From: Mauricio Fernandez <mfp@...>
Date: 2006-01-03T05:50:59+09:00
Subject: Re: Memoization, files and Marshal?

On Tue, Jan 03, 2006 at 04:32:57AM +0900, Daniel Berger wrote:
> > > I also applied those changes to memoize.rb 1.2.0 and generalized it to work
> > > with instance methods, see the patch after memo.rb.
> 
> Looks interesting but I get this with windows xp using his sample code:
> 
> >ruby memoize.rb
> Rehearsal ----------------------------------------------
> period 1   memoize.rb:39:in `has_key?': stack level too deep
> (SystemStackError)
>         from memoize.rb:39:in `fib'
>         from memoize.rb:56:in `fib'
>         from memoize.rb:40:in `fib'
>         from memoize.rb:56:in `fib'
>         from memoize.rb:40:in `fib'
>         from memoize.rb:56:in `fib'
>         from memoize.rb:40:in `fib'
>         from memoize.rb:56:in `fib'
>          ... 539 levels...

Your stack is too small; fib(500) goes 1000 levels deep. Change 
those examples to fib(100) etc.:

batsman@tux-chan:/tmp$ ruby memoize.rb
Rehearsal ---------------------------------------------
period 1  memoize.rb:54:in `fib': let's see how deep we get (RuntimeError)
        from memoize.rb:39:in `fib'
        from memoize.rb:55:in `fib'
        from memoize.rb:39:in `fib'
        from memoize.rb:55:in `fib'
        from memoize.rb:39:in `fib'
        from memoize.rb:55:in `fib'
        from memoize.rb:39:in `fib'
        from memoize.rb:55:in `fib'
         ... 993 levels...
        from /home/batsman/usr/lib/ruby/1.8/benchmark.rb:293:in `measure'
        from /home/batsman/usr/lib/ruby/1.8/benchmark.rb:261:in `bmbm'
        from /home/batsman/usr/lib/ruby/1.8/benchmark.rb:259:in `bmbm'
        from memoize.rb:96

given

batsman@tux-chan:/tmp$ diff -u memoize.rb.mod memoize.rb
--- memoize.rb.mod      2006-01-02 21:38:18.000000000 +0100
+++ memoize.rb  2006-01-02 21:46:10.000000000 +0100
@@ -51,7 +51,7 @@

 if __FILE__ == $0
    def fib(n)
-      return n if n < 2
+      raise "let's see how deep we get" if n < 2
       fib(n-1) + fib(n-2)
    end

@@ -97,10 +97,10 @@
       dummy1 = Dummy1.new
       dummy2 = Dummy2.new
       bm.report("period 1") { runs.times{ fib  500  } }
-      bm.report("period 10"){ runs.times{ fib3 500  } }
-      bm.report("at_exit")  { runs.times{ fib2 500  } }
-      bm.report("at_exit''")  { runs.times{ dummy1.fib 500  } }
-      bm.report("at_exit'''")  { runs.times{ dummy2.fib 500  }; runs = 100000}
+      #bm.report("period 10"){ runs.times{ fib3 500  } }
+      #bm.report("at_exit")  { runs.times{ fib2 500  } }
+      #bm.report("at_exit''")  { runs.times{ dummy1.fib 500  } }
+      #bm.report("at_exit'''")  { runs.times{ dummy2.fib 500  }; runs = 100000}
    end

 end

-- 
Mauricio Fernandez