What does tail-recursion modulo cons mean?
On Mar 16, 2014, at 3:38 PM, Sam Tobin-Hochstadt wrote: > On Sun, Mar 16, 2014 at 2:55 PM, Patrick Useldinger > <uselpa.l...@gmail.com> wrote: >> >> >> My questions are: >> >> (1) Is Racket "tail-recursive modulo cons"? If not, is there a reason for >> this? > > Racket is not "tail-recursive modulo cons". > >> (2) Is the last example "reverse free" or does it use reverse under the >> hood? > > `for/list` uses `reverse` internally -- you can see for yourself how > this works by using the Macro Stepper. > >> (3) finally, what is the recommended way to write this procedure in terms of >> performance? > > I took your program, and made all the functions run on much longer > lists. Here are the timings: > > $ r /tmp/even-list.rkt > 'plain > cpu time: 1288 real time: 1294 gc time: 936 > 't > cpu time: 440 real time: 441 gc time: 320 > 'for/fold > cpu time: 484 real time: 485 gc time: 328 > 'mcons > cpu time: 204 real time: 204 gc time: 148 > 'mcons-convert > cpu time: 632 real time: 631 gc time: 416 > 'for/list > cpu time: 460 real time: 460 gc time: 332 > > 'mcons-convert is one that uses `mcons`, but converts back to plain > `cons` at the end. > > Sam > ____________________ > Racket Users list: > http://lists.racket-lang.org/users ____________________ Racket Users list: http://lists.racket-lang.org/users
