On Wed, 2005-07-20 at 14:27 +0800, Sun Yi Ming wrote: [snip]
i first write this snippet of code: --- import System.IO
mix :: [a] -> [a] -> [a] mix [] ys = ys mix xs [] = xs mix (x:xs) (y:ys) = [x,y] ++ mix xs ys
f1 = do contents1 <- readFile "url1.txt" contents2 <- readFile "url2.txt" let urls1 = lines contents1 urls2 = lines contents2 urls = mix urls1 urls2 writeFile "aha.txt" (unlines urls) -- this works fine, but i think if the two file are very big, and the readFile will consume too many mem.so i need to read the file line by line but stunned by the loop in IO Monad:
Did you try it on a big file to see what happens? There should not be any problem because readFile is lazy. That is it reads the contents of the file on demand, not all at once. The only thing you have to be careful about is that you do not require all the contents of the file before any output can be produced. Bernie.