Support non-identity elements for scan, fold

[seanl]

It seems that the default value is ignored for Prelude.snd $ Acc.scanl. For example

CUDA.run $ Prelude.snd $ Acc.scanl (+) 5 (Acc.use (fromList 10 [0..]) :: Acc (Vector Word32))

should produce

Array () [50]

however, it produces

Array () [45]

which is

0+ 1 + 2 + 3 + 4 + 5 + 6 + 7 + 8 + 9

CUDA.run $ Prelude.snd $ Acc.scanl (*) 5 (Acc.use (fromList 10 [1..]) :: Acc (Vector Word32))

should produce

Array () [18144000]

however it produces

Array () [3628800]

which is

1 * 2 * 3 * 4 * 5 * 6 * 7 * 8 * 9 * 10

[tmcdonell]

More that it did not include the neutral value in the reduction.

[tmcdonell]

I have a patch that addresses this, but the issue is that this is outside the definition of scan in Accelerate. Namely, in the example above 5 is not the neutral element of addition. So, the fact that this works is really an unintended side-effect of the current CUDA implementation, and I do not intend to be tied to it. Indeed, I expect to have completely different implementations for different types.

[starcomrori1977]

Is this really the way it suppose to work? By the what could mean error fatal error access to undeclared static property ?