Does Ruby optimize tail-call recursion?

[Patrick Li]

Hi,
I'm wondering if Ruby 1.9 optimizes tail-call recursion?
I've read some reports that say yes, and some that say no. Does anyone
know?

Thanks
-Patrick

 

[Joost Diepenmaat]

Hi,
I'm wondering if Ruby 1.9 optimizes tail-call recursion?
I've read some reports that say yes, and some that say no. Does anyone
know?

I just compiled the ruby svn trunk with all defaults:

./ruby -v
ruby 1.9.0 (2008-08-30 revision 18932) [i686-linux]


./ruby -e 'def bla(); bla(); end; bla()'
-e:1:in `bla': stack level too deep (SystemStackError)
from -e:1:in `bla'
from -e:1:in `bla'
from -e:1:in `bla'
from -e:1:in `bla'
from -e:1:in `bla'
from -e:1:in `bla'
from -e:1:in `bla'
from -e:1:in `bla'
... 7692 levels...
from -e:1:in `bla'
from -e:1:in `bla'
from -e:1:in `bla'
from -e:1:in `<main>'

So I guess the answer is: no, it does not optimize tail calls.

 

[Thomas Hurst]

I'm wondering if Ruby 1.9 optimizes tail-call recursion? I've read
some reports that say yes, and some that say no. Does anyone know?

vm_opts.h:

#define OPT_TAILCALL_OPTIMIZATION 0

Set to 1, rebuild. The comments suggest it can be changed at runtime
via VM::CompileOption, which doesn't seem to exist. Hopefully it'll be
enabled by default at some point in future.

 

[SASADA Koichi]

Hi,

vm_opts.h:

#define OPT_TAILCALL_OPTIMIZATION 0

Set to 1, rebuild. The comments suggest it can be changed at runtime
via VM::CompileOption, which doesn't seem to exist. Hopefully it'll be
enabled by default at some point in future.

In fact, I don't check this option. So some bugs may hide on this
option. And backtrace (what you see on exception) is changed. It's
convention issue.

 

[Thomas B.]

./ruby -e 'def bla(); bla(); end; bla()'
-e:1:in `bla': stack level too deep (SystemStackError)
from -e:1:in `bla'
from -e:1:in `bla'
from -e:1:in `bla'
from -e:1:in `bla'
from -e:1:in `bla'
from -e:1:in `bla'
from -e:1:in `bla'
from -e:1:in `bla'
... 7692 levels...
from -e:1:in `bla'
from -e:1:in `bla'
from -e:1:in `bla'
from -e:1:in `<main>'

On my machine:

ruby -e 'def bla(); bla(); end; bla()'
-e:1:in `bla': stack level too deep (SystemStackError)
from -e:1:in `bla'
from -e:1

I use Ruby version from windows one-click installer, 1.8.6.