Dear, I made a profile[1] of a test program: Where can I find documentation for the meaning of everything mentioned below? Or alternatively, can anyone explain them? Where can I see the effect of using the -xt option in this profile? Ron [1] /Main +RTS -p -s -xt -hc 1,372,408,024 bytes allocated in the heap 121,255,600 bytes copied during GC (scavenged) 6,584,692 bytes copied during GC (not scavenged) 2,768,896 bytes maximum residency (68 sample(s)) 2649 collections in generation 0 ( 1.11s) 68 collections in generation 1 ( 0.49s) 6 Mb total memory in use INIT time 0.00s ( 0.00s elapsed) MUT time 5.97s ( 6.63s elapsed) GC time 1.60s ( 1.88s elapsed) RP time 0.00s ( 0.00s elapsed) PROF time 0.19s ( 0.20s elapsed) EXIT time 0.00s ( 0.00s elapsed) Total time 7.76s ( 8.71s elapsed) %GC time 20.6% (21.5% elapsed) Alloc rate 229,946,873 bytes per MUT second Productivity 76.9% of total user, 68.5% of total elapsed Ron