On 08/21/12 09:19, felipe zapata wrote:

Hi Haskellers,

I have been playing with the Repa functions and trying the Repa-examples. In order to gain experience with the Repa functions I have written some small linear algebra utilities and import this module to a bigger project. In the beginning of my project I used the mmultP function from the repa-examples to calculate a big matrix, therefore I have and array of type:

arr :: Monad m => m (Array U DIM2 Double)

Then I carried this array in a lot of functions which become Monadic function and then it is necessary to introduce the monadic machinery for manipulating this functions . The Question is then if there is the possibility to work with a pure function in place of the monadic version?

There is something like a runRepa function?

runRepa :: Monad m => m (Array U DIM2 Double) - > Array U DIM2 Double

or could I used the unsafePerformIO function ?

or the evaluation of the parallel arrays must be postponed until the Repa.Array is called in the main function?

When this change was introduced (there wasn't always the arbitrary monad m around everything), I remember I just wrapped my one big repa function in the identity monad and it worked fine. For example, -- Grid.hs import Control.Monad.Identity (Identity) ... zoom :: Values3D -> ScaleFactor -> Identity Values3D -- Main.hs import Control.Monad.Identity (runIdentity) ... let output = runIdentity $ zoom dbl_data zoom_factor This gives you the warm/fuzzy of knowing that the function is pure, but I think I eventually just let it run in IO to avoid introducing mtl as a dependency.