Writing Accelerate programs

Accelerate arrays are indexed by similar data types with Repa arrays, in other words, snoc-style lists:

data Z
data tail :. head = tail :. head

Like Repa, type synonyms are provided for Accelerate indices:

type DIM0 = Z
type DIM1 = DIM0 :. Int
type DIM2 = DIM1 :. Int
...

The Accelerate array type is Array sh e. We can build accelerated arrays from lists with fromList:

> import Data.Array.Accelerate as A
> fromList (Z :. 5) [1..5]
Array (Z :. 5) [1,2,3,4,5]

Now let's try to do something with an Array: reverse it. Accelerate provides the function reverse, but it has this slightly daunting type signature:

reverse :: Elt e => Acc (Vector e) -> Acc (Vector e)

And if we try to apply reverse to an array directly, we are greeted with a type-mismatch error:

> A.reverse (fromList (Z :. 5) [1..] :: Array DIM1 Int)

<interactive>:24:12:
    Couldn't match expected type 'Acc (Vector e)'
                with actual type 'Array DIM1 Int...