Henning Thielemann wrote:

On Wed, 18 Jun 2008, Achim Schneider wrote:

...

Is there a generalisation of scan1, such that eg.

foo (+) [0,1] (1,2) = [0,1,1,2,3,5,8,13,...]

?

What is the (1,2) for?

Specifying the relative indexes an element depends on. Ideally, it should be generalised for n-ary functions.

I could think of foo f = List.unfoldr (\ xt@(x:xs) -> Just (x, xs ++ [f xt]))

foo sum [0,1] = [0,1,1,2,3,5,8,13,21,34,...

I should elaborate: foo (+) [0,1,4] (1,2) = _|_, as 4 isn't 0+1 foo (+) [0,1] (2,3) = [0,1,_|_,1,_|_,_|_] foo (+) [0,1,1,2,3,5] (1,2) = [0,1,1,2,3,5,8,13,...] foo (+) [1] (1,1) = [1,2,4,8,16,32,...] If you allow for inverse functions, you could even say foo (+-) [0,...,3,..] (1,2) = [0,0,0,...,0,0,1,1,2,3,5,...] It seems like I'm searching for some primitive that lets me combine lists and currying. Think of passing a matrix, with each column (or row, if you prefer) separately uniquely typed, into a function. -- (c) this sig last receiving data processing entity. Inspect headers for past copyright information. All rights reserved. Unauthorised copying, hiring, renting, public performance and/or broadcasting of this signature prohibited.