Benchmark: timing 100 iterations of first, grep, pq...
     first: 13 wallclock secs (13.55 usr +  0.00 sys = 13.55 CPU) @ 7.38/s (n=100)
      grep: 59 wallclock secs (58.09 usr +  0.17 sys = 58.27 CPU) @ 1.72/s (n=100)
        pq:  1 wallclock secs ( 0.86 usr +  0.00 sys =  0.86 CPU) @ 116.41/s (n=100)