Re: [Haskell-cafe] HToolkit HSQL on Windows/GHC
Another thought, which I hesitate to even mention, would be to call the commandline tool via System.Cmd, pipe the results to a file, and read the file, and parse the results. Slow and ugly, but you could have it working in an hour. Hadn't even thought of that, must be my clean upbringing. No need even to use a file; just have it output to a pipe and read directly from the pipe... --KW 8-) -- Keith Wansbrough [EMAIL PROTECTED] http://www.cl.cam.ac.uk/users/kw217/ University of Cambridge Computer Laboratory. ___ Haskell-Cafe mailing list [EMAIL PROTECTED] http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] dimension of arrays
Is there a way to get the number of dimension of an array ? i.e. something like : dims :: (Ix a) = Array a b - Int dims = ... a = listArray (1,10) [1,2..] b = listArray ((1,1),(10,10)) [1,2..] dims a -- should be equal to 1 dims b -- should be equal to 2 The key is somewhere in the Ix class but where ? Fred -- --- Dr. Frederic Nicolier Maitre de conferences, laboratoire LAM - URCA Animateur du projet ANITA : http://f.nicolier.free.fr/recherches/ Dept. GEII, IUT de Troyes 9 rue de Quebec 10026 Troyes Cedex Tel: 03 25 42 71 01 Std: 03 25 42 46 46 Fax: 03 25 42 46 43 email: [EMAIL PROTECTED] - ___ Haskell-Cafe mailing list [EMAIL PROTECTED] http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] HToolkit HSQL on Windows/GHC
At 10:59 29/03/04 +0100, Keith Wansbrough wrote: Another thought, which I hesitate to even mention, would be to call the commandline tool via System.Cmd, pipe the results to a file, and read the file, and parse the results. Slow and ugly, but you could have it working in an hour. Hadn't even thought of that, must be my clean upbringing. No need even to use a file; just have it output to a pipe and read directly from the pipe... Like POpen for GHC/Posix? I'm having some trouble getting this to work for Hugs/Windows (even though the basic piping code for Windows is demonstrated to work). #g Graham Klyne For email: http://www.ninebynine.org/#Contact ___ Haskell-Cafe mailing list [EMAIL PROTECTED] http://www.haskell.org/mailman/listinfo/haskell-cafe
RE: [Haskell-cafe] looking for optimization advice
I think that adding the extra check to see if the pointers are identical sped this up enough that it's probably no longer a major issue--I'm pretty certain that the problem was large strings that were identical, so every byte had to be checked, so probably scary non-portable home-made ForeignPtrs would not be worth the effort. (Although I'm somewhat curious as to how it would be done...) A ForeignPtr allocated with mallocForeignPtr in GHC is heap-allocated garbage-collectable storage, and doesn't need a finalizer. The other kind of ForeignPtr created with newForeignPtr is associated with some external storage and needs a finalizer. Finalizers are expensive, and so is malloc(), but mallocForeignPtr is very cheap. This gives rise to a sum-type in the implementation of ForeignPtr: see the source code (libraries/base/GHC/ForeignPtr.hs). You could make a specialised version by ripping out the non-malloc ForeignPtr bits, and make an unboxable ForeignPtr type. A mallocForeignPtr-style ForeignPtr is essentially the same as an IOUArray. In fact, the underlying implementation type is the same (MutableByteArray#), except that a ForeignPtr is allocated in pinned (immovable) storage so that it can be passed to foreign functions. There could easily be a conversion from a malloc ForeignPtr to IOUArray. There is also some overlap with the StorableArray type. A StorableArray has a ForeignPtr inside it. It really looks like the framework could be simplified here, but I remember putting some thought into it and not coming up with a simple solution. Cheers, Simon ___ Haskell-Cafe mailing list [EMAIL PROTECTED] http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] dimension of arrays
On Mon, 29 Mar 2004, Fred Nicolier wrote:
Is there a way to get the number of dimension of an array ? i.e.
something like :
dims :: (Ix a) = Array a b - Int
dims = ...
a = listArray (1,10) [1,2..]
b = listArray ((1,1),(10,10)) [1,2..]
dims a -- should be equal to 1
dims b -- should be equal to 2
The key is somewhere in the Ix class but where ?
In a sense Haskell arrays are always one dimensional. But as you noted
tuples are used to achieve higher dimensionality. As far as I know there
is no way of asking for the dimension of an array. You could write your
own class for that though. Here's a suggestion:
\begin{code}
dims :: (Ix a, HasDimension a) = Array a b - Int
dims arr = dimension (head (range arr))
class HasDimension a where
dimension :: a - Int
instance HasDimension Int where
dimension _ = 1
instance HasDimension Float where
dimension _ = 1
instance HasDimension (a,b) where
dimension _ = 2
instance HasDimension (a,b,c) where
dimension _ = 3
\end{code}
And so forth. Beware. The code is untested.
Hope this helps.
/Josef
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Re: [Haskell-cafe] dimension of arrays
Josef Svenningsson wrote:
In a sense Haskell arrays are always one dimensional. But as you noted
tuples are used to achieve higher dimensionality. As far as I know there
is no way of asking for the dimension of an array. You could write your
own class for that though. Here's a suggestion:
\begin{code}
dims :: (Ix a, HasDimension a) = Array a b - Int
dims arr = dimension (head (range arr))
with the following correction, it is ok.
dims arr = dimension (head (range $ bounds arr))
thanks at lot
Fred
--
---
Dr. Frederic Nicolier
Maitre de conferences, laboratoire LAM - URCA
Animateur du projet ANITA : http://f.nicolier.free.fr/recherches/
Dept. GEII, IUT de Troyes
9 rue de Quebec
10026 Troyes Cedex
Tel: 03 25 42 71 01
Std: 03 25 42 46 46
Fax: 03 25 42 46 43
email: [EMAIL PROTECTED]
-
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[Haskell-cafe] Context for type parameters of type constructors
Sorry for sending this twice, but it seems to me that the newsgroup fa.haskell only logs the discussion of haskell and haskell-cafe. -- Forwarded message -- Date: Mon, 29 Mar 2004 01:18:27 -0800 From: [EMAIL PROTECTED] (Henning Thielemann) Newsgroups: fa.haskell Subject: Context for type parameters of type constructors NNTP-Posting-Host: 134.102.210.249 Message-ID: [EMAIL PROTECTED] I have a problem with type classes that can be illustrated with the following example: I want to declare a class for vector like data. 'Vector' is not meant as a synonyme for 'array' but a 'vector' shall be a mathematical object that allows for some linear operations, namely summing and scaling. Thus I setup a type constructor VectorSpace in the following way: module VectorSpace where class VectorSpace v where zero :: v a add :: v a - v a - v a scale :: a - v a - v a I haven't added context requirements like (Num a) to the signatures of 'zero', 'add', 'scale' because I cannot catch all requirements that instances may need. The problematic part is the 'scale' operation because it needs both a scalar value and a vector. Without the 'scale' operation 'v' could be simply a type (*) rather than a type constructor (* - *). Now let's try some instances: data (Num a) = VList a = VList [a] instance VectorSpace VList where zero = VList (repeat 0) add (VList x) (VList y) = VList (zipWith (+) x y) scale s (VList x) = VList (map (s*) x) data (Num a) = VFunc b a = VFunc (b-a) instance VectorSpace (VFunc b) where zero = VFunc (\_ - 0) add (VFunc f) (VFunc g) = VFunc (\x - (f x) + (g x)) scale s (VFunc f) = VFunc (\x - s*(f x)) But now GHC complains: $ ghc -c VectorSpace.lhs VectorSpace.lhs:37: Could not deduce (Num a) from the context (VectorSpace VList) arising from the literal `0' at VectorSpace.lhs:30 Probable fix: Add (Num a) to the class or instance method `zero' In the first argument of `repeat', namely `0' In the first argument of `VList', namely `(repeat 0)' In the definition of `zero': zero = VList (repeat 0) ... I hoped that when I declare VList within the context (Num a) then it is always asserted that a VList is built on a Num type. If it is necessary to add (Num a) somewhere in the instance declaration - then where? Btw. I'm using $ ghc --version The Glorious Glasgow Haskell Compilation System, version 6.0 ___ Haskell-Cafe mailing list [EMAIL PROTECTED] http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Context for type parameters of type constructors
Could not deduce (Num a) from the context (VectorSpace VList) The problem is in the definition: zero = VList (repeat 0) Is 0 an Int or an Integer? To define zero, instances need to be parameterised by vector type: EG: class VectorSpace v a where zero :: v a add :: v a - v a - v a scale :: a - v a - v a instance VectorSpace VList Int where zero = VList (repeat 0) ... instance VectorSpace VList Float where zero = VList (repeat 0.0) etc... Could not deduce (Num a) from the context (VectorSpace VList) The problem is in the definition: zero = VList (repeat 0) Is 0 an Int or an Integer? To define zero, instances need to be parameterised by vector type: EG: class VectorSpace v a where zero :: v a add :: v a - v a - v a scale :: a - v a - v a instance VectorSpace VList Int where zero = VList (repeat 0) ... instance VectorSpace VList Float where zero = VList (repeat 0.0) etc... Regards, Keean. ___ Haskell-Cafe mailing list [EMAIL PROTECTED] http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Context for type parameters of type constructors
On Mon, Mar 29, 2004 at 06:00:57PM +0200, Henning Thielemann wrote: Thus I setup a type constructor VectorSpace in the following way: module VectorSpace where class VectorSpace v where zero :: v a add :: v a - v a - v a scale :: a - v a - v a I haven't added context requirements like (Num a) to the signatures of 'zero', 'add', 'scale' because I cannot catch all requirements that instances may need. The problematic part is the 'scale' operation because it needs both a scalar value and a vector. Without the 'scale' operation 'v' could be simply a type (*) rather than a type constructor (* - *). Right. I recommend you use multi-parameter type classes, with a type of the scalars and the type of the vectors. For the method you're using, you need to add a 'Num a' context. You say that you 'cannot catch all requirements that instances may need', but certainly any instance will need that context. If you use multi-parameter type classes, then in your instance declaration you can specify exactly what requirements you need. For instance: class VectorSpace v a where zero :: v add :: v - v - v scale :: a - v - v instance VectorSpace IntArray Int where ... instance (Num a) = VectorSpace (GenericArray a) a where ... Peace, Dylan signature.asc Description: Digital signature ___ Haskell-Cafe mailing list [EMAIL PROTECTED] http://www.haskell.org/mailman/listinfo/haskell-cafe
