Thanks for the pointers to the implementation, Jonathan!
Unfortunately, I couldnt' find out yet, which part of the source code
in Clojure 1.3 is responsible for fixing the misbehavior in 1.2. The
parts you point to haven't changed in 1.3.
Cheers,
Dominikus
On May 5, 4:27 pm, Jonathan Fischer Friberg <odysso...@gmail.com>
wrote:
> = uses the clojure.lang.Util/equiv to compare two "things". The source of
> this function is: [1]
>
> static public boolean equiv(Object k1, Object k2){
> if(k1 == k2)
> return true;
> if(k1 != null)
> {
> if(k1 instanceof Number && k2 instanceof Number)
> return Numbers.equiv(k1, k2);
> else if(k1 instanceof IPersistentCollection && k2 instanceof
> IPersistentCollection)
> return ((IPersistentCollection)k1).equiv(k2);
> return k1.equals(k2);
> }
> return false;
>
> }
>
> Which says:
> if k1 and k2 is the same instance (has the same id), return true
> if k1 and k2 are numbers, compare them as numbers
> if k1 and k2 are collections, compare them as collections
> otherwise, use the function "equals" of the k1 object.
>
> The equals function defines "intelligent" (proper) comparison of two
> objects, and is defined by the programmer. If the equals function isn't
> defined, it behaves like == [2]
> The == function returns true if the "things" are of the same instance.
>
> I think functions in clojure are defined in [3], but I'm not entirely sure.
> As you can see, equals isn't implemented, and thus = will only compare
> instance (id), as you have noticed.
>
> Jonathan
>
> [1]https://github.com/richhickey/clojure/blob/master/src/jvm/clojure/lan...
> <https://github.com/richhickey/clojure/blob/master/src/jvm/clojure/lan...>
> [2]http://leepoint.net/notes-java/data/expressions/22compareobjects.html
> [3]https://github.com/richhickey/clojure/blob/master/src/jvm/clojure/lan...
>
> On Thu, May 5, 2011 at 3:04 PM, Dominikus <dominikus.herzb...@gmail.com>
> wrote:
>
>
>
>
>
>
>
>
>
> > My observation is best distilled with the following definition of a
> > function in Clojure 1.2:
>
> > user=> (defn id [x] (list id x))
> > #'user/id
>
> > Interstingly, (id 7) and (eval (id 7)) result in different instances
> > of function id as the number after the '@' char unveils:
>
> > user=> (id 7)
> > (#<user$id user$id@53797795> 7)
> > user=> (eval (id 7))
> > (#<user$id user$id@2de12f6d> 7)
>
> > Consequently, the following comparison leads to false:
>
> > user=> (= (id 7) (eval (id 7)))
> > false
>
> > Why is the instance relevant to '='? What is the precise semantics of
> > two values being equal in Clojure?
>
> > Dominikus
>
> > (Remark: In Scheme, the use of 'eqv?' returns also #f, but the less
> > restrictive 'equal?' does not and returns #t.)
>
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