求めてないかもですがこんなふうならかけますね。
module Main where
import qualified Data.Array.Unboxed as AU
main = do
print $ comb6 !! 2000 !! 1000
print $ comb7_1 !! 1000 !! 1000
print $ comb7_2 1000 1000 AU.! ( 1000, 1000 )
comb6 = ((1 : (repeat 0)) :) $ zipWith (zipWith (+)) comb6 (map (0 :) comb6)
comb7_1 = (repeat 1 :) $ ([ 1 .. ] :)
$ (map (\x -> scanl (+) 1 $ tail x) $ tail comb7_1)
comb7_2 :: Int -> Int -> AU.Array ( Int, Int ) Integer
comb7_2 ly lx = comb7_2_table
where
comb7_2_table = AU.array ( ( 0, 0 ), ( ly, lx ) ) $ concatMap(\i -> map (f i) [ 0 .. lx ]) [ 0 .. ly ]
f 0 x = ( ( 0, x ), 1 )
f y 0 = ( ( y, 0 ), 1 )
f y x = ( ( y, x ) , comb7_2_table AU.! ( (y - 1), x ) + comb7_2_table AU.! ( y, (x - 1) ))