When executing (time (loop for i below (expt 10 8) count t))
it takes a long time, sbcl takes less than a second on this. So not useful when speed is required. More: (time (loop for i below 1000000 count t) takes 7 seconds on my computer, so counting to (exp 10 8) would take 700 seconds, and sbcl do that in 0.1 seconds, so in this example the ratio is 7000 times slower than sbcl.
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