On 27 Nov., 13:06, Meikel Brandmeyer <[EMAIL PROTECTED]> wrote: Hello.
> Maybe I have a wrong understanding of "closure", but > as far as I understand, every function definition in > Clojure - be it defn or #() - finally translates to (fn ...). > And fn creates a closure. Well, from my experience I can say that a lot of people think that “anon function = closure”, which would be fn in Clojure or lambda in Common Lisp. This however is not generally correct. In my previous posting I gave an example of how a named function became a closure. > In fact #(prn "Hello") closes > over the var "prn". Consider the following example: > > (ns foo.bar) > > (def my-closure #(prn "Hello")) Inside the namespace foo.bar the function clojure.core/prn is visible. I think that when you define my-closure the compiler inserts the hard address of clojure.core/prn to know where to jump when called. There is nothing variable bound. It is the same as if you did that while being in the clojure.core namespace. “prn” is globally visible, it is a special variable, not a lexical one. Your my-closure captures the empty lexical environment which I would explicitly like to exclude from a definition of “closure”. > (ns yoyo.dyne > (:refer-clojure > :exclude (prn))) > > (defn prn [x] (clojure.core/prn (str "Modified: " x))) > > (foo.bar/my-closure) > > According to my understanding the output should > be "Hello". I agree. Having the namespace foo.bar did not change anything important here, we could have done the same inside user or clojure.core. While you said (defn my-clojure ...) you accessed something from the global namespace. When someone sees the isolatedcode of a closure this person would have to ask: “What is this variable x?? I can not see it's definition”, as in: (fn [n] (+ n x)) x may be a global variable, in which this anon function would not be a closure. Or this fn is embedded inside a let or fn or whatever, where x is lexically visible and the fn implicitly “inherits” it. > I think the closure is never "empty". It refers to the > environment used at the closure's creation time. > Whether this environment is accessed or not, is not > very interesting, I think. As I see it we had examples where the lexical environment was empty. Global capture is no magic, but the whole reason for having global vars. But even in the case we would ignore that: I would still vote against calling these guys closures, simply as in my opinion any definition is not qualified, which implies that *all* functions are closures. It makes not much sense to invent this special word and confuse thousands of people with it who are eager to learn what closures really are, when they are in the end nothing but functions. --~--~---------~--~----~------------~-------~--~----~ 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 [EMAIL PROTECTED] For more options, visit this group at http://groups.google.com/group/clojure?hl=en -~----------~----~----~----~------~----~------~--~---
