On Mon, Aug 9, 2010 at 6:00 PM, Phil Hagelberg <p...@hagelb.org> wrote: > Just remove the call to recur and it will work, albeit only for lists > small enough to not blow the stack.
I'm assuming from the tone of the original post that the author is trying to generally understand how to write recursive functions in Clojure, rather than use built-ins, and that processing arbitrary-sized lists is a primary goal. The posted code (minus the call to recur), is an elegant recursive formulation that is idiomatic in Scheme because Scheme is (typically) implemented in a way that makes stack limitations (mostly) a non-issue. In Clojure, you have to work around stack limitations imposed by Java, and recursive functions must be "translated" to work on largish lists in Clojure. There is no one recipe to make that translation, but there are several common patterns. If the recursive call is in tail position, you can usually write the function the same way, but replace the self-call with the word "recur". If not in tail position and the function is a list-building function, you may be able to solve the stack problem with a call to lazy-seq -- I touched on this topic in a recent blog post: http://programming-puzzler.blogspot.com/2010/07/translating-code-from-python-and-scheme.html The solution to most recursive problems in Clojure is to build your answer in an accumulator, so you must learn how to design and develop accumulator-style recursive functions. For an in-depth look at this process (in Scheme), I recommend: http://www.htdp.org/2001-11-21/Book/node156.htm For mutually recursive problems, a trampoline may be an option. If none of these options work, you may have to simulate your own call stack (ugh). It can sometimes be frustrating to write code in a language that is built around recursion rather than iteration constructs, and then has such severe limitations on how and when recursion can be safely used, but with practice, the vast majority of code can be easily rewritten in a manner conducive to Clojure. -- 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
