Symbols are late resolved to functions. (def t (fn ...)) means define a Var bound to symbol t, and store the function in it. In JVM terms, the function becomes a new class that is instantiated.
(t (dec x)) means locate the Var bound to symbol t -- at execution time (not compilation time) --- de-reference the function object stored there and invoke it. In fact, t can be temporarily rebound (using the binding macro) or even completely replaced (using alter-var-root!) at any time. The Var remains the same but the contents of the Var are changed. Because of how Clojure is structured, the Var object need only be resolved from the symbol once (in the generated Java bytecode, the Var appears as a static final field). On Wed, Nov 11, 2009 at 5:17 AM, mbrodersen <morten.broder...@gmail.com> wrote: > A quick question about how closures work in Clojure. > > In this simple recursive expression: > > (def t (fn [x] (if (zero? x) 0 (+ x (t (dec x)))))) > > The fn special form is evaluated within a context where t is not yet > bound. > > t is only bound AFTER fn has captured its environment. > > In other words, the closure captured by fn doesn't know anything about > t (or maybe only that t is unbound). > > And yet it still works if I call t: > > (t 5) => 15 > > My question is how Clojure ensures that t is bound to the closure > after the closure has already been captured? > > Thanks > Morten > > -- > 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 -- Howard M. Lewis Ship Creator of Apache Tapestry The source for Tapestry training, mentoring and support. Contact me to learn how I can get you up and productive in Tapestry fast! (971) 678-5210 http://howardlewisship.com -- 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
