6 Jan
2007
6 Jan
'07
6:54 a.m.
Brian Hurt wrote:
nth 0 (x:xs) = Some x nth i (x:xs) = if i < 0 then Empty else nth (i-1) xs nth i [] = Empty [blows stack on large i]
As other people have pointed out, this is due to laziness. I'd write it like: nth 0 (x:_) = Some x nth i (_:xs) = of i < 0 then Empty else (nth $! i-1) xs nth _ [] = Empty where a general rule of thumb is always to replace (fun intexp) by (fun $! intexp) whenever intexp is just a trivial arithmetic expression that doesn't involve traversing (ie forcing of) any other data structure. Brian. -- http://www.metamilk.com