On Tue, Sep 15, 2009 at 9:13 PM, Daniel Fischer
... Still, the body should be read lazily. I'm not sure, but the tracing message may be output because of its position.
With
where readBody = withFile fn ReadMode $ \h -> do b <- hGetContents h seq b $ return (trace ("Read body from: " ++ fn) b)
there's no tracing output.
Impressive as I can't spot the difference. But my question is: is the chunk of data actually read or not? Consider the following code: ---- readBit fn = withFile fn ReadMode $ \h -> Bit <$> (hGetLine h >>= return . read) <*> readBody where readBody = trace "In readBody" $ withFile fn ReadMode $ \h -> do b <- hGetContents h seq b $ return $ trace ("Read body from: " ++ fn) b ---- The message "In readBody" gets written, while "Read body from..." don't. So? I think that the IO action is actually performed but the result is simply discarded. Am I right? Cristiano