Yet another reason why the mlprof numbers are unbelievable. Consider a self-compile. Here are some extremely conservative upper bounds. * number of gcs: 10E2 * number of MLTON_gc copy statements per gc: 10E4 Hence, an upper bound on the total number of copy statements is 10E6. mlprof claims this is taking 71.82% * 303 = 217 seconds, i.e. 2 milliseconds per assignment statement.