Benchmark: timing 1000 iterations of match, subst, swap...
     match:  1 wallclock secs ( 0.97 usr +  0.00 sys =  0.97 CPU) @ 1030.93/s (n=1000)
     subst:  1 wallclock secs ( 0.58 usr +  0.00 sys =  0.58 CPU) @ 1724.14/s (n=1000)
      swap:  1 wallclock secs ( 0.75 usr +  0.00 sys =  0.75 CPU) @ 1333.33/s (n=1000)
        Rate match  swap subst
match 1031/s    --  -23%  -40%
swap  1333/s   29%    --  -23%
subst 1724/s   67%   29%    --