- Haskell-Cafe - Haskell.org

Re: [Haskell-cafe] Portability of Safe Haskell packages
by Roman Cheplyaka 27 Nov '12

27 Nov '12

* Herbert Valerio Riedel <hvr(a)gnu.org> [2012-11-24 00:06:44+0100] > Roman Cheplyaka <roma(a)ro-che.info> writes: > > It has been pointed out before that in order for Safe Haskell to be > > useful, libraries (especially core libraries) should be annotated > > properly with Safe Haskell LANGUAGE pragmas. > > > > However, that would make these libraries unusable with alternative > > Haskell implementations, even if otherwise they these libraries are > > Haskell2010. > > > > To quote the standard: > > > > If a Haskell implementation does not recognize or support a particular > > language feature that a source file requests (or cannot support the > > combination of language features requested), any attempt to compile or > > otherwise use that file with that Haskell implementation must fail > > with an error. > > > > Should it be advised to surround safe annotations with CPP #ifs? > > Or does anyone see a better way out of this contradiction? > > ...but IIRC CPP isn't part of Haskell2010, or is it? It isn't indeed. But: 1) it's a very basic extension which is supported by (almost?) all existing implementations; or 2) if you want to be 100% Haskell2010, you can name your file *.cpphs and let Cabal do preprocessing. 1) is a compromise and 2) is not very practical, so I'm eager to hear other alternatives. Roman

2 1

Problem with benchmarking FFI calls with Criterion
by Janek S. 27 Nov '12

27 Nov '12

I am using Criterion library to benchmark C code called via FFI bindings and I've ran into a problem that looks like a bug. The first benchmark that uses FFI runs correctly, but subsequent benchmarks run much longer. I created demo code (about 50 lines, available at github: https://gist.github.com/4135698 ) in which C function copies a vector of doubles. I benchmark that function a couple of times. First run results in avarage time of about 17us, subsequent runs take about 45us. In my real code additional time was about 15us and it seemed to be a constant factor, not relative to "correct" run time. The surprising thing is that if my C function only allocates memory and does no copying: double* c_copy( double* inArr, int arrLen ) { double* outArr = malloc( arrLen * sizeof( double ) ); return outArr; } then all is well - all runs take similar amount of time. I also noticed that sometimes in my demo code all runs take about 45us, but this does not seem to happen in my real code - first run is always shorter. Does anyone have an idea what is going on? Janek

5 11

1st São Paulo Haskell Meeting [1° Encontro de Haskellers em São Paulo]
by Felipe Almeida Lessa 27 Nov '12

27 Nov '12

Hey! I'd like to invite you to the 1st São Paulo Haskell Meeting! It's going to be something simple, we just want to meet each other and talk about Haskell =). We already have 9 people confirmed on the Google+ event [1], so come join us already! Cheers, PS: We still didn't set the place yet. [1] https://plus.google.com/events/cng3rcv1tjl84g2juddk1i36icg -- Felipe.

1 0

Re: [Haskell-cafe] Executables got bigger using dynamic link.
by Magicloud Magiclouds 27 Nov '12

27 Nov '12

Sorry, I left the profiling option on, which seems to suppress the dynamic options. On Mon, Oct 29, 2012 at 1:29 PM, Magicloud Magiclouds <magicloud.magiclouds(a)gmail.com> wrote: > Hi, > I set "shared: True" in ~/.cabal/config, and using ghc 7.6.1. Then > clear user space hackages and reinstall them. > First of all, I think comparing to static link, dynamic linked > executables file should be smaller. And the libraries (.so) could > benefits from caching to save memory usage. > > Well, I installed cabal-install and alex. I got this: > cabal 9.9M -> 24M > alex 2.7M -> 5.1M > Is this correct? > -- > 竹密岂妨流水过 > 山高哪阻野云飞 > > And for G+, please use magiclouds#gmail.com. -- 竹密岂妨流水过山高哪阻野云飞 And for G+, please use magiclouds#gmail.com.

2 1

Compilers: Why do we need a core language?
by citb＠lavabit.com 26 Nov '12

26 Nov '12

Hello, I know nothing about compilers and interpreters. I checked several books, but none of them explained why we have to translate a high-level language into a small (core) language. Is it impossible (very hard) to directly translate high-level language into machine code?

10 10

Is there a tool like ri from ruby?
by Magicloud Magiclouds 26 Nov '12

26 Nov '12

RI is a very easy using tool that search and show the documents of ruby modules/functions, etc. Using RI, I could get help when programming with a few commands. Quick and simple. And with RI backend (libs), I could also simply integrate ri to my IDE (like one hotkey to show function summary). So I am wondering if there is such thing in Haskell world. I know haddock saves the .haddock files in document folder. But I do not know if there is any existing tools to index and view them. -- 竹密岂妨流水过山高哪阻野云飞 And for G+, please use magiclouds#gmail.com.

3 3

Quasiquotation page on HaskellWiki needs updating
by Erik de Castro Lopo 26 Nov '12

26 Nov '12

Hi all, It seems the Quasiquotation page on HaskellWiki http://www.haskell.org/haskellwiki/Quasiquotation has fallen behind the actually Quasiquotation implementation that is in ghc-7.4.2 and later. Specifically, the QuasiQuoter constructor that the Wiki takes two parameters: data QuasiQuoter = QuasiQuoter { quoteExp :: String -> Q Exp , quotePat :: String -> Q Pat } while the one in ghc-7.4 and later takes four: data QuasiQuoter = QuasiQuoter { quoteExp :: String -> Q Exp , quotePat :: String -> Q Pat , quoteType :: String -> Q Type , quoteDec :: String -> Q [Dec] } I'm just starting out with quasquotation and am not yet qualified to update this page myself. Erik -- ---------------------------------------------------------------------- Erik de Castro Lopo http://www.mega-nerd.com/

2 1

Munich Haskell Meeting
by Heinrich Hördegen 25 Nov '12

25 Nov '12

Dear all, next Tuesday, 27. November 2012, will be our Haskell Meeting in Munich at 19h30 at Cafe Puck. Please go to http://www.haskell-munich.de/dates and hit the button, if you intend to join. Have a good start into your week, Heinrich -- -- Funktionale Programmierung Dr. Heinrich Hördegen Gutenbergstr. 26 80638 München FON: +49 (89) 12 59 79 49 FAX: +49 (89) 12 59 79 50 hoerdegen(a)funktional.info www.funktional.info --

1 0

GHC 7.4.1 hangs and memory usage shoots ups to 100% when compiling with -O2
by magesh b 25 Nov '12

25 Nov '12

I'm facing this problem only when I compiled the code using -O2 Flag. I tried the following, * Compiled with -O1 Flag (7.4.1), It compiled fine * Compiled with ghc-7.0.4 with -O2, it's getting compiled successfully but with the Warning, SpecConstr Function `$wa{v s27vx} [lid]' has one call pattern, but the limit is ... [Module that is getting stuck is using heavy quasiquotation] Env: OS: Ubuntu 12.04 [x86_64] GHC: 7.4.1 Is this a bug? Anything else should I need to try?

1 0

need help with understanding expression
by Daryoush Mehrtash 25 Nov '12

25 Nov '12

I am having hard time understanding how removing the outer parenthesis in (max.(+1)) 2 2 to max.(+1) 2 2 changes the meaning of expression. My expectation was that "max.(+1) takes two numbers and returns the max as defined in the type: :t max.(+1) max.(+1) :: (Ord b, Num b) => b -> b -> b With parenthesis it does what I expect it to: Prelude> :t (max.(+1)) 2 2 (max.(+1)) 2 2 :: (Ord b, Num b) => b Prelude> (max.(+1)) 2 2 3 But if I remove the parenthesis I get a beast that I have no idea what its type signature mean any more Prelude> :t (max.(+1)) 2 2 (max.(+1)) 2 2 :: (Ord b, Num b) => b Prelude> :t max.(+1) 2 2 max.(+1) 2 2 :: (Ord b, Num a1, Num (a1 -> a -> b)) => a -> b -> b How did removal of parenthesis changed the meaning? How do you interpret the type: "(Ord b, Num a1, Num (a1 -> a -> b)) => a -> b -> b"? Thanks -- Daryoush Weblog: http://onfp.blogspot.com/

6 12