Re: [Haskell-cafe] Stupid newbie question

bhurt:

My apologies for wasting bandwidth on what I'm sure is a stupid newbie question.

Given:

-- Reimplementing the wheel here, I know

data Option a = Some a | Empty deriving (Eq,Ord,Show,Read)

nth 0 (x:xs) = Some x nth i (x:xs) = if i < 0 then Empty else nth (i-1) xs nth i [] = Empty

That:

nth 1000000 [1..10000000]

returns the right answer, while:

nth 1000000 [1..]

Now I'm really intrigued, since the standard list-index function also fails: Prelude> [1..] !! (10^6) *** Exception: stack overflow It's implemeeted roughly as: nth xs n | n < 0 = Nothing nth [] _ = Nothing nth (x:_) 0 = Just x nth (_:xs) n = xs `nth` (n-1) main = print $ [1..] `nth` (10^6) -- Don