I guess trampoline allows to emulate tail call optimization on mutually recursive functions, that is functions that, without trampoline and in an environment that would do TCO automatically, have a tail call to the other function, and the other function also has a tail call to another function ... with only tail calls to functions having tail calls.
Your code does not have this property : the function you have written, as implemented, are not mutually recursive on the tail call. Regards, -- Laurent 2009/6/10 Shawn Hoover <shawn.hoo...@gmail.com>: > > On Tue, Jun 9, 2009 at 6:04 PM, arasoft <t...@arasoft.de> wrote: >> >> I tried this: >> >> (declare F) >> >> (defn M [n] >> (if (zero? n) >> 0 >> (- n (F (M (dec n)))))) >> >> (defn F [n] >> (if (zero? n) >> 1 >> (- n (M (F (dec n)))))) >> >> and for large n I got the expected stack overflow. Then I tried to >> trampoline the functions: >> >> (declare F) >> >> (defn M [n] >> (if (zero? n) >> 0 >> #(- n (F (M (dec n)))))) >> >> (defn F [n] >> (if (zero? n) >> 1 >> #(- n (M (F (dec n)))))) >> >> Now (trampoline #(M 7)) yields >> java.lang.ClassCastException: user$M__760$fn__762 cannot be cast to >> java.lang.Number (NO_SOURCE_FILE:0) >> >> Does anybody have an idea to get this to work? > > I don't know how to make it work, but I can tell you why you're getting a > ClassCastException. In the definition of M, you have (F (M (dec n)). This is > returned in a fn, which is fine until it gets called. When called, the inner > M could return a fn, which gets passed to F, which assumes it's a number and > tries to use it in a subtraction operation. > > Shawn > > > > --~--~---------~--~----~------------~-------~--~----~ 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 -~----------~----~----~----~------~----~------~--~---
