Benchmark: timing 5 iterations of int_iterate, iterate, lex_iterate...
int_iterate: 131 wallclock secs (130.94 usr +  0.00 sys = 130.94 CPU) @  0.04/s
(n=5)
   iterate: 172 wallclock secs (172.63 usr +  0.00 sys = 172.63 CPU) @  0.03/s (
n=5)
lex_iterate: 137 wallclock secs (136.66 usr +  0.00 sys = 136.66 CPU) @  0.04/s
(n=5)
            s/iter     iterate lex_iterate int_iterate
iterate       34.5          --        -21%        -24%
lex_iterate   27.3         26%          --         -4%
int_iterate   26.2         32%          4%          --