3 Feb
2009
3 Feb
'09
10:15 a.m.
On Feb 3, 2009, at 10:04 AM, Daniel Fischer wrote:
GHC seems to have a special awareness of cyclic lists. For example, ghci computes
(zip (cycle [1..3]) (cycle [1..4])) !! (1000^1000)
No, it's that the type of (!!) is [a] -> Int -> a, and 1000^1000 :: Int is 0.
immediately, as if it knows enough to compute 1000^1000 mod 12, by repeated squaring.
Thanks. The following takes forever, but it doesn't consume memory:
Prelude> :m Data.List Prelude Data.List> genericIndex (zip (cycle [1..3]) (cycle [1..4])) (1000^1000)
So zip is doing something smart here with cyclic lists.