Benchmark: timing 1000000 iterations of interpolator, joiner...
interpolator:  5 wallclock secs ( 5.13 usr +  0.00 sys =  5.13 CPU) @ 194931.77/s (n=1000000)
    joiner:  4 wallclock secs ( 4.53 usr +  0.00 sys =  4.53 CPU) @ 220750.55/s (n=1000000)
                 Rate interpolator       joiner
interpolator 194932/s           --         -12%
joiner       220751/s          13%           --