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Re: [Haskell-cafe] Lambda and closures in PHP -- could someone please comment?
by Alexander Wagner 19 Jun '08

19 Jun '08

On Wednesday 18 June 2008, Luke Palmer wrote: > I don't know that much PHP, but I find the "lexical" keyword to be a > nuisance. What are the semantics if the lexical keyword is omitted? In PHP Variables are local by default, the keyword global defines them as references to the global namespace. There are some exceptions, like the availability of $this in methods or a couple of predefined superglobal variables that are implicitly global in all functions. <?php $globalVar = 1; $param = "notshared"; $localVar = "notshared"; function foo ($param) { global $globalVar; $localVar = (int) $param; return $localVar + $localVar; } ?> Given how much it works like "global", the keyword "lexical" seems quite consistent with the style of PHP. Gesundheit Wag -- There’s a phrase we live by in America: “In God We Trust”. It’s right there where Jesus would want it: on our money. - Steven Colbert

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cabal-install failure
by Darrin Thompson 19 Jun '08

19 Jun '08

Cabal-install is looking good. It now, for the record, has only two deps outside of Cabal-1.4. I installed cabal-install-0.5 on ubuntu with the haskell.org linux binary for ghc 6.8.2. I then tried cabal-install yi Got this output: ... many successful installs ... Registering vty-3.0.1... Reading package info from "dist/installed-pkg-config" ... done. Saving old package config file... done. Writing new package config file... done. Downloading yi-0.3... [1 of 1] Compiling Main ( Setup.hs, dist/setup/Main.o ) Setup.hs:9:0: Warning: Deprecated use of `showPackageId' (imported from Distribution.Simple, but defined in Distribution.Package): use the Text class instead Linking dist/setup/setup ... Warning: defaultUserHooks in Setup script is deprecated. Configuring yi-0.3... Warning: Instead of 'ghc-options: -DDYNAMIC -DFRONTEND_VTY' use 'cpp-options: -DDYNAMIC -DFRONTEND_VTY' setup: alex version >=2.0.1 && <3 is required but it could not be found. cabal: Error: some packages failed to install: yi-0.3 failed during the configure step. The exception was: exit: ExitFailure 1 Is this a cabal problem of package problem? I would have expected it to fail immediately instead of discover this problem so far into process. Thanks. -- Darrin

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type constructor confusion
by Stephen Howard 19 Jun '08

19 Jun '08

hello list, loading the code below into ghci gives me this error: HttpMessage.hs:36:20: Not in scope: type constructor or class `HttpRequest' The troublesome line is the definition of the cookie function at the end of the code. I've made HttpRequest and HttpResponse constructors of HttpMessage as I've sketched out an action that might return either one. Given that I thought what I was doing below was defining these as type constructors (maybe I have my vocabulary mixed up) I don't know why ghci is returning this error. module HttpMessage ( HttpMessage(..), HttpRequestMethod(..), cookie ) where import Data.Map as M data HttpHeaders = HttpHeaders !(M.Map String String ) data HttpMessage = HttpRequest { headers :: HttpHeaders, body :: String, request_method :: HttpRequestMethod, uri :: URI, http_version :: Float, cookies :: !(M.Map String String) } | HttpResponse { headers :: HttpHeaders, body :: String, status :: HttpStatus } data HttpRequestMethod = Get | Head | Post | Put | Delete | Unsupported String data HttpStatus = OK | NotFound | NotAuthorized | ServerError data URI = URI { protocol :: String, domain :: String, port :: String, path :: String, query :: !(M.Map String String), anchor :: String } cookie :: String -> HttpRequest -> Maybe String cookie n request = M.lookup n (cookies request)

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Gtk2Hs and GCs
by Tim Newsham 19 Jun '08

19 Jun '08

I don't see a way to fetch an existing standard GC from a widget. In other Gtk bindings I usually do this by fetching the widget's style and then grabbing one of the gc's (such as fg_gc[STATE_NORMAL]). In Gtk2Hs docs: http://www.haskell.org/gtk2hs/docs/gtk2hs-docs-0.9.12/Graphics-UI-Gtk-Gener… it looks like you can only get Colors, not the whole GC. I can't seem to find any other way short of making a whole new GC (as is done in Gtk2Hs/demos/graphic/Drawing.hs). Am I missing something? Is there a reason the GC's arent retrievable? Tim Newsham http://www.thenewsh.com/~newsham/

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do and ifthenelse indentation in GHC
by Stefan Monnier 19 Jun '08

19 Jun '08

http://hackage.haskell.org/trac/haskell-prime/wiki/DoAndIfThenElse says (and my memory seems to agree) that GHC has been changed to accept things like readnums f n = do eof <- hIsEOF f if eof then return n else do l <- hGetLine f readnums f (n + read l) where the `then' and `else' are aligned with the `if' rather than being slightly more indented as the Haskell 98 standard requires. Yet, when I try it with GHCi 6.8.2 I get an error: Prelude> :load "/home/monnier/tmp/foo.hs" [1 of 1] Compiling Main ( /home/monnier/tmp/foo.hs, interpreted ) /home/monnier/tmp/foo.hs:6:18: parse error (possibly incorrect indentation) Failed, modules loaded: none. Prelude> Does anybody know what's up with that? Stefan

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Burn ACM
by Achim Schneider 19 Jun '08

19 Jun '08

for monetary reasons. I just wanted my voice to be heard, you may pass on now. -- (c) this sig last receiving data processing entity. Inspect headers for past copyright information. All rights reserved. Unauthorised copying, hiring, renting, public performance and/or broadcasting of this signature prohibited.

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reactive and <<loop>>
by stefan kersten 19 Jun '08

19 Jun '08

hi, i'm having problems with a very simple example using conal elliott's 'reactive' library: module Main where import Control.Applicative import Control.Concurrent import Control.Monad import Data.Reactive import System.Random main :: IO () main = do (e, snk) <- mkEvent forkIO $ forever ((getStdRandom random :: IO Double) >>= snk >> threadDelay 10000) runE (print `fmap` withPrevE e) return () which starts to output this after a while: reactive_loop.hs: <<loop>> this is with ghc 6.8.1 on osx 10.4. any ideas what might be going wrong? many thanks, <sk>

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(Lazy) SmallCheck and peano numbers
by Levi Stephen 19 Jun '08

19 Jun '08

Hi, I have the following definitions type Zero type Succ a so that I can muck around with a Vector type that includes its length encoded in its type. I was wondering whether it was possible to use SmallCheck (or QuickCheck) to generate random Peano numbers? Is there an issue here in that what I actually want to generate is a type rather than a value? I do have reifyInt :: Int -> (forall a. ReflectNum a => a -> b) -> b but, I'm not sure if this can help me when I need to generate other values based upon that type (e.g., two vectors with the same size type) Thanks, Levi

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network-related segfaults
by Brent Yorgey 19 Jun '08

19 Jun '08

Hi all, Has anyone else experienced segfaults related to network stuff? Observe: [11:50:56 brent@xenophon:~]$ ghci -ignore-dot-ghci GHCi, version 6.8.2: http://www.haskell.org/ghc/ :? for help Loading package base ... linking ... done. Prelude> :m +Text.HTML.Download Prelude Text.HTML.Download> txt <- openURL "http://www.google.com" Loading package bytestring-0.9.1.0 ... linking ... done. Loading package mtl-1.1.0.0 ... linking ... done. Loading package parsec-3.0.0 ... linking ... done. Loading package network-2.1.0.0 ... linking ... done. Loading package array-0.1.0.0 ... linking ... done. Loading package containers-0.1.0.1 ... linking ... done. Loading package tagsoup-0.6 ... linking ... done. Segmentation fault (core dumped) This just started happening yesterday. I think I may have just upgraded some packages via cabal-install but I'm not sure which ones. Now is a time when I wish all my terminal sessions were automatically logged. (Hmm, perhaps I should look into that...) -Brent

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Re: Bit Streams
by Dominic Steinitz 19 Jun '08

19 Jun '08

OK, so today I tried to write my first program using the Binary library. And I've hit a snag: It appears the library will only handle data that is byte-aligned. So if I try to write three Bool values, it uses three bytes, not three bits. Before I sit down and spend 3 months designing my own library from scratch, does anybody know of an existing library that allows you to do what Binary does, but with single-bit precision? [I presume Binary is byte-aligned for efficiency...] http://hackage.haskell.org/cgi-bin/hackage-scripts/package/binary-strict

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