10.04.2012, 02:00, Ryan Ingram ryani.s...@gmail.com:
A concurring opinion here, and an example.
iff :: Bol - a - a - a
iff True x _ = x
iff False _ x = x
f, g :: Bool - Bool
f x = x
g x = iff x True False
Are these two functions equal? I would say yes, they are. Yet once you can
Hello! I've just realized that Haskell is no good for working with functions!
First, what are 'functions' we are interested at? It can't be the usual
set-theoretic definition, since it is not constructive. The constructive
definition should imply functions that can be constructed, computed.
If you are to describe a system, which consists of several subsystems, how do
you approach the problem? What types, classes, functions whatever do you
introduce?
I guess it is a common problem, is there a general method? Just to describe,
not to solve (though if the description implies the
Hello! I'm trying to have a class for booleans called Boolean (the methods are
not complete):
class MyEq a where
(===) :: (Boolean b) = a - a - b
class (MyEq a) = Boolean a where
(/\) :: a - a - a
instance MyEq Bool where
x === y = x==y
instance Boolean Bool where
(/\) = ()
Thank you all guys, fromBool did the trick.
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Is there a way to make the following code working?
{-# LANGUAGE TypeFamilies #-}
data family Foo a
data instance (Num a)= Foo a = A a deriving Show
data instance (Fractional a) = Foo a = B a deriving Show
I want to have different constructors for 'Foo a' depending on a class of 'a'.
I want to have Unicode symbols for type operator:
{-# LANGUAGE TypeOperators #-}
data a ── b = Foo a b
But it doesn't work. Any suggestions?
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+0400, Grigory Sarnitskiy wrote:
I want to have Unicode symbols for type operator:
{-# LANGUAGE TypeOperators #-}
Add also:
{-# LANGUAGE UnicodeSyntax #-}
data a ── b = Foo a b
But it doesn't work. Any suggestions?
Regards
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Hello! I just wonder whether it is possible to have a typeclass for topological
spaces?
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Oh, I guess the class would look something like that:
class TopologicalSpace a where
ifOpen :: (Subset a) - Bool
and Subset x is a type corresponding to subsets of x.
11.08.2011, 17:52, Grigory Sarnitskiy sargrig...@ya.ru:
Hello! I just wonder whether it is possible to have a typeclass
It is not possible in Haskell, moreover it seems to be too alien to Haskell.
Nevertheless, is there an extension which would allow to write a function that
returns the type of its argument?
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I've noted several times that GHC doesn't evaluate formulas for Double values
during compilation.
That is using
4.2326514735445615 instead of (512 / 0.844)**(1/3)
or
0.906179845938664 instead of (1/3) * sqrt(5 + 2 * sqrt(10 / 7))
This can lead to significant slowdown if such values are called
Hello!
I'm studying repa package and trying to implement O(N^2) n-body code. I'm using
Array DIM2 Double to represent the collection of particles.
I've managed to write a function which calculates the energy of one particle in
the field of others but I'm struggling to write a code to calculate
Hello!
I'm probing CUDA with Haskell, accelerate package to be exact. Sound stupid,
but I couldn't find how to actually construct an array, for example Vector
Float.
There is quite a number of examples provided with the package, but they seem
not simple enough for me just to start.
There's fromIArray and fromList [1]. Does that answer your question?
Huh, yes, thank you! But still I don't get it. Neither
arr1 = fromList 3 [1,2,3] :: Array DIM1 Int
nor
arr1 = fromList (1,3) [1,2,3] :: Array DIM1 Int
works
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Hello!
I've just started using parallel computations in Haskell. parMap works fine, it
is so easy to use. However, parMap fails with functions returning lazy
structures, e.g. tuples.
This code works as expected:
(parMap rpar) bm tvalues
bm :: Double - Double is some heavy function. But if I
How do I make my program stop whenever it gets somewhere NaN as a result during
a calculation? If there is no appropriate flag for ghc maybe there exist flags
for C to use in optc.
I don't want NaN to propagate, it is merely stupid, it should be terminated.
Hello, I'm searching a way to benefit from modern hardware in my programs.
I consider parallel programing to be actually easier than sequential one.
Parallel computation allows to avoid sophisticated algorithms that were
developed to gain performance on sequential architecture. It should also
I guess that deciding whether two functions are equal in most cases is
algorithmically impossible. However maybe there exists quite a large domain of
decidable cases? If so, how can I employ that in Haskell?
It is a common situation when one has two implementations of the same function,
one
Hello! Assume I have a type MyType with the constructor GeneralConstructor:
data MyType = GeneralConstructor [Double]
but I also want to have a separate name for special case of this constructor:
SpecialConstructor Double
so SpecialConstructor a = GeneralConstructor (a:[]) that is
18.03.2011, 14:22, Roel van Dijk vandijk.r...@gmail.com;:
Remember that constructors are functions, except that you can't
pattern match against them.
..
The downside is that you can't pattern-match against these functions.
The thing is that I need pattern matching, just functions won't
Hello!
I need to deal with functions of type (Double - Double). I need Fourier
transform, integration, + - * / operations, value of a function in a point,
probably composition.
However it is not very effective to use straightforwardly this type. Since
functions in question are rather smooth
I'm not very familiar with algebra and I have a question.
Imagine we have ring K. We also have two expressions formed by elements from K
and binary operations (+) (*) from K.
Can we decide weather these two expressions are equivalent? If there is such an
algorithm, where can I find something
Hello! The question is not about Haskell, but I don't know where else to ask.
In the book Computable functions by Vereshchagin and Shen it is said that it
is possible to invent a programming language such that each programming problem
has a unique solution in it. The author claims that this
I have a simple program that first generates a large (~ 500 mb) file of random
numbers and then reads the numbers back to find their sum.
It uses Data.Binary and Data.ByteString.Lazy.
The problem is when the program tries to read the data back it quickly (really
quickly) consumes all memory.
I have tweaked this program a few ways for you.
The big mistake (and why it runs out of space) is that you take
ByteString.Lazy.length to compute the block size. This forces the entire
file into memory -- so no benefits of lazy IO.
As a separate matter, calling 'appendFile . encode'
In System.Random StdGen is defined as
data StdGen = StdGen Int32 Int32
but its constructor StdGen is not exported. How to make StdGen to be an
instance of Binary? The following won't work:
instance Data.Binary.Binary StdGen where
put (StdGen aa ab) = do
Data.Binary.put aa
{-# OPTIONS_GHC -fglasgow-exts -XGenerics -package lang #-}
Got some problems:
Could not find module `Generics':
it is a member of package ghc-6.8.2, which is hidden
Failed, modules loaded: none.
and for ghci test.hs -fglasgow-exts -XGenerics -package lang
ghc-6.8.2: unknown
This time I've checked that it really compiles. Pretty much sure it works.
But how?! I'can't compile it:
test.hs:11:2:
Conflicting definitions for `put''
Bound at: test.hs:11:2-5
test.hs:13:2-5
test.hs:20:2-5
In the default-methods for class Binary'
Well, I've managed to produce a solution, quite ugly and unefficient. Still it
works (and I really need it). StdGen serialization occurs only once during
computation that lasts several hours, so the speed is not vital for me. Here is
my solution:
module Main where
import System.Random
import
How to install specific version of a package (derive 0.1.4)?
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Hello! I'm trying to derive Binary for StdGen with DrIFT:
module Main where
import System.Random
import Data.Binary
{-!for StdGen derive : Binary !-}
data Foo = Foo StdGen StdGen deriving (Show) {-! derive : Binary !-}
but I got error DrIFT: can't find module System/Random
What shall I do?
Hello! I can't understand why the following dummy example doesn't work.
{-# OPTIONS -XTypeSynonymInstances #-}
{-# OPTIONS -XFlexibleInstances #-}
module Main where
import Data.Array.Unboxed
class Particle p
type ParticleC = (Double, Double, Double)
instance Particle ParticleC
class
Thank you all, and especially Bulat. I've folowed the links and solved the problem in a new way.
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14.07.09, 12:37, Grigory Sarnitskiy sargrig...@ya.ru:
Hello! I can't understand why the following happens.
ghc --make -fforce-recomp -O2 -fexcess-precision -fvia-C -optc-O2 Run.lhs -o
Run -prof -auto-all
and
time ./Run TestSim
seems to be much faster (I got ~4 times faster indeed) than
14.07.09, 15:16, Malcolm Wallace malcolm.wall...@cs.york.ac.uk:
This is only a guess, but maybe there is a context-qualified CAF-like
value that is being re-evaluated multiple times in the non-profiling
case, but is appropriately monomorphised in the profiling case, so it
is only
To sum up here is the example that can write two arrays in one file and then
read this two arrays back. To restore written data it just reads the file into
bytestring, then splits the bytestring into equal parts. The parts are decoded.
I suppose the method is suitable for decoding files with
To sum up here is the example
that can write two arrays in one file and then read this two arrays
back. To restore written data it just reads the file into bytestring,
then splits the bytestring into equal parts. The parts are decoded. I
suppose the method is suitable for decoding files with
2009/05/02 Jason Dusek :The original poster should try serializing a tuple of arrays instead of serializing each array individually.Maybe, but I have some doubts. I have to operate with thousands of arrays --- are tuples good in such case? Moreover it is desirable to write data as it is
Hello!I'm interested in computer simulation of molecular systems, especially liquids. Maybe some would say Haskell is far from best choice in the case, but I really like the ease of writing programs in Haskell.So I wonder of existing projects of such type, both Molecular dynamics and Monte Carlo
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