sicp-ex-4.24

Below are 2 simple tests, loops and calculating fibonacci numbers.

 ; 4-24.test1.scm 
  
 (define (loop n) 
     (if (> n 0) 
         (loop (- n 1)))) 
  
 (loop 1000000) 
 (exit)

 ; 4-24.test2.scm 
  
 (define (fib n) 
     (if (<= n 2) 
         1 
         (+ (fib (- n 1)) (fib (- n 2))))) 
  
 (fib 30) 
 (exit)

My results are:

only eval: loop 9.689s, fib 18.880s

analyze + eval: loop 5.528s, fib 10.682s

master

I wanted to really put our interpreter to the test and see how long it would take it to compute A(4,1), i.e. the Ackermann function and I believe the highest value which is practical to compute. Well, after 40 minutes of waiting for the slow interpreter to finish I decided that it was not going to happen anytime soon. Therefore, I made it compute A(3,8) instead, and after that A(3, 10), which was as high as I was willing to go. Here's some data, including benchmarks from Chez Scheme for reference (which I've heard is the fastest Scheme implementation, it's certainly up there):

 (A 3 8) 
 Slow: ~26.47s 
 Fast: ~15.06s 
 Chez Scheme: basically instantaneous 
  
 (A 3 10) 
 Slow: ~6m32.40s 
 Fast: ~3m33.66s 
 Chez Scheme: basically instantaneous 
  
 (A 4 1) 
 Slow: at least 40m 
 Fast: at least 15m (probably much more, wasn't willing to wait longer) 
 Chez Scheme: ~5.25s

Our interpreter is obviously extremely inefficient. But the extra work at "compile time" really pays off, the analyzing interpreter is roughly twice as fast.