On Mon, Nov 06, 2006 at 06:25:48PM +0000, Malcolm Wallace wrote:
When I use `seq`, it is sometimes in a construction like
unsafePerformIO (emit "squawk!) `seq` x
where I am trying to force the impure side-effect to happen, exactly and immediately before x is evaluated. Whilst this is not good style in a general sense, I argue that it is perfectly safe inside certain kinds of library (e.g. for calculating coverage information, or for emitting tracing information). But if the language itself cannot guarantee this exact placement of side-effects, then it becomes impossible to write computation-reflective tools like Hat and hpc for Haskell, in Haskell. That would surely be a sad state of affairs.
Without admitting the existence of "unsafePerformIO", I submit unsafePerformIO (emit "squawk! >> return x) where >> really does imply sequencing.