October 2013 - Haskell-Cafe

ANNOUNCE: urembed-0.5.0.1 urxml-0.2.0.0
by Sergey Mironov 31 Oct '13

31 Oct '13

Hello. I'm glad to announce the release of Ur/Web[1] helper applications: urembed-0.5.0.1 and urxml-0.2.0.0 Ur is a programming language in the tradition of ML and Haskell, but featuring a significantly richer type system. Ur is functional, pure, statically-typed, and strict. Ur supports a powerful kind of metaprogramming based on row types. Ur/Web is Ur plus a special standard library and associated rules for parsing and optimization. Ur/Web supports construction of dynamic web applications backed by SQL databases. Uermbed and urxml are aimed at making Ur/Web development more pleasant. * Urembed https://github.com/grwlf/urembed Urembed embeds file or files into the Ur/Web project by generating the module which provides the programmer with functions serving the specified file as a binary. This way Ur/Web application no longer requires standalone webserver for serving static content. Also, Urembed supports generating JavaScript FFI signatures for *js files. https://github.com/grwlf/uru project uses urembed and may illustrate it's abilities. * UrXML https://github.com/grwlf/urxml UrXML is yet another XML parser/pretty-printer application. This time, it supports ur/web syntax extensions of XML. One can integrate this tool with VIM editor to indent XML parts of non-XML files like Ur/Web sources. Please, read README.md for the details. Regards, Sergey [1] - http://www.impredicative.com/ur/

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ICFP 2014: Call for Workshop & Co-located Event Proposals
by David Van Horn 30 Oct '13

30 Oct '13

CALL FOR WORKSHOP AND CO-LOCATED EVENT PROPOSALS ICFP 2014 19th ACM SIGPLAN International Conference on Functional Programming August 31 – September 6, 2014 Gothenburg, Sweden http://icfpconference.org/icfp2014/ The 19th ACM SIGPLAN International Conference on Functional Programming will be held in Gothenburg, Sweden on August 31-September 6, 2014. ICFP provides a forum for researchers and developers to hear about the latest work on the design, implementations, principles, and uses of functional programming. Proposals are invited for workshops (and other co-located events, such as tutorials) to be affiliated with ICFP 2014 and sponsored by SIGPLAN. These events should be less formal and more focused than ICFP itself, include sessions that enable interaction among the attendees, and foster the exchange of new ideas. The preference is for one-day events, but other schedules can also be considered. The workshops are scheduled to occur on August 31 (the day before ICFP) and September 4-6 (the three days after ICFP). ---------------------------------------------------------------------- Submission details Deadline for submission: November 15, 2013 Notification of acceptance: December 15, 2013 Prospective organizers of workshops or other co-located events are invited to submit a completed workshop proposal form in plain text format to the ICFP 2014 workshop co-chairs (Sam Tobin-Hochstadt and Tom Schrijvers), via email to icfp2014-workshops(a)ugent.be by November 15, 2013. (For proposals of co-located events other than workshops, please fill in the workshop proposal form and just leave blank any sections that do not apply.) Please note that this is a firm deadline. Organizers will be notified if their event proposal is accepted by December 15, 2013, and if successful, depending on the event, they will be asked to produce a final report after the event has taken place that is suitable for publication in SIGPLAN Notices. The proposal form is available at: http://www.icfpconference.org/icfp2014/icfp14-workshops-form.txt Further information about SIGPLAN sponsorship is available at: http://acm.org/sigplan/sigplan_workshop_proposal.htm ---------------------------------------------------------------------- Selection committee The proposals will be evaluated by a committee comprising the following members of the ICFP 2014 organizing committee, together with the members of the SIGPLAN executive committee. Workshop Co-Chair: Sam Tobin-Hochstadt (Indiana University) Workshop Co-Chair: Tom Schrijvers (Ghent University) General Chair : Johan Jeuring (Utrecht University) Program Chair: Manuel Chakravarty (University of New South Wales) ---------------------------------------------------------------------- Further information Any queries should be addressed to the workshop co-chairs (Sam Tobin-Hochstadt and Tom Schrijvers), via email to icfp2014-workshops(a)ugent.be.

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Re: [Haskell-cafe] interfacing TradeKing API
by Donn Cave 30 Oct '13

30 Oct '13

I worked up a little application for Etrade's API, which is at least the same basic idea. This was some time ago and memory is pretty fuzzy, but ... I see that for some reason I modified hoauth Consumer.hs, replacing showURL with a path-to-text function I wrote myself, and I use my own version of the signRq function from that module that returns an unpacked request value. I'm sure it would be much more helpful to say what problems I was to solving there, sorry! Authentication was the hard part, naturally. Donn

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liftN
by Wvv 30 Oct '13

30 Oct '13

I try to write a function "liftN", but I'm not satisfied with result. lift :: (MonadTrans t) => Monad m => m a -> t m a liftN n | n < 1 = error "liftN: n<1" | n == 1 = lift | otherwise = lift . (liftN (n-1)) 1) I know(?), that it is impossible to write liftN now: typechecker can't decide which signature it is. 2) Main reason is finite recursive constraint 3) Let's think, it is possible to write Main candidates: promoted data and data-kinds For example, lift . lift . lift :: (Monad (t1 (t2 m)), Monad (t2 m), Monad m, MonadTrans t, MonadTrans t1, MonadTrans t2) => m a -> t (t1 (t2 m)) a My best solution looks like: data MT = M | T Int MT liftN :: forall tm. ( forall x n. Monad 'M, Monad (x :: MT), MonadTrans ('T n), ) => Int -> 'M a -> ('T 0) (tm :: MT) a liftN n | n < 1 = error "liftN: n < 1" | n == 1 = lift | otherwise = lift . (liftN (n-1)) Am I miss something? I think this function could look much prettier. But I don't know how. -- View this message in context: http://haskell.1045720.n5.nabble.com/liftN-tp5738612.html Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com.

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interfacing TradeKing API
by Miro Karpis 30 Oct '13

30 Oct '13

Hi, did anybody tried to interface TradeKing API? (couldn't find anything on web) Cheers, m.

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fcntl locks, executeFile and threaded runtime
by diego souza 30 Oct '13

30 Oct '13

Hi, I'm having problems with executeFile as it seems to clear the advisory locks using the threaded runtime. Consider the following snippet (a simplification of what I'm doing): import System.IO import Control.Monad import System.Posix.IO import Control.Concurrent import System.Posix.Files import System.Posix.Process main = do let lock = (WriteLock, AbsoluteSeek, 0, 0) fd <- openFd "/tmp/foobar" ReadWrite (Just stdFileMode) defaultFileFlags {trunc=True} pid <- forkProcess $ do setLock fd lock >> putStrLn "child: ok" executeFile "/usr/bin/sleep" False ["5"] Nothing threadDelay $ 1 * 1000 * 1000 setLock fd lock >> putStrLn "parent: fail!" void $ getProcessStatus True False pid Then I consistentlty get these results: $ ghc -threaded --make test.hs; ./test child: ok parent: fail! $ ghc -rtsopts --make test.hs; ./test child: ok test: setLock: resource exhausted (Resource temporarily unavailable) Any pointers? At first I though it might be an issue with the unix package but that doesn't seem to be the case. $ ghc-pkg list | grep unix unix-2.6.0.1 $ ./test +RTS --info [("GHC RTS", "YES") ,("GHC version", "7.6.3") ,("RTS way", "rts_thr") ,("Build platform", "x86_64-unknown-linux") ,("Build architecture", "x86_64") ,("Build OS", "linux") ,("Build vendor", "unknown") ,("Host platform", "x86_64-unknown-linux") ,("Host architecture", "x86_64") ,("Host OS", "linux") ,("Host vendor", "unknown") ,("Target platform", "x86_64-unknown-linux") ,("Target architecture", "x86_64") ,("Target OS", "linux") ,("Target vendor", "unknown") ,("Word size", "64") ,("Compiler unregisterised", "NO") ,("Tables next to code", "YES") ] Thanks! ~dsouza

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ANNOUNCE: lens-family 1.0.0
by roconnor＠theorem.ca 30 Oct '13

30 Oct '13

Before there was lens there was lens-family.... I'm pleased to announce the second major release of the lens-family pacakges: lens-family-core-1.0.0 and lens-family-1.0.0. They can be found at * <http://hackage.haskell.org/package/lens-family-core> * <http://hackage.haskell.org/package/lens-family> I consider these packages to be kiddie-pool sized lens libraries for those people who are, for whatever reason, too intimidated by the lens library. I think this is a good way to get one's feet wet with lenses. The type for lenses and traversals are completely compatible with the lens library. This release brings two major developments to lens-family: * Support for traversals and folds. * The names have been all renamed to be mostly compatible with the lexicon developed by lens. With a common lexicon, I hope that users will find it easy to transition from lens-family to lens when they outgrow the kiddie pool. The lens-family-core package is a completely Haskell 98 package for those who need the compatibility. The lens-family package is a wrapper around lens-family-core that provides a few useful Rank 2 type synonyms to make using functional references a little easier. P.S. If edwardk is reading, I've used Ryan Ingram's definition from <http://twanvl.nl/blog/haskell/cps-functional-references#comment-comment0> to implement alongside so that it works for both lenses and getters. You probably want to do the same. -- Russell O'Connor <http://r6.ca/> ``All talk about `theft,''' the general counsel of the American Graphophone Company wrote, ``is the merest claptrap, for there exists no property in ideas musical, literary or artistic, except as defined by statute.''

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Unwanted http-conduit buffering of chunked request body?
by Manuel Gómez 30 Oct '13

30 Oct '13

Hi list, I’ve been playing with http-conduit in an attempt to do some manual testing on a HTTP service, and I ran into something I had not expected. I was trying to set up a POST request with a chunked request body from a conduit. The following code does work: > {-# LANGUAGE OverloadedStrings #-} > > import Blaze.ByteString.Builder.ByteString (fromByteString) > import Control.Concurrent (threadDelay) > import Control.Monad.IO.Class (liftIO) > import Control.Monad.Trans.Resource (runResourceT) > import Data.ByteString (getLine) > import Data.Conduit (yield) > import Network.HTTP.Conduit (RequestBody(RequestBodySourceChunked), http, method, parseUrl, rawBody, requestBody, withManager) > > source = do say "a"; wait; say "b"; wait; say "c" > > wait = liftIO $ threadDelay 1000000 > say = yield . fromByteString > > main = runResourceT $ do > req <- parseUrl "http://localhost:12345/" > withManager $ http req > { method = "POST" > , requestBody = RequestBodySourceChunked source > } The important part is the `source` conduit: it yields a string, waits for a bit, yields another, waits for a bit, and yields again. I expected this to send chunks as soon as the source yielded them. However, it seems to be sending all the chunks together at the end, when the source finishes. Doing the same thing without `wait`, and with `forever` as opposed to just sending three bits of string, seems to work closer to my expectations: it seems to buffer for a bit, then it sends what was buffered, then it buffers some more, and so on. Is this http-conduit or Blaze doing undesired buffering? A quick run on `strace` seems to indicate it’s only doing the `send` system call every once in a while, so the buffering seems to be happening inside Haskell. I’m not even sure this is how the HTTP chunked transfer encoding is meant to be used — my actual use case has to do with sending potentially large files and hopefully using constant memory at the other end, but I’m also curious about using this to send asynchronous events and such. Is this how it’s supposed to work?

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Getting types inside a function in ghci
by martin 29 Oct '13

29 Oct '13

Hello all, is there a way to determine types of symbols which are not toplevel but inside a function?

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Re: [Haskell-cafe] reifying based-on type of a newtype or data
by oleg＠okmij.org 29 Oct '13

29 Oct '13

Anthony Clayden wrote: > newtype Foo = Foo Int deriving (Read, Show, Typeable, Data, ...) > someFoo = Foo 7 > ... > What I want is to get the based-on type baked inside `someFoo` > -- that is: `Int` > (It would also be handy to get the name of the data constr, just in case > it's different to the type.) If we have a data type declaration data C a b = D1 a Int b | D2 a | D3 [a] we use methods of module Typeable to get information about the left-hand-side of the equation (about the type expression C a b and its structure, an application of a type constructor C to two arguments). We use methods of module Data.Data to get information about the right-hand-side of the equation (about _data_ constructors D1, D2 and D3 and their arguments). Here is an example: > {-# LANGUAGE DeriveDataTypeable, ScopedTypeVariables #-} > > import Data.Data > > data C a b = D1 a Int b | D2 a | D3 [a] deriving (Data, Typeable) A sample datum of type C > someC = undefined :: C Int Char *Main> typeOf someC C Int Char meaning someC has the type C Int Char. *Main> dataTypeOf someC DataType {tycon = "Main.C", datarep = AlgRep [D1,D2,D3]} Now we see something about the right-hand-side of the equation defining C: C a b is a data type and it has three data constructors, D1, D2 and D3. How to get information about their arguments? First, we extract constructors > getCtor :: Data a => Int -> a -> Constr > getCtor i x = case dataTypeRep $ dataTypeOf x of AlgRep cs -> cs !! i *Main> getCtor 0 someC D1 Now, we reify a data constructor by unfolding it in a particular way > newtype DTInfo a = DTInfo [TypeRep] > -- Get information about the given ctor of a given algebraic data type > -- (the data type value may be undefined -- we only need its type) > ctorInfo :: forall a. Data a => a -> Constr -> [TypeRep] > ctorInfo _ ctor = case go ctor of DTInfo reps -> reverse reps > where > go :: Constr -> DTInfo a > go = gunfold (\ (DTInfo infos :: DTInfo (b->r)) -> > DTInfo (typeOf (undefined:: b) : infos)) > (\r -> DTInfo []) *Main> ctorInfo someC $ getCtor 0 someC [Int,Int,Char] meaning that D1 of the type C Int Char has three arguments, Int, Int, Char -- in that order. *Main> ctorInfo someC $ getCtor 1 someC [Int] *Main> ctorInfo someC $ getCtor 2 someC [[Int]] It is easy to answer the original question about someFoo *Main> getCtor 0 someFoo Foo *Main> ctorInfo someFoo $ getCtor 0 someFoo [Int] -- A faster way for a defined datum *Main> ctorInfo someFoo $ toConstr someFoo [Int] So, someFoo is constructed by data constructor Foo and that data constructor has one Int argument.

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