date:20100601

Re: [Haskell-cafe] Why Either = Left | Right instead of something like Result = Success | Failure

2010-06-01 Thread Patrick LeBoutillier

On Thu, May 27, 2010 at 3:17 PM, Mike Dillon m...@embody.org wrote:
 begin C. McCann quotation:
 Personally, I advocate instead using Sinister and Dexter. Nice and
 catchy, don't you think?

 Has anyone done a translation of the Prelude into Latin?

 modulus PraeLudus ubi

 data Uter a b = Sinister a
               | Dexter b
               derivare (Aequo, Ordinaro, Lego, Monstro)

 Ha.

Not Haskell, but check this one out:

http://search.cpan.org/~dconway/Lingua-Romana-Perligata-0.50/lib/Lingua/Romana/Perligata.pm

Patrick


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-- 
=
Patrick LeBoutillier
Rosemère, Québec, Canada
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[Haskell-cafe] Language Shootout reverse-complement benchmark

2010-06-01 Thread Louis Wasserman

Hey,

I was looking at the reverse-complement benchmark on the Language Shootout,
and among other things, I noticed that the Haskell implementation was using
(filter (/= '\n')) on ByteStrings, and also using lists as queues.

I had a few improvements which using -fasm seem to yield about a 19%
improvement in speed, and a 35% reduction in allocation, on my computer.
 (If both programs are compiled with -fllvm -- I'm not sure whether or not
that's fair game on the Shootout -- my implementation is 35% faster, and
does 10% less allocation.)  I've checked my code on the Shootout's test
input, as well.

Mostly, the improvement comes from a tightly specialized version of (filter
(/= '\n')), although eliminating an intermediate list entirely (and one used
in a queuelike fashion) didn't seem to hurt.  I managed to cut the program
to a point where the program size is about the same as before.

The code is at http://hpaste.org/fastcgi/hpaste.fcgi/view?id=25865; the
previous implementation is at
http://shootout.alioth.debian.org/u32/program.php?test=revcomplang=ghcid=2
.

Let the arguing begin?

Louis Wasserman
wasserman.lo...@gmail.com
http://profiles.google.com/wasserman.louis
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Re: [Haskell-cafe] Haskell + CouchDB, anyone?

2010-06-01 Thread Лев Никитин

I hav not run your examples. But

1. May be you have put to couchdb only *object* (braked by {}) but not array?
2. Why not to define data (data Mydata = Mydata {...}) and
   declare it as instance of JSON
   you can find example of using couchDB via google.com/codesearch
(lang:haskell couchDB)


-- 
Никитин Лев.
n...@lab321.ru, leon.v.niki...@gmail.com
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Re: [Haskell-cafe] Re: [web-devel] Google Summer of Code: BlazeHTML RFC

2010-06-01 Thread Jeremy Shaw

A (hopefully) non-cropped version of the chart, http://tinyurl.com/2cl42js
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[Haskell-cafe] Parselib sample

2010-06-01 Thread C K Kashyap

Hi,
Is there a not-so-trivial parser implementation with Parselib? Parser for a
C like language would be good.
I searched and found Haskell++ -
http://www.cs.chalmers.se/~rjmh/Software/h++.html
However, I'd prefer to look at a parser for a C like language.

-- 
Regards,
Kashyap
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[Haskell-cafe] The state of Hackage: what are we doing about it?

2010-06-01 Thread Don Stewart

I see fairly regular complaints about too many Haskell libraries,
bewildering choice of difficult-to-determine quality.

I've tried to summarize the state of Hackage, and what projects are
active to make it easier to find high quality libraries:

http://tinyurl.com/2cqw9sb

Thoughts?

-- Don
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[Haskell-cafe] Re: LLVM - Haskell

2010-06-01 Thread Aaron Tomb


On May 31, 2010, at 3:02 PM, Tom Hawkins wrote:

 For instance, the LLVM.FFI.BitReader module has some functions that'll get 
 you a ModuleRef from some bitcode.
 
 getBitcodeModuleInContext :: ContextRef  - MemoryBufferRef  - Ptr
 ModuleRef  - Ptr  CString  - IO  Bool
 type ModuleRef = Ptr  Module
 data Module
 
 I'm confused how this works.  How does one get a Ptr ModuleRef to call
 this function?  Module is not Storable, so you can't use alloca or
 malloc.  And I don't see any functions in the library that returns a
 Ptr ModuleRef.  What am I missing?  (Sorry, I lack experience with
 Foreign.Ptr.)

That's a good question, and I'm not sure of the answer. I based my previous 
email  purely on a quick scan the documentation. I've never actually tried to 
use it. :)

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[Haskell-cafe] How to build an Indicator Type for a type class?

2010-06-01 Thread Steffen Schuldenzucker

Dear Cafe,

let:

 data True
 data False

 class C a

(arbitrary instances for C may follow)

Now, how to obtain an Indicator Type for C, i.e. a type IndC that is defined
via a type family / fundep / ... , so that

IndC a = True   forall a which are instances of C
IndC a = False  for all other a.

I've collected some failed approaches here[1]. My key problem is that if I
define (in the 3rd try):

 instance (C a) = IndC3 a True

, it does *not* mean Define this instance for all a which are an instance of
C, but Define the instance IndC3 a True for all types a, but it's not gonna
work if a is not an instance of C.

Does anyone have another idea?

Background:

After having implemented type-level lists[2] and a quicksort on them[3], I'd
like to have type-level sets. In their most simple implementation, sets are
just (unsorted) lists like this:

 data Nil
 data Cons a b
 class Elem x l
(instances for Elem so that Elem x l iff x is an element of the list l)

Now I want:

 type family Insert x s :: *

Insert x s = s  forall (x, s) with (Elem x s)
Insert x s = Cons x s   for all other (x, s).


Thanks a lot!

Steffen


[1] http://hpaste.org/fastcgi/hpaste.fcgi/view?id=25832#a25832
[2] Kiselyov, Peyton-Jones, Shan: Fun with type functions

http://research.microsoft.com/en-us/um/people/simonpj/papers/assoc-types/fun-with-type-funs/typefun.pdf
[3] I rewrote this algorithm using type families instead of fundeps:

http://www.haskell.org/haskellwiki/Type_arithmetic#An_Advanced_Example_:_Type-Level_Quicksort
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Re: [Haskell-cafe] Language Shootout reverse-complement benchmark

2010-06-01 Thread David Leimbach

I'm still trying to figure out what the point of the shootout really is.  If
there's no dedicated folks working with a language there, trying to make
things run faster, a language will come out looking inefficient potentially.
 There's a lot of compile flags and optimizations that can make a difference
in probably all of the languages listed on that page.

I guess all you can get from the shootout is a sense of what a particular
language or set of tools is capable of in the hands of the programmers who
submit implementations.  It doesn't really give you a concrete idea as to
how to evaluate a programming language.

It does still seem kind of fun for some reason though :-)

Dave

On Mon, May 31, 2010 at 5:47 PM, Louis Wasserman
wasserman.lo...@gmail.comwrote:

 Hey,

 I was looking at the reverse-complement benchmark on the Language Shootout,
 and among other things, I noticed that the Haskell implementation was using
 (filter (/= '\n')) on ByteStrings, and also using lists as queues.

 I had a few improvements which using -fasm seem to yield about a 19%
 improvement in speed, and a 35% reduction in allocation, on my computer.
  (If both programs are compiled with -fllvm -- I'm not sure whether or not
 that's fair game on the Shootout -- my implementation is 35% faster, and
 does 10% less allocation.)  I've checked my code on the Shootout's test
 input, as well.

 Mostly, the improvement comes from a tightly specialized version of (filter
 (/= '\n')), although eliminating an intermediate list entirely (and one used
 in a queuelike fashion) didn't seem to hurt.  I managed to cut the program
 to a point where the program size is about the same as before.

 The code is at http://hpaste.org/fastcgi/hpaste.fcgi/view?id=25865; the
 previous implementation is at
 http://shootout.alioth.debian.org/u32/program.php?test=revcomplang=ghcid=2
 .

 Let the arguing begin?

 Louis Wasserman
 wasserman.lo...@gmail.com
 http://profiles.google.com/wasserman.louis

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Re: [Haskell-cafe] name of this monadic combinator?

2010-06-01 Thread Mike Dillon

begin Brent Yorgey quotation:
On Sun, May 30, 2010 at 11:15:40AM -0700, Mike Dillon wrote:
begin Michael Snoyman quotation:
http://hackage.haskell.org/packages/archive/base/4.2.0.1/doc/html/Control-Monad.html#v%3AliftM2

file:///usr/share/doc/ghc6-doc/html/libraries/base-4.2.0.0/Control-Monad.html#v%3AliftM2Strangely,
Hayoo didn't turn this one up... anyone know why?

Hoogle finds it. I didn't think Hayoo was expected to do this sort of
abstract type signature search:

http://haskell.org/hoogle/?hoogle=Monad+m+%3D%3E+%28a+-%3E+a+-%3E+a%29+-%3E+m+a+-%3E+m+a+-%3E+m+a

It comes up as the second hit on that search or the first hit on this
one:

http://haskell.org/hoogle/?hoogle=Monad+m+%3D%3E+%28a+-%3E+b+-%3E+c%29+-%3E+m+a+-%3E+m+b+-%3E+m+c

That second search also shows zipWith in there; I never really thought
about zipWith being like liftM2 for the list Monad. I don't believe
that's actually true for the normal list Monad, but it should be true of
an alternate list Monad along the lines of the Functor and Applicative
instances for the ZipList newtype in Control.Applicative.

As Max noted, ZipList is not a monad. However, you have the right
idea: zipWith is exactly liftA2 (the equivalent of liftM2 for
Applicatives) for ZipList.

Thanks to both you and Max. After you guys responded, I went back and
found an interesting haskell-cafe discussion about how ZipList cannot be
made into a Monad from August 2009.

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