Benchmark: timing 1000 iterations of direct, iterate, recurse...
    direct:  1 wallclock secs ( 1.68 usr +  0.00 sys =  1.68 CPU) @ 595.24/s (n=1000)
   iterate: 10 wallclock secs ( 9.57 usr +  0.00 sys =  9.57 CPU) @ 104.49/s (n=1000)
   recurse:  9 wallclock secs ( 9.54 usr +  0.00 sys =  9.54 CPU) @ 104.82/s (n=1000)
         Rate iterate recurse  direct
iterate 104/s      --     -0%    -82%
recurse 105/s      0%      --    -82%
direct  595/s    470%    468%      --