From: Brian Candler <b.candler@...>
Date: 2008-09-15T16:26:57+09:00
Subject: Re: I thought ruby didn't optimize tailcalls?

cnb wrote:
> Im using ruby 1.8.6 mri. and it seems to optimize tailcalls which I
> have been told it doesn't. what else could be going on here?

With that program, factail(2000) works for me but factail(5000) bombs 
out with "stack too deep". So I guess you just have a larger default 
stack size than me.

Factorials generate very large Bignums which will slow things down 
substantially for large numbers. I suggest you try something simpler:

  def counttail(n, acc=0)
    if n > 0 then counttail(n-1, acc+1)
    else acc end
  end

Then you can try counttail(10_000), counttail(100_000), 
counttail(1_000_000) etc until you can show your stack overflowing.

If counttail(10_000_000) still works, then post your exact version of 
MRI and where you got it from. Perhaps you have some sort of patched 
version (although I've not come across such a patch myself)

Regards,

Brian.
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