On Wed, Mar 26, 2008 at 05:07:10PM -0700, Don Stewart wrote: > droundy: > > On Thu, Mar 27, 2008 at 01:09:47AM +0300, Bulat Ziganshin wrote: > > > > -Collecting rendering stats is not easy without global variables. It > > > > occurs to me that it would be neat if there were some sort of write-only > > > > global variables that can be incremented by pure code but can only be > > > > read from within monadic code; that would be sufficient to ensure that > > > > the pure code wasn't affected by the values. > > > > > > the code is called *pure* exactly because it has no side-effects and > > > compiler may select either to call some function two times or reuse > > > already computed result. actually, you can make sideeffects with > > > unsafePerformIO, but there is no guarantees of how many times such > > > code will be executed. try this: > > > > > > plus a b = unsafePerformIO (modifyIORef counter (+1)) `seq` a+b > > > > This is exactly what he wants to do. The point of putting traces into the > > code is precisely to figure out how many times it is called. The only > > trouble is that unsafePerformIO (I believe) can inhibit optimizations, > > since there are certain transformations that ghc won't do to > > unsafePerformIO code. > > could we just use -fhpc or profiling here. HPC at least will tell you > how many times top level things are called, and print pretty graphs > about it.
It depends what the point is. I've found traces to be very helpful at times when debugging (for instance, to get values as well as counts). Also, I imagine that manual tracing is likely to be far less invasive (if you do it somewhat discretely) than profiling or using hpc. -- David Roundy Department of Physics Oregon State University _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
