This works as I would expect it to.
'rule' brings in 'state' from the global binding into it's scope
giving it priority over the outer scope bindings found in the parent
function.
On Nov 27, 9:15 pm, Andreas Kostler <andreas.koest...@leica-
geosystems.com> wrote:
> Is this a 'bug' with eval?
>
> On 28 November 2010 14:09, Ken Wesson <kwess...@gmail.com> wrote:
>
>
>
> > On Sat, Nov 27, 2010 at 10:42 PM, Andreas Kostler
> > <andreas.koestler.le...@gmail.com> wrote:
> > > Hi all,
> > > Sorry for my noob question (again). I'm trying to understand clojures
> > > binding model.
> > > Typing:
> > > (def state {:status "foo"})
> > > (def rule '(if (= (:status sate) "foo") (println "foo") (println
> > > ("bar")))
>
> > > (defn fn []
> > > (let [state {:status "bar"}]
> > > (eval rule)))
>
> > > This prints "foo". However, I would have expected the binding of state
> > > created by let would shadow the global binding of state.
> > > Now
>
> > > (defn fn1 []
> > > (binding [state {:status "bar"}]
> > > (eval rule)))
> > > Does the right thing. Can someone explain what's going on here please?
>
> > This is eval not seeing local bindings. There is a workaround:
>
> > (defmacro eval-with-local-vars [vars sexp]
> > (let [quoted-vars (vec (map #(list 'quote %) vars))]
> > `(let [varvals# (vec (interleave ~quoted-vars ~vars))]
> > (eval (list 'clojure.core/let varvals# ~sexp)))))
>
> > user=> (let [a 1 b 2] (eval-with-local-vars [a b] '(+ a b)))
> > 3
> > user=> (def state {:status "foo"})
> > #'user/state
> > user=> (def rule
> > '(if (= (:status state) "foo")
> > (println "foo")
> > (println "bar")))
> > #'user/rule
> > user=> (let [state {:status "bar"}]
> > (eval rule))
> > foo
> > nil
> > user=> (let [state {:status "bar"}]
> > (eval-with-local-vars [state] rule))
> > bar
> > nil
>
> > --
> > 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<clojure%2bunsubscr...@googlegroups.com>
> > For more options, visit this group at
> >http://groups.google.com/group/clojure?hl=en
>
> --
> **********************************************************
> Andreas Koestler, Software Engineer
> Leica Geosystems Pty Ltd
> 270 Gladstone Road, Dutton Park QLD 4102
> Main: +61 7 3891 9772 Direct: +61 7 3117 8808
> Fax: +61 7 3891 9336
> Email: andreas.koest...@leica-geosystems.com
>
> ************www.leica-geosystems.com*************
>
> when it has to be right, Leica Geosystems
>
> Please consider the environment before printing this email.
--
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
