foldl1 (.) . fmap (f :: Int -> a -> a) [m..n] semantics in accellerate language?

[alios]

Asuming having a function

f :: Int -> a -> a

which should be used as kind of a generator function creating an a chained n times with an increasing Int which could be expressed in  std Haskell as

foo :: Int -> Int -> a -> a
foo i0 n = foldl1 (.) . fmap f . take n  $ [i0..]

which takes an start index (i0) and the number of iterations (n) and gives you the function f applyed an increasing number from i0 to i0 + n and chaining the resulting functions to a single a -> a using a fold.

So

let a = foo 1 2 a0

should be the same as

let b = f 3 . f 2 . f 1 $ a0

The problem is that this does not work with the accellerate language as it does not allow Arrays of functions.
So using fmap to partialy apply the increasing i to the f function to then take the list of functions an combine them to a single (a -> a) using the fold does not work.

Havent found a way yet to express this in acccellerate other then the b above (writing the calls to f with increasing i and the chain them by hand.

Accellerate has a generate and a iterate function but i'd kind need a combination of those.
As mentioned above although a map function exists , but the mapped function is only allowed to return primitive values and not functions.

Any Ideas?

[Trevor McDonell]

Hi,

Most likely, Accelerate will never support arrays of functions —- this goes against the design philosophy of data-parallelism, where we want to apply the same function to each element of an array.

Still, it may be possible to do what you want. Here is an example where I do something like what you propose above. It is not generating an array of functions, rather it just builds up a chain of operations to execute (which sounds more like what you want, actually).

Does that help?

-Trevor

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