dear R wizards---I am not sure at what point I owe pennance for asking so many questions. I am now wrangling debugging. I want to write a function assert = function( condition, ... ) { if (!condition) { cat(...); cat("\n"); browser(); } stopifnot(condition); } assert( nrow(ds)==12, "My data set has ", nrow(ds), ", rows which is a bad error."); (Please ignore my semicolons.) Then, having invoked "browser()", I would like by hand to be able to move back up one stack frame so that I can look at my variables there. Alas, two "little" problems. First, the cat() does not seem to work. It prints the arguments themselves, rather than 'nrow(ds)'. Second, I have no idea how to move up one stack frame to the calling function so that I can examine better what went wrong. Is this possible? As always, advice is highly appreciated. Regards, /ivo