Re: [Haskell-cafe] Applicative is like an Arrow
Thanks again for the detailed and explanatory answer. That's the reason I'm writing these huge responses, because I hope I can shorten this journey for others. This has certainly helped me grasp some aspects in this regard. While Monad Transformers are awesome and can solve many problems quite easily, I'm pretty sure that there is almost always a nicer, more functional way to solve such a problem. Incidentally, I happened to bump in to this paper, it claims they have found a way that allows us get rid of the need of monad transformers in a more systematic manner, by using what they call Monad coproduct. The paper titled Composing Monads Using Coproducts is here. [1] I haven't understood it much till now, and it seems I will have to try real hard to read this paper. Ref. [1] http://isi.uni-bremen.de/~cxl/habil/papers/icfp02.pdf Thanks and regards, -Damodar Kulkarni ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] ANN: hspec-test-framework - Run test-framework tests with Hspec
Hi, I just released hspec-test-framework[1] and hspec-test-framework-th[2] to Hackage. They can be used to run test-framework tests with Hspec unmodified. This can also be used to work around test-framework's incompatibility with QuickCheck-2.6 and base-4.7.0 ;) Have a look at the README for usage instructions: https://github.com/sol/hspec-test-framework#readme Cheers, Simon [1] http://hackage.haskell.org/package/hspec-test-framework [2] http://hackage.haskell.org/package/hspec-test-framework-th ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] ANN: hspec-test-framework - Run test-framework tests with Hspec
Hi Simon, this is an exciting news! May I ask the question that maybe is lurking in the shadow? Due to the recent announcement of Roman's tasty library, are there plans to basically release something similar to hspec-test-framework and hspec-test-framework-th but targeting tasty instead? Bye :) A. On 18 August 2013 14:50, Simon Hengel s...@typeful.net wrote: Hi, I just released hspec-test-framework[1] and hspec-test-framework-th[2] to Hackage. They can be used to run test-framework tests with Hspec unmodified. This can also be used to work around test-framework's incompatibility with QuickCheck-2.6 and base-4.7.0 ;) Have a look at the README for usage instructions: https://github.com/sol/hspec-test-framework#readme Cheers, Simon [1] http://hackage.haskell.org/package/hspec-test-framework [2] http://hackage.haskell.org/package/hspec-test-framework-th ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] abs minBound (0 :: Int) negate minBound == (minBound :: Int)
The docs at http://www.haskell.org/ghc/docs/latest/html/libraries/base/Prelude.html#v:gcd give a NB mentioning that (abs minBound == minBound) is possible for fixed-width types. This holds, for example, at Int. It is also the case that (negate minBound == minBound). Two questions: 1) This behavior surprised me. Does it surprise enough people to include a warning in the Haddock for abs and negate? IE Here. http://www.haskell.org/ghc/docs/latest/html/libraries/base/Prelude.html#t:Num 2) Is this a common behavior in other languages? My tinkering with gcc suggests it does not support the value -2^63, but instead bottoms out at (-2^63+1). Thanks. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Alternative name for return
Dag Odenhall dag.odenh...@gmail.com writes: I particularly like she's (her?) syntax for Alternative. Not sure whether or not Idris has that. Applicative tuples would be nice too, something like (|a,b,c|) translating to liftA3 (,,) a b c. And operators too, liftA2 (+) a b as (| a + b |)? I patched she and did applicative tuples. Check my recent blog post on it: http://blog.bezirg.net/posts/2013-08-03-enhancement-to-the-strathclyde-haskell-enhancement.html She already does lifting of binary operators, AFAIK. Cheers On Thu, Aug 15, 2013 at 11:08 AM, Erik Hesselink hessel...@gmail.com wrote: On Thu, Aug 15, 2013 at 5:39 AM, Jason Dagit dag...@gmail.com wrote: Also, if anyone wants to look at prior art first, Idris supports applicative brackets. As does she [0]. Erik [0] https://personal.cis.strath.ac.uk/conor.mcbride/pub/she/ idiom.html ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] ANN: processing-1.2.0.0. Graphic web applications with processing.js.
Hello readers of Haskell-Cafe. Yesterday I uploaded a new version of the processing library [1]. == What is this library for? == The library is oriented to create graphic applications that run in a web browser, with no need of running a server. It provides the user with a set of functions and combinators that can be used to create an abstract piece code. This code is rendered to the processing language syntax. Once the code is uploaded, using processing.js [2], the output code is runnable from any browser with JavaScript support. To quickly give you a taste of the library, look at this animation, created with a simple recursive function: http://daniel-diaz.github.io/projects/processing/mill.html The code is here: https://github.com/Daniel-Diaz/processing/blob/master/examples/mill.hs == What's new? == After a couple of weeks working hard to have this library properly working, I think it have reached a point of reasonable usability. As a proof, I have written a simplified version of the Pac-Man game [3]. However, although I have implemented some code optimizations, it seems that the game still does not run smoothly in every web browser. I will definitely keep trying to improve the performance of the code generated by the library. I encourage you to try the library if you are interested, but keep in mind that it is still in an early stage, and may contain bugs, lack some important features, have an incomplete documentation or suffer from API changes. == References == [1] Library at Hackage - http://hackage.haskell.org/package/processing-1.2.0.0 [2] Processing.js - http://processingjs.org [3] Pac-Man game - http://daniel-diaz.github.io/projects/processing/pacman.html ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] ANN: hspec-test-framework - Run test-framework tests with Hspec
Hi, Due to the recent announcement of Roman's tasty library, are there plans to basically release something similar to hspec-test-framework and hspec-test-framework-th but targeting tasty instead? I care about Hspec[1] and want to provide an upgrade path for test-framework users, but I'm looking forward to friendly competition ;) Cheers, Simon [1] http://hspec.github.io/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] MongoDB single insertions super slow
I am trying to write a simple benchmark of testing 1000 single inserts in mongodb, but doing single insertions is super slow. It takes nearly 40 seconds to perform these operations with the haskell mongodb driver, but under a second to perform the same number of operations of single inserts in python. Here are the two files I am working with: https://gist.github.com/hansonkd/6263648 I checked the BSON serialization, and writing it to a socket instead of mongodb driver, makes the script run in under a second so the problem seems to be with the mongodb driver. Any insights would be appreciated. -- Kyle Hanson ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Database.postgreSQL.Simple - ambigious type
Hi Tom,
I played a bit with your suggestion, and it is running now :-)
But instead of IO [Int] I think we need IO [Only Int] because of
the 1-element-tupel problem?
With IO [Only Int] it looks like this:
---
{-# LANGUAGE OverloadedStrings #-}
import Database.PostgreSQL.Simple
myconn :: ConnectInfo
myconn = defaultConnectInfo {
connectUser = test,
connectPassword = test,
connectDatabase = test}
main :: IO ()
main = do
c - connect myconn :: IO Connection
rs - query_ c select 2 + 2 :: IO [Only Int]
putStrLn $ Result from database ++ show (fromOnly $ head rs)
return ()
---
Best regards
Hartmut
On 08/18/2013 12:11 AM, Tom Ellis wrote:
On Sat, Aug 17, 2013 at 11:59:24PM +0200, Hartmut Pfarr wrote:
{-# LANGUAGE OverloadedStrings #-}
import Database.PostgreSQL.Simple
import Database.PostgreSQL.Simple.FromRow
hello :: (FromRow a) = IO [a]
hello = do
conn - connect defaultConnectInfo
query_ conn select 2 + 2
Either
main = print = (hello :: IO [Int])
or give hello a monomorphic type signature, such as
hello :: IO [Int]
Tom
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Re: [Haskell-cafe] MongoDB single insertions super slow
Have you contacted the maintainer? I believe that the Haskell mongodb driver is maintained by someone at 10gen? (Or at least at some point was ) Without spending time looking at the mongo driver, it's hard to know. On Aug 18, 2013 3:58 PM, Kyle Hanson hanoo...@gmail.com wrote: I am trying to write a simple benchmark of testing 1000 single inserts in mongodb, but doing single insertions is super slow. It takes nearly 40 seconds to perform these operations with the haskell mongodb driver, but under a second to perform the same number of operations of single inserts in python. Here are the two files I am working with: https://gist.github.com/hansonkd/6263648 I checked the BSON serialization, and writing it to a socket instead of mongodb driver, makes the script run in under a second so the problem seems to be with the mongodb driver. Any insights would be appreciated. -- Kyle Hanson ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Database.postgreSQL.Simple - ambigious type
On Sun, Aug 18, 2013 at 10:16:06PM +0200, Hartmut Pfarr wrote: I played a bit with your suggestion, and it is running now :-) But instead of IO [Int] I think we need IO [Only Int] because of the 1-element-tupel problem? Yes you're right. I had forgotten that postgresql-simple dealt with single-column tables with Only. Well done for getting it working! Tom ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] abs minBound (0 :: Int) negate minBound == (minBound :: Int)
On 19/08/2013, at 3:38 AM, Nicolas Frisby wrote:
The docs at
http://www.haskell.org/ghc/docs/latest/html/libraries/base/Prelude.html#v:gcd
give a NB mentioning that (abs minBound == minBound) is possible for
fixed-width types.
At least three ways to represent negative integers in binary have been used:
- twos-complement (asymmetric, -INT_MIN == INT_MIN, abs can have a negative
result)
- ones-complement(symmetric, -INT_MIN == INT_MAX, abs is always
non-negative)
- sign-and-magnitude (symmetric, -INT_MIN == INT_MAX, abs is always
non-negative)
Having used a B6700 as an undergraduate, I still think sign-and-magnitude is the
only really safe-and-simple scheme. However, twos-complement has conquered.
The argument for twos-complement, which always puzzled me, is that the other
systems have two ways to represent zero. I never found this to be a problem,
not even for bitwise operations, on the B6700. I *did* find abs x 0
succeeding to be a pain in the posterior. (The B6700 had two different tests:
'are these two numbers equal' and 'are these two bit patterns equal'.)
Two questions:
1) This behavior surprised me. Does it surprise enough people to include a
warning in the Haddock for abs and negate?
We cannot expect everyone who uses Haskell to be familiar with
the eccentricities of popular hardware. I think it's worth mentioning.
2) Is this a common behavior in other languages?
Yes.
My tinkering with gcc suggests it does not support the value -2^63, but
instead bottoms out at (-2^63+1).
Your tinkering was insufficient.
f% cat 2c.c
#include stdio.h
#include limits.h
int main(void) {
printf(%d\n, INT_MIN + INT_MAX);
return 0;
}
f% gcc 2c.c
f% a.out
-1
Oh wait. You said 63, not 31.
Change the key line to
printf(%lld\n, LLONG_MIN + LLONG_MAX);
LLONG_MIN is going to be -(2**63) on any SPARC, x86, x86-64,
Power(PC), Alpha, ARM, MIPS, or z/Series machine, and a host
of others.
Thanks.
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