Hello all, I was wondering what the cost of a cons was, and decided to do an experiment:
scheme@(guile-user)> (define (count-loop n) (let lp ((n n)) (if (> n 0) (lp (1- n))))) scheme@(guile-user)> ,time (count-loop 1000000000) clock utime stime cutime cstime gctime 46.02 45.92 0.00 0.00 0.00 0.00 scheme@(guile-user)> (/ 46.02 1000000000) $1 = 4.602e-8 scheme@(guile-user)> (define (cons-loop n) (let lp ((n n)) (cons n n) (if (> n 0) (lp (1- n))))) scheme@(guile-user)> ,time (cons-loop 1000000000) clock utime stime cutime cstime gctime 109.09 108.43 0.45 0.00 0.00 0.00 scheme@(guile-user)> (- (/ 109.09 1000000000) $1) $2 = 6.307e-8 Now, cons-loop should have optimized out that cons, but it didn't; oh well. The better for my testing. I ran a loop counting down from an (American) billion. Then I ran a loop doing the same, but consing a pair before looping. Memory stayed fairly constant, FWIW. So if I understand this correctly, on my machine, a 2.2 GHz 64-bit intel laptop, a cons takes 63 nanoseconds (amortized), or about 140 cycles (amortized). Then again there is the cost of the local variable refs, which count-loop doesn't have, but that makes this the upper bound for cons cost on this machine. For what it's worth, Andy -- http://wingolog.org/