New to Clojure (find it fascinating so far, in large part due to watching approximately a billion Rich Hickey vids on YouTube). I had a similar question and figured I just resurrect this thread on it.
My naive thought was that when you (re)def a variable, you aren't actually copying over the old memory location, but instead simply re-creating a pointer to a new value or place in memory. To take this example further, I'm wondering what goes on under the hood when I use replace like this: (def my-vec [1 2 3 4 5]) => (var user/my-vec) (def my-vec (assoc my-vec 2 "hello")) => (var user/my-vec) my-vec => [1 2 "hello" 4 5] Is there a good explanation out there of what happens to the old my-vec and whether the new my-vec actually overwrites it, points to it, or points to a completely new location in memory? Another way to phrase this question: is this "real" mutability or just the appearance of mutability? On Tuesday, June 15, 2010 4:51:00 AM UTC-7, Joost wrote: > > On Jun 14, 10:09 pm, Jared <tri...@gmail.com> wrote: > > Also, I thought this language is functional but I'm able to do change > > declarations in the repl. For example: > > user=> (def x 1) > > #'user/x > > user=> x > > 1 > > user=> (def x 2) > > #'user/x > > user=> x > > 2 > > user=> (def x (+ 1 x)) > > #'user/x > > user=> x > > 3 > > > > Why does that happen? This seems to go against the ideas of functional > > programming. I can do the same things with functions too. > > It's true that def isn't a strictly functional construct. > > That's by design, since def is the construct that allows you to define > and set globally accessible vars, which includes all globally > accessible functions. > > If you couldn't re-def a var, you couldn't redefine functions while > coding (or modify/extent existing functions using macros etc). Clojure > (like most Lisps) is a dynamic language with strong support for > interactive development - and you need redefineable vars (or something > similar) for that. The alternative is to recompile/load the whole > program every time you change a function definition. And that sucks > too much. > > In idiomatic code, you only use (def) and its variants to set up > globally reachable data/functions across all threads and you don't, > for example, use def as a way to get "variable variables" - you will > get bitten if you try. > -- 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 --- You received this message because you are subscribed to the Google Groups "Clojure" group. To unsubscribe from this group and stop receiving emails from it, send an email to clojure+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
