Other another bike-shed color: traceWith :: (a -> String) -> a -> a traceWith f a = trace (f a) a traceShowWith :: Show b => (a -> b) -> a -> a traceShowWith f = traceWith (show . f) But on the other hand, pointfree.io tells me that you can write trace =<< f trace =<< show . f so I'm not sure how urgent these are. On Feb 9, 2018 8:08 PM, "Kris Nuttycombe" <kris.nuttycombe@gmail.com> wrote: When using Debug.Trace for debugging, a very common operation is to prefer to trace only some subset or function of an intermediate result. As a consequence, I propose adding the following function to Debug.Trace: traceWith :: (Show b) => (a -> b) -> a -> a traceWith f a = trace (show $ f a) a While it's trivial to define, I have found this to be one of the most useful functions in my trace-based debugging toolkit, hence my proposal that it be added to base. It generalizes `traceShowId` in a meaningful and useful fashion. As this is the first such proposal I've put forth, please let me know if I'm doing anything wrong with it! Thanks, Kris Nuttycombe _______________________________________________ Libraries mailing list Libraries@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/libraries