Benchmark: timing 100000 iterations of eval_string, manual...
eval_string: 10 wallclock secs ( 9.31 usr +  0.05 sys =  9.36 CPU) @ 10683.76/s (n=100000)
    manual:  2 wallclock secs ( 2.07 usr +  0.01 sys =  2.08 CPU) @ 48076.92/s (n=100000)