On Fri, Oct 21, 2011 at 10:14 AM, Stuart Sierra <the.stuart.sie...@gmail.com> wrote: > Clojure does tail-call elimination for simple cases with loop/recur. This is > by far the most common case. Most other tail-recursive situations can be > represented as lazy sequences, which are another way to handle recursive > functions without consuming stack space. For the final rare cases (e.g. > mutually recursive functions) Clojure has `trampoline`, which does something > similar to (on first glance) Erjang.
I agree, it seems that Erjang is doing a form of trampoline automatically. Besides Clojure's solution being manual, another difference is that Clojure returns the data necessary to execute the next step while Erjang stores that data in a mutable spot that's used only by the current thread. > One nice thing about Clojure's approach is that any function can be invoked > from Java just like any other method. On a quick read, I can't tell if the > Erjang approach requires special handling from Java code. This is a critical question for Java. It looks like every Erjang function provides an .invoke() method than handles any required trampolining, so calling that from Java should be safe. > The underlying goal of Clojure's recursion semantics is to always be > explicit about where compilation strategies will differ. Loop/recur, lazy > seqs, and trampoline all have different performance characteristics. You > don't have to guess which method is being used. This, combined with the fact that together these techniques cover an overwhelming majority of use cases (and the fact that they're already done and work) means the cost/benefit of now adding something like Erjang does may not be so good. Hm, and besides performance there are implications for stack traces. Trampolines, either explicit in Clojure or automatic in Erjang, surely would make Java stack traces harder to understand as information about intermediate function calls would be completely missing. Might be an interesting experiment though. So... is a function call that could be either of two things (a loop/recur or a trampoline site) simple or complected? --Chouser -- You received this message because you are subscribed to the Google Groups "Clojure" group. To post to this group, send email to clojure@googlegroups.com Note that posts from new members are moderated - please be patient with your first post. To unsubscribe from this group, send email to clojure+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/clojure?hl=en
