- Haskell-Cafe - Haskell.org

Re: [Haskell-cafe] GHCi shows result of (IO a) only if (a) is in class Show
by Sumit Sahrawat, Maths & Computing, IIT (BHU) 26 Apr '15

26 Apr '15

On 26 April 2015 at 06:10, Alexey Vagarenko <vagarenko(a)gmail.com> wrote: > Yes, but ghci shows an error if it can't print a value, except when the > value is in IO monad. Compare: > Prelude> id > <interactive>:6:1: > No instance for (Show (a0 -> a0)) > (maybe you haven't applied enough arguments to a function?) > arising from a use of `print' > In a stmt of an interactive GHCi command: print it > Prelude> > > and > > Prelude> return id > Prelude> > > This behavior is necessary. For example, if we used any function with result of type IO (), such as writeFile, we don't want an error as we are interested in the side-effects only. > > > воскресенье, 26 апреля 2015 г., 5:48:55 UTC+6 пользователь Sumit Sahrawat, > Maths & Computing, IIT (BHU) написал: >> >> If something can't be shown (converted to a string), then it can't be >> printed (as a string). >> >> On 25 April 2015 at 17:51, Daniel van den Eijkel <dv...@gmx.net> wrote: >> >>> I wrote a parser and it took me a while to realize why GHCi suddenly did >>> not show any result nor an error message anymore. >>> >>> My parsing function has type (IO Expression), Expression is in class >>> Show. >>> >>> After changing the parser to (IO Declaration), it did not show anything >>> anymore, because Declaration was not in class Show. >>> >>> When I typed (parseFile "input.txt" >>= print), I got the error message >>> and understood what was going on. But for I while I was really confused >>> what's happening. >>> >>> Just wanted to share this. >>> >>> Best, >>> Daniel >>> _______________________________________________ >>> Haskell-Cafe mailing list >>> Haskel...@haskell.org >>> http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe >>> >> >> >> >> -- >> Regards >> >> Sumit Sahrawat >> > -- Regards Sumit Sahrawat

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GHCi shows result of (IO a) only if (a) is in class Show
by Daniel van den Eijkel 25 Apr '15

25 Apr '15

I wrote a parser and it took me a while to realize why GHCi suddenly did not show any result nor an error message anymore. My parsing function has type (IO Expression), Expression is in class Show. After changing the parser to (IO Declaration), it did not show anything anymore, because Declaration was not in class Show. When I typed (parseFile "input.txt" >>= print), I got the error message and understood what was going on. But for I while I was really confused what's happening. Just wanted to share this. Best, Daniel

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Re: [Haskell-cafe] How to compile git-annex?
by Chris Wong 25 Apr '15

25 Apr '15

On Apr 26, 2015 10:01 AM, "Peng Yu" <pengyu.ut(a)gmail.com> wrote: > > I clean up all Haskell related things in my home directory. > > rm -rf ~/.cabal > rm -rf ~/Library/Haskell > rm -rf ~.ghc/ Is this a typo? You should have removed ~/.ghc, not ~.ghc. > cabal update > cabal install cabal-install > > > Then I try to install git-annex again, which shows me the following. > What I should do next? > > ~$ cabal install git-annex > Resolving dependencies... > In order, the following would be installed: > HUnit-1.2.5.2 (new package) > SafeSemaphore-0.10.1 (new package) > ansi-terminal-0.6.2.1 (new package) > ansi-wl-pprint-0.6.7.2 (new package) > appar-0.1.4 (new package) > async-2.0.2 (new package) > auto-update-0.1.2.1 (new package) > base16-bytestring-0.1.1.6 (new package) > base64-bytestring-1.0.0.1 (new package) > blaze-builder-0.4.0.1 (new package) > blaze-markup-0.7.0.2 (new package) > blaze-html-0.8.0.2 (new package) > bloomfilter-2.0.0.0 (new package) > byteable-0.1.1 (new package) > byteorder-1.0.4 (new package) > bytestring-builder-0.10.6.0.0 (new package) > cereal-0.4.1.1 (new package) > clock-0.4.5.0 (new package) > cryptohash-0.11.6 (new package) > data-default-class-0.0.1 (new package) > data-default-instances-base-0.0.1 (new package) > data-default-instances-containers-0.0.1 (new package) > data-default-instances-old-locale-0.0.1 (new package) > dataenc-0.14.0.7 (new package) > dlist-0.7.1.1 (new package) > data-default-instances-dlist-0.0.1 (new package) > data-default-0.5.3 (new package) > cookie-0.4.1.4 (new package) > easy-file-0.2.0 (new package) > edit-distance-0.2.1.2 (new package) > entropy-0.3.6 (new package) > fast-logger-2.3.1 (new package) > file-embed-0.0.8.2 (new package) > gnuidn-0.2.1 (new package) > hashable-1.2.3.2 (new package) > case-insensitive-1.2.0.4 (new package) > hourglass-0.2.9 (new package) > asn1-types-0.3.0 (new package) > http-types-0.8.6 (new package) > iproute-1.4.0 (new package) > mime-mail-0.4.8.2 (new package) > mime-types-0.1.0.6 (new package) > monad-loops-0.4.2.1 (new package) > nats-1 (new package) > network-info-0.2.0.5 (new package) > network-multicast-0.0.11 (new package) > parallel-3.2.0.6 (new package) > path-pieces-0.2.0 (new package) > prelude-extras-0.4 (new package) > reflection-1.5.1.2 (new package) > safe-0.3.8 (new package) > scientific-0.3.3.8 (new package) > attoparsec-0.12.1.6 (new package) > css-text-0.1.2.1 (new package) > email-validate-2.1.1 (new package) > http-date-0.0.6 (new package) > securemem-0.1.7 (new package) > crypto-cipher-types-0.0.9 (new package) > cipher-aes-0.2.10 (new package) > cipher-des-0.0.6 (new package) > cipher-rc4-0.1.4 (new package) > setenv-0.1.1.3 (new package) > silently-1.2.4.1 (new package) > simple-sendfile-0.2.18 (new package) > socks-0.5.4 (new package) > stm-chans-3.0.0.3 (new package) > stringsearch-0.3.6.6 (new package) > system-filepath-0.4.13.3 (new package) > system-fileio-0.3.16.2 (new package) > tagged-0.8.0.1 (new package) > tagsoup-0.13.3 (new package) > transformers-0.4.3.0 (new version) > StateVar-1.1.0.0 (new package) > crypto-api-0.13.2 (new package) > gsasl-0.3.5 (new package) > mmorph-1.0.4 (new package) > monads-tf-0.1.0.2 (new package) > gnutls-0.1.5 (new package) > mtl-2.2.1 (new version) > IfElse-0.85 (new package) > asn1-encoding-0.9.0 (new package) > asn1-parse-0.9.0 (new package) > crypto-pubkey-types-0.4.3 (new package) > hfsevents-0.1.5 (new package) > hslogger-1.2.8 (new package) > parsec-3.1.9 (reinstall) changes: mtl-2.1.3.1 -> 2.2.1 > bencode-0.5.0.1 (new package) > json-0.9.1 (new package) > network-uri-2.6.0.1 (reinstall) > pem-0.2.2 (new package) > primitive-0.6 (new package) > regex-base-0.93.2 (new package) > regex-posix-0.95.2 (new package) > regex-compat-0.95.1 (new package) > MissingH-1.3.0.1 (new package) > regex-tdfa-1.2.0 (new package) > skein-1.0.9.3 (new package) > streaming-commons-0.1.12 (new package) > torrent-10000.0.0 (new package) > transformers-compat-0.4.0.4 (new package) > MonadRandom-0.3.0.2 (new package) > distributive-0.4.4 (new package) > exceptions-0.8.0.2 (new package) > optparse-applicative-0.11.0.2 (new package) > transformers-base-0.4.4 (new package) > monad-control-1.0.0.4 (new package) > lifted-base-0.2.3.6 (new package) > enclosed-exceptions-1.0.1.1 (new package) > resourcet-1.1.4.1 (new package) > unix-compat-0.4.1.4 (new package) > unix-time-0.3.5 (new package) > unordered-containers-0.2.5.1 (new package) > semigroups-0.16.2.2 (new package) > utf8-string-1 (new package) > language-javascript-0.5.13.3 (new package) > hjsmin-0.1.4.7 (new package) > publicsuffixlist-0.1 (new package) > http-client-0.4.11.1 (new package) > uuid-types-1.0.1 (new package) > uuid-1.3.10 (new package) > vault-0.3.0.4 (new package) > vector-0.10.12.3 (new package) > aeson-0.8.0.2 +old-locale (new package) > crypto-random-0.0.9 (new package) > cprng-aes-0.6.1 (new package) > clientsession-0.9.1.1 (new package) > crypto-numbers-0.2.7 (new package) > crypto-pubkey-0.2.8 (new package) > mwc-random-0.13.3.2 (new package) > resource-pool-0.2.3.2 (new package) > shakespeare-2.0.4.1 (new package) > hamlet-1.2.0 (new package) > void-0.7 (new package) > conduit-1.2.4 (new package) > conduit-extra-1.1.7.2 (new package) > contravariant-1.3.1 (new package) > comonad-4.2.5 (new package) > cryptohash-conduit-0.1.1 (new package) > dns-1.4.5 (new package) > monad-logger-0.3.13.1 (new package) > persistent-2.1.3 (new package) > esqueleto-2.1.3 (new package) > persistent-sqlite-2.1.4.1 (new package) > persistent-template-2.1.3 (new package) > semigroupoids-4.3 (new package) > bifunctors-4.2.1 (new package) > profunctors-4.4.1 (new package) > free-4.11 (new package) > adjunctions-4.2 (new package) > either-4.3.3.2 (new package) > errors-1.4.7 (new package) > kan-extensions-4.2.1 (new package) > lens-4.9.1 (new package) > wai-3.0.2.3 (new package) > wai-logger-2.2.4 (new package) > warp-3.0.12.1 (new package) > word8-0.1.2 (new package) > wai-extra-3.0.7.1 (new package) > wai-app-static-3.0.1 (new package) > x509-1.5.0.1 (new package) > x509-store-1.5.0 (new package) > x509-system-1.5.0 (new package) > x509-validation-1.5.1 (new package) > tls-1.2.17 (new package) > connection-0.2.4 (new package) > http-client-tls-0.2.2 (new package) > http-conduit-2.1.5 (new package) > warp-tls-3.0.3 (new package) > xml-types-0.3.4 (new package) > libxml-sax-0.7.5 (new package) > network-protocol-xmpp-0.4.6 (new package) > xml-conduit-1.2.4 (new package) > aws-0.11.4 (new package) > tagstream-conduit-0.5.5.3 (new package) > authenticate-1.3.2.11 (new package) > xml-hamlet-0.4.0.10 (new package) > DAV-1.0.4 (new package) > xss-sanitize-0.3.5.5 (new package) > yaml-0.8.11 (new package) > yesod-core-1.4.9.1 (new package) > yesod-default-1.2.0 (new package) > yesod-persistent-1.4.0.2 (new package) > yesod-form-1.4.4.1 (new package) > yesod-auth-1.4.4 (new package) > yesod-1.4.1.5 (new package) > yesod-static-1.4.0.4 (new package) > git-annex-5.20150420 -testsuite -feed (new package) > cabal: The following packages are likely to be broken by the reinstalls: > HTTP-4000.2.19 > Use --force-reinstalls if you want to install anyway. > > > On Sat, Apr 25, 2015 at 4:18 PM, Brandon Allbery <allbery.b(a)gmail.com> wrote: > > > > On Sat, Apr 25, 2015 at 3:45 PM, Peng Yu <pengyu.ut(a)gmail.com> wrote: > >> > >> Why cabal install print so many irrelevant messages? Is it better to > >> follow Unix "Rule of Silence" to only print usage error messages? > > > > > > This is not an irrelevant message: > > > >> asn1-parse-0.9.0 (reinstall) changes: text-1.2.0.4 added > > > > > > It's an indication that things are about to go very wrong, as indeed they > > did. In fact, the errors you got indicate quite a lot of problems with your > > Haskell installation; you apparently have a bunch of broken packages. > > > > -- > > brandon s allbery kf8nh sine nomine associates > > allbery.b(a)gmail.com ballbery(a)sinenomine.net > > unix, openafs, kerberos, infrastructure, xmonad http://sinenomine.net > > > > -- > Regards, > Peng > _______________________________________________ > cabal-devel mailing list > cabal-devel(a)haskell.org > http://mail.haskell.org/cgi-bin/mailman/listinfo/cabal-devel -- Chris Wong https://lambda.xyz

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Re: [Haskell-cafe] Ord for partially ordered sets
by Barak A. Pearlmutter 24 Apr '15

24 Apr '15

> I'm confused. What is supposed to be the result of `g1 <= g2` when `g1` and > `g2` are not comparable according to the partial order? Surely it would make things less confusing to simply follow existing precedent already in the standard prelude? $ ghci Prelude> let nan=0/0::Double Prelude> nan==nan False Prelude> compare 0 nan GT Prelude> compare nan 0 GT Prelude> compare nan nan GT Prelude> 0<=nan False Prelude> nan<=0 False Prelude> nan<=nan False Prelude> let infty=1/0::Double Prelude> infty <= nan False Prelude> nan <= infty False Perhaps not.

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Is there a name for this algebraic structure?
by Gleb Peregud 24 Apr '15

24 Apr '15

Hello I am wondering if there's a well known algebraic structure which follows the following patterns. Let's call it S: It's update-able with some opaque "a" (which can be an element or an operation with an element): update :: S -> a -> S There's a well defined zero for it: empty :: S Operations on it are idempotent: update s a == update (update s a) a Every S can be reconstructed from a sequence of updates: forall s. exists [a]. s == foldl update empty [a] An example of this would be Data.Set: empty = Set.empty update = flip Set.insert Is there something like this in algebra? Cheers, Gleb

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low-cost matrix rank?
by Mike Meyer 24 Apr '15

24 Apr '15

Noticing that diagrams 1.3 has moved from vector-space to linear, I decided to check them both for a function to compute the rank of a matrix. Neither seems to have it. While I'm doing quite a bit of work with 2 and 3-element vectors, the only thing I do with matrices is take their rank, as part of verifying that the faces of a polyhedron actually make a polyhedron. So I'm looking for a relatively light-weight way of doing so that will work with a recent (7.8 or 7.10) ghc release. Or maybe getting such a function added to an existing library. Anyone have any suggestions? Thanks, Mike

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Re: [Haskell-cafe] Space leak with recursion
by Martijn Rijkeboer 24 Apr '15

24 Apr '15

>> pollSockets :: State -> IO () >> pollSockets state = >> void $ poll (-1) >> [ Sock (listenSocket state) [In] (Just $ observerHandleEvts >> state) >> , Sock (snapSocket state) [In] (Just $ snapshotHandleEvts >> state) >> ] >> >> >> observerHandleEvts :: State -> [Event] -> IO () >> observerHandleEvts state _ = do >> void $ receiveMulti $ listenSocket state >> pollSockets state >> >> >> snapshotHandleEvts :: State -> [Event] -> IO () >> snapshotHandleEvts state _ = do >> void $ receiveMulti $ snapSocket state >> pollSockets state > > What happens here if there is an event waiting on both the listen > socket *and* the snap socket? It looks like `observerHandleEvts` > will be called and, since it recursively calles `pollSockets`, > the `snapshotHandleEvts` handler will not be run, although its > continuation will be kept around leaking space. This could be an issue, but during my testing there were no messages sent to the snapshot socket (I haven't implemented the snapshot socket in the client yet). > It seems unwise to make a recursive call to the event loop inside a > handler. How would I update my state and ensure that the next invocation of a handler gets the updated state? With the forever function my state updates are not propagated. Kind regards, Martijn Rijkeboer

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Space leak with recursion
by Martijn Rijkeboer 24 Apr '15

24 Apr '15

Hi, I'm trying to make an observable (code below) that listens to two ZeroMQ sockets and publishes the received messages on a third. Every message that is received gets an incremented sequence number before it is send on the publishing socket. To keep the current sequence number a state object is passed to the polling function and after handling the message, the polling function is called again with the updated state. Unfortunately this recursive calling of the polling function creates a space leak. Any suggestions how to fix this? Note: for brevity I left the incrementing of the sequence number and the sending on the publishing socket out of the code. Kind regards, Martijn Rijkeboer --- Code --- module Observable ( run ) where import Control.Monad (void) import Data.Int (Int64) import System.ZMQ4 data State = State { nextSeqNum :: !Int64 , listenSocket :: !(Socket Pull) , publishSocket :: !(Socket Pub) , snapSocket :: !(Socket Router) } run :: IO () run = do withContext $ \ctx -> withSocket ctx Pull $ \observer -> withSocket ctx Pub $ \publisher -> withSocket ctx Router $ \snapshot -> do setLinger (restrict (0::Int)) observer bind observer "tcp://*:7010" setLinger (restrict (0::Int)) publisher bind publisher "tcp://*:7011" setLinger (restrict (0::Int)) snapshot setSendHighWM (restrict (0::Int)) snapshot bind snapshot "tcp://*:7013" let state = State { nextSeqNum = 0 , listenSocket = observer , publishSocket = publisher , snapSocket = snapshot } pollSockets state pollSockets :: State -> IO () pollSockets state = void $ poll (-1) [ Sock (listenSocket state) [In] (Just $ observerHandleEvts state) , Sock (snapSocket state) [In] (Just $ snapshotHandleEvts state) ] observerHandleEvts :: State -> [Event] -> IO () observerHandleEvts state _ = do void $ receiveMulti $ listenSocket state pollSockets state snapshotHandleEvts :: State -> [Event] -> IO () snapshotHandleEvts state _ = do void $ receiveMulti $ snapSocket state pollSockets state

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[ANN]: the Helium compiler, version 1.8.1
by Jurriaan Hage 24 Apr '15

24 Apr '15

Dear all, we have recently uploaded Helium 1.8.1, the novice friendly Haskell compiler, to Hackage. Improvements in this version - Helium can again work together with our Java-based programming environment Hint. The jar file for Hint itself can be downloaded from the Helium website at: http://foswiki.cs.uu.nl/foswiki/Helium which also has some more documentation on how to use Hint and helium. - the svn location if you are interested in the sources is now the correct one To install Helium simply type cabal install helium cabal install lvmrun Helium compiles with GHC 7.6.3 and 7.8.x, but does not yet compile with 7.10. Any questions and feedback are welcome at helium(a)cs.uu.nl. best regards, The Helium Team

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ANN: dns-server: forward DNS queries to StatDNS REST API
by Erik Dominikus 23 Apr '15

23 Apr '15

Bad news: ISP is intercepting packets to UDP port 53. Good news: There is DNS resolution over HTTP (http://www.statdns.com/api/) Bad news: The software bridging DNS clients and that HTTP service is missing. Good news: I made (a small but working part of) it. I've been using it on my computer. The code is here: https://github.com/edom/dns-server

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