Bradford Cross wrote: > What is the current state of the art for language implementers working > around these issues (tail calls, continuations, etc) in Clojure, > Scala, JRuby, etc? > > I would imagine people are maintaining their own stacks? stacks and > hacks. :-) Sounds like Dr Seuss...I will not hack upon your stack, > i'll hack my stack to get you back. > > We have talked about the fact that certain programs are invalid > without TCO because they will overflow the stack - true enough. > > Does anyone have any crude benchmarks re the perf overhead of doing > these things in hand rolled stacks vs. at the byte code level. I have > to imagine it is massive for certian classes of programs. No one is doing hand rolled stacks. Clojure does explicit trampolining - but that is a very coarse and limited way of doing it. Scala removes tail calls where it can be statically transformed into iteration, but doesn't give any guarantees. Ruby has never had TCO's and JRuby uses the Java stack too.
SISC is one of the few implementations that do full TCO. There are basically a few variations on how to do it. CPS is common, trampolining works too. You can also have your own bytecode engine with your own stack. The overhead of all of these approaches are pretty severe on the JVM since the usage pattern is data driven and far away from how regular Java code looks like. But the most severe problem with it is that all of these approaches make it much hard to do calls into Java methods. Cheers > > On Thu, Apr 2, 2009 at 9:59 AM, kirk <kirk.pepperd...@gmail.com > <mailto:kirk.pepperd...@gmail.com>> wrote: > > > John Cowan wrote: > > On Thu, Apr 2, 2009 at 10:36 AM, kirk <kirk.pepperd...@gmail.com > <mailto:kirk.pepperd...@gmail.com>> wrote: > > > >> why do they have to be exposed? Isn't tail recursion and > implementation > >> detail? And an optimization at that? > >> > > > > No. > > > > Being able to rely on tail recursion is not an implementation > detail; > > Scheme programmers routinely write programs that tail-call > heavily and > > would blow up without it. A state machine implementation where > state > > transition codelets, expressed as functions, are tail-called by the > > dispatcher and tail-call it in turn is a classic example. "Lambda: > > the ultimate goto." > > > Understood, that said I think Patrick hit the nail on the head. > > And since Java exposes the call stack via Exception#fillInStack, the > > *presence* of tail recursion is unfortunately not an implementation > > detail either. > > > I would humbly disagree with this last statement. > > Regards, > Kirk > > > > > > > -- Ola Bini (http://olabini.com) Ioke creator (http://ioke.org) JRuby Core Developer (http://jruby.org) Developer, ThoughtWorks Studios (http://studios.thoughtworks.com) Practical JRuby on Rails (http://apress.com/book/view/9781590598818) "Yields falsehood when quined" yields falsehood when quined. --~--~---------~--~----~------------~-------~--~----~ You received this message because you are subscribed to the Google Groups "JVM Languages" group. To post to this group, send email to jvm-languages@googlegroups.com To unsubscribe from this group, send email to jvm-languages+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/jvm-languages?hl=en -~----------~----~----~----~------~----~------~--~---
