rationals if so needed. Functions are provided to extract one solution, or all possible solutions (as a lazy list). The latter variant is useful for underspecified systems. Regarding performance: SMT solvers are very good at solving such equations, so aside from the overhead of calling out to an external program, it should be fairly fast. I'd expect no practical instance to come to anywhere near the 20 second limit you've mentioned. For most practical instances, the process switch overhead would dominate computation time, which should be negligible. Let me know if you find otherwise. -Levent. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
