球拍中的计时功能

Question

The syntax for the timing function in Scheme is confusing. If I want to check CPU cycles I should be able to wrap my entire code in (time codestuff) and it should produce that should it not? I get an error whenever I try to wrap it in (time).

lambda: no expression after a sequence of internal definitions in: lambda

What other choices do I have to check CPU usage for running my program in Scheme?

Answer 1

Unfortunately, time doesn't seem to work if the last form in the time body isn't an expression. Fortunately, (void) is an expression that is (relatively) free. ¹ You can just add it as the last expression in the body of your time giving you:

(time
  .... your code here ....
  (void))

So for example, the following code will give you a result like this:

> (time
    (define x 
      (for/list ([i (in-range 1000000)])
        i))
    (void))
cpu time: 148 real time: 149 gc time: 124

_{¹ As with anything in CS and timing, whether or not void is going to matter here does depend. But for many cases a single call to void should be fine.}