It's no more mutable than a pure lambda calculus with lazy evaluation. There is no _observable_ mutability. Anything else is an implementation detail.
Single assignment comes from the tradition of logic programming and concurrent process calculus rather than lambda calculus. A single assignment variable is a lot like a pure promise. By pure I mean that one cannot peek at the promise without blocking on it. This is all-important in preventing race conditions in a concurrent setting. If Sophie is interested, I used promises as single assignment variables in the letrec implementation I posted. It's fair to say that while Clojure supports single assignment variables in the form of promises, they are not fundamental language-level constructs the way they are in languages like Prolog or Oz. You have to explicitly dereference them like any other IDeref. -Per On Tue, Apr 6, 2010 at 6:53 AM, Michael Gardner <gardne...@gmail.com> wrote: > On Apr 5, 2010, at 4:34 PM, Sophie wrote: > >> But single-assignment is a quite valid (and more flexible?) form of >> immutability. I'm not convinced cycles are intrinsically tied to it in >> any way. > > If you can assign to it, it's mutable. What you're talking about is creating > a mutable object, then making it immutable at some point (say, after it's > first assigned to). Immutable object cycles are indeed possible if one > permits this; Clojure doesn't, at least not for simple objects. > > -Michael > > -- > 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 > > To unsubscribe, reply using "remove me" as the subject. > -- 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
