Add some Haskell code for shuffling a list.
Chris Pressey
1 year, 4 months ago
| 0 | import System.Random | |
| 1 | import Debug.Trace | |
| 2 | ||
| 3 | pickAt :: [a] -> Int -> (a, [a]) | |
| 4 | pickAt items@(x:xs) n | |
| 5 | | n == 0 = (x, xs) | |
| 6 | | n < 0 = error "range" | |
| 7 | | otherwise = | |
| 8 | let | |
| 9 | (r, rs) = pickAt xs (n-1) | |
| 10 | in | |
| 11 | (r, x:rs) | |
| 12 | ||
| 13 | randomIndex xs gen = | |
| 14 | uniformR (0 :: Int, ((length xs) - 1) :: Int) gen | |
| 15 | ||
| 16 | pickOne xs gen = | |
| 17 | let | |
| 18 | (index, gen') = randomIndex xs gen | |
| 19 | (x, xs') = pickAt xs index | |
| 20 | in | |
| 21 | (x, xs', gen') | |
| 22 | ||
| 23 | shuffle [] gen = ([], gen) | |
| 24 | shuffle xs gen = | |
| 25 | let | |
| 26 | (x, xs', gen') = pickOne xs gen | |
| 27 | (xs'', gen'') = shuffle xs' gen' | |
| 28 | in | |
| 29 | (x:xs'', gen'') | |
| 30 | ||
| 31 | -- for demoing purposes | |
| 32 | shuffleSeed items seed = fst $ shuffle items $ mkStdGen seed |