[Haskell-cafe] Simple network client
judah.jacobson at gmail.com
Wed Jan 30 12:51:14 EST 2008
On Jan 30, 2008 8:31 AM, Bryan O'Sullivan <bos at serpentine.com> wrote:
> Peter Verswyvelen wrote:
> > Then I tried the "seq" hack to force the handle opened by readFile to be closed, but that did not seem to work either. For example, the following still gave access denied:
> > main = do
> > cs <- readFile "L:/Foo.txt"
> > writeFile "L:/Foo.txt" $ seq (length cs) cs
> This is unfortunately a classic beginner's mistake. You got the seq
> wrong here, which is very common.
> You need to float the call to seq out so that it's evaluated before the
> call to writeFile:
> length cs `seq` writeFile cs
Another way of doing things: I've recently become a fan of
main = do
cs <- readFile "L:/Foo.txt"
evalute (length cs)
writeFile "L:/Foo.txt" cs
This might be easier for beginners to understand than messing around
with seq's (as long as you're already in the IO monad).
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