Benchmark: timing 1000 iterations of Do, Grep, Map...
  Do:  8 wallclock secs ( 7.90 usr +  0.00 sys =  7.90 CPU) @ 126.58/s (n=1000)
  Grep:  9 wallclock secs ( 8.74 usr +  0.00 sys =  8.74 CPU) @ 114.42/s (n=1000)
  Map: 11 wallclock secs (11.26 usr +  0.00 sys = 11.26 CPU) @ 88.81/s (n=1000)