Hi, Is it only my machime, or can you confirm that for the Ackermann benchmark, it's very good for C that they chose 9 and not a larger value? For 10, we are significantly faster and for 11,12,13, we can run rings around the C-programme: dafis@linux:~/Documents/haskell/shootout> time ./cacker3 10; time ./acker 10; time ./cacker3 11; time ./acker 11; time ./cacker3 12; time ./acker 12 Ack(3,10): 8189 real 0m0.664s user 0m0.660s sys 0m0.010s Ack(3,10): 8189 real 0m0.405s user 0m0.400s sys 0m0.000s Ack(3,11): 16381 real 0m6.255s user 0m6.220s sys 0m0.000s Ack(3,11): 16381 real 0m1.731s user 0m1.710s sys 0m0.000s Ack(3,12): 32765 real 0m35.270s user 0m35.050s sys 0m0.000s Ack(3,12): 32765 real 0m10.673s user 0m10.590s sys 0m0.000s dafis@linux:~/Documents/haskell/shootout> time ./acker 13; time ./cacker3 13 Ack(3,13): 65533 real 1m4.476s user 1m4.050s sys 0m0.010s Ack(3,13): 65533 real 2m50.645s user 2m47.020s sys 0m0.020s Cheers, Daniel