Re: [Haskell-cafe] Hackage is down?
On Sat, 11 Aug 2012 21:10:24 +0200, Justin Greene justin.j.gre...@gmail.com wrote: Anyone have a download link for the haskell platform for windows? I can't find one with hackage down. This link depends on the OS you are using; I found the Haskell Platform page in the Web Archive[0]. The downloads are at the Galois site[1]. Regards, Henk-Jan van Tuyl [0] http://web.archive.org/web/20110716180206/http://hackage.haskell.org/platform/ [1] http://lambda.galois.com/hp-tmp/2011.2.0.1/ -- http://Van.Tuyl.eu/ http://members.chello.nl/hjgtuyl/tourdemonad.html Haskell programming -- ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Data structure containing elements which are instances of the same type class
Antoine Latter wrote:
It should be pretty easy to write an adapter function of type String -
(Show a = a).
The type needs to be
String - (exists a. Show a = a)
which is equivalent to
String - (forall a. Show a = a - c) - c
Here is the implementation of the adapter
newtype ExistsShow = E { showE :: String }
instance Show ExistsShow where
show = showE
withShow :: String - (forall a. Show a = a - c) - c
withShow s f = f (E s)
Essentially, the point is that the types are equivalent
ExistsShow == exists a. Show a = a
Best regards,
Heinrich Apfelmus
--
http://apfelmus.nfshost.com
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Re: [Haskell-cafe] Data structure containing elements which are instances of the same type class
Hi Oleg,
On Sat, Aug 11, 2012 at 08:14:47AM -, o...@okmij.org wrote:
I'd like to point out that the only operation we can do on the first
argument of MkFoo is to show to it. This is all we can ever do:
we have no idea of its type but we know we can show it and get a
String. Why not to apply show to start with (it won't be evaluated
until required anyway)?
It's only a test case. The real thing is for a game and will be
something like:
class EntityT e where
update :: e - e
render :: e - IO ()
handleEvent :: e - Event - e
getBound:: e - Maybe Bound
data Entity = forall e. (EntityT e) = Entity e
data Level = Level {
entities = [Entity],
...
}
Greetings,
Daniel
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Re: [Haskell-cafe] Hackage is down?
Am 12.08.2012 08:14, schrieb Henk-Jan van Tuyl: [1] http://lambda.galois.com/hp-tmp/2011.2.0.1/ The current version is 2012.2.0.0, it can be found here: http://lambda.haskell.org/platform/download/current/ Cheers, Leo Wörteler ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] pattern matching vs if-then-else
Hi there, I am writing a toy compiler in Haskell to further my skills in functional programming. One of the functions I wrote is to determine the iteration count of a loop. I have a number of different test that I want to do and I find myself now testing some of these using pattern matching and some properties using an if-then-else construction. I do not consider this very pretty. My question is: are there guidelines of when to use pattern matching and when to use if-then-else? Snippet of the function I mentioned: ---8--- itercount (ForLoop [ ( Assignment update_lcv (Op2 + (Content update_lcv') update_expr) ) ] [(Assignment init_lcv init_expr)] (TestStmt (Op2 (Content test_lcv) test_expr)) bodyblock) = if-- All stmts use the same lcv test_lcv == init_lcv test_lcv == update_lcv test_lcv == update_lcv' -- And the lcv is not updated in the body intersect [test_lcv] (blockkills bodyblock) == [] then Just $ simple_itercount init_expr test_expr update_expr else Nothing itercount _ = Nothing ---8--- Thanks, Maarten ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] pattern matching vs if-then-else
On Sun, Aug 12, 2012 at 1:30 PM, Maarten Faddegon haskell-c...@maartenfaddegon.nl wrote: = if-- All stmts use the same lcv test_lcv == init_lcv test_lcv == update_lcv test_lcv == update_lcv' -- And the lcv is not updated in the body This part of the conditional can be written more succinctly as: all (== test_lcv) [init_lcv, update_lcv, update_lcv'] Re: the if statement, you can also use guard syntax. 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] Possible bug in Criterion or Statistics package
On 10.08.2012 22:20, Till Berger wrote: So I am not sure if this is a bug in Criterion itself, the Statistics package or any dependency or if I am doing something obviously wrong. I would be grateful if someone could look into this as it is holding me back from using Criterion for benchmarking my code. I would suspect Statistics.Resampling.resample. From quick glance criterion doesn't use any concurrent stuff. I'll try create smaller test case It looks like I'm wrong. I obtained event log from crashing program and resample completed its work without problems. Crash occured later. Next suspect is bootstrapBCA itself. It uses monad-par to obtain parallelism[1]. I tried to create smaller test case without any success. [1] https://github.com/bos/statistics/blob/master/Statistics/Resampling/Bootstrap.hs#L84 Replacing runPar $ parMap with a simple map on that line seems to fix the bug. At least I could not reproduce it anymore on several runs with my original test case. So it seems to be a bug in the Par monad package as this change shouldn't alter the program's behaviour, should it? Looks like this is the case. But reducing test case to reasonable size (e.g. removing most of criterion and statistics could be quite difficult ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] hGetContents Illegal byte sequence / ghc-pkg
On Sat, Aug 11, 2012 at 4:13 AM, Benjamin Edwards edwards.b...@gmail.comwrote:
Hello café,
I have a program that is crashing, and I have no idea why:
module Main
where
import System.Process (readProcessWithExitCode)
main :: IO ()
main = do _ - readProcessWithExitCode ghc-pkg [describe, hoopl]
putStrLn Should never get here
this is using the process package from hackage. The program crashes with
minimal-test: fd:5: hGetContents: invalid argument (invalid byte sequence)
minimal-test: thread blocked indefinitely in an MVar operation
inspecting the source of readProcessWithExitCode yields an obvious
explanation to the MVar problem, but I don't understand why hGetContents is
so offended.
For the lazy it is defined as follows:
readProcessWithExitCode
:: FilePath -- ^ command to run
- [String] -- ^ any arguments
- String -- ^ standard input
- IO (ExitCode,String,String) -- ^ exitcode, stdout, stderr
readProcessWithExitCode cmd args input = do
(Just inh, Just outh, Just errh, pid) -
createProcess (proc cmd args){ std_in = CreatePipe,
std_out = CreatePipe,
std_err = CreatePipe }
outMVar - newEmptyMVar
-- fork off a thread to start consuming stdout
out - hGetContents outh
_ - forkIO $ C.evaluate (length out) putMVar outMVar ()
-- fork off a thread to start consuming stderr
err - hGetContents errh
_ - forkIO $ C.evaluate (length err) putMVar outMVar ()
-- now write and flush any input
when (not (null input)) $ do hPutStr inh input; hFlush inh
hClose inh -- done with stdin
-- wait on the output
takeMVar outMVar
takeMVar outMVar
hClose outh
hClose errh
-- wait on the process
ex - waitForProcess pid
return (ex, out, err)
Now having looked at the source of ghc-pkg it is dumping it's output using
putStr and friends, so that should be using my local encoding on the
system, right? and so should hGetContents in my program..?
Now, for the curious: the reason I care is that this problem has
effectively prevented me from using virthualenv. Sadness and woe.
I would recommend using ByteStrings. There is a link to a version of
readProcessWithExitCode that uses ByteString instead of String here:
http://www.haskell.org/pipermail/libraries/2012-August/018263.html
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[Haskell-cafe] I use cabal install repa but then WinGHCi says module Data.Array.Rep.Algorithms.Ramdomish not found.
-- -- Regards, KC ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Fixity declaration extension
fixity declaration has form *infix(l|r)? [Digit]* in haskell. I'm pretty sure, that this is not enough for complicated cases. Ideally, fixity declarations should have form *infix(l|r)? [Digit](\.(+|-)[Digit])** , with implied infinitely long repeated (.0) tail. This will allow fine tuning of operator priorities and much easier priority selection. For example, it may be assumed, that bit operations like (..) operator have hightest priority and have priorities like 9.0.1 or 9.0.2, anti-lisps like ($) have lowest priority like 0.0.1, control operators have base priority 1.* and logic operations like () have priority of 2.* and it will be possibly to add new operators between or above all (for example) control operators without moving fixity of other ones. Agda2 language supports wide priority range, but still without 'tails' to my knowledge. Is there any haskell-influenced language or experimental syntactic extension that address the issue? ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] but module Data.Array.Rep.Algorithms.Ramdomish is in package repa-algorithms
On 12-08-12 02:18 PM, KC wrote: I use cabal install repa but then WinGHCi says module Data.Array.Rep.Algorithms.Ramdomish not found. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] but module Data.Array.Rep.Algorithms.Ramdomish is in package repa-algorithms
email is the new twitter On Sun, Aug 12, 2012 at 3:21 PM, Albert Y. C. Lai tre...@vex.net wrote: On 12-08-12 02:18 PM, KC wrote: I use cabal install repa but then WinGHCi says module Data.Array.Rep.Algorithms.**Ramdomish not found. __**_ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/**mailman/listinfo/haskell-cafehttp://www.haskell.org/mailman/listinfo/haskell-cafe -- brandon s allbery allber...@gmail.com wandering unix systems administrator (available) (412) 475-9364 vm/sms ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] I use cabal install repa but then WinGHCi says module Data.Array.Rep.Algorithms.Ramdomish not found.
I think you need to install repa-algorithms. On 13 August 2012 04:18, KC kc1...@gmail.com wrote: -- -- Regards, KC ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe -- Ivan Lazar Miljenovic ivan.miljeno...@gmail.com http://IvanMiljenovic.wordpress.com ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] createProcess running non-existent programs
I just came across the fact that running createProcess (proc asdfasdf []) with non-existing command asdfasdf returns perfectly fine handles. I would expect an exception. You can even hGetContents on stdout: You just get . I find this highly counter-intuitive. Is this intended? Thanks Niklas PS: I checked how some other programming languages do this: Python: import subprocess; subprocess.call(asdfasdf, shell=False) OSError: [Errno 2] No such file or directory Ruby: exec(asdfasdf) Errno::ENOENT: No such file or directory - asdfasdf ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
