On Wednesday 08 November 2006 05:41, DavidA wrote:
To get the result you want, take the list of (letter, probability) pairs, and generate the Cartesian product of k copies of itself.
cartProd 0 xs = [[]] cartProd k xs = [x:ys | x <- xs, ys <- cartProd (k-1) xs]
The result is all sequences of k (letter,probability) pairs, allowing repetitions.
Then you just need to unzip and multiply:
(\lps -> let (ls,ps) = unzip lps in (concat ls, product ps))
It does the basically the same thing but, you might also want to check out the Probabilistic Functional Programming library by Martin Erwig at http://web.engr.oregonstate.edu/~erwig/pfp/ It's got all sorts of other probability goodies in it. By importing the Probability module you can define your distribution and a permute as so probDist = mkD [("A", 0.8), ("B", 0.2)] permute 0 d = mkD [] permute 1 d = d permute k d = mapD (uncurry (++)) (prod d (permute (k - 1) d))