[Haskell-cafe] Efficient object identity (aka symbols as data)
[ TLDR: How do you do Lisp symbols in Haskell? ] What is the Haskell approach to efficient comparison and lookup of objects by their identity? Maybe a toy example would help to explain what I mean. Imagine that I want to use Haskell to maximize happiness in a situation where a bunch of people have to be assigned to certain groups according to their preferences, and some constraints on the group sizes. Conceptually my input data might be structured as follows: data Group = Group GroupName MaxGroupSize data Person = Person Name Group Group Group The program should partition the people into groups, attempting to get everyone into their most favoured groups. Whatever algorithm I choose to use for the optimization, will have to do lots of comparisons of Groups and Persons where their *identity* is all that matters: you don't need to look inside the objects. On the other hand, sometimes we will have to look inside the objects, for example in order to answer queries such as Which group did Johnny get and how far down his list of choices did that group feature?. I should be able to run the program on data that becomes available at run time. The lisper in me is crying out for (lisp-like-)symbols which I can create from the input data at run time and on which some extra information can be hung. How would I organize something like this in Haskell? Thanks. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Efficient object identity (aka symbols as data)
On Thu, May 26, 2011 at 04:45, Jacek Generowicz jacek.generow...@cern.chwrote: What is the Haskell approach to efficient comparison and lookup of objects by their identity? ghc uses Data.Unique to generate unique internal identifiers to associate with things. (Think gensym. Hm, except last time I did anything serious with Lisp, it was Maclisp... does gensym even still exist, or did CL do something inscrutable with it?) Beyond that, the existence of functions such as reallyUnsafePointerEquality# makes me think it's a Hard Problem. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Efficient object identity (aka symbols as data)
On 26 May 2011 10:45, Jacek Generowicz jacek.generow...@cern.ch wrote:
What is the Haskell approach to efficient comparison and lookup of objects
by their identity?
Often you just provide your own and implement Eq.
I should be able to run the program on data that becomes available at run
time.
Typically you define an id generator and zip anything coming from the
input stream up with that generator. So:
persons - fmap (zipWith addId [1..] . map parsePerson)
(hGetContents handle)
where addId id person = person { personId = id }
Whatever algorithm I choose to use for the optimization, will have to do
lots of comparisons of Groups and Persons where their *identity* is all that
matters: you don't need to look inside the objects.
To achieve this abstraction the usual way is just implementing Eq:
instance Eq Person where
Person{personId=id1} == Person{personId=id2} = id1 == id2
You can also implement ordering if required:
instance Ord Person where
Person{personId=id1} `compare` Person{personId=id2} = id1 `compare` id2
Then you can write person1 == person2 and person1 person2, etc.
without looking inside the object, and all the library functions you
have available like the list functions that work on Eq instances and
Ord instances will work for your data type automatically.
There're also some packages on Hackage for generating unique ids.
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Re: [Haskell-cafe] Efficient object identity (aka symbols as data)
On 2011 May 26, at 11:12, Brandon Allbery wrote: On Thu, May 26, 2011 at 04:45, Jacek Generowicz jacek.generow...@cern.ch wrote: What is the Haskell approach to efficient comparison and lookup of objects by their identity? ghc uses Data.Unique to generate unique internal identifiers to associate with things. At first blush it sounds like the sort of thing I'm after. Thanks. (Think gensym. Hm, except last time I did anything serious with Lisp, it was Maclisp... does gensym even still exist, or did CL do something inscrutable with it?) CL has gensym. But gensym does seem to be overkill in the case I presented. I *could*, for example, say data Person = Fred | Johnny | Sally | Belinda | Kate | Roger | Eric [... and so on for a few squillion ...] data Group = Amazing | Brilliant | Cool | Great | Funky [ ... and so on for a few dozen ...] preferences :: Map Person (Group, Group, Group) In this setup (Fred == Johnny) will be very cheap, and (lookup Fred preferences) will be less cheap but possible. I'd use gensym if I need a new symbol right about which I know nothing other than I want it to be new and unique (nobody has created it before, and nobody will in the future). In the example scenario, I know what I want the symbol is to be called, and am prepared to accept the responsibility for avoiding duplicates, but I still want to be able create it at run time. In the Haskell snippet above, the compiler protects me against duplication, but forces me to know the data at compile time. In Lisp terms, I'm looking for make-symbol and intern. Beyond that, the existence of functions such as reallyUnsafePointerEquality# makes me think it's a Hard Problem. :-) ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Efficient object identity (aka symbols as data)
On 2011 May 26, at 11:16, Christopher Done wrote:
On 26 May 2011 10:45, Jacek Generowicz jacek.generow...@cern.ch
wrote:
What is the Haskell approach to efficient comparison and lookup of
objects
by their identity?
Often you just provide your own and implement Eq.
I should be able to run the program on data that becomes available
at run
time.
Typically you define an id generator and zip anything coming from the
input stream up with that generator.
Makes sense.
Whatever algorithm I choose to use for the optimization, will have
to do
lots of comparisons of Groups and Persons where their *identity* is
all that
matters: you don't need to look inside the objects.
To achieve this abstraction the usual way is just implementing Eq:
instance Eq Person where
Person{personId=id1} == Person{personId=id2} = id1 == id2
Any comments on the relative efficiency of the above as compared to
A == B in the context of
data Foo = A | B | C | D | ... lots more ...
?
(I imagine that a Sufficiently Smart Compiler could reduce (==) ::
Person Person to just integer comparison.)
Thank you.
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Re: [Haskell-cafe] Efficient object identity (aka symbols as data)
On Thu, May 26, 2011 at 05:41, Jacek Generowicz jacek.generow...@cern.chwrote: On 2011 May 26, at 11:12, Brandon Allbery wrote: (Think gensym. Hm, except last time I did anything serious with Lisp, it was Maclisp... does gensym even still exist, or did CL do something inscrutable with it?) But gensym does seem to be overkill in the case I presented. (...) In Lisp terms, I'm looking for make-symbol and intern. I think I just landed on inscrutable; (gensym) used to do pretty much that, it rolled symbols starting from 'a for the first one generated in a given interpreter. (It has occurred to me that I was not entirely clear; the Mac in Maclisp was MACSYMA. Ancient stuff.) ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Strange Type Error
Hello, Could anyone help me understand what is wrong with the definition of f2 in the code below? class C a b where convert :: a - b convertToInt :: (C a Int) = a - Int convertToInt x = convert x f1 x = convertToInt x f2 = \x - convertToInt x f3 :: (C a Int) = a - Int f3 = \x - convertToInt x Thank you Regards J-C ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Status of Haskell + Mac + GUIs graphics
fltk definitely has some good points, but I've always found it hideously ugly. Of course the default gtk on osx is ugly too, but some of the available themes are nice. However, getting gtk with OpenGL on osx was fairly easy. Everything worked out of the box except gtkglext (Haskell package). I've submitted some patches for that which hopefully will be applied to the repo soon. This is what I used: git darcs ghc-7.0.3 (self-compiled) cabal-install macports gtk2 +no_x11 +quartz macports gtkglext +no_x11 +quartz gtk2hs from source gtkglext (Haskell) from source I use a self-compiled ghc, but this should work with any ghc. Mixing ghc and macports can cause problems with libiconv, but the solutions are pretty well-known. Since I compile ghc, I configure it to use macports's libiconv so there aren't any conflicts. sudo port install gtkglext +no_x11 +quartz (wait a while...) darcs get --lazy http://code.haskell.org/gtk2hs cd gtk cabal install gtk2hs-buildtools chmod +x bootstrap.sh ./bootstrap.sh -fhave-quartz-gtk (wait a while...) cd .. darcs get --lazy http://code.haskell.org/gtkglext cd gtkglext darcs apply gtkglext.dpatch cabal install Until the source tree gets patched, you'll have to manually apply the patch bundle. If you want to avoid macports, it should be possible to use gtk-osx and gtkglext from source instead. However, I've found gtk-osx to be unstable and quite difficult to build in the past, so I'd strongly recommend macports, at least for now. The source install of gtkglext works just fine and can be used with macports gtk2 (I tested this). Since this path already uses macports there's not much benefit though. Cheers, John L On Wed, May 25, 2011 at 9:07 PM, Evan Laforge qdun...@gmail.com wrote: fltk supports OpenGL on windows, X11, and OS X, though I've never used it. The thing it doesn't have is a haskell binding, but as I mentioned I just bind whatever I need when I need it and since I don't need much it's easy. Dunno if this applies in your case though. Maybe it's my NIH, but I like to start with something too simple and add what I need rather than start with something that has more than I need and try to get it working. On Wed, May 25, 2011 at 11:58 AM, Conal Elliott co...@conal.net wrote: Thanks, John. Encouraging bit of news. Please do let us know what you learn when you try. - Conal On Tue, May 24, 2011 at 1:28 AM, John Lato jwl...@gmail.com wrote: You can use gtkglext to get OpenGL support. With the official release of gtkglext-1.2.0 there's a bit of hacking involved (that was probably me you're referring to), but it looks like the repo head has native Quartz. With any luck, you just need to build gtkglext from the repo, then the gtkglext package. I might have some time to try this later today; I'll report back if I get results. John Lato On Tue, May 24, 2011 at 6:01 AM, Conal Elliott co...@conal.net wrote: Last I tried, there wasn't native support for OpenGL with gtk, and I need OpenGL. Then more recently, I heard of some progress in that area, but requiring lots of hacking to get it all compiling. Any recent news? - Conal On Mon, May 23, 2011 at 2:33 AM, John Lato jwl...@gmail.com wrote: Message: 17 Date: Fri, 20 May 2011 15:59:51 -0700 From: Evan Laforge qdun...@gmail.com Subject: Re: [Haskell-cafe] Status of Haskell + Mac + GUIs graphics To: Erik Hesselink hessel...@gmail.com Cc: haskell-cafe@haskell.org Message-ID: BANLkTi=74mm6ortu2e192jtoot9g49f...@mail.gmail.com Content-Type: text/plain; charset=ISO-8859-1 Note that it is supposed to be possible to build gtk2hs with gtk+osx, which will not use X11 but use the native OS X GUI. I've not been able to get this to work, but it's been a while since I tried. The Haskell wiki mentions it doesn't support Glade, but does support Cairo. If this were to work, gtk2hs would be a serious option as well. I've tried this 3 or 4 times, and failed every time. It's crazy complicated. I used to use this combination regularly. IME the difficulties are primarily with getting a working gtk+osx build. Once that was accomplished, gtk2hs was a straightforward install, provided you build from the src repo with the -quartz flag. Recently I've switched to using macports gtk2 with the quartz, no-x11 variant, which also uses native cocoa. This is much more reliable than gtk+osx. I don't know if it supports Glade though. My biggest problem with wx is that there's no support for building 64-bit wx applications on OS X. If that were fixed I might prefer it. John Lato ___ 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] Strange Type Error
The problem is the monomorphism restriction: http://www.haskell.org/haskellwiki/Monomorphism_restriction http://www.haskell.org/ghc/docs/7.0.2/html/users_guide/monomorphism.html http://stackoverflow.com/questions/tagged/monomorphism-restriction http://www.cs.auckland.ac.nz/references/haskell/haskell-intro-html/pitfalls.html This kicks everyone in the butt at least once. It would be good if GHC could point it out, as mine (6.12.3) just complains about no instance. Maybe GHC7 does point it out. It's a waste of people's time otherwise. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Strange Type Error
On Thu, May 26, 2011 at 06:01, jean-christophe mincke
jeanchristophe.min...@gmail.com wrote:
f1 x = convertToInt x
f2 = \x - convertToInt x
Absent useful things like error messages, I'll assume that you tripped
over the monomorphism restriction. That is, when you have a name that
doesn't take a direct parameter, there are additional constraints on
that name's type. (The inner lambda is not considered for this
purpose, so while in theory f1 and f2 should be identical, in practice
they are not unless you use {-# LANGUAGE NoMonomorphismRestriction
#-}.
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Re: [Haskell-cafe] Strange Type Error
On Thu, May 26, 2011 at 06:10, Christopher Done chrisd...@googlemail.com wrote: This kicks everyone in the butt at least once. It would be good if GHC could point it out, as mine (6.12.3) just complains about no instance. Maybe GHC7 does point it out. It's a waste of people's time otherwise. I think the Haskell standards committee is moving in the direction of eliminating it as being the wrong solution to the problem. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Efficient object identity (aka symbols as data)
On 2011 May 26, at 11:59, Brandon Allbery wrote: On Thu, May 26, 2011 at 05:41, Jacek Generowicz jacek.generow...@cern.ch wrote: On 2011 May 26, at 11:12, Brandon Allbery wrote: (Think gensym. Hm, except last time I did anything serious with Lisp, it was Maclisp... does gensym even still exist, or did CL do something inscrutable with it?) But gensym does seem to be overkill in the case I presented. (...) In Lisp terms, I'm looking for make-symbol and intern. I think I just landed on inscrutable; Nah, it's probably just me confusing you. (gensym) used to do pretty much that, it rolled symbols starting from 'a for the first one generated in a given interpreter. It still does essentially that. (Just don't be fooled by the name a: you can't access that symbol through that name. Aaaah, maybe in Maclisp it really did intern them under that name, but that would surprise me). '(gensym)' in CL is a bit like 'object()' in Python or 'new MyEmptyClass' in C++: the key point being that if you don't bind the thing being created right now, you'll never be able to get your hands on it again. Coming back on topic: Yes, I could use gensym for my purposes (though CL provides a variety of similar yet subtly different tools, which is why gensym feels a bit weird in this context). ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Efficient object identity (aka symbols as data)
On 2011 May 26, at 11:59, Jacek Generowicz wrote: (I imagine that a Sufficiently Smart Compiler could reduce (==) :: Person Person to just integer comparison.) Sorry, I meant (==) :: Person - Person - Bool in the above. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Parallel compilation and execution?
How do I compile and run this parallel program?
Michael
===
import Control.Parallel
nfib :: Int - Intnfib n | n = 1 = 1 | otherwise = par n1 (seq n2 (n1 +
n2 + 1)) where n1 = nfib (n-1) n2
= nfib (n-2)
{-nfib :: Int - Intnfib n | n = 1 = 1 | otherwise = nfib (n-1) + nfib
(n-2)-}
main = do putStrLn $ show $ nfib 39
===
[michael@hostname ~]$ ghc --make -threaded nfib.hs[michael@hostname ~]$ ./nfib
+RTS -N3nfib: the flag -N3 requires the program to be built with
-threadednfib: nfib: Usage: prog args [+RTS rtsopts | -RTS args] ...
--RTS argsnfib: nfib: +RTS Indicates run time system options
follownfib: -RTS Indicates program arguments follownfib: --RTS
Indicates that ALL subsequent arguments will be given to thenfib:
program (including any of these RTS flags)nfib: nfib: The following run time
system options are available:nfib: nfib: -? Prints this message and
exits; the program is not executednfib: --info Print information about the
RTS used by this programnfib: nfib: -Ksize Sets the maximum stack size
(default 8M) Egs: -K32k -K512knfib: -ksize Sets the initial thread stack
size (default 1k) Egs: -k4k -k2mnfib: nfib: -Asize Sets the minimum
allocation area size (default
512k) Egs: -A1m -A10knfib: -Msize Sets the maximum heap size (default
unlimited) Egs: -M256k -M1Gnfib: -Hsize Sets the minimum heap size
(default 0M) Egs: -H24m -H1Gnfib: -mn Minimum % of heap which must be
available (default 3%)nfib: -Gn Number of generations (default: 2)nfib:
-Tn Number of steps in younger generations (default: 2)nfib: -cn
Use in-place compaction instead of copying in the oldest generationnfib:
when live data is at least n% of the maximum heap size set withnfib:
-M (default: 30%)nfib: -c Use in-place compaction for all oldest
generation collectionsnfib: (the default is to use copying)nfib:
-w Use mark-region for the oldest generation (experimental)nfib: nfib:
-t[file] One-line GC statistics (if file omitted, uses stderr)nfib:
-s[file] Summary GC statistics (if file omitted, uses
stderr)nfib: -S[file] Detailed GC statistics (if file omitted, uses
stderr)nfib: nfib: nfib: -Z Don't squeeze out update frames on stack
overflownfib: -B Sound the bell at the start of each garbage
collectionnfib: nfib: -hT Heap residency profile (output file
program.hp)nfib: -isec Time between heap samples (seconds, default:
0.1)nfib: nfib: -Csecs Context-switch interval in seconds.nfib:
0 or no argument means switch as often as possible.nfib: Default:
0.02 sec; resolution is set by -V below.nfib: -Vsecs Master tick interval
in seconds (0 == disable timer).nfib: This sets the resolution for
-C and the profile timer -i.nfib: Default: 0.02 sec.nfib: nfib:
--install-signal-handlers=yes|nonfib: Install signal handlers
(default: yes)nfib: nfib: RTS options may also be specified using the GHCRTS
environment variable.nfib: nfib: Other RTS options may be available for
programs compiled a different way.nfib: The GHC User's Guide has full
details.nfib: [michael@hostname ~]$
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Re: [Haskell-cafe] Parallel compilation and execution?
On Thursday 26 May 2011 13:24:09, michael rice wrote:
How do I compile and run this parallel program?
Michael
===
import Control.Parallel
nfib :: Int - Int
nfib n | n = 1 = 1
| otherwise = par n1 (seq n2 (n1 + n2 + 1))
The 'seq' here should be a 'pseq' to ensure that n2 is (started to be)
calculated before (n1 + n2 +1) is evaluated (iirc, currently, both work
with ghc, but it's not guaranteed for seq).
where
n1 = nfib (n-1)
n2 = nfib (n-2)
{-nfib :: Int - Intnfib n | n = 1 = 1
| otherwise = nfib (n-1) + nfib (n-2)-}
main = do putStrLn $ show $ nfib 39
===
[michael@hostname ~]$ ghc --make -threaded nfib.hs
[michael@hostname ~]$ ./nfib +RTS -N3
In principle, that is the correct way to compile and run it (note that with
ghc-7, you don't need the --make).
nfib: the flag -N3 requires the program to be built with
-threaded
Have you previously compiled the programme without -threaded?
Unless you snipped the compilation messages, their absence strongly
indicates so.
If that is the case, you fell victim to ghc's recompilation-avoidance which
doesn't keep track of the flags a programme/module was compiled with, so it
saw that nothing [as far as it knows] changed, hence didn't recompile.
Then removing .o and .hi or passing -fforce-recomp will make it recompile
and link with the threaded runtime.
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Re: [Haskell-cafe] Function application layout
On 25/05/11 10:00, Jonas Almström Duregård wrote:
As an equivalent to:
f (x a) (y b) (z c)
Of course my intention is that the new keyword should initiate layout
syntax so we can write this:
f applied to
x a
y b
z c
Here's a (tongue-in-cheek) trick that allows for layout close to what
you wanted (spoiler: but not close enough!). We start by switching to
parameterised monads (which allow you to change the type of the monad as
you go down the do-block; look carefully at the second and third
parameters in the monad class):
{-# LANGUAGE RebindableSyntax #-}
import Control.Applicative
import Prelude ((++), (.), Num(..), Eq(..), ($), id, Int, Char,
String, Float, ?, const, Show(..), Fractional(..))
class Monad m where
(=) :: m a b y - (y - m b c z) - m a c z
return :: b - m a a b
() :: Monad m = m a b y - m b c z - m a c z
() m n = m = const n
Then we define a type for wrapping pure functions in this monad:
data Fun a b c = Fun (a - b) c
instance Monad Fun where
(=) (Fun f x) m = let Fun g y = m x in Fun (g . f) y
return x = Fun id x
Then we add a helper for unwrapping it:
($$) :: a - Fun a b c - b
($$) f (Fun g _) = g f
And a function for supplying an argument:
r :: a - Fun (a - b) b a
r x = Fun ($ x) x
And so what does let us do? Well, here's how it's used:
foo :: Int - Char - String - Float - String
foo a b c d = show (a, b, c, d)
eg :: String
eg = foo $$ do
r$ 2 + 1
r$ 'c'
r$ hello ++ goodbye
r$ 3.0
foo is the function we want to apply, and eg shows how to apply it in
do-notation with an argument on each line. I couldn't manage to remove
the r$ at the beginning of each line, which rather ruins the whole
scheme :-( On the plus side, there's no brackets, it's only two extra
characters per line, and you can have whatever you like after the r$.
For those who are interested, you can also use the same trick for
writing Applicatives in a do notation. Continuing the same module, we
can add an analogue for each of the types and functions for Applicative:
data App f a b c = App (f a - f b) c
instance Applicative f = Monad (App f) where
(=) (App f x) m = let App g y = m x in App (g . f) y
return x = App id x
($$) :: Applicative f = f a - App f a b c - f b
($$) f (App g _) = g f
s :: Applicative f = f a - App f (a - b) b (f a)
s x = App (* x) x
Then we can use this on things which are Applicative but not Monad, e.g.
egA :: [String]
egA = getZipList $ pure foo $$ do
s$ ZipList [3, 6, 7]
s$ ZipList hello
s$ ZipList [more, strings]
s$ ZipList [1.0, 1.5, 2.0]
And that's enough silly playing around :-)
Thanks,
Neil.
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Re: [Haskell-cafe] Parallel compilation and execution?
Thank, Daniel
Multiple threads are in evidence in my system monitor, but I wonder why I'm
getting two different answers, one twice the other. The first is the parallel
solution and the second is the non.
Michael
===
{-import Control.Parallel
nfib :: Int - Intnfib n | n = 1 = 1 | otherwise = par n1 (pseq n2 (n1 +
n2 + 1)) where n1 = nfib (n-1) n2
= nfib (n-2)-}
nfib :: Int - Intnfib n | n = 1 = 1 | otherwise = nfib (n-1) + nfib
(n-2)
main = do putStrLn $ show $ nfib 39
=
[michael@hostname ~]$ ghc --make -threaded nfib.hs[1 of 1] Compiling Main
( nfib.hs, nfib.o )Linking nfib ...[michael@hostname ~]$ ./nfib +RTS
-N3204668309[michael@hostname ~]$ ghc --make nfib.hs[1 of 1] Compiling Main
( nfib.hs, nfib.o )Linking nfib ...[michael@hostname ~]$
./nfib102334155[michael@hostname ~]$
--- On Thu, 5/26/11, Daniel Fischer daniel.is.fisc...@googlemail.com wrote:
From: Daniel Fischer daniel.is.fisc...@googlemail.com
Subject: Re: [Haskell-cafe] Parallel compilation and execution?
To: haskell-cafe@haskell.org
Cc: michael rice nowg...@yahoo.com
Date: Thursday, May 26, 2011, 8:16 AM
On Thursday 26 May 2011 13:24:09, michael rice wrote:
How do I compile and run this parallel program?
Michael
===
import Control.Parallel
nfib :: Int - Int
nfib n | n = 1 = 1
| otherwise = par n1 (seq n2 (n1 + n2 + 1))
The 'seq' here should be a 'pseq' to ensure that n2 is (started to be)
calculated before (n1 + n2 +1) is evaluated (iirc, currently, both work
with ghc, but it's not guaranteed for seq).
where
n1 = nfib (n-1)
n2 = nfib (n-2)
{-nfib :: Int - Intnfib n | n = 1 = 1
| otherwise = nfib (n-1) + nfib (n-2)-}
main = do putStrLn $ show $ nfib 39
===
[michael@hostname ~]$ ghc --make -threaded nfib.hs
[michael@hostname ~]$ ./nfib +RTS -N3
In principle, that is the correct way to compile and run it (note that with
ghc-7, you don't need the --make).
nfib: the flag -N3 requires the program to be built with
-threaded
Have you previously compiled the programme without -threaded?
Unless you snipped the compilation messages, their absence strongly
indicates so.
If that is the case, you fell victim to ghc's recompilation-avoidance which
doesn't keep track of the flags a programme/module was compiled with, so it
saw that nothing [as far as it knows] changed, hence didn't recompile.
Then removing .o and .hi or passing -fforce-recomp will make it recompile
and link with the threaded runtime.
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Re: [Haskell-cafe] Function application layout
On Thursday 26 May 2011 14:35:41, Neil Brown wrote: foo is the function we want to apply, and eg shows how to apply it in do-notation with an argument on each line. I couldn't manage to remove the r$ at the beginning of each line, which rather ruins the whole scheme :-( On the plus side, there's no brackets, it's only two extra characters per line, and you can have whatever you like after the r$. Wouldn't that be also achievable with infixl 0 ? (?) :: (a - b) - a - b f ? x = f x eg = foo ? 2 + 1 ? 'c' ? hello ++ goodbye ? 3.0 ? ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Parallel compilation and execution?
2011/5/26 michael rice nowg...@yahoo.com
Thank, Daniel
Multiple threads are in evidence in my system monitor, but I wonder why I'm
getting two different answers, one twice the other. The first is the
parallel solution and the second is the non.
Why do you add n1+n2+1 in the parallel program, but only n1+n2 in the
non-parallel one ?
Michael
===
{-
import Control.Parallel
nfib :: Int - Int
nfib n | n = 1 = 1
| otherwise = par n1 (pseq n2 (n1 + n2 + 1))
where n1 = nfib (n-1)
n2 = nfib (n-2)
-}
nfib :: Int - Int
nfib n | n = 1 = 1
| otherwise = nfib (n-1) + nfib (n-2)
main = do putStrLn $ show $ nfib 39
=
[michael@hostname ~]$ ghc --make -threaded nfib.hs
[1 of 1] Compiling Main ( nfib.hs, nfib.o )
Linking nfib ...
[michael@hostname ~]$ ./nfib +RTS -N3
204668309
[michael@hostname ~]$ ghc --make nfib.hs
[1 of 1] Compiling Main ( nfib.hs, nfib.o )
Linking nfib ...
[michael@hostname ~]$ ./nfib
102334155
[michael@hostname ~]$
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Re: [Haskell-cafe] Parallel compilation and execution?
From: michael rice, Thursday, May 26, 2011 Subject: Re: [Haskell-cafe] Parallel compilation and execution? Thank, Daniel Multiple threads are in evidence in my system monitor, but I wonder why I'm getting two different answers, one twice the other. The first is the parallel solution and the second is the non. Not exactly twice - (2n-1). What you get from counting all nodes in a binary tree (of function calls), compared to counting just the leaves. A program using only pure code, par, and pseq should be deterministic, so if it gets different value by building with and without threaded, changing the number of threads, or just running again, that's a bug in GHC (If it runs out of memory sometimes and not other times, that's not technically a bug, but still interesting). Replacing par with the second argument should also give an equivalent program. pseq isn't really parallel at all, but if you'd like to remove it, then replacing it with seq or just the second argument might change strictness and evaluation order, but shouldn't change the result. Brandon. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Parallel compilation and execution?
Fair question. I copied the parallel version from:
http://www.haskell.org/ghc/docs/6.6/html/users_guide/lang-parallel.html
but pulled the non-parallel version from a text.
Michael
--- On Thu, 5/26/11, David Virebayre dav.vire+hask...@gmail.com wrote:
From: David Virebayre dav.vire+hask...@gmail.com
Subject: Re: [Haskell-cafe] Parallel compilation and execution?
To: michael rice nowg...@yahoo.com
Cc: haskell-cafe@haskell.org, Daniel Fischer
daniel.is.fisc...@googlemail.com
Date: Thursday, May 26, 2011, 8:56 AM
2011/5/26 michael rice nowg...@yahoo.com
Thank, Daniel
Multiple threads are in evidence in my system monitor, but I wonder why I'm
getting two different answers, one twice the other. The first is the parallel
solution and the second is the non.
Why do you add n1+n2+1 in the parallel program, but only n1+n2 in the
non-parallel one ?
Michael
===
{-import
Control.Parallel
nfib :: Int - Intnfib n | n = 1 = 1
| otherwise = par n1 (pseq n2 (n1 + n2 + 1)) where
n1 = nfib (n-1)
n2 = nfib
(n-2)-}
nfib :: Int - Int
nfib n | n = 1 = 1 | otherwise = nfib (n-1) + nfib (n-2)
main = do putStrLn $ show $ nfib 39
=
[michael@hostname ~]$ ghc --make -threaded nfib.hs
[1 of 1] Compiling Main ( nfib.hs, nfib.o )Linking nfib ...
[michael@hostname ~]$ ./nfib +RTS -N3204668309[michael@hostname ~]$ ghc --make
nfib.hs
[1 of 1] Compiling Main ( nfib.hs, nfib.o )Linking nfib
...[michael@hostname ~]$ ./nfib102334155[michael@hostname ~]$
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Re: [Haskell-cafe] Efficient object identity (aka symbols as data)
Based on the description it looks like you could be looking for: http://hackage.haskell.org/package/simple-atom G On Thu, May 26, 2011 at 10:45 AM, Jacek Generowicz jacek.generow...@cern.ch wrote: [ TLDR: How do you do Lisp symbols in Haskell? ] What is the Haskell approach to efficient comparison and lookup of objects by their identity? Maybe a toy example would help to explain what I mean. Imagine that I want to use Haskell to maximize happiness in a situation where a bunch of people have to be assigned to certain groups according to their preferences, and some constraints on the group sizes. Conceptually my input data might be structured as follows: data Group = Group GroupName MaxGroupSize data Person = Person Name Group Group Group The program should partition the people into groups, attempting to get everyone into their most favoured groups. Whatever algorithm I choose to use for the optimization, will have to do lots of comparisons of Groups and Persons where their *identity* is all that matters: you don't need to look inside the objects. On the other hand, sometimes we will have to look inside the objects, for example in order to answer queries such as Which group did Johnny get and how far down his list of choices did that group feature?. I should be able to run the program on data that becomes available at run time. The lisper in me is crying out for (lisp-like-)symbols which I can create from the input data at run time and on which some extra information can be hung. How would I organize something like this in Haskell? Thanks. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe -- Gregory Collins g...@gregorycollins.net ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Efficient object identity (aka symbols as data)
2011/5/26 Jacek Generowicz jacek.generow...@cern.ch:
On 2011 May 26, at 11:16, Christopher Done wrote:
On 26 May 2011 10:45, Jacek Generowicz jacek.generow...@cern.ch wrote:
What is the Haskell approach to efficient comparison and lookup of
objects
by their identity?
Often you just provide your own and implement Eq.
I should be able to run the program on data that becomes available at run
time.
Typically you define an id generator and zip anything coming from the
input stream up with that generator.
Makes sense.
Whatever algorithm I choose to use for the optimization, will have to do
lots of comparisons of Groups and Persons where their *identity* is all
that
matters: you don't need to look inside the objects.
To achieve this abstraction the usual way is just implementing Eq:
instance Eq Person where
Person{personId=id1} == Person{personId=id2} = id1 == id2
Any comments on the relative efficiency of the above as compared to
A == B in the context of
data Foo = A | B | C | D | ... lots more ...
?
(I imagine that a Sufficiently Smart Compiler could reduce (==) :: Person
Person to just integer comparison.)
I'm pretty sure GHC will do that for you.
An approach similar to the one by Chris Done is to use a
bi-directional map between Persons and Ints along the lines of
data IdMap a = IdMap (IntMap a) (Map a Int)
You can then associate a unique Int with each of your Persons and use
this during your comparison. For associating Ints to the Persons, a
simple fold or a State monad computation suffice. For the lookups on
the further properties of Persons, an additional argument or the
Reader monad will do. If you use a State monad and a single operation
that associates an Int to a Person, then you additionally get the
guarantee (inside a monadic computation) that no two Persons will be
associated with the same Int.
Efficiency-wise, you'll have O(log(n)) association, O(min(n,W))
access time, and O(1) comparison time with a very low constant factor.
See the IntMap documentation for the O(min(n,W)) explanation.
Additionally, the code is pure with all the nice properties that come
with it.
By the way this problem is very similar to the one of observable
sharing. See this thread:
http://www.haskell.org/pipermail/haskell-cafe/2008-February/039639.html
best regards,
Simon
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Re: [Haskell-cafe] Function application layout
That's a useful operator! Unfortunately it does not play nice with $. Of less importance: some syntactic constructs can not appear in the arguments without parenthesis, let bindings for instance (although lambda abstraction works parenthesis-free). Also I'm not sure this can be used for defining trees or nested function application since a nesting of the operator inevitably require parenthesis. /J On 26 May 2011 14:52, Daniel Fischer daniel.is.fisc...@googlemail.comwrote: On Thursday 26 May 2011 14:35:41, Neil Brown wrote: foo is the function we want to apply, and eg shows how to apply it in do-notation with an argument on each line. I couldn't manage to remove the r$ at the beginning of each line, which rather ruins the whole scheme :-( On the plus side, there's no brackets, it's only two extra characters per line, and you can have whatever you like after the r$. Wouldn't that be also achievable with infixl 0 ? (?) :: (a - b) - a - b f ? x = f x eg = foo ? 2 + 1 ? 'c' ? hello ++ goodbye ? 3.0 ? ___ 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] Function application layout
On Thursday 26 May 2011 17:22:10, Jonas Almström Duregård wrote: Unfortunately it does not play nice with $. Yes. Also I'm not sure this can be used for defining trees or nested function application since a nesting of the operator inevitably require parenthesis. It can't be nested, like ($) can't be nested. You could however add infixl 1 ?? infixl 2 ??? ... to achieve the possibility of nesting (but you have to be careful with low- precedence operators if you actually want to use that). As far as I'm concerned, a left-associative version of ($) would sometimes be nice (on the other hand, right-associativity of ($) is sometimes also nice), but usually, I don't find parentheses too obnoxious. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Enterprise Haskell -- help
folks: I was advised to post this request here. This is about needs of daily-grind enterprise development. Enterprise developers need 3 categories of books in Haskell urgently: (i) Haskell (CookBooks / Recipes) (ii) Haskell Enterprise Development i.e. how to connect commercial RDBMS and use Haskell along with SQL effectively (iii) Haskell Web/Network Development Books by Don Stewart Miran Lipovaca are excellent for beginner/intermediaries. Erik Meijer's tutorial videos were very useful as well. But they are not enough. This may sound boring, but such books are badly needed today. It's hard to convince clients/devs to start projects without such resources. I am trying to push for Enterprise Haskell projects. Would appreciate pointers to resources for doing large scale Haskell development Thank you -ram ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Enterprise Haskell -- help
On Thu, May 26, 2011 at 9:45 AM, Srinivasan Balram srinivasan_bal...@marlabs.com wrote: folks: I was advised to post this request here. This is about needs of daily-grind enterprise development. Enterprise developers need 3 categories of books in Haskell urgently: (i) Haskell (CookBooks / Recipes) The HaskellWiki has a bit of this CookBook sort of stuff already. I haven't read it so I don't know about the quality, but it should be a good starting point: http://haskell.org/haskellwiki/Cookbook And the wikibooks project has some excellent articles about Haskell as well: http://en.wikibooks.org/wiki/Haskell (ii) Haskell Enterprise Development i.e. how to connect commercial RDBMS and use Haskell along with SQL effectively Database connectivity is a weakspot still. Haskell developers don't seem to use databases nearly as often as Java developers. We have several libraries for this, takusen and hdbc come to mind. Real-World Haskell documents using hdbc. (iii) Haskell Web/Network Development This is very broad. Checkout yesod and snap if you want to generate content from a Haskell based http server. I hope that helps, Jason ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Enterprise Haskell -- help
While it's not a solution (yet) for a book, would a section or special section in the wiki be appropriate at least in the beginning? Our small company has been collecting cookbook-like recipies and best practices for a while now but definitely not anything close to as polished or collated as a book. On Thu, May 26, 2011 at 04:45:15PM +, Srinivasan Balram wrote: folks: I was advised to post this request here. This is about needs of daily-grind enterprise development. Enterprise developers need 3 categories of books in Haskell urgently: (i) Haskell (CookBooks / Recipes) (ii) Haskell Enterprise Development i.e. how to connect commercial RDBMS and use Haskell along with SQL effectively (iii) Haskell Web/Network Development Books by Don Stewart Miran Lipovaca are excellent for beginner/intermediaries. Erik Meijer's tutorial videos were very useful as well. But they are not enough. This may sound boring, but such books are badly needed today. It's hard to convince clients/devs to start projects without such resources. I am trying to push for Enterprise Haskell projects. Would appreciate pointers to resources for doing large scale Haskell development ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Enterprise Haskell -- help
On Thu, May 26, 2011 at 11:17 AM, Clint Moore cl...@ivy.io wrote: While it's not a solution (yet) for a book, would a section or special section in the wiki be appropriate at least in the beginning? Our small company has been collecting cookbook-like recipies and best practices for a while now but definitely not anything close to as polished or collated as a book. That's exactly what the cookbook part of the wiki is for, put your stuff there: http://haskell.org/haskellwiki/Cookbook Jason ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Enterprise Haskell -- help
On Thu, May 26, 2011 at 10:57:42AM -0700, Jason Dagit wrote: Database connectivity is a weakspot still. Haskell developers don't seem to use databases nearly as often as Java developers. We have several libraries for this, takusen and hdbc come to mind. Real-World Haskell documents using hdbc. For what it's worth, we've had very good luck with Persistent. Even though it's not very enterprisey to base a product on an unseasoned library, it solved so many problems that we just couldn't ignore it. Perhaps we should write something in the wiki that goes beyond the tutorial in the Yesod book. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Enterprise Haskell -- help
On Thu, May 26, 2011 at 7:45 PM, Srinivasan Balram srinivasan_bal...@marlabs.com wrote: folks: I was advised to post this request here. This is about needs of daily-grind enterprise development. Enterprise developers need 3 categories of books in Haskell urgently: (i) Haskell (CookBooks / Recipes) (ii) Haskell Enterprise Development i.e. how to connect commercial RDBMS and use Haskell along with SQL effectively (iii) Haskell Web/Network Development Books by Don Stewart Miran Lipovaca are excellent for beginner/intermediaries. Erik Meijer's tutorial videos were very useful as well. But they are not enough. This may sound boring, but such books are badly needed today. It's hard to convince clients/devs to start projects without such resources. I am trying to push for Enterprise Haskell projects. Would appreciate pointers to resources for doing large scale Haskell development Thank you -ram The Yesod book[1] is being actively worked on, and covers web development with the Yesod web framework. Though many of the chapters there should be applicable to other systems, such as the enumerators chapter. Michael [1] http://www.yesodweb.com/book ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Efficient object identity (aka symbols as data)
On 26/05/2011 10:59 AM, Jacek Generowicz wrote: Any comments on the relative efficiency of the above as compared to A == B in the context of data Foo = A | B | C | D | ... lots more ... ? (I imagine that a Sufficiently Smart Compiler could reduce (==) :: Person Person to just integer comparison.) My understanding is that if you have a constructor with no fields, it gets allocated as a compile-time constant. In other words, C is just a pointer to a static data structure somewhere in the program binary, and (==) effectively becomes pointer equity. OTOH, I am not a GHC developer... ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Function application layout
2011/5/26 Daniel Fischer daniel.is.fisc...@googlemail.com As far as I'm concerned, a left-associative version of ($) would sometimes be nice (on the other hand, right-associativity of ($) is sometimes also nice), but usually, I don't find parentheses too obnoxious. I have a whole set of function application/composition/lifting operators that I'm rather fond of, but it involves replacing some standard operators, and in particular changes the fixity of ($) drastically, so it's something I only use in small bits of personal code that I'll never publish anywhere. The main idea is that there are two groups of operators, each of which are internally pretty consistent and vaguely generalized from standard operators. Very low precedence, function application associates toward argument: f | x = x | f = f x, () and () for composition, and (=), (=), (=), and (=) behaving as expected. (|) takes the place of standard ($), and (|) allows a pipe forward style similar to using (=). Mid-to-high precedence, function application associates away from argument: ($) has the same fixity as ($) and (*), as do the binding operators (=$) and (=*), the latter being a function I haven't seen before that does about what you'd expect from the name. Composition is usually just (.) in most cases because of the style in which I use these. What it amounts to is that the first group is used mostly as pseudo-syntax delimiting expressions that would otherwise be parenthesized, while the second group is used for writing expressions that would conceptually be simple one-liners if not for involving lifting into some sort of Functor. The choice of symbols makes it easy to remember which is which, even if it's not perfectly consistent. Mostly, though, this is probably just another reason why my personal coding style would be bafflingly opaque to most people, so oh well. - C. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Efficient object identity (aka symbols as data)
On Thu, May 26, 2011 at 14:56, Andrew Coppin andrewcop...@btinternet.com wrote: My understanding is that if you have a constructor with no fields, it gets allocated as a compile-time constant. In other words, C is just a pointer to a static data structure somewhere in the program binary, and (==) effectively becomes pointer equity. When used as a general function, at least; my understanding is that it's usually reduced to an integer tag (and that this is relied on to do fast conversions internally) ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Efficient object identity (aka symbols as data)
On 26/05/2011 07:56 PM, Andrew Coppin wrote: On 26/05/2011 10:59 AM, Jacek Generowicz wrote: Any comments on the relative efficiency of the above as compared to A == B in the context of data Foo = A | B | C | D | ... lots more ... ? (I imagine that a Sufficiently Smart Compiler could reduce (==) :: Person Person to just integer comparison.) My understanding is that if you have a constructor with no fields, it gets allocated as a compile-time constant. In other words, C is just a pointer to a static data structure somewhere in the program binary, and (==) effectively becomes pointer equity. OTOH, I am not a GHC developer... ...and what I *should* of course have written is go benchmark it. ;-) ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Enterprise Haskell -- help
Without support for at least extensible records and better GUI integration, you'd have a hard time convincing me to use Haskell for enterprise applications (and I use Haskell every day). It's not that Haskell isn't a fine language, it's just that doesn't have sufficient advantage on the state-of-practice that would counter balance its position as a marginal language. There are good reasons why enterprise development is conservative, state-of-the-art languages like Haskell or Erlang excel in domains where they can be disruptive. Best wishes Stephen ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Enterprise Haskell -- help
On Thu, May 26, 2011 at 1:09 PM, Gaius Hammond ga...@gaius.org.uk wrote: On 26 May 2011, at 19:22, Clint Moore wrote: On Thu, May 26, 2011 at 10:57:42AM -0700, Jason Dagit wrote: Database connectivity is a weakspot still. Haskell developers don't seem to use databases nearly as often as Java developers. We have several libraries for this, takusen and hdbc come to mind. Real-World Haskell documents using hdbc. For what it's worth, we've had very good luck with Persistent. Even though it's not very enterprisey to base a product on an unseasoned library, it solved so many problems that we just couldn't ignore it. Perhaps we should write something in the wiki that goes beyond the tutorial in the Yesod book. Over in OCaml-land, I have taken it upon myself to address this: http://gaiustech.github.com/ociml/ Takusen already supports Oracle (and other rdbms) in a resource precise and good performance way, if that's what you're talking about implementing: http://projects.haskell.org/takusen/ Jason ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Enterprise Haskell -- help
On 26 May 2011, at 21:34, Jason Dagit wrote: On Thu, May 26, 2011 at 1:09 PM, Gaius Hammond ga...@gaius.org.uk wrote: Over in OCaml-land, I have taken it upon myself to address this: http://gaiustech.github.com/ociml/ Takusen already supports Oracle (and other rdbms) in a resource precise and good performance way, if that's what you're talking about implementing: http://projects.haskell.org/takusen/ Ah, interesting - I was only aware of HDBC and HSQL. Which in turn begs the question, why isn't this better known among (us) Enterprise dev types? Cheers, G ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Policy for taking over a package on Hackage
On Wed, May 25, 2011 at 4:02 PM, Ivan Lazar Miljenovic ivan.miljeno...@gmail.com wrote: On 26 May 2011 08:49, wren ng thornton w...@freegeek.org wrote: On 5/25/11 1:03 PM, Bryan O'Sullivan wrote: On Wed, May 25, 2011 at 5:59 AM, Ivan Lazar Miljenovic ivan.miljeno...@gmail.com wrote: Well, using the Char8 version. Just because you *could* do that, it doesn't mean that you *should*. It's a bad idea to use bytestrings for manipulating text, yet the only plausible reason to have wl-pprint handle bytestrings is so that they can be used as text. It's worth highlighting that even with the Char8 version of ByteStrings you still run into encoding issues. Remember the days before Unicode came about? True, 8-bit encodings are often ASCII-compatible and therefore the representation of digits and whitespace are consistent regardless of (ASCII-compatible) encoding, but that's still just begging for issues. What are the semantics of the byte 0xA0 with respect to pretty-printing issues like linewraps? Are they consistent among all extant 8-bit encodings? What about bytes in 0x80..0x9F? What about 0x7F for that matter? I won't say that ByteStrings should never be used for text (there are plenty of programs whose use of text involves only whitespace splitting and moving around the resultant opaque blobs of memory). But at a bare minimum, the use of ByteStrings for encoding text needs to be done via newtype wrapper(s) which keep track of the encoding. Especially for typeclass instances. *shrug* this discussion on #haskell came about because lispy wanted to generate textual ByteStrings (using just ASCII) and would prefer not to have the overhead of Text. Actually, I am okay with Text. My application is translating GHC Core to other languages. I may have misrepresented my position on IRC. Oops. In the case of GHC Core, all the unicode bytes are z encoded [1] away so that I'm certain to just have ascii bytes, and I don't think performance will be an issue. Being able to choose between String and Text in the same library is nice. Once you add support for letting the user specify their choice of String or Text, does it really cost that much to add ByteString? I think there are some cases where ByteString might make sense. Take darcs patches. Darcs does it's best to be encoding agnostic about patch hunk data, yet the syntax surrounding the hunk data is just ascii compatible bytes. Last time I checked, ByteString was still used to store the patch hunks as just a blob of bytes. You end up passing that to some pretty printer code when serializing it, even though you're doing your best not to dictate the encoding. I know darcs has had a lot of important utf-8 changes since I looked at the hunk representation code so what I said above may no longer be the case. Admittedly it's a rare case. Jason [1] http://hackage.haskell.org/package/zenc ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Enterprise Haskell -- help
On Thu, May 26, 2011 at 1:43 PM, Gaius Hammond ga...@gaius.org.uk wrote: On 26 May 2011, at 21:34, Jason Dagit wrote: On Thu, May 26, 2011 at 1:09 PM, Gaius Hammond ga...@gaius.org.uk wrote: Over in OCaml-land, I have taken it upon myself to address this: http://gaiustech.github.com/ociml/ Takusen already supports Oracle (and other rdbms) in a resource precise and good performance way, if that's what you're talking about implementing: http://projects.haskell.org/takusen/ Ah, interesting - I was only aware of HDBC and HSQL. Which in turn begs the question, why isn't this better known among (us) Enterprise dev types? I'm not certain, but I think the biggest problems getting in the way of Takusen's greater adoption are: * It requires a deeper understanding of Haskell than HDBC due to use of functional dependencies, rank-2 types, and left-fold enumerators. * Less documentation than its competitors * The name is good (it's the japanese word for oracle), but doesn't evoke that's clearly a db library in most english speakers. As the current maintainer (and I've been a really lazy maintainer, still hoping to find a proper long term maintainer), I'm interested in any feedback about Takusen. Things I would like to eventually implement: * HDBC compatibility layer to make it easier to transition from HDBC to Takusen * Replace the left-fold enumerator code with a proper iteratee library (Takusen is by Oleg but predates his work that generalized the approach). Jason ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] (no subject)
As you my friend I invite you to visit my own site first!. http://prospero.ch/friends_links.php?uGIS=45ru4 ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Parallel compilation and execution?
Are the tools of Control.Parallel comparable to OpenMP?
Michael
--- On Thu, 5/26/11, michael rice nowg...@yahoo.com wrote:
From: michael rice nowg...@yahoo.com
Subject: Re: [Haskell-cafe] Parallel compilation and execution?
To: David Virebayre dav.vire+hask...@gmail.com
Cc: Daniel Fischer daniel.is.fisc...@googlemail.com,
haskell-cafe@haskell.org
Date: Thursday, May 26, 2011, 9:32 AM
Fair question. I copied the parallel version from:
http://www.haskell.org/ghc/docs/6.6/html/users_guide/lang-parallel.html
but pulled the non-parallel version from a text.
Michael
--- On Thu, 5/26/11, David Virebayre dav.vire+hask...@gmail.com wrote:
From: David Virebayre dav.vire+hask...@gmail.com
Subject: Re:
[Haskell-cafe] Parallel compilation and execution?
To: michael rice nowg...@yahoo.com
Cc: haskell-cafe@haskell.org, Daniel Fischer
daniel.is.fisc...@googlemail.com
Date: Thursday, May 26, 2011, 8:56 AM
2011/5/26 michael rice nowg...@yahoo.com
Thank, Daniel
Multiple threads are in evidence in my system monitor, but I wonder why I'm
getting two different answers, one twice the other. The first is the parallel
solution and the second is the non.
Why do you add n1+n2+1 in the parallel program, but only n1+n2 in the
non-parallel one ?
Michael
===
{-import
Control.Parallel
nfib :: Int - Intnfib n | n = 1 = 1
| otherwise = par n1 (pseq n2 (n1 + n2 + 1)) where
n1 = nfib (n-1)
n2 = nfib
(n-2)-}
nfib :: Int - Int
nfib n | n = 1 = 1 | otherwise = nfib (n-1) + nfib (n-2)
main = do putStrLn $ show $ nfib 39
=
[michael@hostname ~]$ ghc --make -threaded nfib.hs
[1 of 1] Compiling Main ( nfib.hs, nfib.o )Linking nfib ...
[michael@hostname ~]$ ./nfib +RTS -N3204668309[michael@hostname ~]$ ghc --make
nfib.hs
[1 of 1] Compiling Main ( nfib.hs, nfib.o )Linking nfib
...[michael@hostname ~]$ ./nfib102334155[michael@hostname ~]$
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[Haskell-cafe] Email spam from my account on May 26, 2011
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[Haskell-cafe] Escaping of string literals
Hi all,
I'm working on a program right now that will involve embedding some
static files inside my Haskell program as bytestrings. I've done this
in the past with file-embed[1]. In this case, I have a strange
requirement: I need to be able to modify the embedded data after the
compiler has run. In general, I've gotten the code to work (and will
soon be following up with a blog post explaining). But in this
process, I ran into something I found interesting. If I run this
program:
{-# LANGUAGE TemplateHaskell #-}
import Data.ByteString.Unsafe (unsafePackAddressLen)
import Language.Haskell.TH.Syntax
import qualified Data.ByteString as S
main = do
fromAddr - unsafePackAddressLen 7 $(return $ LitE $
StringPrimL 123\0\456)
print fromAddr
let fromStr = S.pack $ map (toEnum . fromEnum) $(return $ LitE
$ StringL 123\0\456)
print fromStr
I get the result:
123\192\128\45
123\NUL456
My understanding is that GHC is automatically escaping the non-ASCII
characters in the strings. When I use StringL, GHC also automatically
unescapes the bytes, so everything works as expected. In the case of
StringPrimL, there is no point at which the unescaping occurs.
I haven't been able to find the rules on how this escaping functions.
Can anyone point it out to me? Also, for my case, it would be very
useful to be able to bypass the escaping. I can easily do so with a
post-process on the executable to embed raw bytes, but I'm wondering
if there's some way to convince StringPrimL not to do any escaping.
Thanks,
Michael
[1] http://hackage.haskell.org/package/file-embed
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