Re: [Haskell-cafe] GADT and instance deriving
Hi Tillmann and Richard, Thanks for your answers. I have tried to analyze the code snippets you proposed. I've tried to transpose your examples to what I need, but it is not easy. The problem I see with putting the list of independent variables (*) at the type level is that at some time in my code I want for instance to perform formal mathematical operations, for example I want a function deriv that takes f(x(t),y(t),z(t)) as input, and returns df/dt = ∂f/∂x*dx/dt + ∂f/∂y*dy/dt + ∂f/∂z*dz/dt If the list of dependencies is encoded at the type level, I don't see how to produce the previous output from the knowledge of f(x(t),y(t),z(t)). You understand that what I want to do is some type of basic Computer Algebra System library. Moreover, I want overloading for infix functions as '*', '/', '⋅' (scalar product), × (vector product) etc., that is why I have used typeclasses (see the code I showed in my previous post). For example, for the time being I will restrict myself to scalar product between vector and vector, vector and dyadic, dyadic and vector (a dyadic is a tensor of order 2, a matrix if you prefer). So I have three instances for scalar product '⋅'. I don't see how to combine this idea of overloading or derivation function with what you proposed. But I have perhaps missed something. Thanks, TP (*): That is to say the list of tensors of which one tensor depends, e.g. [t,r] for E(t,r), or simply [x,y,z] for f(x(t),y(t),z(t)) where x, y, and z themselves are scalars depending on a scalar t). In the test file of my library, my code currently looks like: - type Scalar = Tensor Zero type Vector = Tensor One [...] let s = (t s []) :: Scalar let v = (t v [i s]) :: Vector let c1 = v + v let c2 = s + v⋅v - t is a smart constructor taking a string str and a list of independent variables, and makes a (Tensor order) of name str. So in the example above, s is a scalar that depends on nothing (thus it is an independent variable), v is a vector that depends on s (i is a smart constructor that wraps s into a Box constructor, such that I can put all independent variables in an heterogeneous list). c1 is the sum of v and v, i.e. is equal to 2*v. c2 is the sum of s and v scalar v. If I try to write: let c3 = s + v I will obtain a compilation error, because adding a scalar and a vector has no meaning. Is there some way to avoid typeable in my case? Moreover, if I wanted to avoid the String in the first argument of my smart constructor t, such that let s = (t []) :: Scalar constructs an independent Scalar of name s, googling on the topic seems to indicated that I am compelled to use Template Haskell (I don't know it at all, and this is not my priority). Thus, in a general way, it seems to me that I am compelled to use some meta features as typeable or Template Haskell to obtain exactly the result I need while taking benefit from a maximum amount of static type checking. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] ghc release schedule
I give ghc release schedule to google and get at/near the top: http://hackage.haskell.org/trac/ghc/wiki/Status/Releases whose title is Release plans for ghc 6.12 ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Cabal config file Guide
On 13-05-25 04:52 PM, Daniel Díaz Casanueva wrote: As you already know, cabal-install is configured in the file config. It has a lot of fields, but I didn't find a single place where each field is explained with detail. There is none, but my new and timely http://www.vex.net/~trebla/haskell/cabal-cabal.xhtml talks about a few, and one of them is a real surprise. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Fwd: Cabal config file Guide
Thank you, Albert, what you wrote is very useful. Why the Cabal Guide is lacking this kind of information? Maybe I should start gathering information in one place myself! Thank you, Daniel Díaz. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] ANNOUNCE: new bridge! (prelude-prime)
On Thu, May 23, 2013 at 6:13 AM, Roman Cheplyaka r...@ro-che.info wrote: * Manuel Gómez tar...@gmail.com [2013-05-23 08:33:15-0430] On Thu, May 23, 2013 at 3:07 AM, Roman Cheplyaka r...@ro-che.info wrote: Pull requests are welcome, but let's stick to widely agreed changes (like the Foldable/Traversable one). I think one of the reasons why other Preludes haven't been adopted is because they were too radical. * Andreas Abel andreas.a...@ifi.lmu.de [2013-05-20 13:26:05+0200] Maybe instead of fiddling with the current Prelude (which might break backwards compatibility), we should design a new prelude which is not automatically loaded but contains roughly the current prelude (with the list functions generalized to collections) plus the modern type class stack: Functor, Applicative, Monad, Foldable, Traversable, Monoid etc. Is this strategy adequate for attacking the issue of the type class stack, though? Defining, say, a new Monad class with the desired Functor constraint wouldn’t be of much use, as everything else on Hackage (and on the GHC libraries!) would still use the “real” Monad. No, it definitely isn't. I think that there is enough interest in fixing the functor typeclass hierarchy that we should probably get the ball rolling on making it a part of the next Haskell language standard. Yes, it would break code. Probably a lot of code. Which is exactly why it should be a part of the language standard, instead of an ad hoc compiler change. Ideally, the change would be synchronized with the release of a new Haskell Platform, as well, like the Haskell Platform 2010.2 (I think -- the first one tied to GHC 7.*) In particular, it would be very nice if we could just change Cabal files to explicitly use the haskell98 and haskell2010 packages to get the old interface back. Presumably, those packages would eventually be deprecated. Also, we might want the language standard to reserve the module namespace Haskell.* for modules like IO, instead of just plain IO. (So that we'd have Haskell.System.IO instead of IO /AND/ System.IO) I don't remember the details, but these module names are the only reason my code won't work with haskell98/2010 packages. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
