From: cnb <circularfunc@...>
Date: 2008-09-14T05:03:04+09:00
Subject: I thought ruby didn't optimize tailcalls?

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?

###################

def factail(n, acc=1)
    if n > 0 then factail(n-1, n*acc)
    else acc end
end

irb(main):163:0> factail(10000)
factail(10000)
284625968091705451890641321 and so on...


###################

def facto(n)
    if n > 0 then n * facto(n-1)
    else 1 end
end


irb(main):164:0> facto(10000)
facto(10000)
SystemStackError: stack level too deep
	from (irb):155:in `facto'
	from (irb):155:in `facto'
	from (irb):158
	from :0
irb(main):165:0>


########################

def fact(n)
    def f(n, acc)
        if n > 0
            then f(n-1, n*acc)
            else acc
        end
    end
    f(n, 1)
end


irb(main):183:0> fact(10000)
fact(10000)
2846259680917054518 ...

also works.