hankgong:
Hi, all
I'm just a newbie for Haskell and functional programming world. The idea I currently read is quite different and interesting.
I have one general question about the recursively looping style. For example:
myMax [ ] = error "empty list"
myMax [x] = x
myMax [x:xs] = if x>= (myMax xs) then x else (myMax xs)
I just list out this kind of very simple program. However, if the list size if a big number such as 10000000, the Does it mean that the functional programming is lacking of scalability? I do know that we can manually change the stack size for it. But that's not a good solution according to my opinion.
No, your code is just really inefficient (think about how many times its traversing the list). Try rewriting it as a simple accumulating pass over the list, carrying the largest element you've seen so far. mymax [] = undefined mymax (x:xs) = f x xs where f x [] = x f x (y:ys) | y > x = f y ys | otherwise = f x ys However, 'f' is just a foldl inlined: import Data.List mymax [] = undefined mymax (x:xs) = foldl' (\a b -> if b > a then b else a) x xs And the lambda is just 'max': import Data.List mymax [] = undefined mymax (x:xs) = foldl' max x xs Now, we already check for the empty list, so avoid checking again: import Data.List mymax [] = undefined mymax xs = foldl1' max xs And that'll do. -- Don