Thanks a lot for your message. I can use a recent version of GHC 7.6.x (I will install the last version of Kubuntu for that purpose). However, it will take me some time to understand correctly this code (e.g. I do not know "data kinds"), I will go back to you if I encounter difficulties.
Thanks, TP On Monday, April 29, 2013 08:19:43 Richard Eisenberg wrote: > There's a lot of recent work on GHC that might be helpful to you. Is it > possible for your application to use GHC 7.6.x? If so, you could so > something like this: > > {-# LANGUAGE DataKinds, GADTs, KindSignatures #-} > > data Nat = Zero | Succ Nat > > type One = Succ Zero > type Two = Succ One > type Three = Succ Two > > -- connects the type-level Nat with a term-level construct > data SNat :: Nat -> * where > SZero :: SNat Zero > SSucc :: SNat n -> SNat (Succ n) > > zero = SZero > one = SSucc zero > two = SSucc one > three = SSucc two > > data Tensor (n :: Nat) a = MkTensor { dims :: SNat n, items :: [a] } > > type Vector = Tensor One > type Matrix = Tensor Two > > mkVector :: [a] -> Vector a > mkVector v = MkTensor { dims = one, items = v } > > vector_prod :: Num a => Vector a -> Vector a > vector_prod (MkTensor { items = v }) = ... > > specializable :: Tensor n a -> Tensor n a > specializable (MkTensor { dims = SSucc SZero, items = vec }) = ... > specializable (MkTensor { dims = SSucc (SSucc SZero), items = mat }) = ... > > > This is similar to other possible approaches with type-level numbers, but it > makes more use of the newer features of GHC that assist with type-level > computation. Unfortunately, there are no "constructor synonyms" or "pattern > synonyms" in GHC, so you can't pattern match on "MkVector" or something > similar in specializable. But, the pattern matches in specializable are > GADT pattern-matches, and so GHC knows what the value of n, the type > variable, is on the right-hand sides. This will allow you to write and use > instances of Tensor defined only at certain numbers of dimensions. > > I hope this is helpful. Please write back if this technique is unclear! > > Richard _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe