On Saturday 20 December 2008 06:29, verec wrote: > At about 72:54 of the clojure sequence talk, Rich explains that he > doesn't want to provide "false guaranties" to people used to "true > tail calls" even though he could detect such "tail position calls" > and basically transforms them into what recur currently does. > > I'm just curious about examples where such a "magic transformation" > would result in violated assumptions.
Write some Clojure code and use recur freely, without regard to whether it's in tail position and the compiler will tell you when it's not. Though I don't know where "magic" does or would enter the picture. > If the detection of the tail call position is not too involved, > (after all, detecting that recur is in tail position seems simpler > than detecting that an arbitrary function call is) I fail to see what > the problem is. The problem is that if local bindings are needed after the recursive call returns then a new stack frame must be created for that recursive call. If not, the local bindings may be abandoned (or, more to the point, reused) and the stack need not grow to accommodate the recursion. In the tail-call case (explicitly requested by the programmer and validated by the compiler), the "recursive call" becomes rebinding of the locals followed by a "go-to." > Anyone cares to elaborate? > Many Thanks Randall Schulz --~--~---------~--~----~------------~-------~--~----~ 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 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 -~----------~----~----~----~------~----~------~--~---
